ANISOTROPY OF OXYGEN TRACER DIFFUSION IN SINGLE-CRYSTAL YBA2CU3O7-DELTA

Oxygen tracer diffusion has been measured in single-crystalline YBa2CU3O7-delta from 300 to 650-degrees-C in the c direction, at a few temperatures in the ab plane of twinned crystals, and in the b direction of an untwinned crystal. The diffusion coefficient in the c direction, D(c), is almost-equal-to 10(6) lower than the diffusion coefficient in polycrystals at 400-degrees-C and diffusion in the b direction is at least 100 times faster than diffusion in the a direction at 300-degrees-C. The oxygen diffusion coefficient in polycrystals is, within an experimental uncertainty of a factor of 2, independent of oxygen partial pressure at 400-degrees-C, in agreement with previous results measured at 600-degrees-C. Some suggestions are presented on tbe mechanism of diffusion, the relation of diffusion and internal friction in YBa2CU3O7-delta, and on the meaning of the activation energy.