PREPARATIVE CONDITIONS FOR THE TRANSITION FROM SUPERCONDUCTIVITY TO NONSUPERCONDUCTIVITY IN OXYGENATED ORTHORHOMBIC YBA2(CU1-XNIX)(3)O-Y

When materials YBa2(Cu-1-x)(3)O-y with x = 0.05 are quenched from T-A similar to 1000 K in air (designated Kp compounds in this state) and s ubsequently reoxygenated near T-a = 670 K (Ko compounds), they are ort horhombic but can have lost superconductivity and gained paramagnetism . This contrasts with the behavior of conventionally slow cooled oxyge nating preparations (OF) which produce T-c similar to 75 K. Presented here are structural, magnetic and superconducting behaviors for materi als given various thermal treatments. It is demonstrated that material s quenched from air annealing temperatures in the range of 950-1100 K (designated Kp) show volume expansion anomalies and slow reoxygenation kinetics, probably connected with charge localization. On reoxygenati on a complex sequence of states is indicated, including the loss of di amagnetism and the gain of semiconductive type behavior. After long eq uilibrating annealing at 673 K in air, a reversal to conventional supe rconducting behavior can be achieved.