Growth rate dependence of physical properties of YBa2Cu3Ox single crystals

Abstract We present magnetization measurements on YBa 2 Cu 3 O x single crystals cooled at various rates (0.1–1.0°C/h) during the growth process. The oxygen concentration dependence of the superconducting transition temperature, T c , as determined from the low-field magnetization, is very different for samples grown at different cooling rates. Crystals grown at 1.0 and 0.7°C/h display the typical T c vs. x maximum, with a maximum T c of 93.4 K at an oxygen concentration of x =6.94 (oxygenation at 480°C in flowing O 2 ). Crystals grown at the rate of 0.3°C/h show a similar maximum in T c vs. x , but with a maximum value of T c of only 92 K. Crystals grown at an even slower rate (0.2 and 0.1°C/h) no longer display a maximum in T c vs. x . For these crystals, T c monotonically decreases with decreasing oxygen concentration. The maximum T c of 91 K is reached at the lowest oxygenation temperature of 375°C. This difference in T c vs. oxygen concentration is accompanied by significant differences in the pinning behavior as determined from hysteresis loop measurements. The microscopic conditions giving rise to this behavior are not understood.