Study on Phase Diagram of Ba-Cu-Y-O Quaternary System and Microstructure Control of Superconductor

研究了在氧氩混合气氛下Y-Ba-Cu-O四元系相图及相应的三元系相图。为了确定实验相图，进行了粉末X射线衍射、电子探针分析、显微镜观察和热分析。当碳酸盐用作起始材料和/或样品在包括碳酸气体的天然空气中煅烧时，容易形成一些三元和四元含氧碳酸盐。在Y-Cu-O三元系中，存在Y_2O_3、CuO、Cu_2O、YCuO_2和Y_2Cu_2O_5五个相，它们组成了依赖于氧分压的相图。在Ba-Cu-O三元系中，在1atm左右的氧压下，存在BaCuO_（13）EA_2和Ba_2CuO_3两种多晶型物相。在Ba-Y-O三元系中，发现Y_4Ba_4O_9和Y_2BaO两相是真正的氧化物，而迄今报道的其它相是氧碳酸盐。在准13 EA：三元体系中，有YBa_2Cu_3O_（6+x），Y_2BaCuO_5，YBa_4Cu_3O_（6+x），YBa_6Cu_3O_（6 + x）和YBa_2Cu_4O_（6 + x）五种四元<8.5><10.5>相<7.5>在空气中是稳定的。测定了1263、1223和1173 K的三个等温截面，详细研究了该体系的相关系。结合热分析结果，建立了Y-Ba-Cu-O四元体系在0.21atm氧分压下的单变量反应全序列图。此外，两个不变的反应被证实存在于四元系统中的氧分压依赖的相关系。在此基础上，讨论了改善超导电性的微观结构控制。

Phase diagram of Y-Ba-Cu-O four component and ite relating three component systems have been investigated under air of mixed gas of oxygen with argon. In order to determine experimentally the phase diagrams, powder X-ray diffraction, EMPA, microscop13EA\ : ic observation and thermal analysis were carried out. When the carbonates are used as starting materials and/or the specimen is calcined in natural air including carbonic acid gas, some ternary and quaternary oxycarbonates are easily formed. In the Y-Cu-O ternary system, there are five phases of Y_2O_3, CuO, Cu_2O, YCuO_2 and Y_2Cu_2O_5 and these phases compose the phase diagram depending on oxygen partial pressure. In the Ba-Cu-O ternary system, there are three ternary phases of BaCuO13EA\ : _2 and two polymorphisms of Ba_2CuO_3 under oxygen pressure around 1 atm. In the Ba-Y-O ternary system, it was found that two phases of Y_4Ba_4O_9 and Y_2BaO are the true oxide, but other phases reported till now are oxycarbonates. In the qua13EA\ : ternary system, five quaternary phases YBa_2Cu_3O_<6+x>, Y_2BaCuO_5, YBa_4Cu_3O_<8.5>, YBa_6Cu_3O_<10.5> and YBa_2Cu_4O_<7.5> are stable under air. Three isothermal sections at 1263, 1223 and 1173 K were determined and the phase relation has b13EA\ : een in detail investigated. Combining the results of htermal analysis, the whole sequence diagram for univariant reactions has been established in the Y-Ba-Cu-O quaternary system under oxygen partial pressure of 0.21 atm. Furthermore, two invariant reactions were confirmed to exist in the quaternary system from the oxygen partial pressure dependence of phase relations. Based on the knowledge mentioned above, the control of microstructure has been discussed to improve superconductivity.