Growth of rare-earth niobate-based pyrochlores on textured Ni–W substrates with ionic radii dependency

Epitaxial films of rare-earth (RE) niobates, RE₃NbO₇ with pyrochlore structures, were grown on biaxially textured nickel–3 at.% tungsten (Ni–W) substrates using a chemical solution deposition process. A precursor solution of 0.3–0.50 M concentration of total cations was spin coated on to short samples of Ni–W substrates, and the films were crystallized at 1050–1100 °C in a gas mixture of Ar–4% H₂ for 15 min. Detailed studies revealed that RE-niobates with ionic radius ratio R_RE/R_Nb (R = ionic radius) from 1.23 to 1.40 (i.e., Sm, Eu, Gd, Ho, Y, and Yb) grow epitaxially with the pyrochlore structure. X-ray studies showed that the films of pyrochlore RE niobate films were highly textured with cube-on-cube epitaxy. Scanning electron and atomic force microscopy investigations of RE₃NbO₇ films revealed a fairly dense and smooth microstructure without cracks and porosity. The rare-earth niobate layers may be potentially used as buffer layers for YBa₂Cu₃O_7−δ coated conductors.