Reductive solid phase epitaxy of layered Y₂O₂Bi with Bi^2- square net from (Y, Bi) powders and Y₂O₃ amorphous thin film

Ingenious solid phase epitaxy of ThCr₂Si₂-type Y ₂O₂Bi thin film with a Bi^2- square net was developed. A Y₂O₃ amorphous thin film with Y and Bi powders was heated in two steps under reductive atmosphere on a nonoxide lattice-matched CaF₂ substrate. This procedure was indispensable for the epitaxial growth of Y₂O₂Bi, circumventing the formation of the C-rare earth type (Y,Bi)₂O₃ with Bi ³⁺. Highly oxidizable Y metal was a key to accomplish the unusual reductive state of Bi^2-. The lattice-matched CaF₂ substrate possessing a similar structure to the Y₂O₂ ²⁺ unit in Y₂O₂Bi promoted the spontaneous c-axis orientation of the thin film.