High temperature growth kinetics and texture of surface-oxidised NiO for coated superconductor applications

Thick NiO films were grown in air, on biaxially textured (001) Ni and as-rolled Ni tapes, at temperatures from 1050 to 1350 °C. Ni diffusion through the NiO film mainly contributes to the growth since is much faster than oxygen diffusion and occurs by a vacancy diffusion mechanism in the lattice at high temperatures. Parabolic growth kinetics were found for both NiO film thickness and grain growth, and compared with the literature data. Competitive growth of (111) and (001) oriented grains establishes the final NiO orientation at temperatures below 1250 °C, while at higher temperatures leakage diffusion at/towards grain boundaries, grain coarsening and (110) oriented grains disrupt the (100) texture. Hence, development of epitaxy of NiO on textured Ni tapes was found to be largely due to growth kinetics depending on both, time and temperature. We report here a systematic study of the microstructure and kinetics of formation of textured NiO substrate for application as a buffer layer in coated conductor technology.