Chemical State Analysis of Transition-metal Ions in Complex Oxides with Spinel Structure

点击翻译按钮获取中文摘要

Many oxide spinels containing transition-metal ions have technologically interesting physical and/or chemical properties and are used widely. It is important to investigate the relation between the conditions of the production of the crystals and the chemical state of the transition metal ions in the crystal.In this study, we produced iron spinels, nickel aluminate ferrites, nickel-zinc ferrites, and manganese-zinc ferrites under various conditions. We determined the cation distributions by the x-ray diffraction, EXAFS analysis and Mossbauer analysis. We produced the computer program for Rietveld analysis and determined the cation distribution by powder x-ray diffraction. X-ray diffraction is usually the most effective method of analyzing the cation distribution. When, however, the crystal contains several kinds of transition-metal ions with somewhat similar atomic scattering factors, it is difficult to distinguish among the transition-metal ions by x-ray diffraction. On the contrary, the x-, ray absorption edges are well separated from each other, the distribution of a certain transition-metal ion can be analyzed independently by EXAFS. We produced the computer program for the EXAFS analysis, and applied it to determining the cation distributions.The cation distribution of spinel oxides are determined mainly by the electrostatic energy, the crystal-field stabilization energy, and the polarization energy. By these energies, the octahedral site preference of Mn^<3+> and Ni^<2+>, the tetrahedral site preference of Zn^<2+> and Fe^<2+>, and the no site preference of Mn^<2+> and Fe^<3+> are introduced, which were fair coincident with the result of the above analysis. It is considered that the chemical state of the transition-metal ions can be estimated practically by these energies.