Direct Synthesis of a Low Temperature Stable Oxide, Ba_2Cu_3O_<5+d>, Using Barium Nitrate as a Flux

硝酸钡与CuO的摩尔比为2：3，过量BaO为BaO：CuO，在700ﾟC左右的高压容器上反应，易生成Ba2Cu3O5+d&gt；对从熔剂中机械分离的样品进行了显微维氏硬度测试，其硬度与方解石的硬度相近。本研究的最终目的是研究用Ba(NO3)2助熔剂直接合成正交型YBa2Cu3OX超导体。在BaO-Y_2O_3反应体系中，加入BaO(NO_3)_2助熔剂后，未检测到任何反应产物以保存未反应的Y_2O_3，即使在含有过量硝酸钡的样品中也是如此。在BaO-Y_2O_3-CuO体系中，将阳离子比为2：1：3的BaO-Y_2O_3和CuO组成的混合物在高压容器中以690ﾟC进行热处理。反应容器在690ﾟC下浸泡40h后冷却，不释放气体，容器内压力保持在0.5 Mpa，690ﾟC释放气体，主要产物为Y2Cu2O5和YBa2Cu3OX。当反应温度为690ﾟC，压力为0.1 Mpa时，除Ba2Cu3O；5+d&gt外，还能生成YBa2Cu3Ox；而未反应的Y_2O_3和Ba(NO_3)_2。透射电子显微镜观察表明，YBa2Cu3OX晶体中没有观察到缠绕结构，而用普通方法制备的样品在900ﾟC合成YB2Cu3OX后，在500ﾟC的氧气气氛中进行热处理后，晶体中观察到了缠绕结构。

Reaction of barium nitrate and CuO mixtures having the composition of molar ratio from 2 : 3 to excess BaO as BaO : CuO using a high-pressure-vessel produced Ba_2Cu_3O_<5+d> crystals easily at the temperature about 700ﾟC.It was difficult to purify the crystals by means of a chemical separation because the materials are easily altered by a moisture or a samll amount of water. Micro-Vickers hardness test for the sample separated mechanically from a flux showed the hardness is a similar value to that of calcite. The final objective of this study is to examine the direct synthesis of orthorhombic form of YBa_2Cu_3O_X superconductor by using a Ba (NO_3) _2 flux. In the reaction system of BaO-Y_2O_3 using a Ba (NO_3) _2 flux, no reaction products were not detected to preserve unreacted Y_2O_3, even in the specimen having excess barium nitrate.In the system of BaO-Y_2O_3-CuO,the composition mixture of barium nitrate, Y_2O_3, and CuO having cation ratio of 2 : 1 : 3 was heat-treated at 690ﾟC in the high-oressure-vessel. In the case of reactions that the reaction vessel was cooled after soaking at 690ﾟC for 40h not to release gases from the vessel and that the pressure in the vessel was kept at 0.5MPa at 690ﾟC to release gases, the main product was Y_2Cu_2O_5 and YBa_2Cu_3O_X was not detected. In the case of reaction that the pressure in the vessel was kept at 0.1MPa equal to the ambient pressure at 690ﾟC to decompose barium nitrate, YBa_2Cu_3O_X was able to form in addition of Ba_2Cu_3O_<5+d> and unreacted Y_2O_3 and Ba (NO_3) _2. TEM observation showed that no twined structure was not detected in the crystals of YBa_2Cu_3O_X, though a twined structure was observed in the crystals of specimen prepared by an ordinary method that the heat-treatment was conducted at 500ﾟC in oxygen atmosphere after YB_2Cu_3O_X was synthesized at 900ﾟC.It was infered that the orthorhmbic YBa_2Cu_3O_X superconductor was directly synthesized by the barium nitrate flux method.