Conversion kinetics of oxyfluoride-derived YBCO films

Abstract

YBa2Cu3O7-x (YBCO) thin films were prepared on lanthanum aluminate (LAO) single crystals and buffered (5000 Y20 3, 500 Ce02) Ni-single crystal substrates by metal organic deposition (MOD) process. Glassy films were converted to epitaxial YBCO films, by heating in wet atmosphere of N2/02 mixture. A novel technique was used to determine the rate of conversion of films from glassy state to crystalline YBCO films. In this approach, the concentration of residual fluoride in the partially converted films was examined using fluoride ion selective electrode. Results obtained by this method were compared to results obtained by such methods as X-ray analysis and in-situ resistivity measurements. Analysis of data obtained by different methods showed that fluoride concentration measurement method is a fast and very accurate method. The influence of different factors on conversion rate was investigated by this approach, including high and low vapor pressure of water in the processing atmosphere, temperature and influence of substrate material on conversion. A simple model was proposed to describe the growth of crystalline YBCO film for diffusion controlled and reaction controlled growth kinetics. Results obtained by in-situ resistivity measurements were compared to results predicted by the model. The obtained data fits the model that describes interface reaction limited growth kinetics.