The structural evolution of thin layers of Co3O4 elaborated on nickel-based substrates in the Li2CO3-Na2CO3 carbonate eutectic at 650 degreesC as a function of time immersion is reported. Raman microspectrometry has been applied in order to provide more information on the nature of the protective cobalt oxide layers. The typical Raman fingerprint of the LT-LiCoO2 compound has been obtained, with four well defined bands at 449, 484, 590 and 605 cm(-1), while XRD data are unable to distinguish the layered phase (HT) from the spinel one (LT). The mechanical stability of such films does not exceed 10 h in direct contact with the molten carbonate bulk at 650 degreesC; nevertheless, these conditions are much more corrosive than in a molten carbonate fuel cell (MCFC). (C) 2003 Elsevier B.V. All rights reserved.