Compressional behavior of MgCr2O4 spinel from first-principles simulation

The compressional behavior of the MgCr₂O₄ spinel has been investigated with the CASTEP code using density functional theory and planewave pseudopotential technique. We treated the exchange-correlation interaction by both the local density approximation (LDA) and generalized gradient approximation (GGA) with the Perdew-Burker-Ernzerhof functional. Our simulation was conducted for the pressure range of 0–19 GPa. We obtained the isothermal bulk modulus (K_T) of the MgCr₂O₄ spinel as 181.46(48) GPa (GGA; low boundary) or 216.1(11) GPa (LDA; high boundary), with its first derivative (K'_T) as 4.41(6) or 4.5(1), respectively. The oxygen parameter u is not constant but negatively correlated with P, and decreases by about 0.5–0.6% for the investigated P range. The component polyhedra have different compressibilities, increasing in the order of (O₄)₁<CrO₆<(O₄)₂<O₆<MgO₄. The Mg-O bond in the MgO₄ tetrahedron is much more compressible than the Cr-O bond in the CrO₆ octahedron.