Structural, mechanical and electronic properties of CaB2C2 at high pressure

Abstract

Under high pressure, the graphite-like materials present complex structural behaviors, interesting mechanical properties, and fascinating electronic structures. We here report two novel high-pressure structures of oF40-CaB2C2 and HPtI20-CaB2C2 by using the newly developed particle swarm optimization algorithm based on first-principles calculations. The oF40-CaB2C2 and HPtI20-CaB2C2 exhibit a 3D sp3 B-C bonded network under compression, which is verified by the inspections of their crystal structures and partial densities of states. The study of mechanical anisotropy reveals that the degree of anisotropy for CaB2C2 is gradually enhanced with its structural transformations under pressure. Intriguingly, the originally indirect band-gap CaB2C2 at ambient pressure transform into a direct band-gap semiconductor under extreme pressure (beyond 214.4 GPa).