On the current critical density in ceramic high-Tc superconducting samples

Critical current dependence on the area δ of Y1Ba2Cu3O7-x ceramics sample cross section is investigated. Cylindrical samples of circular and rectangular cross sections are studied. It is ascertained that in a wide cross section interval the mean critical current density jcr. of fresh-prepared samples is proportional to s-1/3. Dependence of jcr. (s) becomes weaker in the area of low cross sections. The effect is conditioned by the effect of intrinsic current magnetic field. Experimental results are explained within the framework of representations concerning critical state based on the proposed model dependence B: jcr = j0/[1+(B/B0)2]. The model parameters are determined by magnetization curves measured. For the best samples j0 value makes up 363 A/cm2. Results of calculating jcr.(s) agree with the experiment. It is detected that continuous presence of samples in the open air leads to a stronger jcr (s) dependence