Phase transition and electronic properties of barium fluoride at high pressure

Abstract

Pressure is a useful tool to profoundly modify the volume and electronic structure of materials, resulting in the formation of new structures with exotic physical and chemical properties. The high-symmetry cubic barium fluoride (BaF2) with a space group of Fm-3m (Z = 4) is the prototypical fluorite-type compounds at ambient condition, which is shared with many alkaline-earth fluorides. The study of high-pressure evolution of the BaF2 phase is of fundamental importance in helping to understand the structural sequence and principles of crystallography. In this work, we here have systematically investigated the high-pressure structural transition of BaF2 up to 200 GPa using an effective CALYPSO methodology. Strikingly, two thermodynamically favored phases with orthorhombic Pnma and hexagonal P63/mmc symmetry are found at 3.6 and 19.2 GPa, respectively. Distinguishingly, P63/mmc phase remains stable up to 90.5 GPa, and then transform to Pnma structure. Further electronic calculations indicate that BaF2 maintains insulating feature until 200 GPa. Our current results have broad implications for other AB2-type compounds that may harbor similar novel structured evolution behavior at high pressure.