THERMALLY ACTIVATED FLUX CREEP AND CURRENT CONDUCTION IN YBCO + BZO COMPOSITES

Abstract

BaZrO 3 submicron powder obtained from chemical route was added to YBCO for preparation of YBCO + xBZO (x = 0, 1, 2.5, 5, 10 rm wt%) composites samples. The X-ray peak profile analyses and the scanning electron microscopy have indicated that the mean powder size for BZO ranges from 500 to 800 nm. In fact, the presence of BZO brings about a significant modification in the microstructure of the composites. The resistive transition in presence of magnetic field (0–8 T) was investigated. With application of magnetic field, Tc0 decreases significantly, suggesting that grain boundaries (Josephson junctions) are affected more than the grains (Abrikosov junctions). Activation energy is found dependent not only on the particle size, but also on penetration depth and decreases with increasing doping concentration of BZO submicron size particles in contrast to what has been recently observed by M. Safonchik et al. with grain sizes of 40 nm BZO. It has also been observed by H. Shakeripour, M. Akhavan [Supercond. Sci. Technol.14, 234 (2001)] and Gamchi et al. [Phys. Rev. B50, 12950 (1994)] that the activation energy depends not only on the temperature and magnetic field, but also on the doping concentration.