Structural Phase Transition and Disproportionation of MnF₃ Under High Pressure and High Temperature

Materials that once suffered under high-pressure and high-temperature conditions often display unusual phenomena that challenge traditional understanding. MnF₃, an intermediate valence state Mn-F compound, exhibits a distorted octahedral crystal structure influenced by the Jahn-Teller effect. Here we report the structural phase transition and self-disproportionation of MnF₃ under high pressure and high temperature. The initial octahedra phase <i>I</i>2/<i>a</i>-MnF₃ transforms into the hendecahedra <i>Pnma</i> phase under high pressure. Subsequently, we found that molten <i>Pnma</i>-MnF₃ self-disproportionate into MnF₂ and MnF₄ with the aid of laser heating at a pressure above 57.1 GPa. Raman spectra and UV-vis absorption experiments confirmed these changes that were ultimately confirmed by synchrotron radiation XRD. The equation of states for the volume with the pressure of these Mn-F compounds was also given. This work expands the study of Mn-F systems and provides guidance for the behavior of transition metal fluorides under high pressures and high temperatures.