Electronic States and Physical Propertied of Mixed Valent Metal Oxides

过渡金属离子在其氧化物中表现出不同的价态，导致其物理化学性质的变化。然而，由于过渡金属离子的价态复杂，即d轨道能级、金属d轨道与氧p轨道重叠引起的原子间相互作用等，人们对它们的价态还没有很好的了解.本文用DV-X α方法计算了过渡金属氧化物的团簇模型的电子结构，并研究了过渡金属棒的价态和化学键。值得注意的是，混合价态倾向于出现在高价离子的氧化物中，如Fe^<4+>和Cu^<3+>，它们具有令人感兴趣的物理性质。在低温下，在钙钛矿型Fe^<4 +>氧化物中发生了2 Fe ^<4+> -> Fe^<3+> + Fe^<5+>的还原反应。在Cu^<3+>氧化物中，发现了高温超导性，用团簇模型计算的结果与各种实验结果符合得很好。对于Fe^<4+>氧化物，该计算可以很好地解释穆斯堡尔效应的实验结果，并证明了低温下晶格振动猝灭引起歧化反应的模型。对于Cu^<3+>氧化物，计算结果与实验光电子谱符合得很好，可以解释高温超导体的磁性。对于这两种氧化物，从氧到金属的大量电荷转移是电子态的特征之一。

Transition metal ions in their oxides show various valence states which cause variety of physcal and clemical properties. however, the valence states of the transition metal ions have not well been understood, because of their complexity, namely, d orbital levels, interatomic interactions due to overlap between metal d and oxygen p orbitals.In the present research, we have calculated the electronic structures of cluster models for the transition metal oxides by the use of the DV-X alpha method, and have investigated valence states and chemical bondings of the transition metal lolls. It is noted that mixed valent states tend to appear in the oxides of high-valent ions such as Fe^<4+> and Cu^<3+> which possess interesting physical properties. At low temperatures, disproportionation reaction 2Fe^<4+> -> Fe^<3+> + Fe^<5+> in a perovskite type Fe^<4+> oxide has been reported. Among Cu^<3+> oxides, high-temperature superconductivity has been found. The results of the cluster model calculations for these oxides show good agreement with various experimental results. For Fe^<4+> oxide, the calculation can well explain the experimental results of Mossbauer effect and the model that the disproportionation reaction is caused by quenching of lattice vibration at low temperature has been proved. For Cu^<3+> oxide, the results of calculations are in good agreement with the experimental photoemission spectra and can interpret the magnetic properties of high-temperature superconductors. For both these oxides, a large amount of charge transfer from oxygen to metal is one of the characteristics of the electronic state.