CRYSTAL-STRUCTURE, MICROSTRUCTURE, SURFACE-MORPHOLOGY, AND TRANSPORT-PROPERTIES OF ER5BA7CU12OY HIGH-TEMPERATURE-SUPERCONDUCTOR THIN-FILMS

Er5Ba7Cu12Oy is a thin-film high-temperature superconductor (critical transition temperature, T(c) = 93 K). The crystal structure, microstru cture, surface morphology, and transport properties of Er5Ba7Cu12Oy th in films were investigated by x-ray diffraction (XRD), scanning electr on microscopy (SEM), and four-point dc-resistivity measurements under magnetic fields. Oriented Er5Ba7Cu12Oy thin films on cubic ZrO2(100), MgO(100), LaAlO3(100), and SrTiO3(100) substrates were prepared by mol ecular-beam deposition and post annealing in wet and dry O2 (BaF2 tech nique; annealing temperature =850-890-degrees-C). The 0.4-mum Er5Ba7Cu 12Oy thin films on cubic ZrO2(100) and MgO(100) substrates grew with m ixed b and c orientations. The 0.4-mum Er5Ba7Cu12Oy thin films on LaAl O3(100) and SrTiO3(100) substrates annealed at 850-degrees-C had c- an d a-oriented grains, whereas the films annealed in the temperature ran ge 870-890-degrees-C displayed (001) epitaxy. By XRD, the lattice cons tants of Er5Ba7Cu12Oy were derived as a0 = 10.38 angstrom, b0 = 10.52 angstrom, c0 = 11.65 angstrom, and alpha = beta = gamma = 90-degrees. In the SEM studies, the 0.4-mum Er5Ba7Cu12Oy thin films were found to have a smooth-surface morphology. The shape of a-oriented grains in th e Er5Ba7Cu12Oy thin films was found to be thick-rod-like. The transpor t data of superconducting resistive transitions under magnetic fields (0-5 T) were analyzed with the models of thermally activated giant flu x creep. The activation energy for flux creep was determined to be U ( K) = [3 X 10(4)(1 - T/T(c))1.8]/H0.7 (H(perpendicular-to) ab plane), w here H = magnetic field (T) and T = temperature (K).