Stabilization of Tl-1223 Phase by Arsenic Substitution

Systematic studies on the Tl_1−x As _x Ba₂Ca₂Cu₃O_9−δ system, with 0.0≤x≤0.3, were carried out to investigate the effect of arsenic on the superconductivity of Tl-1223 phase. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), electron dispersive X-ray (EDX) and electrical resistivity measurements. XRD studies indicated that the tetragonal structure of Tl-1223 phase does not change by arsenic substitution whereas the lattice parameters a and c do. The elemental compositions analysis, determined from EDX, indicated that the arsenic was successfully introduced into the microstructure of Tl-1223 phase. The superconducting transition temperature T _c , determined from electrical resistivity data, increased from 122 to 127 K as x increased from 0.0 to 0.025 and then it suppressed with further increase in x. This means that the lower As-content may stabilize the Tl-1223 phase. In order to study the effect of arsenic substitution on the thermodynamic fluctuations of the Cooper pairs, above T _c , the excess conductivity analysis were performed using Aslamazov–Larkin (AL) theory. The results clarified that there are four regions appeared as the temperature increases namely critical (cr), three-dimensional (3D), two-dimensional (2D), and short-wave (sw) fluctuations. The zero-temperature coherence length along c-axis, the effective layer thickness of the two dimensional system, and the interlayer coupling strength were estimated as a function of the As-content. Furthermore, the thermodynamics critical field, lower critical magnetic field, upper critical magnetic field, critical current density, and Fermi energy were calculated from the above measurements.