Exploration of stable stoichiometries, ground-state structures, and mechanical properties of the W-Si system

Refractory tungsten silicides have been identified as typical high-temperature structural materials with excellent mechanical and thermal properties in various industrial applications. Here, we show the first extensive crystal structures search of W-Si system over a wide range of stoichiometries at ambient condition, using first-principles swarm intelligence structure search methods. Besides the well-known W5Si3 and WSi2, three novel and unexpected stoichiometries of W2Si, WSi, and W3Si4 with tetragonal ground-state structures were firstly uncovered and suggested to be experimentally synthesizable according to the convex hull calculations. It is found that the high silicon content benefits the formation of the puckered double W-Si zigzag covalent chains in WmSin, resulting in the enhanced resistance to shear deformation related to the macroscopic hardness. Results on the ideal tensile and shear strengths calculations indicated that the failure modes in the studied WmSin are mainly dominated by the shear type along the (110)[1 (1) over bar0]directions. Further analysis of atomic shear deformation demonstrates that the collapse of Si-W building blocks is responsible for the lattice stability and achievable mechanical strength of WmSin.