The Role of Ca in Superconducting and Magnetic Properties of Y1-x Ca x Ba2Cu3O7-δ (x=0.0-0.30)

We report the structural, superconducting, magnetic and granular properties of Y1-x Ca (x) Ba2Cu3O7-delta ; x=0.0, 0.1, 0.2 and 0.3. Rietveld fitted X-ray diffraction data confirm the single-phase formation for all the samples. The orthorhombicity of the parent compound (x=0.0) decreases and becomes closer to the tetragonal structure for higher Ca concentration. The superconducting transition temperature (T (c)) decreases with increasing Ca content due to both over-doping and ensuing disorder in the superconducting CuO2 planes with Ca doping. DC susceptibility measurements reveal a reduction of the Meissner fraction with Ca doping, suggesting the flux pining effect. The ac susceptibility measurements reveal the enhancement of grain coupling with increasing Ca content in the system. The average grain size is found to increase with Ca doping. Scanning Electron Microscopy (SEM) observations indicate better grain connectivity in terms of narrow grain boundaries for Ca doped samples. It is concluded that limited Ca doping enhances the superconducting performance of the YBa2Cu3O7-delta system.