Mechanical properties of thermoelectric Mg₂Si using molecular dynamics simulations

In this paper, the mechanical properties of thermoelectric Mg₂Si are investigated using molecular dynamics (MD) method, with Mg₂Si in the forms of bulk, nanofilm, and nanowire, respectively. The effects of the Mg vacancy on the mechanical properties of Mg₂Si in these three forms are studied in details. First of all, the equilibrium state of Mg₂Si is simulated after choosing the proper potential function, boundary conditions, and the speed algorithm. Nondimensionalization is also implemented during the simulations. This part of simulation aims to verify the correctness of the crystal model established via the use of the molecular dynamics analysis. Next, the models of Mg₂Si in the forms of bulk, nanofilm, and nanowire are established with different Mg vacancy proportions, and then the mechanical properties of each model are studied via the uniaxial tensile test. Finally, the stress–strain curve and subsequently the ultimate tensile strength are obtained for each model. Simulation results indicate that the ultimate tensile strength of Mg₂Si in each model is decreased with the increase of the Mg vacancy proportion. Moreover, through the comparison of the ultimate tensile strengths of Mg₂Si bulk, nanofilm, and nanowire, it is found that low-dimensionalization significantly reduces the ultimate tensile strength of thermoelectric Mg₂Si. Results obtained in this paper can provide valuable guidance to the future applications of thermoelectric devices.