CONCENTRATION-DEPENDENT OXYGEN DIFFUSIVITY IN YBA2CU3O6+X .2. OXYGEN PARTIAL-PRESSURE STUDIES

Electrical resistance measurements were used to determine the equilibrium resistivity characteristics and the oxygen diffusion behavior in YBa2Cu3O6+x (YBCO) as a function of oxygen partial pressure at temperatures ranging from 450-850-degrees-C. The equilibrium resistivity values depended on the oxygen partial pressures as n = partial derivative Log rho/partial derivative Log[P(O2)], where n ranged from approximately - 1/6 up to - 1/2 from low to high temperatures. A clear p-type to n-type transition was observed near 750-degrees-C for an oxygen content of 6.1 (x = 0.1). Values of the oxygen exponent, n, for single crystal YBCO at 650-degrees-C and 708-degrees-C were similar to those for polycrystalline specimens. Measurements of the time-dependent resistivity behavior between different oxygen partial pressures yielded diffusion kinetics between well-established boundary values of the oxygen content, x. In single crystal specimens, the chemical diffusivity for oxygen in-diffusion was observed to increase with decreasing oxygen content. The kinetic data for the polycrystalline specimens between 450-850-degrees-C also depended on the oxygen concentration; however, the temperature dependence was non-Arrhenius.