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

研究了在氧气和Ar混合气体中，Y-Ba-Cu-O四元系和ITE相关三元系的相图。为了从实验上确定相图，进行了粉末X射线衍射、EMPA、显微镜观察和热分析。当以碳酸盐为原料和/或样品在含有碳酸气体的自然空气中焙烧时，容易形成一些三元和四元的含氧碳酸盐。在Y-Cu-O三元体系中，存在Y_2O_3、CuO、Cu2O、YCuO_2和Y_2Cu2O_5五个相，这些相组成的相图取决于氧分压。在BaCuO13Ea_2和Ba2CuO_3三元系中，氧分压在1大气压附近时，BaCuO13Ea_2和Ba2CuO_3有两种不同的晶型。在Ba-Y-O三元体系中，Y_4Ba4O_9和Y_2BaO两相是真正的氧化物，而目前报道的其他相是氧化碳酸盐。在四元系中，五个四元相YBa2Cu3O；6+x&gt；Y_2BaCuO_5；YBa4Cu3O_3；8.5；测定了1263、1223和1173K下的三个等温截面，并详细研究了它们的相关系.结合过热分析结果，建立了氧分压为0.21atm的Y-Ba-Cu-O四元系单变反应全序列图。此外，从氧分压对相关系的依赖关系证实了该四元体系中存在两个不变反应。在此基础上，对提高超导电性的微观结构控制进行了讨论。

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.