Growth and properties of YBa2Cu3O7 thin films on non-lattice-matched and polycrystalline substrates

The authors have investigated the nature of the in-situ growth of c-axis normal YBa2Cu3O7 thin films on non-lattice-matched, vicinal, and polycrystalline MgO substrates and on buffer layers of MgO. It is found that the preparation of the MgO surface determines the structural and transport properties of the films. In particular, the authors were able to reproducibly grow films exhibiting either weak link behavior or very high critical current densities. The variation of the thin-film microstructure, oxygen content, and superconductive properties with the changes in the thin- film crystal structure that result from the different growth situations is discussed. The structural and transport measurements of YBCO films grown on various MgO surfaces clearly indicate the importance of obtaining a nucleation stage which will result in high-quality YBCO on non-lattice- matched substrates. Such considerations are of prime importance when the low-temperature growth of the cuprate superconductors is required in order to obtain a morphology which facilitates the use of lithographic processing and the growth of multilayer structures. (I.E.)