Effect of Hf substitutions on the formation and superconductivity of Tl-1212 type phase TlSr2(Ca1−xHfx)Cu2O7−δ

Abstract

The TlSr2(Ca1−xHfx)Cu2O7−δ (Tl-1212) superconductor for x = 0.0 to 0.4 has been prepared by the solid state reaction method and studied by powder X-ray diffraction method, electrical resistance and scanning electron microscope (SEM). Most of the samples showed the Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Hf-substitution (x ≤ 0.15 or x ≤ 0.25) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature (Tc onset) between 38 and 47 K for Hf substitution.