Al doping influence on crystal growth, structure and superconducting properties of Y(Ca)Ba2Cu3O7−y whiskers

► Optimization of YBCO whiskers synthesis by Al2O3 addition. ► First complete crystal cell characterization of undoped YBCO whiskers. ► Characterization of the doped whiskers structural and electrical properties. ► New important evidences for the bottom-up growth mechanisms. We synthesized Al doped Y(Ca)Ba2Cu3O7−y (YBCO) whiskers via the solid state reaction method. Al doping was systematically varied in the nominal cationic stoichiometry of YBa2Cu3CaTe0.5AlxO7−y, with 0⩽x⩽0.5. The amount of the grown whiskers increases for nominal Al addition up to x=0.05, decreasing for larger concentrations. The concentration of Al incorporated in the crystals (x′) 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 x′, with a transition from the orthorhombic to the tetragonal system for x′=0.13, which is in agreement with the worsening of electrical transport properties and disappearing of superconductivity for x′=0.19.