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Theoretical Characterizations of Spinels Containing Iron and Vanadium via ab initio Calculations

机译：通过从头算计算含铁和钒的尖晶石的理论表征

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We have employed ab initio approaches to investigate normal and inverse spinels containing iron and vanadium. The valence states of tetrahedral and octahedral Fe and V were firstly calibrated with reference oxides FeO (rocksalt), Fe_(2)O_(3) (corundum), VO (rocksalt) and Fe_(2)O_(3) (corundum). The Mulliken charges analyses suggest the valence states of Fe and V are interstices dependent. In Fe rich condition (VFe_(2)O_(4)), bivalent cations Fe~(2+) and V~(2+) prefer tetrahedral interstices, while trivalent cations Fe~(3+) and V~(3+) prefer octahedral interstices. In V rich condition (FeV_(2)O_(4)), Fe valence states in tetrahedral and octahedral interstices are the same as those in Fe rich cases. However, the V cations have contrary valence states, namely, V~(3+), in tetrahedral interstices, and mixed valence states in octahedral states.The crystalline formation energies of normal and inverse spinels were addressed to determine their stability. The inverse spinels are obviously more favorable than normal spinels. We have quantified probability of two isomeric inverse spinels in Fe rich condition in equilibrium at 300 K and 1700 K. It is in agreement with that entropy plays a more significant role at high temperature. Electronic structures of tetrahedral and octahedral Fe and V cations have also been analyzed using computed x-ray absorption near edge structure (XANES). The chemical shift of white lines, going from Fe~(2+) to Fe~(3+) cations in spinels, and 3d orbitals splitting of tetrahedral and octahedral V cations are distinguishable in XANES spectra. Thus, the different electronic structure of Fe and V cations in tetrahedral and octahedral interstices can provide important interpretations of experimental works of spinels containing iron and vanadium elements.
机译：我们采用了从头算的方法来研究含铁和钒的正尖晶石和反尖晶石。首先用参考氧化物FeO（岩盐），Fe_（2）O_（3）（刚玉），VO（岩盐）和Fe_（2）O_（3）（刚玉）校准四面体和八面体Fe和V的价态。 Mulliken电荷分析表明Fe和V的化合价态依赖于间隙。在富铁条件下（VFe_（2）O_（4）），二价阳离子Fe〜（2+）和V〜（2+）倾向于四面体间隙，而三价阳离子Fe〜（3+）和V〜（3+）更喜欢八面体间隙。在富V条件下（FeV_（2）O_（4）），四面体和八面体间隙中的Fe价态与富Fe情况相同。但是，V阳离子在四面体间隙中具有相反的价态V〜（3+），而在八面体态中具有混合价态。通过研究正尖晶石和反尖晶石的晶体形成能来确定其稳定性。反尖晶石显然比普通尖晶石更有利。我们已经量化了富铁条件下两个异构体反向尖晶石在300 K和1700 K处于平衡状态的概率。这与熵在高温下的作用更为重要相一致。还使用计算得到的近边缘结构（XANES）的x射线吸收量分析了四面体和八面体Fe和V阳离子的电子结构。在XANES光谱中，白线的化学位移从尖晶石中的Fe〜（2+）变为Fe〜（3+）阳离子，以及四面体和八面体V阳离子的3d轨道分裂。因此，四面体和八面体间隙中Fe和V阳离子的不同电子结构可以为含铁和钒元素的尖晶石的实验工作提供重要的解释。

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