Effects of Cu substitution on superconductivity and excess conductivity of Tl_(1-x)Cu_xSr_(1.8)Yb_(0.2)CaCu_2O_(7-δ) (x=0-0.6) ceramics

摘要

TISr1212 samples were synthesised from Tl_(1-x)Cu_xSr_(1.8)Yb_(0.2)CaCu_2O_(7-δ) (x=0-0.6) starting composition using the solid state synthesis, method. Temperature dependent electrical resistance measurements showed gradual change of normal state resistance behaviour from metallic (x=0.0 to 0.3) to semimetallic (x=0.4) and to semiconductor-like behaviour (x=0.5 to 0.6). The best superconducting behaviour for the series was observed at x=0.4 with zero resistance critical temperature T_(c zero) of 77.6 K. The effects of Cu substitution on superconducting properties are discussed in terms of the concept of average Cu valence. In addition, excess conductivity behaviour was analysed using Asmalazov-Larkin theory to study the effect of Cu substitution on superconductivity fluctuation behaviour. The analysis showed characteristic cross-over from two-dimensional to three-dimensional behaviour with decreasing temperature.