A high-pressure Raman study of mixed perovskites BaCexZr1-xO3 (0 <= x <= 1)

A high-pressure Raman study of polycrystalline samples of BaCexZr1-xO3 is p erformed at room temperature, The evolution of Raman spectra with pressure is compared to the evolution of the Raman spectra of BaZrO3 and BaCeO3. The effect of composition on the pressure-induced phase transitions is monitor ed from the Raman spectra, Transitions toward lower symmetry phases as pres sure increases are evidenced. A phase diagram in the binary system BaZrO3-B aCeO3 based on the Raman spectra characteristic of the different structures of BaCeO3 (Pnma, Imma, R (3) over bar c, Pm3m) is proposed. The transition pressures toward low-symmetry structures decrease when Ce is replaced for Zr, This study allows us to interpret the BaCexZr1-xO3 (0 less than or equa l to x less than or equal to 1) Raman spectra at ambient pressure on the ba sis of nanodomains and nanophases. These objects tend to disappear upon pre ssure increase. The octahedra to dodecahedra volumes ratio is used as a cri tical parameter that is able to reproduce qualitatively some of the phase t ransitions in the mixed perovskites BaCexZr1-xO3. In order to calculate thi s parameter vs pressure, a derivation of the samples' compressibility based on a polyhedral approach is performed and is found in the range [0.7 x 10( -11)-1.0 x 10(-11) Pa-1]. (C) 2000 Academic Press.