A novel high-pressure polymorph of TaSi2

Abstract

We report a novel high-pressure cubic cF24 phase of TaSi2 which is stable above 185 GPa through first-principles swarm intelligence structure search method. Results on enthalpy difference show that the structural transition of TaSi2 from the ambient hexagonal C40 phase to cF24 phase is first order with a volume drop of 4.1%. Under compression, the formation of cubic cF24 phase originates from the dramatic polymerization of one dimensional helical Si chain in the low-pressure C40 phase creating peculiar 3D Si tetrahedrons framework embedded in diamond-like Ta sublattice. The emergence of 3D Si tetrahedrons framework in cF24 phase are suggested to be the main causes for its weaker metallic nature compared to the hexagonal C40 phase.