A neutron diffraction study of BaCexZr1-xO3

High resolution neutron diffraction patterns of BaCexZr1-xO3 (x = 0, 0.1, 0 .4, 0.8) were obtained at various temperatures. The phase diagram that nas deduced from Raman measurements has been confirmed. Structural transitions occur in a fixed order Pnma-Imma- R(3) over bar c-Pm3m as a function of tem perature or composition. For BaCeO3, the large volume change that has been previously claimed at the Imma-R(3) over bar c transition has been revisite d and found inconsistent. For a given composition, the cell volume increase s when temperature increases; but the MO6 (M=Ce-Zr) octahedron volume decre ases. It is shown that the ratio of the cell volume to the octahedron volum e is a good indicator of the phase transitions. Transitions occur at fixed values (5.77, 5.80 and 6 for the Pnma-Imma, Imma-R(3) over bar c and R(3) o ver bar c-Pm3m transitions respectively) independently of composition.