Solid-phase epitaxial growth of oxide buffer materials for Rba₂Cu₃O_7−y(R: rare earth and Y) superconductor

We prepared various oxide buffer films on single-crystalline oxide substrates using chemical solution deposition to investigate general interfacial problems of buffer layers for coated conductors, such as epitaxial relationships between buffer material and the substrate. We found that (i) interfaces between the films and the substrates having the same crystal structure were compatible, even in a range of misfit value up to 7%, showing in-plane alignment; however (ii) interfaces between the films and substrates of other combinations of interface structures, with and without occupying tetragonal sites, narrow the range of the epitaxial growth. The former results (i) can be explained by the arrangement of oxygen ions, but for the latter cases (ii), cation arrangement is also important in forming a compatible interface as well as an anion arrangement. The general tendency is largely explained by the ionic arrangement at the interface. The interface structure becomes unstable by the electrostatic repulsive force since the distance between cations at the interface becomes shorter than that in each original crystal structure.