HETEROEPITAXIAL GROWTH OF CHEMICALLY DERIVED EX-SITU BA2YCU3O7-X THIN-FILMS

Heteroepitaxial growth of Ba2YCu3O7-x (BYC) thin films prepared by pos tdeposition annealing on (001) LaAlO3 was characterized by TEM and x-r ay diffraction studies of specimens rapidly cooled from various points in the growth heat treatment. Heteroepitaxial nucleation of BYC occur red between 720 and 770 degrees-C during heating at 25 degrees-C/min t o the annealing temperature of 830 degrees-C. The c-axis normal BYC ra pidly coalesced into a continuous film with nearly complete coverage o f the substrate surface after growth of a film of several unit cells t hickness. The experimental results were not consistent with purely sol id phase heteroepitaxial nucleation and growth or epitaxial grain grow th, mechanisms for microstructural evolution of other chemically deriv ed epitaxial oxide thin films. The nature of the transformation and th e microstructure of the final superconducting films were consistent, i nstead, with growth of epitaxial BYC from a liquid phase that is prese nt transiently during the anneal. This hypothesis was supported by the rmal analysis results obtained from the precursor material of which th e films are composed prior to transformation to BYC.