Microstructure and Critical Currents of YBa2Cu3O7-x Thin Films on SrTiO3 and a New Substrate: KTaO3
Superconducting thin films of high-TC materials are of interest for use in fundamental research as well as for a variety of device applications. Epitaxial thin films of high-TC superconductors have previously been produced using substrates such as SrTiO3, cubic ZrO2, MgO, and Al2O3 with the best results being reported for (100) surfaces of strontium titanate. In the present work, the properties of epitaxial films of YBa2Cu3O7-x (Y123) formed by coevaporation of Y, Cu, and BaF2 onto (100) surfaces of SrTiO3 are presented and compared with those found for identical films on a new substrate material: single crystal KTaO3 or potassium tantalate. This material, like SrTiO3, is also a cubic perovskite with a suitable lattice constant for promoting epitaxial growth. In Sections I and II of the present work, the details of the film preparation are outlined, along with the properties of the resulting high-Ta films formed on (100) and (110) surfaces of SrTiO3. These results are similar to the findings by others and a critical dependency on the film microstructure and orientation is found. In Section III, the results obtained for the new substrate material KTaO3 are presented. It is shown that the properties of Y123 films epitaxially grown on the (100) surface of KTaO3 single crystals compare favorably with those of films formed on SrTiO3. In Section IV more detailed comparisons of the microstructural properties of epitaxial films on the two substrate types are made. The results show that KTaO3 represents a promising new substrate material for the epitaxial growth of high-TC Y123 films.
KeywordsCritical Current Density Growth Surface Rutherford Backscatter Spectroscopy Epitaxial Film Strontium Titanate
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