Synthesis of the high-T_c superconductor YBa₂Cu₃O_7–δ in small particle size

Abstract

Technological exploitation of the recently discovered high-T_c superconducting oxides requires processing the materials at modest temperatures. A first step toward this goal is the synthesis of the material in small particle size. This requires, in turn, the design of a synthetic route at temperatures below those where sintering takes place. Here we report the preparation of YBa₂Cu₃O_7–δ as small particles by firing the coprecipitated oxalates at temperatures T ≤780^°C; sintering begins above 800^°C. Properties of the materials depend on the highest temperatures reached. As noted independently by Torardi et al.¹, low-temperature synthesis in air results in a tetragonal, semiconducting product rather than the orthorhombic, superconducting phase. Therefore we also report a low-temperature (T<780 ^°C) method of converting the tetragonal phase to the superconducting phase without sintering of the small particles