Formation of Tl-1212 Phase in Bi- and Cr-Substituted (Tl0.5Pb0.5−x M x )Sr2CaCu2O7 Superconductor

Abstract

The (Tl0.5Pb0.5−xMx)Sr2CaCu2O7 (Tl-1212) superconductor with M=Bi and Cr for x=0.0–0.5 has been prepared and studied by a powder X-ray diffraction method, and by electrical resistance and AC susceptibility measurements. All samples showed the Tl-1212 as the major phase and 1201 and 1223 as the minor phases. The Cr-substituted samples showed a higher onset temperature compared to the Bi-substituted materials. Bi-substitution maintained the Tl-1212 phase but Cr-substitution led to the formation of the Tl-1223 phase. Our results indicate the very different role of Bi and Cr in the formation of the superconducting phases.