Investigation of structural, electronic and elastic properties of matlockite-type SrFI under high pressure: An Ab-initio study

Abstract

In this study, Matlockite (PbFCl) type SrFI compound with a two-dimensional layered structure has been studied using density functional theory (DFT) and generalized gradient approximation (GGA) under high hydrostatic pressure. Calculations were made using the Siesta Method. In ambient conditions, matlockite type structures crystallize in tetragonal structure with space group P4/nmm. In nature, these structures are known as alkaline earth fluoro-halides. When gradually increasing pressures were applied to this structure, the phase transition was observed to the orthorhombic structure with space group Pmmn. In addition to these studies, some physical properties of SrFI, such as lattice parameters, bulk modulus, the derivative of the bulk modulus, and volume values were also calculated. On the other hand, total energy and enthalpy calculations were made to obtain the phase transition pressure values that are in good agreement with the experimental results. According to these calculations, phase transition pressure was predicted at about 44.8 GPa. Besides, how electronic and elastic properties of SrFI compound change with applied pressure were also examined. In the electronic structure calculations, about 5.09 eV band gap value was obtained for P4/nmm phase at 0 GPa pressure. Under increasing pressure, the 0.16 eV band gap value was calculated for the Pmmn phase of SrFI. According to these results, the stable phases obtained of the SrFI compound have semiconductor characters since the both phases have a conceivable band gap. In addition, elastic constants were calculated and two structures of SrFI were found to be mechanically stable.