Experimental and theoretical investigation on the compression mechanism of FeF3up to 62.0 GPa

Abstract

VF₃-type FeF₃is generally considered as a perovskite with a completely vacantAsite. The high-pressure structural evolution of FeF₃has been studied by both X-ray diffraction and theoretical simulation up to 62.0 GPa. Experimental and theoretical results demonstrate that VF₃-type FeF₃is stable up to 50 GPa. The structural evolution presents three features at different pressure ranges. AtP< 10 GPa, the volume reduction is dominated by the FeF₆octahedral rotation, and a small octahedral strain develops upon compression, which represents an elongation of FeF₆octahedra along thecaxis. Between 10 and 25 GPa, the volume reduction is mainly attributed to the Fe—F bond length decreasing, and the octahedral strain gradually disappears. Between 25 and 50 GPa, an octahedral elongation along theaaxis quickly develops, resulting in a substantial structural distortion. Structural instability is predicted atP> 51 GPa on the basis of a soft mode occurring in phonon calculations. The pressure–volume relationship is described by a third-order Birch–Murnaghan equation-of-state withB₀= 14 (1) GPa,B₀′ = 17 (1) by experiment andB₀= 10.45 (1) GPa,B′₁₀= 12.13 (1) by calculation.