Preparation of Ultrafine YBa_2Cu_3O_(7-x) Superconductor Powders by the Poly (vinyl alcohol)-Assisted Sol—Gel Method

摘要

The ultrafine high-T_c YBa_2Cu_3O_(7-x) superconductor powders were prepared by the sol—gel method using poly(vinyl alcohol) (PVA) as a protecting agent of metal ions. The conditions of the sol formation from the aqueous solution of metal nitrates containing PVA were determined, and the thermal decomposition process of the gel precursor was examined to determine the crystallization temperature. It was found that a nearly pure phase of polycrystalline YBa_2Cu_3O_(7-x) could be obtained by calcining the gel precursor above 900℃ for 2 h in air. Polycrystalline YBa_2Cu_3O_(7-x) powders prepared at 920℃ consisted of very uniformly-sized ultrafine particulates with an average particle size of about 25 nm and showed a good superconducting property with T_c around 94 K.