Dg. Ko et H. Oesterreicher, PREPARATIVE CONDITIONS FOR THE TRANSITION FROM SUPERCONDUCTIVITY TO NONSUPERCONDUCTIVITY IN OXYGENATED ORTHORHOMBIC YBA2(CU1-XNIX)(3)O-Y, Ceramics international, 21(4), 1995, pp. 293-296
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.