Granular nature and superconductive coupling of YBa₂Cu₃O₇ polycrystals observed by microwave absorption measurements

Abstract

The results of measurements of the H-modulated microwave absorption of of YBa₂Cu₃O₇ ceramic in the transition temperature region and with fields in the range 0–10 kOe are presented. They give clear evidence of the weak-link inter-grain nature of the gross part of the dissipation and support the idea of stronger links, or microbridges of a more intrinsic species, involved in the high-field intra-grain absorption component. A semiquantitative analysis of the absorption process is suggested and applied to the derivative spectra in the T-swept form (at fixed external field). It allows to deduce information about T_c, the superconductive coupling, and the H- and T-dependences of the critical currents involved in the inter- and intra-grain regions. When applied to YBa₂Cu₃O₇ powders, obtained by finely grinding a ceramic pellet, it gives also evidence of a generalized suppression of coupling induced by the grinding process