Effect of zinc addition on the superconducting properties of YBa2Cu3O7 ceramic

Synthesize of YBa2Cu3O7, Zn = 0,1,2,3,4 and 5 wt.% particles-superconductor composites by solid-state reaction technique and characterize the effects of zinc (Zn) particles on structural and superconducting properties of YBa2Cu3O7 phase. Unaltered crystal structure of host YBa2Cu3O7 phase confirmed the existence of Zn particles at intercrystallite sites. The observed an improvement in grains size and intergrains connectivity by healing up the voids after incorporation of Zn particles in YBa2Cu3O7 superconductor. Superconducting properties of Zn and YBa2Cu3O7 composites were suppressed for all Zn particles concentrations. Suppression of zero resistivity critical temperature Tc(0) and variation in normal state resistivity ρ300 (Ω-cm) were attributed to reduction of superconducting volume fractions and enhanced scattering cross section of mobile carriers. Single crystals of YBa2Cu3-xZnxO7-y were obtained through long periodic step growth by adding ZnO to the primary phase region of the YBa2Cu3O7-y phase on the YBa2Cu3O7-y-BaCu3O4 pseudo-binary line. The solubility of zinc in YBCO is found to be relatively low. The chemical composition (including oxygen) has been accurately determined for all the Zn addition YBCO crystals by EPMA. XRD showed that all the crystals were orthorhombic and the unit cell volume increased continuously with increasing zinc concentration. The primary phase was found to be located at the region having high fractions of BaCu3O4. In the course of the crystal growth study, several insulating compounds with approximate formulae YBaZn3-xCuxOy, Y2(Cu,Zn)xOy and (Y,Cu)BaZn2Oy were also found from the melt after solidification. The phase of YBaZn3-xCuxOy was identified to be hexagonal with a approximately 5.0 angstrom and c approximately 9.5 angstrom. The temperature spectra of internal friction for Zn addition ceramic YBa2(Cu1-xZnx)3O6+delta are presented with zinc content x varying from 0,1,2,3,4 and 5 wt%. Two thermally activated peaks (P1, P2) near the superconducting transition temperature Tc were found to show different behaviours upon zinc doping: the peak at 110 K (P1) decreases rapidly with increasing of x while another one at 120 K (P2) has no significant change. The relaxation mechanism of P1 is interpreted in terms of jumps of apical oxygen atoms between off-centred positions produced by the Jahn-Teller effect. The effect of zinc substitution on the depression of superconductivity is also discussed.