Behavior of oxygen diffusion in buffer layers for coated conductors

Abstract

We have evaluated the effect of annealing in oxygen atmosphere on the structure, texture and phase transformation of LZO films deposited on YSZ (yttria-stabilized zirconia) (0 0 l) single crystal substrates and textured NiW substrates by metal-organic deposition (MOD) method. The results show that the structure stability of the LZO films is heavily dependent on the oxygen partial pressure in annealing process. Then we have in details studied the behavior of oxygen diffusion in three kinds of buffer layer architectures on NiW substrates by varying the temperature, oxygen partial pressure and dwelling time in the annealing process. The oxygen diffusion within buffer layers leads to the oxidation of substrate, and even the texture and structure of buffer layers are destroyed with the increase of the thickness of the oxides layer related to NiW substrate. It reveals that the relative volume of oxides related to NiW substrate increases exponentially with the annealing temperature, and increases linearly with the annealing time at logarithmic scale. The relative intensity of texture peaks of buffer layers decreases and even disappears with the increase of the oxygen partial pressure in annealing process because of the acceleration of the oxidation reaction of substrate. The influence of annealing temperature, oxygen partial pressure and dwelling time on the oxygen diffusion is related to the intrinsic oxygen diffusion coefficient of buffer layers materials. Compared with the increase of oxygen partial pressure, the elongation of dwelling time shows a less effect on the oxidation rate of NiW substrate and a weak destruction of the texture of buffer layers. Except choosing the oxide materials with small oxygen diffusion coefficient as buffer layers in coated conductors, the degree of oxidation about NiW substrate could be greatly controlled and it would result in the less destruction of texture and structure of buffer layers by adjusting the annealing temperature, oxygen partial pressure and dwelling time in the process of YBCO deposition.