Enhanced superconducting transition temperature for Cr-substituted Tl2Ba2CaCu2O8-δ

Abstract

Cr-substituted Tl2Ba2CaCu2O8-δ (Tl-2212) high temperature superconductor for x = 0–0.5 has been prepared using the standard solid-state reaction method. The precursor powders consisting of Ba2CaCu2Od were sintered at 900 °C for 24 h. The powders were then added with Tl and Cr, ground and pressed into pellets. The pellets were heated at 910 °C in oxygen flow for 4 min followed by furnace cooling. The d.c. electrical resistance (R) versus temperature (T) measurements were carried out using the four-point probe method with silver paste contacts. The transition temperature was determined from the slope of the resistance versus temperature graph. The superconducting critical region was divided into three: onset transition temperature (Tc-onset), middle transition temperature (Tc-mid) and zero-resistance temperature (Tc-zero). The non-substituted sample showed onset transition temperature, Tc-onset of 97 K. The x = 0.2 sample (Tl1.8Cr0.2Ba2CaCu2O8-δ) showed the highest Tc-onset (102 K). Further substitutions of Cr (x ≥ 0.3) decreased the transition temperature. All samples except the non-substituted samples showed at least two peaks in the dR/dT curves. This indicated that superconductivity within grains and intergrain occurred at different temperatures for all Cr-substituted samples. This work showed that Cr (x = 0.2) slightly enhanced the transition temperature of Tl-2212.