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

ABSTRACT

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 I2/a-MnF3 transforms into the hendecahedra Pnma phase under high pressure. Subsequently, we found that molten Pnma-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.