Determination of the intergrain critical-current distribution for polycrystalline (Tl,Pb)(Ba,Sr)2Ca2Cu3Oy superconductors from ac-susceptibility data.

Abstract

The intergrain critical-current-density (${\mathit{J}}_{\mathit{c}\mathit{i}}$) distribution and intergranular volume fraction of ceramic superconductors were determined from ac-susceptibility measurements. The sample was melt-treated polycrystalline (Tl,Pb)(Ba,Sr${)}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ [Tl (1:2:2:3)] high-${\mathit{T}}_{\mathit{c}}$ (\ensuremath{\sim}119 K in zero field) superconductor for fields up to 80 K Oe and temperatures between 30 K and ${\mathit{T}}_{\mathit{c}}$. Experimental conditions were chosen so that the data could be analyzed with Bean's critical-state model associated with an extended version of the effective-medium model for the material's magnetic-shielding properties. Within this context equations relating the statistical distribution of intergrain critical currents in the sample with the measured susceptibility were derived.