Nanocrystalline films of delta-Bi2O3 were electrodeposited at 65 degrees 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 degrees 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 delta-Bi2O3 is rotated 90 degrees relative to the Au (110) substrate. The epitaxial relationship between film and substrate may also serve to stabilize the high-temperature structure.