High-pressure Raman study of the perovskite BaCeO3

A high-pressure Raman study of BaCeO3 was performed at room temperature. This perovskite compound undergoes two phase transitions at about 22 and 28 GPa. The increase in the number of bands is an indication that the symmetry is lowered and that the compound does not evolve towards the ideal cubic perovskite structure as has been observed for some perovskites. Raman-active modes exhibit large differences in their temperature and pressure dependences, and it is impossible to deduce thermoelastic coefficients directly. In order to circumvent this difficulty, a method based on the Gruneisen model is proposed for deriving compressibility and expansion coefficients from selected modes involving mainly bond stretching for each type of polyhedron. The additivity rules are discussed and provide reduced compressibility and expansion coefficients. Discrepancies between the measured thermal expansion coefficient obtained from diffraction results and calculated values are analysed in terms of anharmonicity.