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

研究了氧氩混合气体中Y-Ba-Cu-O四组分体系和ite三组分体系的相图。为了实验确定相图，进行了粉末x射线衍射，EMPA，显微镜13ea观察和热分析。当碳酸盐用作起始材料和/或试样在包括碳酸气体在内的自然空气中煅烧时，容易形成一些三元和季氧碳酸盐。在Y-Cu-O三元体系中，Y_2O_3、CuO、Cu_2O、YCuO_2和Y_2Cu_2O_5五相组成了随氧分压变化的相图。在Ba-Cu-O三元体系中，在1atm左右的氧压下，存在BaCuO13EA\: _2的三个三元相和Ba_2CuO_3的两个多晶态。在Ba-Y-O三元体系中，发现Y_4Ba_4O_9和Y_2BaO两相是真正的氧化物，但迄今为止报道的其他相都是碳酸氧化合物。在qua13EA三元体系中，YBa_2Cu_3O_<6+x>、Y_2BaCuO_5、YBa_4Cu_3O_<8.5>、YBa_6Cu_3O_<10.5>和YBa_2Cu_3O_< 7.5>这5个四相在空气中稳定存在。测定了1263、1223和1173 K的等温截面，并对其相关系进行了详细的研究。结合热分析结果，建立了Y-Ba-Cu-O四元体系在0.21 atm氧分压条件下的全无变反应序列图。此外，从相关系对氧分压的依赖性来看，证实了在四元体系中存在两个不变性反应。在此基础上，讨论了提高超导性的微观结构控制。

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.