Raman scattering study of phase transitions in undoped and rare earth ion‐doped BaCeO₃ and SrCeO₃

Polycrystalline samples of perovskite‐structured BaCeO 3 and SrCeO 3 were studied by Raman scattering spectroscopy in the temperature range 77–983 K. Changes in the spectra of BaCeO 3 with temperature are explained in terms of a second‐order phase transition ( D 2 h → D 4 h ) at T 0 = 427 K. Analysis of the temperature dependence of soft modes suggests a partial displacive character. A dramatic decrease in band intensity above 1000 K indicates a transition to the cubic ( O h ) structure, for which no Raman bands are expected. The Raman spectra of SrCeO 3 indicate that no phase transitions occur in the temperature range 77–983 K. Room temperature spectra of BaCeO 3 doped with various rare earth ions (Nd 3+ , Gd 3+ , Yb 3+ ) 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.