Comparative study of structural and superconducting properties of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ phase substituted by copper fluoride and thallium fluoride

Abstract

A series of (Cu0.5−xTl0.5−y)-1223 superconductor samples, doped with varying amounts of (CuF2)x and (TlF)y compounds with x = y = 0.0, 0.1, 0.2, 0.3 and 0.4, were synthesized via a single-step solid-state reaction. X-ray diffraction (XRD) revealed that all the samples have a tetragonal symmetry of (Cu0.5Tl0.5)-1223 phase. Additionally, with increasing fluorine content up to x = 0.2 CuF2 and y = 0.1 TlF, the phase fraction and the superconducting transition Tc were enhanced. The scanning electron microscopy (SEM) images exhibited mainly plate-like rectangular shape grains confirming the formation of (Cu0.5Tl0.5)-1223 phase. The Fourier transform infrared (FTIR) spectra of CuF2- and TlF-substituted (Cu0.5−xTl0.5−y)-1223 show a slight softening and hardening in few peaks related to the apical oxygen atoms and CuO2 planar modes. The stoichiometry of elemental composition for all prepared samples has been confirmed using ion beam analysis (IBA) methods. The excess conductivity Δσ above Tc was analyzed through the Aslamasov–Larkin (AL) approach. Using the Ginzburg–Landau (GL) number (NG) and equations, the coherence length, the effective layer thickness, the lower critical field Bc1(0), the upper critical field Bc2(0) and the critical current density Jc(0) were estimated. It was found that the addition of an optimum concentration of CuF2 and TlF, controlled the microstructure, the grains coupling and hence enhanced the physical properties of (Cu0.5Tl0.5)-1223 phase.