Zr, Hf, Mo and W-containing oxide phases as pinning additives in Bi-2212 superconductor

Phase formation was investigated in Bi-Sr-Ca-Cu-M-O (M = Mo, W) systems at 850-900 °C. It was found that Sr2CaMO6 phases were chemically compatible with Bi-2212. The composites Bi-2212-Sr2CaMO6 and Bi-2212-SrAO3 (A = Zr, Hf) were obtained from a sol-gel precursor using crystallisation from the melt. The materials consisted of Bi-2212 matrix and submicron or micron grains of the corresponding dispersed phase. Tc was equal or exceeded that for undoped Bi-2212, reaching Tc = 97 K in the Mo-containing composite. The composites exhibited enhanced pinning in comparison with similar prepared pure Bi-2212, especially at T = 60 K. The best pinning parameters were observed for the Bi-2212-Sr2CaWO6 composite.