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Title: Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}

Abstract

Two cations A and B in A{sub 2}BO{sub 4} spinels appear in precise 2:1 Daltonian ratio ('line compounds') only at very low temperature. More typically, at finite temperature, they tend to become either A rich or B rich. Here we survey the experimentally observed stoichiometry asymmetries and describe the first-principles framework for calculating these. Defect calculations based on first principles are used to calculate the enthalpies of substitution of A atom {Delta}H(A{sub T{sub d}}) and B atom {Delta}H(B{sub O{sub h}}) and determine their site occupancies leading to (non)-stoichiometry. In Co{sub 2}ZnO{sub 4}, the result of the calculation for site occupancy compares well with that measured via anomalous x-ray diffraction. Further, the calculated phase boundary also compares well with that measured via Rietveld refinement of x-ray diffraction data on bulk ceramic sintered samples of Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}. These results show that Co{sub 2}ZnO{sub 4} is heavily Co nonstoichiometric above 500 deg. C, whereas Rh{sub 2}ZnO{sub 4} is slightly Zn nonstoichiometric. We found that, in general, the calculated {Delta}H(A{sub T{sub d}}) is smaller than {Delta}H(B{sub O{sub h}}), if the A-rich competing phase is isostructural with the A{sub 2}BO{sub 4} host, for example, A{sub 2}AO{sub 4}, whereas B-rich competingmore » phase is not, for example, BO. This observation is used to qualitatively explain nonstoichiometry and solid solutions observed in other spinels.« less

Authors:
; ; ;  [1]; ; ;  [2]; ;  [3];  [3];  [4]
  1. National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
  2. Northwestern University, Evanston, Illinois 60208 (United States)
  3. SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)
  4. (United States)
Publication Date:
OSTI Identifier:
21596841
Resource Type:
Journal Article
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 84; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevB.84.064109; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1098-0121
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; ASYMMETRY; ATOMS; CATIONS; CERAMICS; COBALT COMPOUNDS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; CRYSTAL DEFECTS; ENTHALPY; OXYGEN COMPOUNDS; RHODIUM COMPOUNDS; SOLID SOLUTIONS; SPINELS; STOICHIOMETRY; X-RAY DIFFRACTION; ZINC COMPOUNDS; CHARGED PARTICLES; COHERENT SCATTERING; CRYSTAL STRUCTURE; DIFFRACTION; DISPERSIONS; EVALUATION; HOMOGENEOUS MIXTURES; IONS; MINERALS; MIXTURES; OXIDE MINERALS; PHYSICAL PROPERTIES; REFRACTORY METAL COMPOUNDS; SCATTERING; SIMULATION; SOLUTIONS; THERMODYNAMIC PROPERTIES; TRANSITION ELEMENT COMPOUNDS

Citation Formats

Paudel, Tula R., Lany, Stephan, D'Avezac, Mayeul, Zunger, Alex, Perry, Nicola H., Nagaraja, Arpun R., Mason, Thomas O., Bettinger, Joanna S., Toney, Michael F., Shi, Yezhou, and Stanford University, Stanford, California 94305. Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}. United States: N. p., 2011. Web. doi:10.1103/PHYSREVB.84.064109.
Paudel, Tula R., Lany, Stephan, D'Avezac, Mayeul, Zunger, Alex, Perry, Nicola H., Nagaraja, Arpun R., Mason, Thomas O., Bettinger, Joanna S., Toney, Michael F., Shi, Yezhou, & Stanford University, Stanford, California 94305. Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}. United States. doi:10.1103/PHYSREVB.84.064109.
Paudel, Tula R., Lany, Stephan, D'Avezac, Mayeul, Zunger, Alex, Perry, Nicola H., Nagaraja, Arpun R., Mason, Thomas O., Bettinger, Joanna S., Toney, Michael F., Shi, Yezhou, and Stanford University, Stanford, California 94305. Mon . "Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}". United States. doi:10.1103/PHYSREVB.84.064109.
@article{osti_21596841,
title = {Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}},
author = {Paudel, Tula R. and Lany, Stephan and D'Avezac, Mayeul and Zunger, Alex and Perry, Nicola H. and Nagaraja, Arpun R. and Mason, Thomas O. and Bettinger, Joanna S. and Toney, Michael F. and Shi, Yezhou and Stanford University, Stanford, California 94305},
abstractNote = {Two cations A and B in A{sub 2}BO{sub 4} spinels appear in precise 2:1 Daltonian ratio ('line compounds') only at very low temperature. More typically, at finite temperature, they tend to become either A rich or B rich. Here we survey the experimentally observed stoichiometry asymmetries and describe the first-principles framework for calculating these. Defect calculations based on first principles are used to calculate the enthalpies of substitution of A atom {Delta}H(A{sub T{sub d}}) and B atom {Delta}H(B{sub O{sub h}}) and determine their site occupancies leading to (non)-stoichiometry. In Co{sub 2}ZnO{sub 4}, the result of the calculation for site occupancy compares well with that measured via anomalous x-ray diffraction. Further, the calculated phase boundary also compares well with that measured via Rietveld refinement of x-ray diffraction data on bulk ceramic sintered samples of Co{sub 2}ZnO{sub 4} and Rh{sub 2}ZnO{sub 4}. These results show that Co{sub 2}ZnO{sub 4} is heavily Co nonstoichiometric above 500 deg. C, whereas Rh{sub 2}ZnO{sub 4} is slightly Zn nonstoichiometric. We found that, in general, the calculated {Delta}H(A{sub T{sub d}}) is smaller than {Delta}H(B{sub O{sub h}}), if the A-rich competing phase is isostructural with the A{sub 2}BO{sub 4} host, for example, A{sub 2}AO{sub 4}, whereas B-rich competing phase is not, for example, BO. This observation is used to qualitatively explain nonstoichiometry and solid solutions observed in other spinels.},
doi = {10.1103/PHYSREVB.84.064109},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
issn = {1098-0121},
number = 6,
volume = 84,
place = {United States},
year = {2011},
month = {8}
}