STRUCTURE AND GROWTH OF YBA2CU3O7-DELTA THIN-FILMS ON MG2TIO4 (001) .1. GROWTH-CONDITIONS AND FILM STRUCTURE - TRANSMISSION ELECTRON-MICROSCOPY

Single-crystal Mg2TiO4 spinel layers have been grown by a topotaxial solid-state reaction on {100} cleavage faces of MgO single-crystal crystal substrates. A detailed study by transmission electron microscopy, electron diffraction and Rutherford backscattering spectrometry trometry has shown that these layers have grown in a genuinely single-crystalline way. having a perfect cube-to-cube orientation and the expected stoichiometry. Experimentally gained indications of a clean, structurally perfect and chemically stable surface of these layers and further properties of Mg2TiO4 as reported in the literature allow one to consider them as substrates suitable for the growth of thin films of the high-temperature superconductor YBa2Cu3O7-delta (YBCO). Some of their properties promise to be superior to those of MgO substrates. YBCO thin films have been grown on these single-crystal Mg2TiO4 spinel layers by pulsed laser deposition. They have been characterized by transmission electron microscopy and selected area electron diffraction with respect to their orientation, structure and morphology in dependence on the substrate temperature during growth. Under optimum growth conditions, YBCO films single-phase orthorhombic and uniformly (001) oriented were obtained having a good in-plane alignment. They are superconductive with T(c)onset up to 88 K, as is shown in Part II of this article.