Metallization and softening of B6O at high pressure

Abstract Structural stability, elastic and electronic properties of boron suboxide, B 6 O, up to 300 GPa were investigated by first-principles calculations. Structural searching and enthalpy differences calculations identify a high-pressure phase for B 6 O with monoclinic C c structure (denoted as β -B 6 O), which is energetically preferable to the known R -3 m-type phase above 245 GPa. β -B 6 O phase forms a three-dimensional covalent network mainly composed of pentagonal pyramids and zig-zag O–B1–O chains extended along c -direction. β -B 6 O phase is found to be stable examined by the calculated elastic constants and phonon dispersion and exhibits metallic behavior and greater elastic and hardness anisotropy, totally different from the semiconducting character and relative isotropy of ground state structure. Moreover, β -B 6 O is predicted to soften significantly with a Vicker’s hardness of about 20.7 GPa.