Micro-structural properties of YBa₂Cu₃O_7-x/ZnO nanorods on SrTiO₃

We examined the local structural and the interfacial properties of YBa₂Cu₃O_7-x (YBCO)/ZnO nanorods on SrTiO₃ (STO) substrates using various measurements. Vertically aligned ZnO nanorods were synthesized on STO substrates using a catalyst-free metal-organic chemical vapor deposition. YBCO films were deposited ex-situ on the ZnO nanorods/STO templates using a DC magnetron sputtering deposition. X-ray diffraction revealed that the YBCO films were crystallized along their c-axes on the ZnO nanorods/STO templates. Transmission electron microscopy measurements demonstrated that YBCO filled the space between ZnO nanorods and that both interfaces of YBCO/ZnO nanorods and ZnO nanorods/STO were quite clean with no disorder. Polarization-dependent extended X-ray absorption fine structure measurements at the Cu K edge showed extra disorder in the CuO₂ planes of YBCO/ZnO nanorods/STO, compared with that of YBCO/STO. The superconductivity transition temperature (T_c) of YBCO/ZnO nanorods/STO was approximately 50 K whereas that of YBCO/STO was 93 K. The decrease of T_c of YBCO/ZnO nanorods/STO was ascribed to the structural disorder of CuO₂ planes as well as grain boundaries in the YBCO films.