Effect of zinc substitution on internal friction in YBCO superconductors

The temperature spectra of internal friction for Zn doped ceramic YBa2(Cu1- xZnx)(3)O6+delta are presented with zinc content x varying from 0 to 0.1. T wo thermally activated peaks (P1, P2) near the superconducting transition t emperature T-c were found to show different behaviours upon zinc doping: th e peak at 110 It (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-centre d positions produced by the Jahn-Teller effect. The effect of zinc substitu tion on the depression of superconductivity is also discussed.