Effect of starting materials on the critical parameters of superconducting Tl  Ca  Ba  Cu  O compounds

Abstract

Using different batches of starting materials (samples I, TINO 3, CaO, Ba 2Cu 3O 5; II, TINO 3, CaO, BaO, CuO; III, TINO 3, CaO, Ba(NO 3) 2, CuO; IV, TINO 3, CaO, BaCuO 2; V, TINO 3, CaO, Ba(NO 3) 2, CuO, O 2) and the same heat treatment process, high T c superconducting systems of nominal composition TICaBaCuO 4.5 were prepared. Different superconducting phases were formed depending on the starting compounds used. Specimens I and IV had a single-phase (2,1,2,2) character. In samples II and III the dominant (2,1,2,2) phase was accompanied by (2,0,2,1) and by (1,2,2,3) and (2,2,2,3) phases in small quantity, respectively, while specimens V can be characterized by the existence of CuO and Cu 2O beside the chief (2,1,2,2) phase. The superconducting properties were affected by starting materials, which manifests itself in the difference in onset and critical temperatures, lower and upper critical magnetic fields, paramagnetic limits, coherence length, penetration depth and Ginzburg - Landau parameter of specimens of different kinds. Due to the weak coupling created by interstitial material, different intergrain, intragrain and direct transport critical currents were determined, depending on the type of samples. The main aim of this work was to compare the experimental data with the corresponding theories to draw conclusions on the role of the starting compounds.