Bismuth doping of top-seeding melt-texture-grown YBa2Cu3O7-delta ceramics

摘要

We have investigated the effects of Bi2O3 additions, up to 1 wt% of Bi2O3, on the superconducting properties and microstructures of top-seeding-melt-texture-growth-processed YBa2Cu3O7-delta ceramics. Differential thermal analysis (DTA) measurements show that these additions do not change the decomposition temperature of the mixtures. Energy dispersive x-ray spectroscopy (EDS) studies of the microstructures after texturation have shown that bismuth additions have no effect on the size of the Y211 particles and do not hinder the action of CeO2 on the inhibition of the coarsening of these particles. However, secondary phase particles, presenting no particular shape, and containing both cerium and bismuth, have been pointed out even for samples with the lowest content of bismuth. The higher the added amount of bismuth, the more numerous the particles are. The composition of these small particles (about 2 mum) evolves with the amount of bismuth added to the starting composition; as the added bismuth content increases, the amount of bismuth increases in the secondary phase particles whereas the amount of cerium is lowered. The critical current densities (77 K, self-field) present an optimum value (67 000 A cm(-2)) for an addition of 0.125 wt% of Bi2O3. A subsequent annealing treatment (430-300 degreesC, 100 h) leads to self-field values of 88 000 A cm(-2). Bi-doped samples synthesized without the usual pre-sintering step exhibit an optimum value (81000 A cm(-2)) for a lower doping rate of 0.0325 wt% of Bi2O3 and the subsequent annealing treatment (430-300 C, 100 h) leads to self-field values of 95 000 A cm(-2). [References: 32]