High pressure structural investigations on K2Zr(PO4)2

High pressure behavior of K₂Zr(PO₄)₂ has been investigated using combined Raman spectroscopy, x-ray diffraction and first principles calculations. Our studies show that the ambient trigonal phase (P$\overline{3}$) is stable only up to ∼0.5 GPa. Upon compression, the compound shows clear evidences of two first order structural phase transformations at 0.5 GPa and 3 GPa, as observed using x-ray diffraction and spectroscopic measurements. Across these pressures, the spectroscopic and theoretical data show softening of phosphate internal vibrations and collapse of inter-polyhedral bond angle Zr–O–P respectively, which indicate that polyhedral distortion drives the structural phase transitions. The second high pressure phase, observed above 3 GPa, is stable up to the highest pressure (i.e. 21 GPa) in the experiments. However, upon decompression, it reverts back to the ambient phase, with traces of first high pressure phase, on complete release of pressure.