Cation disorder in MgX2O4 (X = Al, Ga, In) spinels from first principles

We have performed first-principles density functional theory calculations to investigate the possible physical origins of the discrepancies between the existing theoretical and experimental studies on cation distribution in MgX2O4 (X = Al, Ga, In) spinel oxides. We show that for MgGa2O4 and MgIn2O4, it is crucial to consider the effects of lattice vibrations to achieve agreement between theory and experiment. For MgAl2O4, we find that neglecting short-range order effects in thermodynamic modeling can lead to significant underestimation of the degree of inversion. Furthermore, we demonstrate that the common practice of representing disordered structures by randomly exchanging atoms within a small periodic supercell can incur large computational error due to either insufficient statistical sampling or finite supercell size effects.

我们进行了第一性原理密度泛函理论计算，以研究关于MgX₂O₄（X = Al，Ga，In）尖晶石氧化物中阳离子分布的现有理论和实验研究之间差异的可能物理根源。我们表明，对于MgGa₂O₄和MgIn₂O₄，考虑晶格振动的影响对于实现理论和实验之间的一致性至关重要。对于MgAl₂O₄，我们发现，在热力学建模中忽略短程有序效应会导致对反位程度的严重低估。此外，我们证明，通过在小的周期性超胞内随机交换原子来表示无序结构的常见做法，由于统计抽样不足或有限超胞尺寸效应，可能会产生较大的计算误差。