Polycrystalline samples of perovskite-structured BaCeO, and SrCeO, were studied by Raman scattering spectroscopy in the temperature range 77-983 K. Changes in the spectra of BaCeO, with temperature are explained in terms of a second-order phase transition (DZh + D4,) at To = 427 K. Analysis of the temperature dependence of soft modes suggests a partial displacive character. A dramatic decrease in band intensity above 1O00 K indicates a transition to the cubic (0,) structure, for which no Raman bands are expected. The Raman spectra of SrCeO, indicate that no phase transitions occur in the temperature range 77-983 K. Room temperature spectra of BaCeO, doped with various rare earth ions (Nd3+, Gd3+, Yh3+) are compared. Doping with 5 and 10 mol.% Nd stabilizes the high-temperature tetragonal and cubic phases, respectively. The crystal structure is a sensitive function of Nd dopant concentration.
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