مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

Effects of Cr, Ta and Pb substitutions for Sr/Tl on phase formation and superconductivity of Tl0.8 Bi0.2 Sr2-x CrxC a0.9Y0.1Cu2O7, Tl0.9Bi0.1Sr2-yTayCa0.9Y0.1Cu2O7 and Tl1-zPbzSr1.8Sb0.2CaCu2O7 ceramics were investigated. Powder X-ray diffraction patterns for the three series showed major 1212 phase with 1201 phase as the minor phase. Electrical (dc) resistance measurements showed that the elemental substitutions at Sr site for Tl0.8Bi0.2Sr2-xCrxCa0.9Y0.1Cu2O7, (x = 0-0.3) and Tl0.9Bi0.1Sr2-yTayCa0.9Y0.1Cu2O7 (y = 0-0.3) series induced metal-insulator transition in normal state behavior accompanied by deterioration of superconductivity. On the other hand, Tl1-zPbzSr1.8Sb0.2CaCu2O7 (z = 0.1-0.6) series showed metallic normal state behaviors and enhancement in Tc zero from 26 K (z = 0.1) to a maximum of 80 K (z = 0.5). Results of structural investigation and phase formation using powder X-ray diffraction are reported and effects of Cr, Ta and Pb substitutions on superconductivity of Tl1212 are discussed in terms of ionic radius of substituting elements and the concept of average Cu valence.