Preparative Conditions for the Transition from Superconductivity to Nonsuperconductivity in Oxygenated Orthorhombic YBa_2(Cu_(1-x)Ni_x)_3O_y

摘要

When materials YBa_2(Cu_(1-x))_3O_y with x = 0.05 are quenched from T_A ～ 1000 K in air (designated Kp compounds in this state) and subsequently reoxy-genated near T_a = 670 K (Ko compounds), they are orthorhombic but can have lost superconductivity and gained paramagnetism. This contrasts with the behavior of conventionally slow cooled oxygenating preparations (OP) which produce T_c ～ 75 K. Presented here are structural, magnetic and superconducting behaviors for materials given various thermal treatments. It is demonstrated that materials quenched from air annealing temperatures in the range of 950-1100 K (designated Kp) show volume expansion anomalies and slow reoxy-genation kinetics, probably connected with charge localization. On reoxygenation a complex sequence of states is indicated, including the loss of diamagnetism and the gain of semiconductive type behavior. After long equilibrating annealing at 673 K in air, a reversal to conventional superconducting behavior can be achieved.