Abstract
By using the particle swarm optimization algorithm, the crystal structures of tungsten diboride have been investigated up to 200 GPa at 0 K. We support that WB2 has an ReB2-type structure (hP6-WB2) with the space group P63/mmc at zero pressure and hP6-WB2 undergoes a phase transition to the MoB2-type phase (hR6-WB2) at about 10.8 GPa. Further, we predict that a tetragonal phase (tI12-WB2) with a space group of I41/amd will be the most stable structure above 133.6 GPa. Phonon dispersion curves suggest that these phases possess dynamical stabilities in a wide range of 0–200 GPa. The elastic constants and hardness are also estimated at 0 K and zero pressure. hP6-WB2 and hR6-WB2 have hardnesses of 37.3 and 29.2 GPa, respectively. However, tI12-WB2 just possesses the smallest hardness value of 7.9 GPa. Finally, a temperature–pressure phase diagram is derived within the quasi-harmonic approximation method, and the finite temperature phase boundaries are determined.
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