Solid State Ionics 131 (2000) 97–107 www.elsevier.com / locate / ssi Low-temperature electrodeposition of the high-temperature cubic polymorph of bismuth(III) oxide Eric W. Bohannan, Christopher C. Jaynes, Mark G. Shumsky, Julie K. Barton, * Jay A. Switzer University of Missouri-Rolla, Department of Chemistry and Graduate Center for Materials Research, Rolla, MO 65409-1170, USA Received 1 September 1999; received in revised form 1 November 1999; accepted 1 December 1999 Abstract Nanocrystalline films of d-Bi O were electrodeposited at 658C directly from alkaline solutions of tartrate-complexed 2 3 Bi(III). This face-centered-cubic polymorph of Bi O is normally only stable at high temperatures (729–8258C). The 2 3 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 d-Bi O is rotated 908 relative to the Au (110) substrate. The epitaxial 2 3 relationship between film and substrate may also serve to stabilize the high-temperature structure.  2000 Elsevier Science B.V. All rights reserved. Keywords: Bismuth oxide; Electrodeposition; Epitaxial growth; Solid electrolyte PACS: 81.15.P (Electrodeposition) 1. Introduction lower than the cubic form of Bi O [1]. A significant 2 3 limitation of the bismuth oxide system is that the Oxide-ion conducting solid electrolytes are of face-centered-cubic phase exists only between 7298C great interest for use in fuel cells, oxygen sensors, and the melting point of the material, 8258C [2]. and oxygen pumps. The most widely used solid Substitution of rare-earth oxides stabilizes d-Bi O 2 3 electrolytes with high oxide ion conductivity are down to room temperature, however there is a those derived from zirconia, with yttria-stabilized coincident lowering of the oxide ion conductivity by zirconia being the most widely applied. However, over two orders of magnitude [3]. zirconia-based solid electrolytes have an oxide ion The polymorphism of pure bismuth sesquioxide conductivity that is up to two orders of magnitude has been studied by several investigators [4–8] since ´ the work of Sillen [9], who proposed that four polymorphs exist. Below 7298C Bi O exists as the 2 3 *Corresponding author. Tel.: 11-573-341-4383; fax: 11-573- monoclinic a-phase. When cooling from tempera- 341-4383. E-mail address: jswitzer@umr.edu (J.A. Switzer) tures above 7298C, the face-centered cubic (fcc) 0167-2738 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0167-2738(00)00625-1