Microstructure and flux pinning properties of melt textured grown doped YBa 2Cu 3O 7−δ

Abstract

The physical properties and the microstructure of highly textured YBa 2Cu 3O 7/Y 2BaCuO 5 ceramics, doped with platinum and/or cerium have been investigated by high resolution electron microscopy (HREM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The Ce, Pt and Ce + Pt doped samples show different J c behaviours as function of the applied field and a systematic comparison of the microstructure at different scales has been performed. The combination of both dopants leads to a drastic improvement of the critical current density either under zero field or with an external magnetic field (fishtail effect). A critical current density up to 56 000 A/cm 2 has been observed, which remains 43 000 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 YBa 2Cu 3O 7−δ matrix locally changes the superconducting properties, and enhances the flux pinning properties. Micron size BaCeO 3 particles, which appear with a preferential orientation in the YBa 2Cu 3O 7−δ matrix, are also potential candidates for strong pinning. Other secondary phases, formed during the growth and the presence of a nanocrystalline phase in the plate like gap of the Ce + Pt doped samples are other admixtures. Finally a high density of twins is observed in all samples with some differences between the cerium and the platinum doped samples. They most probably contribute to pinning under intermediate field.