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Xu M, Niu J, Wu G, Liao Q, Tan X, Yang D, Liu L, Li Y, Xia Y. Pressure-induced phase transition of Lu 2Ti 2O 7and Lu 1.5Ce 0.5Ti 2O 7+xpyrochlores. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:165402. [PMID: 38198736 DOI: 10.1088/1361-648x/ad1d1e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 01/10/2024] [Indexed: 01/12/2024]
Abstract
This study utilizes both experimental and computational approaches to investigate the performance of Lu2Ti2O7(LTO) and Lu1.5Ce0.5Ti2O7+x(LCTO) pyrochlores under high pressure. The structural changes of LTO and LCTO pyrochlores were characterized usingin-situsynchrotron x-ray diffraction (SXRD) andin-situRaman spectroscopy at pressures up to 44.6 GPa. The kinks inP-aandP-Vcurves at around 5 GPa are mainly attributed to the interaction between the pressure medium and the isostructural changes. The onset pressures for transitioning from the cubic pyrochlore phase (Fd-3 m) to the monoclinic phase (P21) are observed at 32.5 GPa and 38.1 GPa, respectively. It is important to note that at the highest measured pressures, the phase transition remains incomplete. This partial transition is likely the result of oriented disorder among cations and anions under high pressure. In addition, introducing Ce as a dopant significantly enhances structural stability. This can be explained by the larger ionic radius of Ce, which hinders the disordering process.
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Affiliation(s)
- Min Xu
- School of Nuclear Science and Technology, University of South China, Hengyang 421001, People's Republic of China
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
| | - Jingjing Niu
- State Key Laboratory of Tibetan Plateau Earth System Science, Resources and Environment (TPESRE), Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, People's Republic of China
| | - Guanfeng Wu
- School of Nuclear Science and Technology, University of South China, Hengyang 421001, People's Republic of China
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
| | - Qian Liao
- School of Nuclear Science and Technology, University of South China, Hengyang 421001, People's Republic of China
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
| | - Xi Tan
- School of Nuclear Science and Technology, University of South China, Hengyang 421001, People's Republic of China
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
| | - Dongyan Yang
- School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, People's Republic of China
| | - Longcheng Liu
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
- China Institute of Atomic Energy, Beijing 102413, People's Republic of China
| | - Yuhong Li
- School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, People's Republic of China
| | - Yue Xia
- School of Nuclear Science and Technology, University of South China, Hengyang 421001, People's Republic of China
- R&D Center of Radioactive Waste Treatment, Disposal and Modeling, University of South China, Hengyang 421001, People's Republic of China
- School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, People's Republic of China
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Abstract
Fuel cells (FCs), water electrolyzers (WEs), unitized regenerative fuel cells (URFCs), and metal-air batteries (MABs) are among the emerging electrochemical technologies for energy storage, fuel (H2), oxidant (O2), and clean energy production. Their commercial applications are hindered by the low oxygen reduction reaction/oxygen evolution reaction (ORR/OER) bifunctional activity (for URFCs and MABs), OER selectivity (brine electrolysis in seawater and Martian environments), and high cost of the benchmark electrocatalysts (OER: RuO2, IrO2 and ORR: Pt/C) which affects the performance and affordability of the devices. Low-cost electrocatalysts with highly symmetric ORR/OER bifunctional activity and high OER selectivity are crucial for large-scale FC, WE, URFC, and MAB application. Recent studies have revealed that tuning the structure of pyrochlore oxides provides a pathway to enhancing OER and ORR activity over a wide range of pH. Pyrochlore oxides commonly contain a cubic A2B2O7-x structure with two types of tetrahedrally coordinated O atoms containing (1) A-O-A and (2) A-O-B types with a cationic radii mismatch of rA/rB > 1.5 and propensity toward oxygen vacancy formation. The variety of pyrochlore oxides and their tunable properties make them attractive for a wide spectrum of applications. Among all the metal oxides, Ru-based pyrochlores (e.g., Pb2Ru2O7-x) exhibit the best bifunctional oxygen electrocatalytic activity, i.e., low bifunctionality index (BI), in alkaline medium. Furthermore, pyrochlores exhibit high OER selectivity in brine electrolytes due to the presence of surface oxygen vacancies, making them suitable for space applications (brine electrolysis on Mars) and coastal hydrogen generation. Their bifunctional activity and selectivity can be further amplified by (1) substituting "A" and "B" sites of pyrochlores (AA'BB'O7-x), (2) tuning metal oxidation states of A and B by varying synthesis conditions, and (3) modulating oxygen vacancy concentration, each of which yield favorable structural and electronic variations. In recent years, research on the synthesis and understanding of pyrochlores has significantly enhanced their viability, offering a new horizon in the quest for economical and active electrocatalysts. However, an account that focuses on critical developments in this field is still lacking.In this Account, we focus on the recent development of a variety of pyrochlore electrocatalysts to understand intrinsic structure-activity-selectivity-stability relationships in these materials. Recent developments and applications of pyrochlore-based electrocatalysts are discussed under the following headings: (1) modulation of crystal and electronic structure of pyrochlores, (2) structure-activity-stability relationships of different pyrochlores for OER and ORR, (3) development of OER-selective pyrochlores for brine electrolysis, and (4) the application of pyrochlores in electrochemical devices. Finally, we highlight some unaddressed issues such as the precise identification of active sites, which can be addressed in the future through advanced in situ and ex situ characterization techniques coupled with the density functional theory-based analyses. This Account provides foundational understanding to guide the comprehensive development of highly active, selective, stable and low-cost structurally engineered pyrochlores for high performance electrochemical devices.
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Affiliation(s)
- Pralay Gayen
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, United States
| | - Sulay Saha
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, United States
| | - Vijay Ramani
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, United States
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3
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Wardini JL, Vahidi H, Guo H, Bowman WJ. Probing Multiscale Disorder in Pyrochlore and Related Complex Oxides in the Transmission Electron Microscope: A Review. Front Chem 2021; 9:743025. [PMID: 34917587 PMCID: PMC8668443 DOI: 10.3389/fchem.2021.743025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Accepted: 10/15/2021] [Indexed: 11/13/2022] Open
Abstract
Transmission electron microscopy (TEM), and its counterpart, scanning TEM (STEM), are powerful materials characterization tools capable of probing crystal structure, composition, charge distribution, electronic structure, and bonding down to the atomic scale. Recent (S)TEM instrumentation developments such as electron beam aberration-correction as well as faster and more efficient signal detection systems have given rise to new and more powerful experimental methods, some of which (e.g., 4D-STEM, spectrum-imaging, in situ/operando (S)TEM)) facilitate the capture of high-dimensional datasets that contain spatially-resolved structural, spectroscopic, time- and/or stimulus-dependent information across the sub-angstrom to several micrometer length scale. Thus, through the variety of analysis methods available in the modern (S)TEM and its continual development towards high-dimensional data capture, it is well-suited to the challenge of characterizing isometric mixed-metal oxides such as pyrochlores, fluorites, and other complex oxides that reside on a continuum of chemical and spatial ordering. In this review, we present a suite of imaging and diffraction (S)TEM techniques that are uniquely suited to probe the many types, length-scales, and degrees of disorder in complex oxides, with a focus on disorder common to pyrochlores, fluorites and the expansive library of intermediate structures they may adopt. The application of these techniques to various complex oxides will be reviewed to demonstrate their capabilities and limitations in resolving the continuum of structural and chemical ordering in these systems.
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Affiliation(s)
- Jenna L. Wardini
- Materials Science and Engineering, University of California, Irvine, Irvine, CA, United States
| | - Hasti Vahidi
- Materials Science and Engineering, University of California, Irvine, Irvine, CA, United States
| | - Huiming Guo
- Materials Science and Engineering, University of California, Irvine, Irvine, CA, United States
| | - William J. Bowman
- Materials Science and Engineering, University of California, Irvine, Irvine, CA, United States
- Irvine Materials Research Institute, Irvine, CA, United States
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Subramani T, Voskanyan A, Jayanthi K, Abramchuk M, Navrotsky A. A Comparison of Order-Disorder in Several Families of Cubic Oxides. Front Chem 2021; 9:719169. [PMID: 34540800 PMCID: PMC8440809 DOI: 10.3389/fchem.2021.719169] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 08/02/2021] [Indexed: 11/23/2022] Open
Abstract
Order-disorder on both cation and oxygen sites is a hallmark of fluorite-derived structures, including pyrochlores. Ordering can occur on long- and short-range scales and can result in persistent metastable states. In various cubic oxide systems, different types of disorder are seen. The purpose of this paper is to review and compare the types and energetics of order-disorder phenomena in several families of cubic oxides having pyrochlore, weberite, defect fluorite, perovskite, rocksalt, and spinel structures. The goal is to better understand how structure, composition, and thermodynamic parameters (enthalpy and entropy) determine the feasibility of different competing ordering processes and structures in these diverse systems.
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Affiliation(s)
| | | | | | | | - A. Navrotsky
- School of Molecular Sciences and Navrotsky Eyring Center for Materials of the Universe, Arizona State University, Tempe, AZ, United States
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5
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Li X, Yan Z, Rahman S, Zhang J, Yang K, Li X, Kim J, Sun X, Wang L. Pressure induced band gap narrowing and phase transitions in Dy 2Ti 2O 7. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:215401. [PMID: 31978908 DOI: 10.1088/1361-648x/ab6f82] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
An isostructural phase transition and a cubic to tetragonal phase transition in spin-frustrated pyrochlore Dy2Ti2O7 (DTO) at 35 GPa and 46 GPa, respectively, were detected by x-ray diffraction (XRD) and Raman spectroscopy studies at room temperature under high pressure. The band gap of DTO gradually increased with the increasing pressure up to 20 GPa, after which it narrowed significantly around 35 GPa, and further manifested with a slight discontinuity around 46 GPa. Below 35 GPa, the evolution of band gap with pressure maintained a close relationship with the Ti-O bond length and the distortion of TiO6 octahedron. The remarkable narrowing of the band gap around 35 GPa implied the changes of the band structure and confirmed the isostructural phase transition. These findings provide an in-depth understanding of the evolution of the structure and the band gap of DTO under high pressure.
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Affiliation(s)
- Xin Li
- Department of Physics, Fudan University, Shanghai 200433, People's Republic of China. Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, People's Republic of China
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6
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Ali RF, Ovens JS, Starosta K, Gates BD. Novel defect-fluorite pyrochlore sodium niobate nanoparticles: solution-phase synthesis and radiation tolerance analysis. NANOSCALE 2019; 11:5489-5498. [PMID: 30860217 DOI: 10.1039/c8nr10385b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Materials possessing a defect-fluorite pyrochlore structure can have a range of useful properties that are sought after, which include their radiation tolerance, nuclear waste immobilization, and phase stability at elevated temperatures. In this study, we demonstrate for the first time the synthesis and a detailed analysis of defect-fluorite pyrochlore sodium niobate (NaNbO3) nanoparticles. This analysis included an investigation into their stability to elevated temperatures and neutron irradiation. A surfactant-assisted solvothermal method is used to prepare nanoparticles of NaNbO3. This solution-phase approach results in the formation of crystalline nanoparticles of a defect-fluorite pyrochlore NaNbO3 at relatively low temperatures. The products had an average diameter of ∼74 ± 11 nm. The nanoparticles adopted a defect-fluorite pyrochlore phase and matched the cubic Fm3[combining macron]m space group. This pyrochlore form of NaNbO3 was found to be stable up to 500 °C. The nanoparticles transformed into the orthorhombic and rhombohedral perovskite phases of NaNbO3 along with the introduction of a pseudo-hexagonal Nb2O5 at higher temperatures. These defect-fluorite pyrochlore nanoparticles of NaNbO3 also exhibited a resistance to radiation induced amorphization. The dimensions, phase, and crystallinity of the defect-fluorite pyrochlore nanoparticles after exposure to a flux of neutrons were comparable to those of the as-synthesized product. The thermal stability and radiation tolerance of these pyrochlore nanoparticles could be useful in the design of thermally resilient materials, high temperature catalysts, and durable materials for the handling and storage of radioactive waste.
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Affiliation(s)
- Rana Faryad Ali
- Department of Chemistry and 4D LABS, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
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Gupta S, Abdou M, Ghosh PS, Zuniga JP, Mao Y. Thermally Induced Disorder-Order Phase Transition of Gd 2Hf 2O 7:Eu 3+ Nanoparticles and Its Implication on Photo- and Radioluminescence. ACS OMEGA 2019; 4:2779-2791. [PMID: 31459510 PMCID: PMC6648517 DOI: 10.1021/acsomega.8b03458] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Accepted: 01/17/2019] [Indexed: 05/23/2023]
Abstract
Crystal structure has a strong influence on the luminescence properties of lanthanide-doped materials. In this work, we have investigated the thermally induced structural transition in Gd2Hf2O7 (GHO) using Eu3+ ions as the spectroscopic probe. It was found that complete phase transition from the disordered fluorite phase (DFP) to the ordered pyrochlore phase (OPP) can be achieved in GHO with the increase of annealing temperature from 650 → 1100 → 1300 °C. OPP is the more stable structural form for the GHOE nanoparticles (NPs) annealed at a higher temperature based on the energy calculation by density functional theory (DFT). The asymmetry ratio of the GHOE-650 NPs was the highest, whereas the quantum yield, luminescence intensity, and lifetime values of the GHOE-1300 NPs were the highest. Emission intensity of Eu3+ ions increases significantly with the phase transition from the DFP to OPP phase and is attributed to the higher radiative transition rate (281 s-1) of the 5D0 level of the Eu3+ ion in the environment with relatively lower symmetry (C 2v ) because of the increase of crystal size. As the structure changes from DFP to OPP, radioluminescence showed tunable color change from red to orange. The Eu3+ local structure obtained from DFT calculation confirmed the absence of inversion symmetry in the DFP structure, which is consistent with the experimental emission spectra and Stark components. We also elucidated the host to dopant optical energy transfer through density of states calculations. Overall, our current studies present important observations for the GHOE NPs: (i) thermally induced order-disorder phase transition, (ii) change of point group symmetry around Eu3+ ions in the two phases, (iii) high thermal stability, and (iv) tunability of radioluminescent color. This work provides fundamental understanding of the relationship between the crystal structure and photophysical properties of lanthanide-doped materials and helps design a strategy for advanced optoelectronic materials.
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Affiliation(s)
- Santosh
K. Gupta
- Department
of Chemistry and School of Earth, Environmental, and Marine
Sciences, University of Texas Rio Grande
Valley, 1201 West University Drive, Edinburg, Texas 78539, United States
- Radiochemistry Division and Materials Science
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Maya Abdou
- Department
of Chemistry and School of Earth, Environmental, and Marine
Sciences, University of Texas Rio Grande
Valley, 1201 West University Drive, Edinburg, Texas 78539, United States
| | - Partha Sarathi Ghosh
- Radiochemistry Division and Materials Science
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Jose P. Zuniga
- Department
of Chemistry and School of Earth, Environmental, and Marine
Sciences, University of Texas Rio Grande
Valley, 1201 West University Drive, Edinburg, Texas 78539, United States
| | - Yuanbing Mao
- Department
of Chemistry and School of Earth, Environmental, and Marine
Sciences, University of Texas Rio Grande
Valley, 1201 West University Drive, Edinburg, Texas 78539, United States
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8
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Niu J, Wu X, Zhang H, Qin S. Pressure-induced phase transition of La2Zr2O7 and La0.5Gd1.5Zr2O7 pyrochlore. RSC Adv 2019; 9:18954-18962. [PMID: 35516883 PMCID: PMC9065121 DOI: 10.1039/c9ra03438b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 06/12/2019] [Indexed: 11/21/2022] Open
Abstract
In situ high-pressure experiments on La2Zr2O7 and La0.5Gd1.5Zr2O7 have been carried out at up to approximately 40 GPa using synchrotron X-ray diffraction and Raman spectroscopy combined with a diamond anvil cell technique.
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Affiliation(s)
- Jingjing Niu
- Key Laboratory of Orogenic Belts and Crustal Evolution
- School of Earth and Space Sciences
- MOE
- Peking University
- Beijing 100871
| | - Xiang Wu
- State Key Laboratory of Geological Processes and Mineral Resources
- China University of Geosciences (Wuhan)
- P. R. China
| | - Haibin Zhang
- Innovation Research Team for Advanced Ceramics
- Institute of Nuclear Physics and Chemistry
- China Academy of Engineering Physics
- Mianyang
- China
| | - Shan Qin
- Key Laboratory of Orogenic Belts and Crustal Evolution
- School of Earth and Space Sciences
- MOE
- Peking University
- Beijing 100871
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Park S, Tracy CL, Zhang F, Park C, Trautmann C, Tkachev SN, Lang M, Mao WL, Ewing RC. Radiation-induced disorder in compressed lanthanide zirconates. Phys Chem Chem Phys 2018; 20:6187-6197. [PMID: 29431823 DOI: 10.1039/c7cp08664d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The effects of swift heavy ion irradiation-induced disordering on the behavior of lanthanide zirconate compounds (Ln2Zr2O7 where Ln = Sm, Er, or Nd) at high pressures are investigated. After irradiation with 2.2 GeV 197Au ions, the initial ordered pyrochlore structure (Fd3[combining macron]m) transformed to a defect-fluorite structure (Fm3[combining macron]m) in Sm2Zr2O7 and Nd2Zr2O7. For irradiated Er2Zr2O7, which has a defect-fluorite structure, ion irradiation induces local disordering by introducing Frenkel defects despite retention of the initial structure. When subjected to high pressures (>29 GPa) in the absence of irradiation, all of these compounds transform to a cotunnite-like (Pnma) phase, followed by sluggish amorphization with further compression. However, if these compounds are irradiated prior to compression, the high pressure cotunnite-like phase is not formed. Rather, they transform directly from their post-irradiation defect-fluorite structure to an amorphous structure upon compression (>25 GPa). Defects and disordering induced by swift heavy ion irradiation alter the transformation pathways by raising the energetic barriers for the transformation to the high pressure cotunnite-like phase, rendering it inaccessible. As a result, the high pressure stability field of the amorphous phase is expanded to lower pressures when irradiation is coupled with compression. The responses of materials in the lanthanide zirconate system to irradiation and compression, both individually and in tandem, are strongly influenced by the specific lanthanide composition, which governs the defect energetics at extreme conditions.
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Affiliation(s)
- Sulgiye Park
- Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA.
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10
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Park S, Rittman DR, Tracy CL, Chapman KW, Zhang F, Park C, Tkachev SN, O'Quinn E, Shamblin J, Lang M, Mao WL, Ewing RC. A 2TiO 5 (A = Dy, Gd, Er, Yb) at High Pressure. Inorg Chem 2018; 57:2269-2277. [PMID: 29420026 DOI: 10.1021/acs.inorgchem.7b03106] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The structural evolution of lanthanide A2TiO5 (A = Dy, Gd, Yb, Er) at high pressure is investigated using synchrotron X-ray diffraction. The effects of A-site cation size and of the initial structure are systematically examined by varying the composition of the isostructural lanthanide titanates and the structure of dysprosium titanate polymorphs (orthorhombic, hexagonal, and cubic), respectively. All samples undergo irreversible high-pressure phase transformations, but with different onset pressures depending on the initial structure. While each individual phase exhibits different phase transformation histories, all samples commonly experience a sluggish transformation to a defect cotunnite-like (Pnma) phase for a certain pressure range. Orthorhombic Dy2TiO5 and Gd2TiO5 form P21am at pressures below 9 GPa and Pnma above 13 GPa. Pyrochlore-type Dy2TiO5 and Er2TiO5 as well as defect-fluorite-type Yb2TiO5 form Pnma at ∼21 GPa, followed by Im3̅m. Hexagonal Dy2TiO5 forms Pnma directly, although a small amount of remnants of hexagonal Dy2TiO5 is observed even at the highest pressure (∼55 GPa) reached, indicating kinetic limitations in the hexagonal Dy2TiO5 phase transformations at high pressure. Decompression of these materials leads to different metastable phases. Most interestingly, a high-pressure cubic X-type phase (Im3̅m) is confirmed using high-resolution transmission electron microscopy on recovered pyrochlore-type Er2TiO5. The kinetic constraints on this metastable phase yield a mixture of both the X-type phase and amorphous domains upon pressure release. This is the first observation of an X-type phase for an A2BO5 composition at high pressure.
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Affiliation(s)
- Sulgiye Park
- Department of Geological Science, Stanford University , Stanford, California 94305, United States
| | - Dylan R Rittman
- Department of Geological Science, Stanford University , Stanford, California 94305, United States
| | - Cameron L Tracy
- Department of Geological Science, Stanford University , Stanford, California 94305, United States
| | - Karena W Chapman
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Fuxiang Zhang
- Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Changyong Park
- HPCAT, Carnegie Institution of Washington , Argonne, Illinois 60439, United States
| | - Sergey N Tkachev
- Center for Advanced Radiation Sources, University of Chicago , Chicago, Illinois 60637, United States
| | - Eric O'Quinn
- Department of Nuclear Engineering, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Jacob Shamblin
- Department of Nuclear Engineering, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Maik Lang
- Department of Nuclear Engineering, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Wendy L Mao
- Department of Geological Science, Stanford University , Stanford, California 94305, United States.,Stanford Institute for Materials & Energy Sciences, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States
| | - Rodney C Ewing
- Department of Geological Science, Stanford University , Stanford, California 94305, United States
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11
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Turner KM, Tracy CL, Mao WL, Ewing RC. Lanthanide stannate pyrochlores (Ln 2Sn 2O 7; Ln = Nd, Gd, Er) at high pressure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:504005. [PMID: 29176046 DOI: 10.1088/1361-648x/aa9960] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Lanthanide stannate pyrochlores (Ln2Sn2O7; Ln = Nd, Gd, and Er) were investigated in situ to 50 GPa in order to determine their structural response to compression and compare their response to that of lanthanide titanate, zirconate, and hafnate pyrochlores. The cation radius ratio of A3+/B4+ in pyrochlore oxides (A2B2O7) is thought to be the dominant feature that influences their response on compression. The ionic radius of Sn4+ is intermediate to that of Ti4+, Zr4+, and Hf4+, but the 〈Sn-O〉 bond in stannate pyrochlore is more covalent than the 〈B-O〉 bonds in titanates, zirconate, and hafnates. In stannates, based on in situ Raman spectroscopy, pyrochlore cation and anion sublattices begin to disorder with the onset of compression, first measured at 0.3 GPa. The extent of sublattice disorder versus pressure is greater in stannates with a smaller Ln3+ cation. Stannate pyrochlores (Fd-3m) begin a sluggish transformation to an orthorhombic, cotunnite-like structure at ~28 GPa; similar transitions have been observed in titanate, zirconate, and hafnate pyrochlores at varying pressures (18-40 GPa) with cation radius ratio. The extent of the phase transition versus pressure varies directly with the size of the Ln3+ cation. Post-decompression from ~50 GPa, Er2Sn2O7 and Gd2Sn2O7 adopt a pyrochlore structure, rather than the multi-scale defect-fluorite + weberite-type structure adopted by Nd2Sn2O7 that is characteristic of titanate, zirconate, and hafnate pyrochlores under similar conditions. Like pyrochlore titanates, zirconates, and hafnates, the bulk modulus, B 0, of stannates varies linearly and inversely with cation radius ratio from 1 1 1 GPa (Nd2Sn2O7) to 251 GPa (Er2Sn2O7). The trends of bulk moduli in stannates in this study are in excellent agreement with previous experimental studies on stannates and suggest that the size of the Ln3+ cation is the primary determining factor of B 0. Additionally, when normalized to r A/r B, the bulk moduli of stannates are comparable to those of zirconates and hafnates, which vary from titanates. Our results suggest that the cation radius ratio strongly influences the bulk moduli of stannates, as well as their overall compression response.
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Affiliation(s)
- Katlyn M Turner
- Department of Geological Sciences, Stanford University, 359 Green Earth Sciences Building, 367 Panama Street, Stanford, CA 94305-2115, United States of America
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