New insight into the structural stability, ductility and melting point of Mo5SiB2 under high-pressure environment

Abstract

Mo5SiB2 is an attractive high-temperature ceramic because of the excellent mechanical and thermodynamic properties. However, the role of high pressure on the structural stability and the related properties of Mo5SiB2 is entirely unclear. In this work, we apply the first-principles calculations to study the influence of pressure on the structural stability, mechanical properties and melting point of Mo5SiB2. Here, three possible Mo5SiB2 phases: D8l-Mo5SiB2, D8m-Mo5SiB2 and Cmcm-Mo5SiB2 are considered. The results show that all Mo5SiB2 are thermodynamic stability. In particular, it is found that the thermodynamic stability of Mo5SiB2 follows the order of D8l-Mo5SiB2>cmcm-Mo5SiB2> D8m-Mo5SiB2. The calculated bulk modulus and Young's modulus of D81-Mo5SiB2 under zero pressure are bigger than the cmcm-Mo5SiB2 and D8m-Mo5SiB2. Importantly, the pressure significantly improves the ductility of all Mo5SiB2 because the pressure can adjust the localized hybridization between Mo, Si and B atoms. In addition, it is found that the calculated melting point of all Mo5SiB2 increases with increasing the pressure. The melting point of the Cmcm-Mo5SiB2 is higher than the D8l and D8m phases under high pressure.