Infield magnetic measurements of (Cu0.5Tl0.5)Ba2Ca3(Cu4−xTix)O12−δ (x = 0, 0.25, 0.50, 0.75) samples

We have synthesized (Cu0.5Tl0.5)Ba2Ca3(Cu4−xTix)O12−δ (x = 0, 0.25, 0.50, 0.75) superconductor samples at 880 °C and studied their superconducting features by XRD analysis, resistivity measurements, ac susceptibility measurements, FTIR absorption spectroscopy, and detailed infield magnetic measurements. By increasing x concentration of Ti doping, the a axis length of the tetragonal unit cell increases, whereas its c axis length decreases. Also, the Tc(onset), Tc(R = 0), and the magnitude of diamagnetism suppresses. The peak position of the apical oxygen modes stay unchanged, however the CuO2/TiO2 planar oxygen modes are softened with increasing x. The critical current density Jc of the samples suppress with an increased field. Suppression of Jc is more steep in doped samples. The doped atoms increase the population of confined defects, which act as pinning cores that increase energy per unit length of flux vortex ɛ. The pinning strength essentially depends on the ɛ; therefore, it also increases with x concentration of Ti doping. The superconductivity enhancement of doped samples is witnessed in increased coherence length ξc, suppression of the Ginzburg-Landau parameter κ, and the penetration depth λD. The superior infield characteristics of doped samples indicated that Ti atoms act as efficient flux pinning centers whereas due to their presence in the final compound, the phase coherence of Cooper pairs in various unit cells is marginalized, which induces the suppression in Tc's and magnitude of diamagnetism in ac susceptibility measurements.