Magnetic, electrical, and microstructural properties of YBa₂ Cu₃ O₇: A comparison of sol-gel, co-precipitated, and solid state processing routes

Samples of YBa₂ Cu₃ O₇ were prepared by sol-gel, co-precipitation, and solid state processes. Sol-gel samples were prepared from a solution of yttrium, barium, and copper nitrates dissolved in ethylene glycol, co-precipitated samples were made by the amorphous citrate method, and solid state samples were prepared by conventional high temperature reaction of the appropriate metal oxides and carbonates. The sol-gel process was shown to yield superconducting samples of superior Meissner effect, critical current, and critical field. The co-precipitated samples contain impurities that affect the critical properties. The sol-gel and co-precipitated processes yield materials with well-formed, plate-like particles with a fairly uniform size of about 10 μm. The grains in the solid state sample are smaller but have a much wider distribution of sizes than the samples prepared by solution methods.