Structural phase transformations under high pressure and investigation of transformation mechanism in MgF2

In this study, the high pressure behavior of MgF2 was investigated using ab-initio technique. Pressure was gradually increased up to 130 GPa beginning from the zero-pressure structure for this material. Through simulations of Siesta package, two high-pressure phases of MgF2 were observed. These phases were determined as Pnnm and Pnma under 20 GPa and 90 GPa pressures, respectively. It was concluded that the rutile-type structure of this material undergoes a phase transformation into the CaCl2-type structure with space group Pnnm at 20 GPa and CaCl2-type structure of this material undergoes another phase transformation into the α-PbCl2-type structure with space group Pnma. It was determined that the later transformation occurs following three intermediate phases with space groups P21/m, P21 and P212121. It was performed the total energy and enthalpy calculations to investigate conformity of the phase transitions obtained in this study with the experimental results. As a result of these calculations it was concluded that the first transformation should occurs around 9 GPa and the later around 35 GPa. It was seen that these results are in good agreement with literature. According to all our precisely literature investigations, it was concluded that the P21/m, P21 and P212121 intermediate phases obtained through second phase transformation were observed for the first time in this study.