Asymmetric cation nonstoichiometry in spinels: Site occupancy in Co 2 ZnO 4 and Rh 2 ZnO 4

Tula R. Paudel*, Stephan Lany, Mayeul D'Avezac, Alex Zunger, Nicola H. Perry, Arpun R. Nagaraja, Thomas O Mason, Joanna S. Bettinger, Yezhou Shi, Michael F. Toney

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

Two cations A and B in A 2 BO 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 ΔH(AT d ) and B atom ΔH(BO h ) and determine their site occupancies leading to (non)-stoichiometry. In Co 2 ZnO 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 2 ZnO 4 and Rh 2 ZnO 4 . These results show that Co 2 ZnO 4 is heavily Co nonstoichiometric above 500C, whereas Rh 2 ZnO 4 is slightly Zn nonstoichiometric. We found that, in general, the calculated ΔH(AT d ) is smaller than ΔH(BO h ), if the A-rich competing phase is isostructural with the A 2 BO 4 host, for example, A 2 AO 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.

Original languageEnglish (US)
Article number064109
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume84
Issue number6
DOIs
StatePublished - Aug 22 2011

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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