Grain growth of rapid-thermal-annealed Y-Ba-Cu oxide superconducting thin films

A study of the microstructure of Cu-rich and stoichiometric Y-Ba-Cu oxide thin-film superconductors is presented. The films were deposited on 〈100〉 SrTiO3 by the nonvacuum technique of metalorganic deposition followed by rapid thermal annealing in oxygen. Analysis showed that for annealing temperatures below 900 °C, grain size increased with increased annealing temperature, with an enhancement in grain growth for the Cu-rich films. Annealing near or above the melting point of the 1-2-3 phase causes only a slight increase in the rate of grain growth and no detectable effects of the excess Cu. Annealing above 920 °C produces segregated CuO islands 5–10 μm in size in the Cu-rich films. Oriented grain growth was found for the 1-2-3 grains with their c axis perpendicular and parallel to the SrTiO3 substrates. Sheet resistivity measurements were correlated with grain size, phase separation, and oriented grain growth. An anomalous behavior in the resistance-temperature plot at 220–240 K of the Cu-rich films is shown to be related to the presence of the excess Cu.