CRITICAL-TEMPERATURE OPTIMIZATION IN BI2SR2CACU2O8+DELTA CRYSTALS

Transition temperatures as high as 96 K were reproducibly achieved in crystals of Bi2Sr2CaCu2O8+delta (Bi-2212) by changing their oxygen content through annealing and quenching in specific (T, p(O-2)) conditions. In both Ar and air atmosphere, the critical temperature T-c increases with the temperature of annealing. The possibilities for obtaining a higher T-c with this process is limited only by the phase-stability boundary of Bi-2212 at high temperatures. In all our samples, T-c is an increasing function of the a and c cell parameter, suggesting that all samples studied lie on the overdoped side of the maximum value for the transition temperature of the Bi-2212 phase, which has not yet been reached in single crystals.