PRODUCTION OF A HIGH-TEMPERATURE SUPERCONDUCTING CERAMIC

The parameters for producing high-Tc superconductors in the Y-Ba-Cu-O system were refined for the entire process cycle. Different methods of mixing and grinding the charge components were tried. Granules gave the greatest amount of single-phase reaction product. The formation of YBa2Cu3O7-x and other phases for various synthesis temperatures was studied by X-ray phase analysis. The optimum synthesis temperature was considered. Below 925 C, unreacted starting components and impurity phases still remain, whereas above 950-960 C the product is difficult to work and shrinkage becomes a problem. A temperature of 960 C gives the highest Tc with the sharpest transition. The effect of semidry pressing and hot casting under pressure with PVA or paraffin binder was studied. Sample shrinkage during annealing was plotted on the basis of either a poorly calcined sinter synthesised at 935 C or a well-calcined sinter synthesised at 960 C. Samples of poorly calcined sinter densified more readily. A 1.5 h anneal at 935 C gave the 1-2-3 composition with a practically homogeneous orthorhombic structure. 5 refs.