酸化物材料の酸素欠損配列の規則・不規則転移 ―熱分析による解析

抄録

One of the promising methods to develop new oxide ion conductor is changing ordered oxide ion vacancy in oxide material into random one. It was reported that ordered oxide ion vacancy in Ba₂In₂O₅ and Ba₂Fe₂O₅ changed to disorder one at the structural phase transition at about 910 ºC and 850 ºC, respectively. In this report, thermal analyses of the order-disorder phase transition have been summarized. It has been clarified that enough enthalpy is absorbed at the structural phase transition of Ba₂In₂O₅ to make the ordered oxide ion vacancy arrangement completely random. It has also been revealed that the phase transition of Ba₂Fe₂O₅ involves not only order-disorder transition of oxide ion vacancy arrangement but also uptake of oxygen from gas phase, resulting in generation of cubic Ba₂Fe₂O_5+δ at higher temperature than the phase transition temperature. The higher stability of Ba₂Fe₂O_5+δ than Ba₂Fe₂O₅ at high temperature despite of higher oxidation state of Fe can be attributed to larger heat absorption accompanied with order-disorder transition than heat generation due to oxidation of Fe.