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Biswas S, Naushad N, S K, Kamble VB. Resistive Avalanches in La 1-xSr xCoO 3-δ ( x = 0, 0.3) Thin Films and Their Reversible Evolution by Tuning Lattice Oxygen Vacancies (δ). ACS MATERIALS AU 2024; 4:308-323. [PMID: 38737118 PMCID: PMC11083121 DOI: 10.1021/acsmaterialsau.3c00101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 01/18/2024] [Accepted: 01/23/2024] [Indexed: 05/14/2024]
Abstract
Strong correlations are often manifested by exotic electronic phases and phase transitions. LaCoO3-δ (LCO) is a system that exhibits such strong electronic correlations with lattice-spin-charge-orbital degrees of freedom. Here, we show that mesoscopic oxygen-deficient LCO films show resistive avalanches of about 2 orders of magnitude due to the metal-insulator transition (MIT) of the film at about 372 K for the 25 W RF power-deposited LCO film on the Si/SiO2 substrate. In bulk, this transition is otherwise gradual and occurs over a very large temperature range. In thin films of LCO, the oxygen deficiency (0 < δ < 0.5) is more easily reversibly tuned, resulting in avalanches. The avalanches disappear after vacuum annealing, and the films behave like normal insulators (δ ∼0.5) with Co2+ in charge ordering alternatively with Co3+. This oxidation state change induces spin state crossovers that result in a spin blockade in the insulating phase, while the conductivity arises from hole hopping among the allowed cobalt Co4+ ion spin states at high temperature. The chemical pressure (strain) of 30% Sr2+ doping at the La3+ site results in reduction in the avalanche magnitude as well as their retention in subsequent heating cycles. The charge nonstoichiometry arising due to Sr2+ doping is found to contribute toward hole doping (i.e., Co3+ oxidation to Co4+) and thereby the retention of the hole percolation pathway. This is also manifested in energies of crossover from the 3D variable range hopping (VRH) type transport observed in the temperature range of 300-425 K, while small polaron hopping (SPH) is observed in the temperature range of 600-725 K for LCO. On the other hand, Sr-doped LCO does not show any crossover and only the VRH type of transport. The strain due to Sr2+ doping refrains the lattice from complete conversion of δ going to 0.5, retaining the avalanches.
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Affiliation(s)
- Soumya Biswas
- School of Physics, Indian Institute
of Science Education and Research, Thiruvananthapuram 695551, India
| | - Noora Naushad
- School of Physics, Indian Institute
of Science Education and Research, Thiruvananthapuram 695551, India
| | - Kalyani S
- School of Physics, Indian Institute
of Science Education and Research, Thiruvananthapuram 695551, India
| | - Vinayak B. Kamble
- School of Physics, Indian Institute
of Science Education and Research, Thiruvananthapuram 695551, India
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Nwambaekwe KC, Ramoroka ME, Yussuf ST, Morudu TC, Ndipingwi MM, Iwuoha EI. Tb- and Eu-doped yttrium oxyselenides as novel absorber layers for superstrate thin-film photovoltaics: improved spectral optical absorption and green-red phosphor activation. NANOSCALE 2023; 15:17147-17172. [PMID: 37853791 DOI: 10.1039/d3nr01162c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2023]
Abstract
To generate and deliver alternative sustainable energy in the face of the current energy crisis, new materials that can capture solar energy and transform it into other useful energies are required. Rare-earth (RE) oxychalcogenides are now being used more frequently as up/down-conversion materials in established photovoltaic (PV) devices to boost their PV performance. Here, through an efficient microwave assisted synthesis procedure, novel nanoplate/sheet shaped nanomaterials of yttrium oxyselenide (YOSe) and its analogues doped with Tb and Eu (YOSe:Tb and YOSe:Eu) were successfully synthesized. Analyses of the structure, stability, morphology, light absorption, and electrochemistry were performed. This work showed that the parent YOSe exhibited green (543 nm) and red (615 nm) emission luminescence when doped with Tb and Eu with a luminescence quantum yield (LQY) of 0.56 and 0.53 for YOSe:Tb and YOSe:Eu nanomaterials, respectively. The surface and material conductivity of YOSe improved with the addition of the dopant elements, with the best outcome shown in YOSe:Eu, according to electrokinetic research evidenced by the enhanced current peaks, reduced charge-transfer resistance (Rct) and low impedance magnitude (Zmag) through electrochemical experiments. These improvements were induced by the distinctive properties of the dopant elements. PCEs of 0.25%, 0.67%, and 1.20% were obtained for YOSe, YOSe:Tb, and YOSe:Eu-based PV devices, respectively, using the nanomaterials as novel absorber layers in a superstrate device design. Our results can initiate further exploitation of the doped host structure for effective down-conversion NIR luminescence for applications in PV devices and to boost the PV performance of existing solar cells.
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Affiliation(s)
- Kelechi C Nwambaekwe
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
| | - Morongwa E Ramoroka
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
| | - Sodiq T Yussuf
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
| | - Tshaamano C Morudu
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
| | - Miranda M Ndipingwi
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
| | - Emmanuel I Iwuoha
- Key Laboratory for NanoElectrochemistry, University of the Western Cape Sensor Laboratories (SensorLab), 4th Floor Chemical Sciences Building, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Cape Town, South Africa.
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Wang X, Li M, Wang P, Sun D, Ding L, Li H, Tang Y, Fu G. Spin-Selective Coupling in Mott-Schottky Er 2 O 3 -Co Boosts Electrocatalytic Oxygen Reduction. SMALL METHODS 2023:e2300100. [PMID: 37029579 DOI: 10.1002/smtd.202300100] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/15/2023] [Indexed: 06/19/2023]
Abstract
Alkaline oxygen reduction reaction (ORR) is critical to electrochemical energy conversion technology, yet the rational breaking of thermodynamic inhibition for ORR through spin regulation remains a challenge. Herein, a Mott-Schottky catalyst consisting of Er2 O3 -Co particles uniformly implanted into carbon nanofibers (Er2 O3 -Co/CNF) is designed for enhancing ORR via spin-selective coupling. The optimized Er2 O3 -Co/CNF affords a high half-wave potential (0.835 V vs reversible hydrogen electrode, RHE) and onset potential (0.989 VRHE ) for the ORR surpassing individual Co/CNF and Er2 O3 /CNF. Theoretical calculations reveal the introduction of Er2 O3 optimizes the electronic structure of Co through Er(4f)-O(2p)-Co(3d) gradient orbital coupling, resulting in significantly enhanced ORR performance. Through gradient orbital coupling, the induced spin-up hole in Co 3d states endows the Er-O-Co unit active site with a spin-selective coupling channel for electron transition. This favors the decrease of the energy gap in the potential-limiting step, thus achieving a high theoretical limiting potential of 0.77 VRHE for the Er2 O3 -Co. Moreover, the potential practicability of Er2 O3 -Co/CNF as an air-cathode is also demonstrated in Zn-air batteries. This work is believed to provide, new perspectives for the design of efficient ORR electrocatalysts by engineering spin-selective coupling induced by rare-earth oxides.
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Affiliation(s)
- Xuan Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Meng Li
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Pu Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Dongmei Sun
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Linfei Ding
- Advanced Analysis and Testing Center, Nanjing Forestry University, Nanjing, 210037, China
| | - Hao Li
- Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai, 980-8577, Japan
| | - Yawen Tang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Gengtao Fu
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
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Wang X, Wang J, Wang P, Li L, Zhang X, Sun D, Li Y, Tang Y, Wang Y, Fu G. Engineering 3d-2p-4f Gradient Orbital Coupling to Enhance Electrocatalytic Oxygen Reduction. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2206540. [PMID: 36085436 DOI: 10.1002/adma.202206540] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 08/24/2022] [Indexed: 06/15/2023]
Abstract
The development of highly efficient and economical materials for the oxygen reduction reaction (ORR) plays a key role in practical energy conversion technologies. However, the intrinsic scaling relations exert thermodynamic inhibition on realizing highly active ORR electrocatalysts. Herein, a novel and feasible gradient orbital coupling strategy for tuning the ORR performance through the construction of Co 3d-O 2p-Eu 4f unit sites on the Eu2 O3 -Co model is proposed. Through the gradient orbital coupling, the pristine ionic property between Eu and O atoms is assigned with increased covalency, which optimizes the eg occupancy of Co sites, and weakens the OO bond, thus ultimately breaking the scaling relation between *OOH and *OH at Co-O-Eu unit sites. The optimized model catalyst displays onset and half-wave potential of 1.007 and 0.887 V versus reversible hydrogen electrode, respectively, which are higher than those of commercial Pt/C and most Co-based catalysts ever reported. In addition, the catalyst is found to possess superior selectivity and durability. It also reveals better cell performance than commercial noble-metal catalysts in Zn-air batteries in terms of high power/energy densities and long cycle life. This study provides a new perspective for electronic modulation strategy by the construction of gradient 3d-2p-4f orbital coupling.
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Affiliation(s)
- Xuan Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Jingwen Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Pu Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Liangcheng Li
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Xinyue Zhang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Dongmei Sun
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Yafei Li
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Yawen Tang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Yu Wang
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
| | - Gengtao Fu
- Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing, 210023, China
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Stankov S, Merkel DG, Kalt J, Göttlicher J, Łażewski J, Sternik M, Jochym PT, Piekarz P, Baumbach T, Chumakov AI, Rüffer R. Phonon confinement and interface lattice dynamics of ultrathin high- k rare earth sesquioxide films: the case of Eu 2O 3 on YSZ(001). NANOSCALE ADVANCES 2021; 4:19-25. [PMID: 36132967 PMCID: PMC9419856 DOI: 10.1039/d1na00728a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 11/23/2021] [Indexed: 06/16/2023]
Abstract
The spatial confinement of atoms at surfaces and interfaces significantly alters the lattice dynamics of thin films, heterostructures and multilayers. Ultrathin films with high dielectric constants (high-k) are of paramount interest for applications as gate layers in current and future integrated circuits. Here we report a lattice dynamics study of high-k Eu2O3 films with thicknesses of 21.3, 2.2, 1.3, and 0.8 nm deposited on YSZ(001). The Eu-partial phonon density of states (PDOS), obtained from nuclear inelastic scattering, exhibits broadening of the phonon peaks accompanied by up to a four-fold enhancement of the number of low-energy states compared to the ab initio calculated PDOS of a perfect Eu2O3 crystal. Our analysis demonstrates that while the former effect reflects the reduced phonon lifetimes observed in thin films due to scattering from lattice defects, the latter phenomenon arises from an ultrathin EuO layer formed between the thin Eu2O3 film and the YSZ(001) substrate. Thus, our work uncovers another potential source of vibrational anomalies in thin films and multilayers, which has to be cautiously considered.
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Affiliation(s)
- Svetoslav Stankov
- Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology D-76344 Eggenstein-Leopoldshafen Germany +49 (0)721 608-26 172 +49 (0)721 608-28 680
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology D-76131 Karlsruhe Germany
| | - Dániel G Merkel
- Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Hungarian Academy of Sciences H-1525 Budapest Hungary
- Centre for Energy Research POB 49 H-1525 Budapest Hungary
| | - Jochen Kalt
- Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology D-76344 Eggenstein-Leopoldshafen Germany +49 (0)721 608-26 172 +49 (0)721 608-28 680
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology D-76131 Karlsruhe Germany
| | - Jörg Göttlicher
- Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology D-76344 Eggenstein-Leopoldshafen Germany +49 (0)721 608-26 172 +49 (0)721 608-28 680
| | - Jan Łażewski
- Institute of Nuclear Physics, Polish Academy of Sciences PL-31342 Kraków Poland
| | - Małgorzata Sternik
- Institute of Nuclear Physics, Polish Academy of Sciences PL-31342 Kraków Poland
| | - Paweł T Jochym
- Institute of Nuclear Physics, Polish Academy of Sciences PL-31342 Kraków Poland
| | - Przemysław Piekarz
- Institute of Nuclear Physics, Polish Academy of Sciences PL-31342 Kraków Poland
| | - Tilo Baumbach
- Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology D-76344 Eggenstein-Leopoldshafen Germany +49 (0)721 608-26 172 +49 (0)721 608-28 680
- Laboratory for Applications of Synchrotron Radiation, Karlsruhe Institute of Technology D-76131 Karlsruhe Germany
| | | | - Rudolf Rüffer
- ESRF-The European Synchrotron F-38043 Grenoble France
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