High pressure-high temperature effect on melt-textured YBa2Cu3O7-delta high temperature superconductive material

High pressure-high temperature (HP-HT) treatment of melt-textured YBa2Cu3O7 -delta at 2 GPa, and in the 800-950 degrees C pressure-temperature range fo r 15-30 min in contact with monoclinic pre-annealed zirconia induces: (1) t he increase of the material density from 5.7 to 6.3 g/cm(3) (by 9%), (2) th e increase of critical current density in the direction of c-axis of YBa2Cu 3O7-delta grains from 3-3.5 x 10(3) up to 7 x 10(3) A/cm(2) (in the self-fi eld at 77 K) while in the ab-plane it remains unchanged (10(4) A/cm(2)), (3 ) the increase of Vickers microhardness from 3.95 up to 5.3 GPa (estimated under the 4.91-N load). The increase in dislocation density in the (001) pl anes of HP-HT treated YBa2Cu3O7-delta grains from 10(8) up to 10(12) cm(-2) may be one of the reasons of the increase in critical current density. The spaces between twin domains in YBa2Cu3O7-delta before treatment were 100-1 50 nm. Completely detwinned wide areas or regions, where each second twin d omain was narrowed to approximately 20 nm or tapered down to zero thickness within the first domain and the disappearance of 1/6 [301] stacking faults have been observed in the treated samples. (C) 2000 Kluwer Academic Publis hers.