Hydrostatic pressure induced structural phase transition and mechanical properties of fluoroperovskite.

ABSTRACT

We perform the first-principles calculations combined with the particle swarm optimization algorithm to investigate the high-pressure phase diagrams of Na[Formula see text]F3 ([Formula see text] = Mn, Ni, Zn). Two reconstructive phase transitions are predicted from Pv-[Formula see text] to pPv-[Formula see text] at about 9 GPa and pPv-[Formula see text] to ppPv-[Formula see text] at around 26 GPa for NaZnF3. That is not the case for NaMnF3-a direct transition (reconstructive transition in nature but with the same Pnma space group) from Pv-[Formula see text] to ppPv-[Formula see text] phase around 12 GPa. Strikingly, our simulated results manifest that a disproportionation phase of NaZnF3 post-perovskite is uncovered along the way, which provides a successful explanation for the observed results in experiment. Additionally, the mechanical and thermal properties, especially the dynamical property, of the four NaZnF3 phases have also been studied. Here, we reveal the obvious softening of [Formula see text]-wave velocity and bulk sound speed in pPv-[Formula see text]-to-ppPv-[Formula see text] transition, which may result in the discontinuity of seismic waves propagation through the Earth's interior.