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

Abstract

Using a new starting material of Ba2Cu3O5 and a three step heat treatment, single phase Tl2Ca1Ba2Cu2O8 high-Tc superconducting samples have been prepared, possessing the onset-and critical temperatures To = 114 K and Tc = 105 K. The morphology dependent value of Hc1 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 λJ = 0.8 mm, HJc = 0.28 Oe and JJc = 2.2 A/cm 2 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.PACS. 74.25.-q General properties; correlations between physical properties in normal and superconducting states -74.40.+k Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.) -75.40.-s Critical-point effects, specific heats, short-range order

DecoupledCuO2andRuO2layers in superconducting and magnetically

“…The ac susceptibility curves in other HTSC ex- hibit nearly the same shapes and transition temperature widths for ceramic and powder samples of the same compound. [33,34] In contrast, in Fig. 2 we observe that a large diamagnetic shielding, which starts below 33 K in the ceramic sample, is not present in the powder.…”