Structural\nPhase Transition and Disproportionation\nof MnF<sub>3</sub> Under High Pressure and High Temperature

Materials\nthat once suffered under high-pressure and\nhigh-temperature\nconditions often display unusual phenomena that challenge traditional\nunderstanding. MnF<sub>3</sub>, an intermediate valence state Mn–F\ncompound, exhibits a distorted octahedral crystal structure influenced\nby the Jahn–Teller effect. Here we report the structural phase\ntransition and self-disproportionation of MnF<sub>3</sub> under high\npressure and high temperature. The initial octahedra phase <i>I</i>2/<i>a</i>-MnF<sub>3</sub> transforms into the\nhendecahedra <i>Pnma</i> phase under high pressure. Subsequently,\nwe found that molten <i>Pnma</i>-MnF<sub>3</sub> self-disproportionate\ninto MnF<sub>2</sub> and MnF<sub>4</sub> with the aid of laser heating\nat a pressure above 57.1 GPa. Raman spectra and UV–vis absorption\nexperiments confirmed these changes that were ultimately confirmed\nby synchrotron radiation XRD. The equation of states for the volume\nwith the pressure of these Mn–F compounds was also given. This\nwork expands the study of Mn–F systems and provides guidance\nfor the behavior of transition metal fluorides under high pressures\nand high temperatures.