THE INFLUENCE OF THERMAL TREATMENTS, FABRICATION METHODS AND SHAPES ON THE MAGNETIC TRANSITION OF HIGH-TEMPERATURE SUPERCONDUCTING COMPOUNDS

We discuss the problem of characterizing a superconducting transition and the question of comparing samples originating from different fabrication processes and/or obtained under various shapes or morphologies (bulk, wires, thin films, single crystals, ...). We present two different methods for the analyses of the AC susceptibility (for both the real and the imaginary part) in the low field limit. Strength of flux pinning and intergrain/intragrain contributions are discussed. Both analyses are applied to different inhomogeneous superconductors like high-T(c) compounds (YBCO, LCO, LSCO, LBCO, B(P)SCCO, NCCO), Chevrel phases, etc. The dynamic critical field given by such an analysis allows an estimation of the quality and/or homogeneity of the superconducting sample and is a measure of the first intergrain (or Josephson) critical field.