Al doping influence on crystal growth, structure and superconducting properties of Y(Ca)Ba2Cu3O7y whiskers

We synthesized Al doped Y(Ca)Ba2Cu3O7Ày (YBCO) whiskers via the solid state reaction method. Al dop- ing was systematically varied in the nominal cationic stoichiometry of YBa2Cu3CaTe0.5AlxO7Ày, with 0 6 x 6 0.5. The amount of the grown whiskers increases for nominal Al addition up to x = 0.05, decreas- ing for larger concentrations. The concentration of Al incorporated in the crystals (x0 ) is always higher with respect to the starting stoichiometry and shows a gradient along its length, with a higher amount at the tip regions. The single crystal diffraction analyses show an increasing tetragonal character with increasing x0 , with a transition from the orthorhombic to the tetragonal system for x0 = 0.13, which is in agreement with the worsening of electrical transport properties and disappearing of superconductivity for x0 = 0.19.