Epitaxial growth of yttria-stabilised zirconia buffer layers on X-cut LiNbO3 for superconducting electrodes

We report on the epitaxial growth of yttria-stabilised zirconia (YSZ) buffer layers on X-cut LiNbO3 (LNO) single crystals by pulsed laser deposition. Despite the low chemical stability of the substrates at high temperature, high quality fully reproducible films were obtained over a relatively broad range of processing conditions. The films were (00h) out-of-plane single oriented and the in-plane edge of the YSZ unit cell was aligned with the polar axis of the LNO. However, the YSZ deposition also promoted the formation of the compound LiNb3O8. This compound is epitaxial and located at the interface. The homogeneous YSZ film presents a uniform surface, free of outgrowths and with a low roughness. These characteristics are suitable for the epitaxial growth of other oxides, as has been demonstrated with the preparation of YBa2Cu3O7/CeO2/YSZ/LNO heterostructures. The superconducting YBa2Cu3O7 films were epitaxial, with the c axis perpendicular to the surface and single in-plane orientation, and presented good transport properties (critical temperatures around 86 K and critical current densities close to 106 A/cm2 at 77 K).