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Zhang J, Shi L, Miao X, Zhou S, Yang L. Promotion of Acid-Water Oxidation by Lattice Distortion and Orbital Hybridization Induced by Ionic Dopant in Pyrochlore Y 2Ru 2O 7. ACS Appl Mater Interfaces 2024; 16:21905-21914. [PMID: 38634487 DOI: 10.1021/acsami.4c01890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/19/2024]
Abstract
For acid-water oxidation, pyrochloric ruthenates are thought to be extremely effective electrocatalysts. In this work, through partial B-site replacement with larger M2+ cations, the electronic states of Y2Ru2O7 with strong electron correlations are reasonably managed, by which the inherent performance is tremendously promoted. Based on this, the improved Y2Ru1.9Sr0.1O7 electrocatalyst exhibits an outstanding durability and presents a highly inherent mass activity of 1915.1 A gRu-1 (at 1.53 V vs RHE). The enhanced oxygen-evolving reaction (OER) activity by ionic dopant in YRO pyrochlore can be attributed to two aspects, i.e., the lattice distortion induced inhibition of the grain coarsening, which results in a large surface area for YRO-M and increases the OER active sites, and the weakening of electron correlation via broadening of the Ru 4d bandwidths due to the increase of the average radius of B-site ions, which gives rise to an enhancement of conductivity and a strengthened hybridization between Ru 4d and O 2p orbitals and improves the reaction kinetics. The synergistic effects of lattice distortion and orbital hybridization promote the enhanced OER activity. The results would provide fresh concepts for the design of improved electrocatalysts and underscore the significance of managing the intrinsic performance through the dual modification of microstructure morphology and electronic structure.
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Affiliation(s)
- Jinhui Zhang
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
| | - Lei Shi
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
| | - Xianbing Miao
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
| | - Shiming Zhou
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
| | - Liping Yang
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
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2
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Zhou Z, Li C, Zhang J, Gao Q, Wang J, Zhang Q, Han Y. Dry Reforming of Methane over Pyrochlore-Type La 2Ce 2O 7-Supported Ni Catalyst: Effect of Particle Size of Support. Molecules 2024; 29:1871. [PMID: 38675691 PMCID: PMC11054847 DOI: 10.3390/molecules29081871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 04/16/2024] [Accepted: 04/16/2024] [Indexed: 04/28/2024] Open
Abstract
The properties of supports (such as oxygen vacancies, oxygen species properties, etc.) significantly impact the anti-carbon ability due to their promotional effect on the activation of CO2 in dry reforming of methane (DRM). Herein, pyrochlore-type La2Ce2O7 compounds prepared using co-precipitation (CP), glycine nitrate combustion (GNC) and sol-gel (S-G) methods, which have highly thermal stability and unique oxygen mobility, are applied as supports to prepare Ni-based catalysts for DRM. The effect of the calcining temperature (500, 600 and 700 °C) on La2Ce2O7(CP) has also been investigated. Based on multi-technique characterizations, it is found that the synthesis method and calcination temperature can influence the particle size of the La2Ce2O7 support. Changes in particle size strongly modulate the pore volume, specific surface area and numbers of surface oxygen vacancies of the La2Ce2O7 support. As a result, the distribution of supported Ni components is affected due to the different metal-support interaction, thereby altering the activity of the catalysts for cracking CH4. Moreover, the supports' abilities to adsorb and activate CO2 are also adjusted accordingly, accelerating the removal of the carbon deposited on the catalysts. Finally, La2Ce2O7(CP 600) with an appropriate particle size exhibits the best catalytic activity and stability in DRM.
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Affiliation(s)
- Zeling Zhou
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chao Li
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Junfeng Zhang
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
| | - Qiliang Gao
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jiahao Wang
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qingde Zhang
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
| | - Yizhuo Han
- State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
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3
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Guo J, Chan CK. Lithium Dendrite Propagation in Ta-Doped Li 7La 3Zr 2O 12 (LLZTO): Comparison of Reactively Sintered Pyrochlore-to-Garnet vs LLZTO by Solid-State Reaction and Conventional Sintering. ACS Appl Mater Interfaces 2024; 16:4519-4529. [PMID: 38233079 DOI: 10.1021/acsami.3c11421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
Ta-doped Li7La3Zr2O12 (LLZTO) garnet is a promising Li-ion-conducting ceramic electrolyte for solid-state batteries. However, it is still challenging to use LLZTO in Li metal batteries operating at high current densities because of the tendency for Li metal to nucleate and propagate along the grain boundaries. In this study, we carry out a detailed investigation to elucidate the effect of microstructure and grain size on the electrochemical properties and short circuit behavior in LLZTO. Pellets were prepared using reactive sintering from pyrochlore precursors (a method called pyrochlore-to-garnet, P2G) and compared with LLZTO synthesized using solid-state reaction (SSR) followed by conventional pressureless sintering. Both preparation methods were controlled to keep the phase and elemental composition, ionic and electronic conductivity, relative density, and area-specific resistance of the pellets constant. Reflection electron energy loss spectroscopy and X-ray photoelectron spectroscopy confirm that both types of LLZTO have similar band gaps and chemical states. Microstructure analysis shows that the P2G method results in LLZTO with an average grain size of around 3 μm, which is much smaller than the grain sizes (as large as 20 μm) seen in SSR LLZTO. Galvanostatic Li stripping/plating and linear sweep voltammetry measurements show that P2G LLZTO can withstand higher critical current densities (up to 0.4 mA/cm2 in bidirectional cycling and >1 mA/cm2 for unidirectional) than those seen in SSR LLZTO. Post-mortem examination reveals much less Li deposition along the grain boundaries of P2G LLZTO, particularly in the bulk of the pellet, compared to SSR LLZTO after cycling. The improved cycling behavior in P2G LLZTO despite the higher grain boundary area could be from more homogeneous current density at the interfaces and different grain boundary properties arising from the liquid-phase, reactive sintering method. These results suggest that the effect of grain size on Li dendrite propagation in LLZO may be highly dependent on the synthesis and sintering method employed.
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Affiliation(s)
- Jinzhao Guo
- Materials Science and Engineering, School for Engineering of Matter, Transport and Energy, Arizona State University, P.O. Box 876106, Tempe, Arizona 85827, United States
| | - Candace K Chan
- Materials Science and Engineering, School for Engineering of Matter, Transport and Energy, Arizona State University, P.O. Box 876106, Tempe, Arizona 85827, United States
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4
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Shang F, Wang B, An B, He H, Shui Y, Cai H, Liang C, Yang S. Na Substitution Steering RuO 6 Unit in Ruthenium Pyrochlores for Enhanced Oxygen Evolution in Acid. Small 2023:e2310323. [PMID: 38109157 DOI: 10.1002/smll.202310323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2023] [Indexed: 12/19/2023]
Abstract
Although Ruthenium-based pyrochlore oxides can function as promising catalysts for acidic water oxidation, their limitations in terms of stability and activity still need to be addressed for further application in practical conditions. In this work, the possibility to enhance both oxygen evolution reaction activity and durability of Gd2 Ru2 O7- δ through partial replacement with Na+ in Gd3+ sites is first offered, leading to the electronic and geometric regulation of active center RuO6 . Na+ triggers the emergence of Ru<4+ and the electron rearrangement of active-centered RuO6 . Specifically, Ru ions with a negative d-band center after Na+ doping exhibit weaker adsorption energies of *O and result in the conversion of the rate-limiting step from *O/*OOH to *OH/O*, reducing energy barriers for boosting activities. Therefore, the Nax Gd2- x Ru2 O7- δ requires a low overpotential of 260 mV at 10 mA cm-2 in 0.1 m HClO4 electrolyte. Moreover, the higher formation energy of Ru vacancy and less distorted RuO6 enable the as-prepared Nax Gd2- x Ru2 O7- δ to operate steadily at 10 mA cm-2 for 300 h and multi-current chronopotentiometry with current densities from 20 to 100 mA cm-2 for 60 h in acidic proton exchange membrane electrolyzer, respectively.
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Affiliation(s)
- Fanfan Shang
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Bin Wang
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- Shaanxi Collaborative Innovation Center for Hydrogen Fuel Cell Performance Improvement, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Bei An
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Huijie He
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Yuan Shui
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Hairui Cai
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- Shaanxi Collaborative Innovation Center for Hydrogen Fuel Cell Performance Improvement, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Chao Liang
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- Shaanxi Collaborative Innovation Center for Hydrogen Fuel Cell Performance Improvement, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
| | - Shengchun Yang
- MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, Key Laboratory of Shaanxi for Advanced Materials and Mesoscopic Physics, State Key Laboratory for Mechanical Behavior of Materials, School of Physics, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- National Innovation Platform (Center) for Industry-Education Integration of Energy Storage Technology, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
- Shaanxi Collaborative Innovation Center for Hydrogen Fuel Cell Performance Improvement, Xi'an Jiaotong University, No. 28 West Xianning Road, Xi'an, 710049, China
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Kai HY, Shang L, Wong KL, Duan CK, Tanner PA. Comment on "Charge Transfer-Triggered Bi 3+ Near-Infrared Emission in Y 2Ti 2O 7 for Dual-Mode Temperature Sensing". ACS Appl Mater Interfaces 2023; 15:43226-43233. [PMID: 37695948 PMCID: PMC10772939 DOI: 10.1021/acsami.3c11758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 08/29/2023] [Indexed: 09/13/2023]
Abstract
Undoped Y2Ti2O7 exhibits impurity emission bands at low temperatures due to Mn4+ and Cr3+, as established by codoping with these ions. Contrary to a recent report by Wang et al., ACS Appl. Mater. Interfaces 2022, 14, 36834-36844, we do not observe Bi3+ emission in this codoped host, as also is the case for Fe3+. The emission reported in that paper as being due to Bi3+ in fact corresponds to Cr3+ emission. The Cr3+ and Mn4+ emissions are quenched with increasing temperature, so that Mn4+ emission is scarcely observed above 80 K. We present variable temperature optical data for Y2Ti2O7 and this host codoped with Mn, Cr, Fe, and Bi, as well as a theoretical justification of our results.
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Affiliation(s)
- Hei-Yui Kai
- Department
of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong 999077, Hong Kong S. A. R., P. R. China
| | - Longbing Shang
- CAS
Key Laboratory of Microscale Magnetic Resonance, School of Physical
Sciences, University of Science and Technology
of China, Hefei 230026, P. R. China
- CAS
Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, P. R. China
| | - Ka-Leung Wong
- Department
of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon 999077, Hong Kong S. A. R., P. R. China
| | - Chang-Kui Duan
- CAS
Key Laboratory of Microscale Magnetic Resonance, School of Physical
Sciences, University of Science and Technology
of China, Hefei 230026, P. R. China
- CAS
Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, P. R. China
| | - Peter A. Tanner
- Department
of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong 999077, Hong Kong S. A. R., P. R. China
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Colomban P, Gironda M, Simsek Franci G, d’Abrigeon P. Distinguishing Genuine Imperial Qing Dynasty Porcelain from Ancient Replicas by On-Site Non-Invasive XRF and Raman Spectroscopy. Materials (Basel) 2022; 15:5747. [PMID: 36013883 PMCID: PMC9412328 DOI: 10.3390/ma15165747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Revised: 08/12/2022] [Accepted: 08/18/2022] [Indexed: 06/15/2023]
Abstract
The combined use of non-invasive on-site portable techniques, Raman microscopy, and X-ray fluorescence spectroscopy on seven imperial bowls and two decorated dishes, attributed to the reigns of the Kangxi, Yongzheng, Qianlong, and Daoguang emperors (Qing Dynasty), allows the identification of the coloring agents/opacifiers and composition types of the glazes and painted enamels. Particular attention is paid to the analysis of the elements used in the (blue) marks and those found in the blue, yellow, red, and honey/gilded backgrounds on which, or in reserve, a floral motif is principally drawn. The honey-colored background is made with gold nanoparticles associated with a lead- and arsenic-based flux. One of the red backgrounds is also based on gold nanoparticles, the second containing copper nanoparticles, both in lead-based silicate enamels like the blue and yellow backgrounds. Tin and arsenic are observed, but cassiterite (SnO2) is clearly observed in one of the painted decors (dish) and in A676 yellow, whereas lead (calcium/potassium) arsenate is identified in most of the enamels. Yellow color is achieved with Pb-Sn-Sb pyrochlore (Naples yellow) with various Sb contents, although green color is mainly based on lead-tin oxide mixed with blue enamel. The technical solutions appear very different from one object to another, which leads one to think that each bowl is really a unique object and not an item produced in small series. The visual examination of some marks shows that they were made in overglaze (A608, A616, A630, A672). It is obvious that different types of cobalt sources were used for the imprinting of the marks: cobalt rich in manganese for bowl A615 (Yongzheng reign), cobalt rich in arsenic for bowl A613 (but not the blue mark), cobalt with copper (A616), and cobalt rich in arsenic and copper (A672). Thus, we have a variety of cobalt sources/mixtures. The high purity of cobalt used for A677 bowl indicates a production after ~1830-1850.
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Affiliation(s)
- Philippe Colomban
- MONARIS UMR8233, Sorbonne Université, CNRS, 4 Place Jussieu, 75005 Paris, France
| | | | - Gulsu Simsek Franci
- Surface Science and Technology Center (KUYTAM), College of Sciences, Rumelifeneri Campus, Koç University, 34450 Istanbul, Turkey or
| | - Pauline d’Abrigeon
- Musée des Arts d’Extrême-Orient, Fondation Baur, Rue Munier-Romilly 8, 1206 Geneva, Switzerland
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7
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Wang X, Jahanbazi F, Wei J, Segre CU, Chen W, Mao Y. Charge Transfer-Triggered Bi 3+ Near-Infrared Emission in Y 2Ti 2O 7 for Dual-Mode Temperature Sensing. ACS Appl Mater Interfaces 2022; 14:36834-36844. [PMID: 35921172 DOI: 10.1021/acsami.2c09361] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Trivalent bismuth is a popular main group ion showing versatile luminescent behaviors in a broad spectral range from ultraviolet to visible, but barely in the near-infrared (NIR) region. In this study, we have observed unexpected NIR emission at ∼744 nm in a Bi3+-doped pyrochlore, Y2Ti2O7 (YTOB). Our first-principles electronic structure calculation and analysis of the Bi local structure via extended X-ray absorption fine structure indicate that only Bi3+ species appears in YTOB and it has a similar local environment to that of Y3+. The NIR emission is assigned to a Ti4+ → Bi3+ metal-to-metal charge transfer process. Moreover, we have demonstrated dual-mode luminescence thermometry based on the luminescence intensity ratio (LIR) and lifetime (τ) in 0.5% Bi3+ and 0.5% Pr3+ co-doped Y2Ti2O7 (YTOB0.5P0.5). It exhibits high thermometric sensitivity simultaneously in the cryogenic temperature range from 78 to 298 K based on τ of the NIR emission of Bi3+ at 748 nm and in the temperature range of 278-378 K based on the LIR of Bi3+ to Pr3+ emissions (I748/I615). As a novel LIR-τ dual-mode thermometric material over a wide temperature range, the maximum relative sensitivities of the YTOB0.5P0.5 reach 3.53% K-1 at 298 K from the τ mode and 3.52% K-1 at 318 K based on the LIR mode. The dual-mode luminescence thermometry with high responsivity from our Bi3+-based pyrochlore Y2Ti2O7 phosphor opens a new avenue for more luminescent materials toward multi-mode thermometry applied in complex temperature-sensing conditions.
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Affiliation(s)
- Xianli Wang
- Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616, United States
| | - Forough Jahanbazi
- Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616, United States
| | - Jialiang Wei
- Department of Mechanical, Materials, and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, United States
| | - Carlo U Segre
- Center for Synchrotron Radiation Research and Instrumentation and Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616, United States
| | - Wei Chen
- Department of Mechanical, Materials, and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, United States
| | - Yuanbing Mao
- Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616, United States
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8
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Teng Z, Tan Y, Zhang H. High-Entropy Pyrochlore A 2B 2O 7 with Both Heavy and Light Rare-Earth Elements at the A Site. Materials (Basel) 2021; 15:129. [PMID: 35009272 PMCID: PMC8745905 DOI: 10.3390/ma15010129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 12/22/2021] [Accepted: 12/23/2021] [Indexed: 06/14/2023]
Abstract
A novel class of high-entropy pyrochlore ceramics (HEPCs) with multiple heavy and light rare-earth elements at the A site were successfully synthesized via solid-state reaction. Both the XRD patterns and Raman spectroscopy demonstrated the single pyrochlore structure feature of seven kinds of HEPCs. Electron microscopic images revealed the typical morphology and the homogeneous distribution of all rare-earth elements. It can be concluded that the significance of configuration entropy in the HEPC system has promoted the tervalent lanthanide nuclides to form a single pyrochlore structure. This work is expected to provide guidance for the further design of high-entropy pyrochlore/fluorite ceramics.
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Affiliation(s)
- Zhen Teng
- Department of Materials Science, Fudan University, 220 Handan Road, Shanghai 200433, China;
- Innovation Research Team for Advanced Ceramics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;
| | - Yongqiang Tan
- Innovation Research Team for Advanced Ceramics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;
| | - Haibin Zhang
- Innovation Research Team for Advanced Ceramics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;
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9
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Finkeldei SC, Chang S, Ionescu M, Oldfield D, Davis J, Lumpkin GR, Simeone D, Avdeev M, Brandt F, Bosbach D, Klinkenberg M, Thorogood GJ. Insight Into Disorder, Stress and Strain of Radiation Damaged Pyrochlores: A Possible Mechanism for the Appearance of Defect Fluorite. Front Chem 2021; 9:706736. [PMID: 34858941 PMCID: PMC8630592 DOI: 10.3389/fchem.2021.706736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 10/01/2021] [Indexed: 11/13/2022] Open
Abstract
We have examined the irradiation response of a titanate and zirconate pyrochlore-both of which are well studied in the literature individually-in an attempt to define the appearance of defect fluorite in zirconate pyrochlores. To our knowledge this study is unique in that it attempts to discover the mechanism of formation by a comparison of the different systems exposed to the same conditions and then examined via a range of techniques that cover a wide length scale. The conditions of approximately 1 displacement per atom via He2+ ions were used to simulate long term waste storage conditions as outlined by previous results from Ewing in a large enough sample volume to allow for neutron diffraction, as not attempted previously. The titanate sample, used as a baseline comparison since it readily becomes amorphous under these conditions behaved as expected. In contrast, the zirconate sample accumulates tensile stress in the absence of detectable strain. We propose this is analogous to the lanthanide zirconate pyrochlores examined by Simeone et al. where they reported the appearance of defect fluorite diffraction patterns due to a reduction in grain size. Radiation damage and stress results in the grains breaking into even smaller crystallites, thus creating even smaller coherent diffraction domains. An (ErNd)2(ZrTi)2O7 pyrochlore was synthesized to examine which mechanism might dominate, amorphization or stress/strain build up. Although strain was detected in the pristine sample via Synchrotron X-ray diffraction it was not of sufficient quality to perform a full analysis on.
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Affiliation(s)
- Sarah C Finkeldei
- Department of Chemistry, University of California, Irvine, Irvine, CA, United States.,Department of Chemical and Biomolecular Engineering, University of California, Irvine, Irvine, CA, United States.,Department of Materials Science and Engineering, University of California, Irvine, Irvine, CA, United States
| | - Shirley Chang
- Department of Chemistry, University of California, Irvine, Irvine, CA, United States
| | - Mihail Ionescu
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Daniel Oldfield
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Joel Davis
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Gregory R Lumpkin
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - David Simeone
- CEA/DEN/DMN/SRMA/LA2M-LRC CARMEN, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Max Avdeev
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Felix Brandt
- Forschungszentrum Juelich GmbH, Institute of Energy and Climate Research, IEK-6: Nuclear Waste Management and Reactor Safety, Juelich, Germany
| | - Dirk Bosbach
- Forschungszentrum Juelich GmbH, Institute of Energy and Climate Research, IEK-6: Nuclear Waste Management and Reactor Safety, Juelich, Germany
| | - Martina Klinkenberg
- Forschungszentrum Juelich GmbH, Institute of Energy and Climate Research, IEK-6: Nuclear Waste Management and Reactor Safety, Juelich, Germany
| | - Gordon J Thorogood
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia.,Department of Nuclear System Safety Engineering, Nagaoka University of Technology, Nagaoka, Japan
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10
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Lumpkin GR, Aughterson RD. Perspectives on Pyrochlores, Defect Fluorites, and Related Compounds: Building Blocks for Chemical Diversity and Functionality. Front Chem 2021; 9:778140. [PMID: 34869225 PMCID: PMC8632815 DOI: 10.3389/fchem.2021.778140] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Accepted: 10/25/2021] [Indexed: 11/13/2022] Open
Abstract
In this article we provide some perspectives on a range of pyrochlore and defect fluorite type compounds with nominal A2B2O7, A2BO5, ABC2O7, and other stoichiometries. Typically, the phase transformations and stability fields in these systems are mapped as a function of the ionic radii of the A and B-site cations, e.g., the A/B cation radius ratio (rA/rB). This provides a useful guide to compatible structures and compositions for the development of advanced materials. Pyrochlore commonly transforms to a defect fluorite structure at high temperature in many systems; however, it is not uncommon to observe defect fluorite as the initial metastable phase at low temperature. The patterns of order-disorder observed in these materials are primarily due to the energetics of layer stacking, the defect formation and migration energies of cations and anions, or modulations of the parent cubic structure in 3 + n dimensional space. The first lead to predominantly non-cubic derivatives of the parent defect fluorite structure (e.g., zirconolite polytypes), the second control the order-disorder processes, and the latter lead to a variety of subtle additional scattering features within the cubic parent structure. Although the energetics of cation disorder and anion-vacancy disorder have become more accessible via atomistic approaches (e.g., MD and DFT), we continue to find interesting physical-chemical problems in these materials. For example, although there are significant differences in composition (Tb/Zr ratio and O content) between Tb2Zr2O7 and Tb2ZrO5, both of which are defect fluorites, we note that the modulations found in these two compounds by electron scattering are virtually identical with regard to the direction and magnitude of displacement from the normal Bragg diffracted beams. This suggests that neither the A/B cation ratio nor the oxygen stoichiometry have a significant effect on the modulations. The general observations on the systems of compounds noted in this paper rest primarily in the context of industrial materials for nuclear waste disposal, potential applications in inert matrix fuel designs, and other important technological applications such as ionic conductivity, electrical conductivity, and magnetism. Scientific advances in these areas have been underpinned by recent advances in ion irradiation, synchrotron X-ray, neutron scattering, and modelling and simulation capabilities. Furthermore, there has been some renewed interest in natural samples, e.g., Th-U zirconolite and pyrochlore as analogues for potential host phases in nuclear waste forms. In particular, the natural pyrochlores have provided additional details with regard to radiation damage ingrowth, percolation transitions, and the relationships between accumulated dose and physical properties including hardness, elastic modulus. Specific details of the thermal annealing of these samples have also been elucidated in considerable detail.
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Affiliation(s)
- Gregory R. Lumpkin
- Australian Nuclear Science and Technology Organisation, Sydney, NSW, Australia
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Gayen P, Saha S, Liu X, Sharma K, Ramani VK. High-performance AEM unitized regenerative fuel cell using Pt- pyrochlore as bifunctional oxygen electrocatalyst. Proc Natl Acad Sci U S A 2021; 118:e2107205118. [PMID: 34593643 DOI: 10.1073/pnas.2107205118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/30/2021] [Indexed: 11/18/2022] Open
Abstract
The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb2Ru2O7-x is synthesized by depositing Pt on Pb2Ru2O7-x wherein Pt individually exhibits high ORR while Pb2Ru2O7-x shows high OER and moderate ORR activity. Pt-Pb2Ru2O7-x exhibits higher OER (η@10mAcm-2 = 0.25 ± 0.01 V) and ORR (η@-3mAcm-2 = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO2, η@10mAcm-2 = 0.35 ± 0.02 V) and ORR (Pt/C, η@-3mAcm-2 = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb2Ru2O7-x shows a lower bifunctionality index (η@10mAcm-2, OER - η@-3mAcm-2, ORR) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and Pb2Ru2O7-x (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb2Ru2O7-x and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/gcat -1 at 1.8 V and 56 ± 2 A/gcat -1 at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm-2, underlying improvement in AEM FG-URFC electrocatalyst design.
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Kocevski V, Pilania G, Uberuaga BP. Modeling Disorder in Pyrochlores and Other Anion-Deficient Fluorite Structural Derivative Oxides. Front Chem 2021; 9:712543. [PMID: 34532309 PMCID: PMC8438134 DOI: 10.3389/fchem.2021.712543] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 07/08/2021] [Indexed: 12/05/2022] Open
Abstract
Their very flexible chemistry gives oxide materials a richness in functionality and wide technological application. A specific group of oxides that have a structure related to fluorite but with less oxygen, termed anion-deficient fluorite structural derivatives and with pyrochlores being the most notable example, has been shown to exhibit a diversity of useful properties. For example, the possibility to undergo a transition from an ordered to disordered state allows these oxides to have high radiation tolerance. Atomistic-scale calculations in the form of molecular dynamics (MD) and density functional theory (DFT) have been extensively used to understand what drives this order/disorder transition. Here we give a brief overview of how atomistic-scale calculations are utilized in modeling disorder in pyrochlores and other anion-deficient fluorite structural derivatives. We discuss the modeling process from simple point defects to completely disordered structures, the dynamics during the disordering process, and the use of mathematical models to generate ordered solid-solution configurations. We also attempt to identify the challenges in modeling short range order and discuss future directions to more comprehensive models of the disordered structures.
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Affiliation(s)
- V Kocevski
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - G Pilania
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - B P Uberuaga
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, United States
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Kennedy BJ, Ablott TA, Avdeev M, Carter ML, Losurdo L, Saura-Muzquiz M, Thorogood KJ, Ting J, Wallwork KS, Zhang Z, Zhu H, Thorogood GJ. Synthesis and Structure of Oxygen Deficient Lead-Technetium Pyrochlore, the First Example of a Valence V Technetium Oxide. Front Chem 2021; 9:706269. [PMID: 34277573 PMCID: PMC8281135 DOI: 10.3389/fchem.2021.706269] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 06/08/2021] [Indexed: 11/13/2022] Open
Abstract
The structure of lead-technetium pyrochlore has been refined in space group Fd3¯m with a = 10.36584(2) Å using a combination of synchrotron X-ray and neutron powder diffraction data and confirmed via Electron Diffraction. The oxide is found to be oxygen deficient with a stoichiometry of Pb2Tc2O7-d. Displacive disorder of the Pb cations is evident from the refinements, as has been observed in Bi2Tc2O7-d. X-ray absorption spectroscopic measurements at the Tc K-edge demonstrate the valence of the Tc is greater than 4.0 as anticipated from the refined oxygen stoichiometry. Raman spectroscopy confirms the presence of disorder leading us to conclude that this pyrochlore is the first example of a valence V technetium oxide.
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Affiliation(s)
- Brendan J Kennedy
- School of Chemistry, The University of Sydney, Sydney, NSW, Australia
| | - Timothy A Ablott
- Nuclear Fuel Cycle, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Maxim Avdeev
- School of Chemistry, The University of Sydney, Sydney, NSW, Australia.,Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Melody L Carter
- Nuclear Fuel Cycle, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Linda Losurdo
- School of Chemistry, The University of Sydney, Sydney, NSW, Australia
| | | | - Kevin J Thorogood
- Nuclear Materials, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Jimmy Ting
- School of Chemistry, The University of Sydney, Sydney, NSW, Australia
| | - Kia S Wallwork
- Australian Synchrotron, Australian Nuclear Science and Technology Organisation, Clayton, VIC, Australia
| | - Zhaoming Zhang
- Nuclear Fuel Cycle, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Hanliang Zhu
- Nuclear Fuel Cycle, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia
| | - Gordon J Thorogood
- Nuclear Fuel Cycle, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia.,Department of Nuclear System Safety Engineering, Nagaoka University of Technology, Nagaoka, Japan
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Ma CL, Wang ZQ, Sun W, Cao LM, Gong XQ, Yang J. Surface Reconstruction for Forming the [IrO 6]-[IrO 6] Framework: Key Structure for Stable and Activated OER Performance in Acidic Media. ACS Appl Mater Interfaces 2021; 13:29654-29663. [PMID: 34148341 DOI: 10.1021/acsami.1c06599] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The surface reconstruction of iridium-based derivatives (AxIryOz) was extensively demonstrated to have an excellent oxygen evolution reaction (OER) performance in an acidic medium. It is urgent to use various spectroscopy and computational methods to explore the electronic state changes in the surface reconstruction process. Herein, the underestimated Lu2Ir2O7 was synthesized and investigated. Four typical forms of electrochemistry impedance spectra involved in the reconstruction process revealed three dominating forms of reconstructed pyrochlore in the OER stage, including the inner intact pyrochlore, mid metastable [IrO6]-[IrO6] framework, and the outer collapse amorphous layer. The enhancing electron transport efficiency of the corner-shared [IrO6]-[IrO6] framework was revealed as a critical role in acidic systems. The density of state (DOS) for the constructed [IrO6]-[IrO6] framework corroborated the enhancement of Ir-O hybridization and the downshift of the d-band center. Additionally, we contrast the pristine and reconstruction properties of the Pr2Ir2O7, Eu2Ir2O7, and Lu2Ir2O7 in alkaline and acidic media. The DOS and the XANES results reveal the scale relationship between the O 2p band center and the intrinsic activity for bulk pyrochlore in alkaline media. The highest O 2p center and the highest Ir-O hybridization of Lu2Ir2O7 exhibited the best OER performance among the Ir-based pyrochlore, up to a ninefold improvement in Ir-mass activity compared to IrO2. Our findings emphasize the electrochemical behavior of the reconstruction process for activated water-splitting performance.
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Affiliation(s)
- Cheng-Long Ma
- School of Resources and Environmental Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China
| | - Zhi-Qiang Wang
- Key Laboratory for Advanced Materials, Centre for Computational Chemistry and Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
| | - Wei Sun
- College of Ecology and Environment, Hainan University, Haikou 570228, China
| | - Li-Mei Cao
- School of Resources and Environmental Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China
| | - Xue-Qing Gong
- Key Laboratory for Advanced Materials, Centre for Computational Chemistry and Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
| | - Ji Yang
- School of Resources and Environmental Engineering, East China University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China
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Abstract
NASA's current mandate is to land humans on Mars by 2033. Here, we demonstrate an approach to produce ultrapure H2 and O2 from liquid-phase Martian regolithic brine at ∼-36 °C. Utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst and a Pt/C H2-evolution electrocatalyst, we demonstrate a brine electrolyzer with >25× the O2 production rate of the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) from NASA's Mars 2020 mission for the same input power under Martian terrestrial conditions. Given the Phoenix lander's observation of an active water cycle on Mars and the extensive presence of perchlorate salts that depress water's freezing point to ∼-60 °C, our approach provides a unique pathway to life-support and fuel production for future human missions to Mars.
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Chishkala V, Lytovchenko S, Mazilin B, Gevorkyan E, Shkuropatenko V, Voyevodin V, Rucki M, Siemiątkowski Z, Matijošius J, Dudziak A, Caban J, Kilikevičius A. Novel Microwave-Assisted Method of Y2Ti2O7 Powder Synthesis. Materials (Basel) 2020; 13:ma13245621. [PMID: 33317137 PMCID: PMC7764300 DOI: 10.3390/ma13245621] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 12/05/2020] [Accepted: 12/07/2020] [Indexed: 11/16/2022]
Abstract
In the paper, a novel technique for highly dispersed pyrochlore Y2Ti2O7 is proposed. The experimental results proved that the application of microwave irradiation at a certain stage of calcination allowed synthesizing of Y2Ti2O7 in much shorter time, which ensured substantial energy savings. An increase up to 98 wt.% in the content of the preferred phase with a pyrochlore-type structure Y2Ti2O7 was obtained after 25 h of yttrium and titanium oxides calcination at a relatively low temperature of 1150 °C, while the microwave-supported process took only 9 h and provided 99 wt.% of pyrochlore. The proposed technology is suitable for industrial applications, enabling the fabrication of large industrial amounts of pyrochlore without solvent chemistry and high-energy mills. It reduced the cost of both equipment and energy and made the process more environmentally friendly. The particle size and morphology did not change significantly; therefore, the microwave-assisted method can fully replace the traditional one.
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Affiliation(s)
- Vladimir Chishkala
- Department of Reactor Engineering Materials and Physical Technologies, V. N. Karazin Kharkiv National University, 4 Svobody Sq., 61022 Kharkiv, Ukraine; (V.C.); (S.L.); (B.M.)
| | - Serhiy Lytovchenko
- Department of Reactor Engineering Materials and Physical Technologies, V. N. Karazin Kharkiv National University, 4 Svobody Sq., 61022 Kharkiv, Ukraine; (V.C.); (S.L.); (B.M.)
| | - Bohdan Mazilin
- Department of Reactor Engineering Materials and Physical Technologies, V. N. Karazin Kharkiv National University, 4 Svobody Sq., 61022 Kharkiv, Ukraine; (V.C.); (S.L.); (B.M.)
| | - Edwin Gevorkyan
- Department of Quality, Standardization, Certification and Manufacturing Technology, Ukraine State University of Railway Transport, 7 Feuerbach Sq., 61010 Kharkiv, Ukraine;
| | - Vladimir Shkuropatenko
- Institute of Solid State Physics, Materials Science and Technology NSC KIPT NAS of Ukraine, 1 Academichna Str., 61108 Kharkiv, Ukraine; (V.S.); (V.V.)
| | - Viktor Voyevodin
- Department of Reactor Engineering Materials and Physical Technologies, V. N. Karazin Kharkiv National University, 4 Svobody Sq., 61022 Kharkiv, Ukraine; (V.C.); (S.L.); (B.M.)
- Institute of Solid State Physics, Materials Science and Technology NSC KIPT NAS of Ukraine, 1 Academichna Str., 61108 Kharkiv, Ukraine; (V.S.); (V.V.)
| | - Mirosław Rucki
- Faculty of Mechanical Engineering, Kazimierz Pulaski University of Technology and Humanities in Radom, ul. Stasieckiego 54, 26-600 Radom, Poland;
- Correspondence: (M.R.); (A.D.)
| | - Zbigniew Siemiątkowski
- Faculty of Mechanical Engineering, Kazimierz Pulaski University of Technology and Humanities in Radom, ul. Stasieckiego 54, 26-600 Radom, Poland;
| | - Jonas Matijošius
- Institute of Mechanical Science, Vilnius Gediminas Technical University, J. Basanavičiaus g. 28, 03224 Vilnius, Lithuania; (J.M.); (A.K.)
| | - Agnieszka Dudziak
- Faculty of Production Engineering, University of Life Sciences in Lublin, Głęboka 28 Str., 20-612 Lublin, Poland
- Correspondence: (M.R.); (A.D.)
| | - Jacek Caban
- Faculty of Mechanical Engineering, Lublin University of Technology, Nadbystrzycka 36, 20-618 Lublin, Poland;
| | - Artūras Kilikevičius
- Institute of Mechanical Science, Vilnius Gediminas Technical University, J. Basanavičiaus g. 28, 03224 Vilnius, Lithuania; (J.M.); (A.K.)
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Scheie A, Kindervater J, Zhang S, Changlani HJ, Sala G, Ehlers G, Heinemann A, Tucker GS, Koohpayeh SM, Broholm C. Multiphase magnetism in Yb 2Ti 2O 7. Proc Natl Acad Sci U S A 2020; 117:27245-54. [PMID: 33097668 DOI: 10.1073/pnas.2008791117] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We use neutron scattering to show that ferromagnetism and antiferromagnetism coexist in the low T state of the pyrochlore quantum magnet [Formula: see text] While magnetic Bragg peaks evidence long-range static ferromagnetic order, inelastic scattering shows that short-range correlated antiferromagnetism is also present. Small-angle neutron scattering provides direct evidence for mesoscale magnetic structure that we associate with metastable antiferromagnetism. Classical Monte Carlo simulations based on exchange interactions inferred from [Formula: see text]-oriented high-field spin wave measurements confirm that antiferromagnetism is metastable within the otherwise ferromagnetic ground state. The apparent lack of coherent spin wave excitations and strong sensitivity to quenched disorder characterizing [Formula: see text] is a consequence of this multiphase magnetism.
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Pokhrel M, Dimakis N, Dannangoda C, Gupta SK, Martirosyan KS, Mao Y. Structural Evolution and Magnetic Properties of Gd 2Hf 2O 7 Nanocrystals: Computational and Experimental Investigations. Molecules 2020; 25:E4847. [PMID: 33096660 DOI: 10.3390/molecules25204847] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 10/14/2020] [Accepted: 10/16/2020] [Indexed: 11/17/2022] Open
Abstract
Structural evolution in functional materials is a physicochemical phenomenon, which is important from a fundamental study point of view and for its applications in magnetism, catalysis, and nuclear waste immobilization. In this study, we used x-ray diffraction and Raman spectroscopy to examine the Gd2Hf2O7 (GHO) pyrochlore, and we showed that it underwent a thermally induced crystalline phase evolution. Superconducting quantum interference device measurements were carried out on both the weakly ordered pyrochlore and the fully ordered phases. These measurements suggest a weak magnetism for both pyrochlore phases. Spin density calculations showed that the Gd3+ ion has a major contribution to the fully ordered pyrochlore magnetic behavior and its cation antisite. The origin of the Gd magnetism is due to the concomitant shift of its spin-up 4f orbital states above the Fermi energy and its spin-down states below the Fermi energy. This picture is in contrast to the familiar Stoner model used in magnetism. The ordered pyrochlore GHO is antiferromagnetic, whereas its antisite is ferromagnetic. The localization of the Gd-4f orbitals is also indicative of weak magnetism. Chemical bonding was analyzed via overlap population calculations: These analyses indicate that Hf-Gd and Gd-O covalent interactions are destabilizing, and thus, the stabilities of these bonds are due to ionic interactions. Our combined experimental and computational analyses on the technologically important pyrochlore materials provide a basic understanding of their structure, bonding properties, and magnetic behaviors.
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Gupta AK, Arora G, Aidhy DS, Sachan R. ∑3 Twin Boundaries in Gd 2Ti 2O 7 Pyrochlore: Pathways for Oxygen Migration. ACS Appl Mater Interfaces 2020; 12:45558-45563. [PMID: 32915546 DOI: 10.1021/acsami.0c12250] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Understanding the chemistry at twin boundaries (TB) is a well-recognized challenge, which could enable the capabilities to manipulate the functional properties in complex oxides. The study of this atomic imperfection becomes even more important, as the presence of twin boundaries has been widely observed in materials, regardless of the dimensionalities, due to the complexities in growth methods. In the present study, we provide atomic-scale insights into a ∑3(111̅) ⟨11̅0⟩ twin boundary present in pyrochlore-structured Gd2Ti2O7 using atomic-resolution electron microscopy and atomistic modeling. The formation of the observed TB occurs along (111̅) with a 71° angle between two symmetrically arranged crystals. We observe distortions (∼3 to 5% strain) in the atomic structure at the TB with an increase in Gd-Gd (0.66 ± 0.03 nm) and Ti-Ti (0.65 ± 0.02 nm) bond lengths in the (11̅0) plane, as compared to 0.63 nm in the ordered structure. Using atomistic modeling, we further calculate the oxygen migration barrier for vacancy hopping at 48f-48f sites in the pyrochlore structure, which is the primary diffusion pathway for fast oxygen transport. The mean migration barrier is lowered by ∼25% to 0.9 eV at the TB as compared to 1.23 eV in the bulk, suggesting the ease in oxygen transport through the ∑3 twin boundaries. Overall, these results offer a critical understanding of the atomic arrangement at the twin boundaries in pyrochlores, leading to control of the interplay between defects and properties.
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Affiliation(s)
- Ashish Kumar Gupta
- School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, United States
| | - Gaurav Arora
- Department of Mechanical Engineering, University of Wyoming, Laramie, Wyoming 82071, United States
| | - Dilpuneet S Aidhy
- Department of Mechanical Engineering, University of Wyoming, Laramie, Wyoming 82071, United States
| | - Ritesh Sachan
- School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, United States
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Abbott DF, Pittkowski RK, Macounová K, Nebel R, Marelli E, Fabbri E, Castelli IE, Krtil P, Schmidt TJ. Design and Synthesis of Ir/Ru Pyrochlore Catalysts for the Oxygen Evolution Reaction Based on Their Bulk Thermodynamic Properties. ACS Appl Mater Interfaces 2019; 11:37748-37760. [PMID: 31535842 DOI: 10.1021/acsami.9b13220] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Density functional theory (DFT) has proven to be an invaluable and effective tool for identifying highly active electrocatalysts for the oxygen evolution reaction (OER). Herein, we take a computational approach to first identify a series of rare-earth pyrochlore oxides based on Ir and Ru as potential OER catalysts. The DFT-based phase diagrams, Pourbaix diagrams (E vs pH), projected density of states, and band energy diagrams were used to identify prospective OER catalysts based on rare-earth Ir and Ru pyrochlores. The predicted materials were synthesized using the spray-freeze freeze-drying approach to afford nanoparticulate oxides conforming to the pyrochlore structural type A2B2O7 where A = Nd, Gd, or Yb and B = Ir or Ru. In agreement with the computed Pourbaix diagrams, the materials were found to be moderately stable under OER conditions. All prepared materials show higher stability as compared to the benchmark IrO2 catalyst, and the OER mass activity of Yb2Ir2O7 and the ruthenate pyrochlores (Nd2Ru2O7, Gd2Ru2O7, and Yb2Ru2O7) were also found to exceed those of the benchmark IrO2 catalyst. We find that the OER activity of each pyrochlore series (i.e., iridate or ruthenate) generally improves as the size of the A-site cation decreases, indicating that maintaining control over the structure can be used to influence the electrocatalytic properties.
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Affiliation(s)
| | - Rebecca K Pittkowski
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , Dolejškova 3 , 18223 , Prague , Czech Republic
| | - Kateřina Macounová
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , Dolejškova 3 , 18223 , Prague , Czech Republic
| | - Roman Nebel
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , Dolejškova 3 , 18223 , Prague , Czech Republic
| | | | | | - Ivano E Castelli
- Department of Energy Conversion and Storage , Technical University of Denmark , DK-2800 Kgs. Lyngby , Denmark
| | - Petr Krtil
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , Dolejškova 3 , 18223 , Prague , Czech Republic
| | - Thomas J Schmidt
- Laboratory of Physical Chemistry , ETH Zürich , CH-8093 Zürich , Switzerland
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Niu J, Wu X, Zhang H, Qin S. Pressure-induced order-disorder transition in Gd 1.5Ce 0.5Ti 2O 7 pyrochlore. R Soc Open Sci 2019; 6:190842. [PMID: 31598308 PMCID: PMC6774973 DOI: 10.1098/rsos.190842] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Accepted: 08/12/2019] [Indexed: 06/10/2023]
Abstract
An experimental study on ordered pyrochlore structured Gd1.5Ce0.5Ti2O7 ( F d 3 ¯ m ) was carried out up to 45 GPa by synchrotron radiation X-ray diffraction and Raman spectroscopy. Experimental results show that Gd1.5Ce0.5Ti2O7 transfers to a disordered cotunnite-like phase (Pnma Z = 4) at approximately 42 GPa. Compared with the end member Gd2Ti2O7, the substitution of Ce3+ for Gd3+ increases the transition pressure and the high-pressure stability of the pyrochlore phase. This pressure-induced structure transition is mainly controlled by cationic order-disorder modification, and the cationic radius ratio r A/r B may also be effective for predicting the pyrochlore oxides' high-pressure stability. Two isostructural transitions are observed at 6.5 GPa and 13 GPa, and the unit-cell volume of Gd1.5Ce0.5Ti2O7 as a function of pressure demonstrates its compression behaviour is rather complex.
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Affiliation(s)
- Jingjing Niu
- Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, People's Republic of China
- Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University and School of Earth and Space Sciences, Peking University, Beijing 100871, People's Republic of China
- Innovation Research Team for Advanced Ceramics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, People's Republic of China
| | - Xiang Wu
- State key laboratory of geological processes and mineral resources, China University of Geosciences (Wuhan), Wuhan 430074, People's Republic of China
| | - Haibin Zhang
- Innovation Research Team for Advanced Ceramics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, People's Republic of China
| | - Shan Qin
- Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University and School of Earth and Space Sciences, Peking University, Beijing 100871, People's Republic of China
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Shlyakhtina AV, Abrantes JCC, Gomes E, Lyskov NV, Konysheva EY, Chernyak SA, Kharitonova EP, Karyagina OK, Kolbanev IV, Shcherbakova LG. Evolution of Oxygen-Ion and Proton Conductivity in Ca-Doped Ln 2Zr 2O 7 (Ln = Sm, Gd), Located Near Pyrochlore-Fluorite Phase Boundary. Materials (Basel) 2019; 12:ma12152452. [PMID: 31374863 PMCID: PMC6696096 DOI: 10.3390/ma12152452] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 07/16/2019] [Accepted: 07/29/2019] [Indexed: 11/16/2022]
Abstract
Sm2-xCaxZr2O7-x/2 (x = 0, 0.05, 0.1) and Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore-fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100-900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700-950 °C. The Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen-ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) is ~ 1 × 10-4 S/cm. The fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) to fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2-xCax)Zr2O7-δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2-xCaxZr2O7-x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.
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Affiliation(s)
- A V Shlyakhtina
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow 119991, Russia.
| | - J C C Abrantes
- UIDM, ESTG, Instituto Politécnico de Viana do Сastelo, 4900-348 Viana do Castelo, Portugal
| | - E Gomes
- UIDM, ESTG, Instituto Politécnico de Viana do Сastelo, 4900-348 Viana do Castelo, Portugal
| | - N V Lyskov
- Institute of Problems of Chemical Physics RAS, Moscow region, Chernogolovka 142432, Russia
| | - E Yu Konysheva
- University of Nottingham Ningbo China, Ningbo 315100, China
- Institute of Solid State Chemistry, the Ural Branch of the Russian Academy of Sciences, Pervomayskaya Str. 91, Ekaterinburg 620990, Russia
| | - S A Chernyak
- Moscow State University, Leninskie gory 1, Moscow 119991, Russia
| | - E P Kharitonova
- Moscow State University, Leninskie gory 1, Moscow 119991, Russia
| | - O K Karyagina
- Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow 119991, Russia
| | - I V Kolbanev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow 119991, Russia
| | - L G Shcherbakova
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow 119991, Russia
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Kim J, Shih PC, Qin Y, Al-Bardan Z, Sun CJ, Yang H. A Porous Pyrochlore Y 2 [Ru 1.6 Y 0.4 ]O 7-δ Electrocatalyst for Enhanced Performance towards the Oxygen Evolution Reaction in Acidic Media. Angew Chem Int Ed Engl 2018; 57:13877-13881. [PMID: 30160366 DOI: 10.1002/anie.201808825] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Indexed: 01/20/2023]
Abstract
A robust porous structure is often needed for practical applications in electrochemical devices, such as fuel cells, batteries, and electrolyzers. While templating approach is useful for the preparation of porous materials in general, it is not effective for the synthesis of oxide-based electrocatalysts owing to the chemical instability of disordered porous materials thus created. Now the synthesis of phase-pure porous yttrium ruthenate pyrochlore oxide using an unconventional porogen of perchloric acid is presented. The lattice oxygen defects are formed by the mixed-valence state of Ru4+/5+ through the partial substitution of Ru4+ with Y3+ cations, leading to the formation of mixed B-site Y2 [Ru1.6 Y0.4 ]O7-δ . This porous Y2 [Ru1.6 Y0.4 ]O7-δ electrocatalyst exhibits a turnover frequency (TOF) of 560 s-1 (at 1.5 V versus RHE) for the oxygen evolution reaction, which is two orders of magnitude higher than that of the RuO2 reference catalyst (5.41 s-1 ).
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Affiliation(s)
- Jaemin Kim
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA
| | - Pei-Chieh Shih
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA
| | - Yao Qin
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA.,The Institute for Advanced Materials & Nano Biomedicine, Tongji University, 67 Chifeng Rd., Shanghai, 200092, P. R. China
| | - Zaid Al-Bardan
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA
| | - Cheng-Jun Sun
- X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL, 60439, USA
| | - Hong Yang
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL, 61801, USA
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Ai L, Wang Z, Cui C, Liu W, Wang L. Catalytic Oxidation of Soot on a Novel Active Ca-Co Dually-Doped Lanthanum Tin Pyrochlore Oxide. Materials (Basel) 2018; 11:E653. [PMID: 29695051 DOI: 10.3390/ma11050653] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 04/03/2018] [Accepted: 04/19/2018] [Indexed: 12/04/2022]
Abstract
A novel active Ca-Co dually-doping pyrochlore oxide La2−xCaxSn2−yCoyO7 catalyst was synthesized by the sol-gel method for catalytic oxidation of soot particulates. The microstructure, atomic valence, reduction, and adsorption performance were investigated by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2-TPR (temperature-programmed reduction), and in situ diffuse reflection infrared Fourier transformed (DRIFTS) techniques. Temperature programmed oxidation (TPO) tests were performed with the mixture of soot-catalyst under tight contact conditions to evaluate the catalytic activity for soot combustion. Synergetic effect between Ca and Co improved the structure and redox properties of the solids, increased the surface oxygen vacancies, and provided a suitable electropositivity for oxide, directly resulting in the decreased ignition temperature for catalyzed soot oxidation as low as 317 °C. The presence of NO in O2 further promoted soot oxidation over the catalysts with the ignition temperature decreased to about 300 °C. The DRIFTS results reveal that decomposition of less stable surface nitrites may account for NO2 formation in the ignition period of soot combustion, which thus participate in the auxiliary combustion process.
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Li XF, Sun YQ, Wang ZP, Mu ZG, Cui ZJ. [Catalytic Combustion of Soot Particulates over Rare Earth Pyrochlore Oxides Doped with Transition Metals]. Huan Jing Ke Xue 2017; 38:1348-1356. [PMID: 29965135 DOI: 10.13227/j.hjkx.201609228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Catalytic combustion is an efficient way to remove soot particulates from automobile exhausts. A series of rare earth pyrochlore oxides La2Sn1.8TM0.2O7 (TM=Sn, Mn, Fe, Co, Cu) were prepared with CTAB-assisted sol-gel method. The products were characterized by XRD,N2 Adsorption-Desorption, SEM, FT-IR, H2-TPR and PL techniques. Their catalytic activity for soot oxidation was investigated by TPO under tight conditions in both O2 and NO+O2 atmospheres. After calcination at 900℃, the as-synthesized oxides with pure pyrochlore phase displayed nanospheres with diameter of 30-60 nm and relatively large surface areas. The partial substitution of Sn with transition metals largely influenced the reduction behavior of pyrochlores especially on the low temperature range in H2-TPR profiles, which was due to the interactions between Sn and transition metals. The improved oxygen mobility might be derived from the structure defects induced by transition metals doping, which could be helpful in oxidation reactions. In comparison with uncatalyzed reactions, the La2Sn2O7 catalyst exhibited modest catalytic activity for soot combustion, while transition metals incorporation further enhanced the activity and selectivity. The improved activity of transition metals doped samples was likely to be associated with the improved reducibility and increased surface oxygen vacancies on the pyrochlore oxides. The presence of NO in the gas phase significantly enhanced the soot oxidation activity, which was due to the promotion effect of NO2. Especially, the densities of active oxygen sites and turnover frequency (TOF) values of the catalysts, quantified by isothermal anaerobic titration with soot as a probe molecule, were used to explain the different soot combustion behaviors. Among the pyrochlore oxides, the Co-doped pyrochlore sample displayed the highest ignition activity and the largest intrinsic activity with TOF of 3.20×10-3 s-1.
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Affiliation(s)
- Xi-Feng Li
- School of Environmental Science and Engineering, Shandong University, Ji'nan 250100, China
- College of Chemistry and Chemical Engineering, University of Ji'nan, Ji'nan 250022, China
| | - Yu-Qi Sun
- College of Chemistry and Chemical Engineering, University of Ji'nan, Ji'nan 250022, China
| | - Zhong-Peng Wang
- College of Chemistry and Chemical Engineering, University of Ji'nan, Ji'nan 250022, China
| | - Zong-Gang Mu
- College of Chemistry and Chemical Engineering, University of Ji'nan, Ji'nan 250022, China
| | - Zhao-Jie Cui
- School of Environmental Science and Engineering, Shandong University, Ji'nan 250100, China
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26
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Fischer C, Finkeldei S, Brandt F, Bosbach D, Luttge A. Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore. ACS Appl Mater Interfaces 2015; 7:17857-17865. [PMID: 26186697 DOI: 10.1021/acsami.5b04281] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.
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Affiliation(s)
- Cornelius Fischer
- ‡Earth Science Department, Rice University, 6100 Main Street, Houston, Texas 77005, United States
| | - Sarah Finkeldei
- §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany
| | - Felix Brandt
- §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany
| | - Dirk Bosbach
- §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany
| | - Andreas Luttge
- ‡Earth Science Department, Rice University, 6100 Main Street, Houston, Texas 77005, United States
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De los Santos DM, Navas J, Aguilar T, Sánchez-Coronilla A, Fernández-Lorenzo C, Alcántara R, Piñero JC, Blanco G, Martín-Calleja J. Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase. Beilstein J Nanotechnol 2015; 6:605-16. [PMID: 25821701 PMCID: PMC4362206 DOI: 10.3762/bjnano.6.62] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 02/05/2015] [Indexed: 05/16/2023]
Abstract
Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm(3+). ICP-AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm(3+) was confirmed by X-ray photoelectron spectroscopy and UV-vis spectroscopy: the incorporation of Tm(3+) was confirmed by the generation of new absorption bands that could be assigned to Tm(3+) transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase.
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Affiliation(s)
- Desiré M De los Santos
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Javier Navas
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Teresa Aguilar
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Antonio Sánchez-Coronilla
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Concha Fernández-Lorenzo
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Rodrigo Alcántara
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Jose Carlos Piñero
- Departamento de Ciencias de los Materiales, Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Ginesa Blanco
- Departamento de Ciencias de los Materiales, Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
| | - Joaquín Martín-Calleja
- Departamento de Química Física, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
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28
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Niven JF, Johnson MB, Bourque A, Murray PJ, James DD, Da̧bkowska HA, Gaulin BD, White MA. Magnetic phase transitions and magnetic entropy in the XY antiferromagnetic pyrochlores (Er 1-x Y x ) 2Ti 2O 7.. Proc Math Phys Eng Sci 2014; 470:20140387. [PMID: 25383026 DOI: 10.1098/rspa.2014.0387] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 08/08/2014] [Indexed: 11/12/2022] Open
Abstract
We present the results of experimental determination of the heat capacity of the pyrochlore Er2Ti2O7 as a function of temperature (0.35-300 K) and magnetic field (up to 9 T), and for magnetically diluted solid solutions of the general formula (Er1-x Y x )2Ti2O7 (x≤0.471). On either doping or increase of magnetic field, or both, the Néel temperature first shifts to lower temperature until a critical point above which there is no well-defined transition but a Schottky-like anomaly associated with the splitting of the ground state Kramers doublet. By taking into account details of the lattice contribution to the heat capacity, we accurately isolate the magnetic contribution to the heat capacity and hence to the entropy. For pure Er2Ti2O7 and for (Er1-x Y x )2Ti2O7, the magnetic entropy as a function of temperature evolves with two plateaus: the first at [Formula: see text], and the other at [Formula: see text]. When a very high magnetic field is applied, the first plateau is washed out. The influence of dilution at low values is similar to the increase of magnetic field, as we show by examination of the critical temperature versus critical field curve in reduced terms.
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Affiliation(s)
- John F Niven
- Department of Physics and Atmospheric Science , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
| | - Michel B Johnson
- Institute for Research in Materials , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
| | - Alex Bourque
- Department of Chemistry , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
| | - Patrick J Murray
- Department of Chemistry , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
| | - David D James
- Department of Chemistry , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
| | - Hanna A Da̧bkowska
- Brockhouse Institute for Materials Research , McMaster University , Hamilton, Ontario, L8S 4M1, Canada
| | - Bruce D Gaulin
- Brockhouse Institute for Materials Research , McMaster University , Hamilton, Ontario, L8S 4M1, Canada ; Department of Physics and Astronomy , McMaster University , Hamilton, Ontario, L8S 4M1, Canada
| | - Mary Anne White
- Department of Physics and Atmospheric Science , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada ; Institute for Research in Materials , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada ; Department of Chemistry , Dalhousie University , Halifax, Nova Scotia, B3H 4R2, Canada
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29
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Mouta R, Silva RX, Paschoal CWA. Tolerance factor for pyrochlores and related structures. Acta Crystallogr B Struct Sci Cryst Eng Mater 2013; 69:439-445. [PMID: 24056352 DOI: 10.1107/s2052519213020514] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 07/23/2013] [Indexed: 06/02/2023]
Abstract
In this work a new empirical tolerance factor for compounds with pyrochlore structure is proposed. This suggested tolerance factor is based on experimental structural data and on the tolerance factors proposed. However, since it does not depend on the structural data, this new tolerance factor permits the prediction of some properties of these compounds directly. Also, a good structure stability field for the pyrochlore formation is observed when this tolerance factor is used.
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Affiliation(s)
- R Mouta
- Departamento de Física, CCET, Universidade Federal do Maranhão, 65085-580, São Luís - MA, Brazil
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