Pressure induced phase transitions in BaZr(PO4)2 studied using x-ray diffraction, Raman spectroscopy, and first principles calculations

Abstract

Structural stability and polymorphic phase transitions in barium zirconium diorthophosphate, a technologically important compound consisting of the polyhedral framework structure, has been studied under high pressure (HP). With the combined study of x-ray diffraction (up to ∼12 GPa) and Raman spectroscopy at high pressure (up to ∼16 GPa), we observed three reversible pressure induced polymorphic phase transitions. The ambient phase transforms at a very low pressure (0.4 GPa) to a triclinic structure (HP-1 phase). Ambient and HP-1 phases coexist up to ∼2 GPa before transforming to the monoclinic HP-2 phase. Further, another transition is observed around ∼8 GPa (HP-3). On complete release of pressure, the sample reverts to the ambient phase with traces of the HP-1 phase. First principles based phonon and structural relaxation calculations are used to compare experimental findings. This study establishes a polymorphic structural sequence in yavapaiite type compounds.