Preparation of Ultrafine YBa2Cu3O7-x Superconductor Powders by the Poly(vinyl alcohol)-Assisted Sol−Gel Method

The ultrafine high- T c YBa 2 Cu 3 O 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 2 Cu 3 O 7- x could be obtained by calcining the gel precursor above 900 °C for 2 h in air. Polycrystalline YBa 2 Cu 3 O 7- x powders prepared at 920 °C 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.