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

过渡金属离子混合导电钙钛矿氧化物的价态和配位态分析

基本信息

批准号：
06650779
负责人：
YAO Takeshi
金额：
$ 1.34万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06650779/
关键词：
Perovskite structure Crystal structure analysis Rietveld method Mangenese ion Jahn-Teller effect Cobalt ion Electrical conductivity Valence バンド構造金属-絶縁体転移

项目摘要

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.

在不同的氧分压和温度下，对不同碱土组成的混合导电性能的稀土钙钛矿氧化物进行了不同氧分压和温度下的热处理。用粉末X射线Rietveld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价态和配位态的变化与电导率等性质的关系。La：Mn=1：1，La取代La-Sr-Mn-O或取代Mn的La-Mn-Mg-O钙钛矿氧化物在不同氧分压下进行热处理。用化学分析测定了样品中的锰的价态，用粉末X射线衍射和Rietveld分析对样品的晶体结构进行了精炼。通过低氧分压下的热处理，形成了一种新型的含Mn~(2+)&lt；~(2+)&Gt~(2+)离子的正交型钙钛矿相。该结构非常接近立方体对称。推测Mn~(2+)&Gt~(2+)离子的微观Jahn-Teller效应几乎相互抵消。用粉末X射线Rietveld分析精确测定了钙钛矿结构La_&lt；1-x&Gt；Sr_xCoO_3的晶体结构，用碘量法测定了钴离子的平均价态，并研究了它们与电学性质的关系。当锶含量较低时，钴离子的价态表现出化学计量比的变化，但随着锶含量的增加，钴离子的化学计量偏差增大。Rietveld分析表明，随着锶含量的增加，钴离子的CoO距离急剧减小，电导率由半导体向金属转变。认为O-2p带和Co-d带之间的电荷转移间隙是由于晶体结构的变化而闭合的。