Theoretical explanation of the uniform compressibility behavior observed in oxide spinels

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Simple algebraic equations show that the bulk compressibility in spinel-type compounds can be expressed by means of cation oxide polyhedral compressibilities and a term that accounts for the pressure effect on the internal oxygen position in the unit cell. The equations explain (i) the difference of compressibilities at octahedral and tetrahedral sites, (ii) why the macroscopic bulk modulus can be estimated as the average of these polyhedral bulk moduli, and (iii) the uniform behavior found in oxide spinels under hydrostatic pressure. Quantum-mechanical ab initio perturbed ion results on MgAl2O4, ZnAl2O4, ZnGa2O4, and MgGa2O4 direct spinels and on MgGa2O4 inverse spinel are reported to illustrate the interpretative capabilities of the proposed equations.

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Physical Review B - Condensed Matter and Materials Physics