Crystal structure, microstructure, surface morphology, and transport properties of Er5Ba7Cu12Oy high-temperature-superconductor thin films.

Abstract

${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ is a thin-film high-temperature superconductor (critical transition temperature, ${\mathit{T}}_{\mathit{c}}$=93 K). The crystal structure, microstructure, surface morphology, and transport properties of ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and four-point dc-resistivity measurements under magnetic fields. Oriented ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films on cubic ${\mathrm{ZrO}}_{2}$(100), MgO(100), ${\mathrm{LaAlO}}_{3}$(100), and ${\mathrm{SrTiO}}_{3}$(100) substrates were prepared by molecular-beam deposition and post annealing in wet and dry ${\mathrm{O}}_{2}$ (${\mathrm{BaF}}_{2}$ technique; annealing temperature =850--890 \ifmmode^\circ\else\textdegree\fi{}C). The 0.4-\ensuremath{\mu}m ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films on cubic ${\mathrm{ZrO}}_{2}$(100) and MgO(100) substrates grew with mixed b and c orientations. The 0.4-\ensuremath{\mu}m ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films on ${\mathrm{LaAlO}}_{3}$(100) and ${\mathrm{SrTiO}}_{3}$(100) substrates annealed at 850 \ifmmode^\circ\else\textdegree\fi{}C had c- and a-oriented grains, whereas the films annealed in the temperature range 870--890 \ifmmode^\circ\else\textdegree\fi{}C displayed (001) epitaxy.By XRD, the lattice constants of ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ were derived as ${\mathit{a}}_{0}$=10.38 \AA{}, ${\mathit{b}}_{0}$=10.52 \AA{}, ${\mathit{c}}_{0}$=11.65 \AA{}, and \ensuremath{\alpha}=\ensuremath{\beta}=\ensuremath{\gamma}=90\ifmmode^\circ\else\textdegree\fi{}. In the SEM studies, the 0.4-\ensuremath{\mu}m ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films were found to have a smooth-surface morphology. The shape of a-oriented grains in the ${\mathrm{Er}}_{5}$${\mathrm{Ba}}_{7}$${\mathrm{Cu}}_{12}$${\mathrm{O}}_{\mathit{y}}$ thin films was found to be thick-rod-like. The transport data of superconducting resistive transitions under magnetic fields (0--5 T) were analyzed with the models of thermally activated giant flux creep. The activation energy for flux creep was determined to be U (K) =[3\ifmmode\times\else\texttimes\fi{}${10}^{4}$(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{1.8}$]/${\mathit{H}}^{0.7}$ (${\mathit{H}}_{\mathrm{\ensuremath{\perp}}}$ ab plane), where H=magnetic field (T) and T=temperature (K).