Superconducting and normal state behaviors of (Tl,Bi)Sr2−xTixCa0.9Y0.1Cu2O7 ceramics

Effects of Bi and Ti substitutions at Tl and Sr sites, respectively, on superconducting and normal state behaviors of (Tl,Bi)Sr2−xTixCa0.9Y0.1Cu2O7 (x=0–0.5) and Tl1−yBiySr1.9Ti0.1Ca0.9Y0.1Cu2O7 ceramics have been investigated. Temperature-dependent resistance measurements on Tl0.9Bi0.1Sr2−xTixCa0.9Y0.1Cu2O7 (x=0) showed metallic normal state behavior with Tc onset of 96 K and Tc zero of 61 K. Substitution of Ti caused deterioration of superconductivity and gradual change of normal state resistance from metallic behavior (x=0–0.3) to semiconductor-like behavior (x=0.4–0.5). Resistance versus temperature measurements on Tl1−yBiySr1.9Ti0.1Ca0.9Y0.1Cu2O7 (y=0–0.6) showed optimum superconductivity for y=0.3 with Tc onset of 98 K and Tc zero of 68 K. The effects of Bi and Ti substitutions on superconducting and normal state behaviors of the ceramics are discussed in terms of ionic radius of elements and the concept of average Cu valence.