A comparative study of processing methods and property relations of Y-Ba-Cu-O superconductors

Superconducting YBa/sub 2/Cu/sub 3/O/sub 6+x/ samples were made from powders prepared by three different routes: solid state reaction, coprecipitation of all components from nitrates and coprecipitation of Y and Ba oxalates on CuO particles. The powders produced by solid-state reaction were given different degrees of milling, calcined and either sintered or hot-pressed. The powders synthesized from solutions were precipitated either by mixing or spraying and were subsequently sintered and then annealed in oxygen at 600 C. In all cases, sintering at 920 C was found to give the lowest normal state resistivity. Samples hot pressed at 875 C required a subsequent annealing at higher temperatures to regain the superconducting phase. The solid-state reaction and coated-CuO methods gave single-phase material after sintering. Samples made from the conventional coprecipitation method always showed some nonsuperconducting phases. The latter specimens did exhibit superconductivity with T/sub c/ values of about 70 K; subsequent annealing did not significantly improve T/sub c/. Optimized attrition milled samples and those made by the coated-CuO method gave the lowest values of resistivity in the normal state. The extent of corrosion by interaction with water was studied. It was found that within one hour in water at 60 C, the samples lost most of their superconductivity. Ba was preferentially leached out compared to yttrium and copper.<>