ANOMALOUS PHENOMENOLOGY IN NICKEL SUBSTITUTED CUPRATES

We present structural, magnetic, and superconducting behaviors for YBa 2(Cu1-xNix)3Oy with emphasis on x =0.05 given various thermal redox se quencings, We demonstrate that materials quenched from various air ann ealing temperatures display an unusual extension of the orthorhombic r egime compared to unsubstituted materials. In the range of annealing t emperature near 970K, this is accompanied by volume expansion anomalie s and slow reoxygenation kinetics probably connected with partial 3+ c harge localization on Cu. A second volume expansion anomaly occurs nea r 1080K, probably connected with partial 3+ charge localization on Ni. These materials can show diamagnetism up to 150K, possibly indicating a small amount of superconductivity. On reoxygenation at 673K materia ls undergo a slow transition, first to a paramagnetic-semiconducting s tate (designated K(o) compounds) and then after several days to a supe rconducting state similar to conventionally slow cooled oxygenating pr eparations (OP) which produce T(c) approximately 74K. These supercondu ctors display anomalous Meissner effects, i.e. the observation of para magnetism below Tc on small field cooling. This effect is connected wi th flux trapping in 2 types of regions, namely grain boundaries or loc al cluster inhomogeneities of the bulk.