High-resolution neutron powder diffractometry has been used to characterize the structural phase transitions which occur in PrBGO5 at 550 and 750°C. The change in lattice parameters of the trigonal unit cell as a function of temperature, observed in the range from ambient to 800°C, shows that the 550°C transition is associated with an abrupt contraction of the unit cell volume. The crystal structure stable in the temperature interval between 550 and 750°C is isomorphous with the stillwellite structure of LaBGeO5 in its polar variant stable up to 530°C. The phase transition at 752°C to a non-polar variant of the structure mimics the 530°C transition in LaBGeO5. The structural parameters of these two PrBGeO5 phases have been refined from data taken at 650, 770 and 800°C. The structure of the PrBGeO5 phase stable at ambient temperature gives rise to extra reflections not given by the stillwellite structure. These can be indexed on a triple cell with a′ ≈ √3a, c′ ≈ c and the structure has been determined and refined from a combination of neutron powder data and an ambient temperature single crystal x-ray diffraction study.
