Valence and Coordination State Analysis for Transition Metal Ions Mixed Conductive Perovskite Oxides

在不同的氧分压和温度条件下，对具有离子和电子作为载流子移动的混合导电性能的稀土钙钛矿氧化物进行热处理。用粉末x射线里特费尔德分析对晶体结构进行了精确分析。然后研究了过渡金属离子的价态和配位态的变化与导电性能的关系。对La: Mn= 1:1、La取代La- sr -Mn- o或Mn取代La-Mn- mg - o钙钛矿氧化物在不同氧分压下进行热处理。通过化学分析测定了样品的Mn价态，并通过粉末x射线衍射和Rietveld分析对样品的晶体结构进行了细化。在低氧分压条件下进行热处理，形成了一种含有Mn^<2+>离子的新型斜向钙钛矿相。这个结构非常接近立方对称。假设Mn^<2+>离子的微jann - teller效应几乎是相互抵消的。用粉末x射线Rietveld法精确测定了钙钛矿La_<1-x>Sr_xCoO_3的晶体结构，用碘量法测定了钴离子的均价，并研究了其电学性能的相关性。在Sr含量较低时，钴离子的价态发生化学计量变化，但随着Sr含量的增加，与化学计量的偏差增大。随着Sr含量的增加，Rietveld分析发现CoO距离突然减小，电导率从半导体向金属转变。认为存在于O-2p带和Co-d带之间的电荷转移间隙被晶体结构的改变所封闭。

Rare earth containing perovskite oxides with mixed conductive properties in which both ions and electrons move as charge carriers were heat-treated under various oxygen partial pressures and temperatures for various kinds of alkaline earth compositions. The crystal structures were precisely analyzed by powder X-ray Rietveld analysis. Then the relations between the changes in valence and coordination states of the transition metal ions and the properties such as electrical conductivity etc.were investigated. La : Mn=1 : 1, La substituted La-Sr-Mn-O or Mn substitute La-Mn-Mg-O perovskite oxides were heat-treated under various oxygen partial pressures. The Mn valence of the samples were measured by a chemical analysis, and the crystal structure were refined by the powder X-ray diffraction and the Rietveld analysis. A novel orthor-hombic perovskite phase containing Mn^<2+> ions was formed by heat-treatment under low oxygen partial pressures. The structure was very close to a cubic symmetry. It is supposed that the micro Jahn-Teller effects of Mn^<2+> ions were nearly canceled by one another. Crystal structure of perovskite La_<1-x>Sr_xCoO_3 was precisely determined by powder X-ray Rietveld analysis, the mean valence of cobalt ion was measured by iodometry, and the correlation with the electrical property was investigated. The valence of the cobalt ion showed a stoichiometric change for the lower amount of Sr, however, the deviation from the stoichiometry increased with the increase of Sr. With the increase of Sr amount, there observed an abrupt decrease for CoO distance by the Rietveld analysis, and the transition from semiconducting to metallic in the electrical conductivity. It is considered that the charge transfer gap existing between O-2p band and Co-d band was closed by the change in the crystal structure.