ABSENCE OF CRITICAL-TEMPERATURE PLATEAUS IN QUENCHED SAMPLES OF YBA2CU3OX

Palleted samples of YBa2Cu3Ox which were quenched into Hg after equilibration at high temperatures, showed no evidence of ∼90 K and ∼60 K plateaux in plots of critical temperature against x. Also, their Tc values were 15-25 K lower than those reported for samples prepared by low temperature reduction. Homogeneity in oxygen distribution through the pellets was ensured by long time anneals of porous pellets prior to quenching and confirmed by X-ray diffraction and thermogravimetry. For a given x, the Tc values were insensitive to quench temperature, as shown by preparing samples with the same x at different temperatures and oxygen partial pressure. Tc was also unaffected by subsequent annealing in Ar at 300-350°C. The absence of Tc plateaux and the reduced Tc values is quenched samples may be associated with the occurrence of oxygen vacancies in the (z) positions which effectively act as mobile-hole traps. © 1990.