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Positron annihilation studies of the iron-substituted oxide superconductor YBa2(Cu1-xFex)3O7-y

Positron lifetime measurements were performed on YBa2(Cu1-xFex)3O7-y with x=0, 0.01, 0.02, 0.03, 0.06, 0.09 and 0.12 as a function of temperature between 20 K and room temperature. The positron mean lifetime and its thermal behaviour strongly depend on the iron concentration. A plausible model is proposed, in which the observed results are explained in terms of positron weak localisation due to copper-oxygen chain disordering.