High temperature optical absorption spectroscopy at pure and Y-doped BaCeO3

The defect induced optical absorption has been investigated at different oxygen partial pressures and at temperatures up to 800 degrees C for the high temperature protonic conductor BaCeO3. Thin films of pure and 10 mol% Y-doped BaCeO3 with thickness up to 11 mu m have been deposited on transparent MgO single crystal substrates by means of RF-magnetron sputtering techniques. After separating the different contributions to the optical absorption we have concentrated on the part of the spectra which is attributed to free small polarons. Under reducing external gas atmospheres these polarons are generated in the film along with oxygen vacancies and contribute to the electronic conductivity by their hopping processes. We report on time resolved measurements of the defect reaction kinetics after a change of the external gas atmosphere and investigate the influence Of the doping atoms by comparing BaCe0.9Y0.1O3-delta and BaCeO3. The observations are discussed in terms of the diffusion behavior of the oxygen vacancies. (C) 1999 Elsevier Science Limited. All rights reserved.