Pressure and temperature induced phase transition in WB4: A first principles study

Abstract

Using an unbiased structure search method based on particle-swarm optimization algorithms in combination with density functional theory calculations, we investigate the phase stability and electronic properties of WB4 under high pressures. Through structural searching as implemented in the CALYPSO code, we obtained the most state hexagonal phase (P63/mmc, named hp10) at ambient condition and a new monoclinic phase (C2/m structure, mp5) at high pressures for WB4. The P63/mmc structure transforms to the C2/m phase at about 71 GPa. Surprisingly, the two phases are both dynamically and mechanically stable at ambient conditions. The high bulk and shear modulus, low Poisson’s ratio for both phases in WB4, place WB4 as a promising low compressible material. Both phases with high hardness are stable due to the strong covalent bonding nature from electronic density of states and electron localization function analysis. To guide experimental finding of more metastable superhard materials, the high pressure high temperature phase diagram of WB4 is established within the quasi-harmonic approximation.