PREPARATION OF ULTRAFINE YBA2CU3O7-X SUPERCONDUCTOR POWDERS BY THE POLY(VINYL ALCOHOL)-ASSISTED SOL-GEL METHOD

The ultrafine high-T-c YBa2Cu3O7-x superconductor powders were prepare d by the sol-gel method using poly(vinyl alcohol) (PVA) as a protectin g agent of metal ions. The conditions of the sol formation from the aq ueous solution of metal nitrates containing PVA were determined, and t he thermal decomposition process of the gel precursor was examined to determine the crystallization temperature. It was found that a nearly pure phase of polycrystalline YBa2Cu3O7-x could be obtained by calcini ng the gel precursor above 900 degrees C for 2 h in air. Polycrystalli ne YBa2Cu3O7-x powders prepared at 920 degrees C consisted of very uni formly-sized ultrafine particulates with an average particle size of a bout 25 nm and showed a good superconducting property with T-c around 94 K.