An X-ray absorption study of the local structure of cerium in electrochemically deposited thin films

We have utilized the technique of X-ray absorption fine structure (XAFS) to study the oxidation state and structure of cerium in electrochemically deposited thin films of cerium oxide (hydroxide). We find that anodic deposition results in a hydrous cerium oxide phase in which the oxidation state of cerium is 4+. This material is highly structurally disordered but still has a medium range local structure (similar to 4 Angstrom) similar to CeO2. On the other hand, cathodic deposition leads to a Ce3+ phase, which is susceptible to oxidation on exposure to air or by dissolved oxygen in solution. Our results may be relevant to understanding the structure of cerium inhibitors incorporated in corrosion films on aluminium and its alloys. (C) 1999 Elsevier Science S.A. All rights reserved.