Cation interdiffusion at YBCO/MgO interfaces

Resistivity measurements of YBCO thin films on MgO substrates show that the transition to the superconducting state depends on film thickness. TEM investigations of the films revealed interdiffusion of Cu and Mg. The concentrations of the cations at the interface were quantitatively measured. These data show that their diffusion rates are much different (MgODCu/YBCODMg = 30); this indicates that the diffusion mechanism is complicated by the layered structure of the perovskite-like films. No impurity segregation was detected at the interface. Diffraction study of several YBCO grains confirms that the film c-axis is oriented perpendicular to the substrate, but that the a/b plane has no fixed orientation, indicating that no epitaxial relationship exists