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，这导致了不同的物理和化学性质。然而，由于过渡金属离子价态的复杂性，即d轨道能级，金属d和氧p轨道的重叠导致的原子间相互作用，我们用DV-Xα方法计算了过渡金属氧化物原子簇模型的电子结构，并研究了过渡金属离子的价态和化学键。指出高价离子如Fe^&lt；4+&gt；和Cu^&lt；3+&gt；等具有有趣物理性质的氧化物中往往会出现混合价态。报道了钙钛矿型Fe^&lt；4+&gt；氧化物中低温歧化反应2Fe^&lt；4+&gt；-&gt；Fe^&lt；3+&gt；+Fe^&lt；5+&gt；在Cu2+&Lt；3+&Gt；氧化物中发现了高温超导电性。这些氧化物的团簇模型计算结果与各种实验结果符合得很好。对于Fe^&lt；4+&gt；氧化物，计算结果较好地解释了穆斯堡尔效应的实验结果，证明了歧化反应是由低温晶格振动猝灭引起的。对于Cu2+&lt；3+&Gt；氧化物，计算结果与实验光电子能谱符合得很好，可以解释高温超导体的磁性。对于这两种氧化物，大量的电荷从氧转移到金属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.