OXYGENATION CONTROL OF YBA2CU3O6+Z POLYCRYSTALLINE SAMPLES VIA INSITU DETERMINATION OF ELECTRIC-CONDUCTIVITY

The electric conductivity of sintered YBa2Cu3O6+z, even at high temperatures, strongly depends on the oxygen content. Its in situ determination, therefore, is a simple method by which to optimize the oxygen uptake. At constant temperatures (T = 300-800-degrees) the time dependence of resistance was measured after small variations of the oxygen partial pressure. The analysis of this relaxation yields effective diffusion constants which were compared for polycrystalline samples prepared by various methods. Absolute values and temperature dependence of the time constants of the oxygen uptake differ strongly for the different samples. The results are correlated to the microstructure and critical current density and are discussed with respect to different oxygen transport mechanisms. In particular, the importance of diffusion along cracks and pores could be shown.