Eur. Phys. J. B 9, 389-399 (1999)
https://doi.org/10.1007/s100510050782

Particle size effect of a.c. superconducting properties in Tl₂Ca₁Ba₂Cu₂O₈ compound

¹ Institute of Physics, Eötvös University, 1117 Budapest, Hungary
² Wihuri Physical Laboratory, University of Turku, 20014 Turku, Finland
³ Institute of Experimental Physics, Kossuth University, 4001 Debrecen, Hungary
⁴ Centre for High Temperature Superconductivity, Imperial College, SW7 2BZ London, Great Britain

Received: 10 October 1998
Published online: 15 June 1999

Abstract

Using a new starting material of Ba₂Cu₃O₅ and a three step heat treatment, single phase Tl₂Ca₁Ba₂Cu₂O₈ high-T_c superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of H_c1 is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility, r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated as 3D Josephson network) as mm, Oe and A/cm² at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously by metallic S-N-S weak links.