Low-temperature Electrodeposition of the High-temperature Cubic Polymorph of Bismuth(III) Oxide

Nanocrystalline films of δ-Bi₂O₃ were electrodeposited at 65 °C directly from alkaline solutions of tartrate-complexed Bi(III). This face-centered-cubic polymorph of Bi₂O₃ is normally only stable at high temperatures (729-825 °C). The material has the highest known oxide ion mobility. We propose that the high temperature form of the oxide is stabilized due to the nanocrystalline (70 nm) size of the particles in the film. The oxide also deposits epitaxially onto a single-crystal Au(110) substrate with strong in-plane and out-of-plane orientation. The large lattice mismatch (35.4%) is accommodated by forming a coincidence lattice, in which the δ-Bi₂O₃ is rotated 90° relative to the Au (110) substrate. The epitaxial relationship between film and substrate may also serve to stabilize the high-temperature structure.