Solid-state reactions in high-temperature superconductor-ceramic interfaces; Y-Ba-Cu-O on Al2O3 versus yttria-stabilized ZrO2, and MgO

We have prepared, using molecular-beam epitaxial techniques, superconducting Y-Ba-Cu-O films directly on Al2O3, yttria-stabilized ZrO2 (YSZ), and MgO without buffer layers. The structure and stoichiometry of the films on Al2O3 are compared with those prepared on YSZ and MgO and found in large part determined by reactions with the substrates. The films on Al2O3 consist of textured Y2Ba4Cu8O20−x with superconducting onset at 80 K and zero resistance at 69 K, whereas on YSZ and MgO, YBa2Cu3O7−z films are formed. Auger electron depth profile spectroscopy in conjunction with structural and transport studies suggest that copper is depleted from the region near the Al2O3 substrate.