High-pressure structural study ofMnF2

Abstract

Manganese fluoride $({\mathrm{MnF}}_{2})$ with the tetragonal rutile-type structure has been studied using a synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy in a diamond anvil cell up to 60 GPa at room temperature combined with first-principles density functional calculations. The experimental data reveal two pressure-induced structural phase transitions with the following sequence: rutile $\ensuremath{\rightarrow} {\mathrm{SrI}}_{2}$ type (3 GPa)$\ensuremath{\rightarrow} \ensuremath{\alpha}\ensuremath{-}{\mathrm{PbCl}}_{2}$ type (13 GPa). Complete structural information, including interatomic distances, has been determined in the case of ${\mathrm{MnF}}_{2}$ including the exact structure of the debated first high-pressure phase. First-principles density functional calculations confirm this phase transition sequence, and the two calculated transition pressures are in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phases. The results are discussed in line with the possible practical use of rutile-type fluorides in general and specifically ${\mathrm{MnF}}_{2}$ as a model compound to reveal the HP structural behavior of rutile-type ${\mathrm{SiO}}_{2}$ (Stishovite).