Phase Transition and Mechanical Properties of Scandium Diboride under High Pressure

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The phase transition, mechanical properties, and minimum thermal conductivity of scandium diboride (ScB 2 ) under pressures up to 400 GPa have been investigated using the CALYPSO algorithm in combination with density functional theory calculations. Our results revealed that the P 6/ mmm structure of ScB 2 ( hP 3-ScB 2 ) is the most stable phase at ambient conditions and transforms to the C 2/ m phase ( mC 12-ScB 2 ) at around 204 GPa. The calculated elastic constants and phonon dispersion curves indicated that hP 3-ScB 2 and mC 12-ScB 2 possess mechanical and dynamic stability in wide pressure ranges of 0–204 and 204–400 GPa, respectively. Moreover, the Vickers hardness study suggested that hP 3-ScB 2 can be used as a superhard material at ambient conditions, while mC 12-ScB 2 is a potentially hard material at high pressures. Additionally, the evaluation of the minimum thermal conductivity showed that both hP 3-ScB 2 and mC 12-ScB 2 are unsuitable as thermal barrier coating materials under different pressure conditions. Finally, the high-pressure and high-temperature phase diagram of ScB 2 was constructed based on the quasiharmonic approximation method. It is found that the transition pressure of hP 3-ScB 2 → mC 12-ScB 2 will gradually increase with the increase of temperature.