Effects of Cu substitution on superconductivity and excess conductivity of Tl1–xCuxSr1·8Yb0·2CaCu2O7–δ (x=0–0·6) ceramics

Abstract

TlSr1212 samples were synthesised from Tl1–xCuxSr1·8Yb0·2CaCu2O7–δ (x=0·0 to 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 Tc 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.