We have examined the fabrication conditions of epitaxial CeO2 films on a-plane sapphire substrates, and also examined epitaxial growth of YBa2Cu3O7-δ(YBCO) films on CeO 2/a-plane sapphire substrate. The θ/2θ XRD analysis of these composite films revealed that grains of the CeO2 and YBCO on CeO2/a-plane sapphire substrate were perpendicular to the substrate. From the φ-scan XRD measurement, we found that the four 102 φ-scan peaks of the YBCO film were observed and the peak positions were shifted by 45° compared with those of the CeO2 films. From the peak shifts we could estimate that the angle between the  axis of the CeO2 and the  axis of the YBCO was 45°. From temperature dependence of resistivity of the YBCO/CeO2/a-plane sapphire substrates, we obtained a zero-resistance temperature (TC) of 88.6 K. We found that their crystallinity and critical temperature (TC) were quite similar to those of YBCO film on CeO2/r-plane sapphire substrate. At the moment, YBCO thin films on a-plane sapphire are inferior to YBCO thin film on r-plane sapphire in terms of surface resistance.
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