Abstract
We report the results of density functional theory ab-initio calculations and monochromatic synchrotron X-ray diffraction study carried out for orthorhombic NaZnF 3 in the pressure range 0–40 GPa. Perovskite-to-postperovskite phase transition was anticipated by first-principles computations and then observed in high-pressure diamond anvil cell synchrotron diffraction experiment between 14 and 22 GPa. Above 25 GPa postperovskite structure (CaIrO 3 type, space group Cmcm) coexists with another phase, yet unidentified. On decompression, pure postperovskite-type structure was found to be stable down to 4 GPa; below this pressure sample contained both perovskite and postperovskite modifications. Fit of experimental P–V data to the third-order Birch–Murnaghan equation of state gave bulk moduli, K P, 0 64.98±2.67 and 69.88±3.69 GPa for perovskite and postperovskite modifications, respectively. Both phases demonstrated strong anisotropy of compressibility. For postperovskite NaZnF 3, the highest compression was observed along the direction perpendicular to the planes of ZnF 6 octahedra arrangement.
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