Phase changes in Na1/2Pr1/2TiO3: A synchrotron X-ray powder diffraction study

A temperature dependent synchrotron X-ray powder diffraction study has been carried out on Na1/2Pr1/2TiO3 up to 850 °C. The compound shows orthorhombic (Pbnm) → orthorhombic (Ibmm) → tetragonal (I4/mcm) transitions at ∼150 °C, and ∼750 °C, respectively. An unusual volume expansion below 500 °C has been noticed in the Ibmm phase, suggesting the onset of another, yet unknown, physical phenomenon unrelated to the crystallographic changes below this temperature.