MICROSTRUCTURE AND FLUX-PINNING PROPERTIES OF MELT-TEXTURED GROWN DOPED YBA2CU3O7-DELTA

The physical properties and the microstucture of highly textured YBa2C u3O7/Y2BaCuO5 ceramics, doped with platinum and/or cerium have been in vestigated by high resolution electron microscopy (HREM), scanning ele ctron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The Ce, Pt and Ce + Pt doped samples show different J(c) behaviours as fu nction of the applied field and a systematic comparison of the microst ructure at different scales has been performed. The combination of bot h dopants leads to a drastic improvement of the critical current densi ty either under zero field or with an external magnetic field (fishtai l effect). A critical current density up to 56000 A/cm(2) has been obs erved, which remains 43000 A/cm(2) under 1 T in a sample doped with 2 wt% cerium oxide and 0.5 wt% platinum oxide, We suggest that a slight introduction of Ce in the YBa2Cu3O7-delta matrix locally changes the s uperconducting properties, and enhances the flux pinning properties. M icron size BaCeO3 particles, which appear with a preferential orientat ion in the YBa2Cu3O7-delta matrix, are also potential candidates for s trong pinning. Other secondary phases, formed during the growth and th e presence of a nanocrystalline phase in the plate like gap of the Ce + Pt doped samples are other admixtures. Finally a high density of twi ns is observed in all samples with some differences between the cerium and the platinum doped samples. They most probably contribute to pinn ing under intermediate field.