Molecular Dynamics Study On The Thermodynamic Properties Of Mg₂Si Nanomerter Thin Films

Thermoelectric materials have attracted more and more attention due to their environmental friendliness and energy transfer, and the research on thermoelectric materials is increasing. Mg₂ Si is one kind of middle temperature thermoelectric material. Mg₂ Si receives wide attention and a good prospect because it has many advantages. Such as: good thermal stability, rich and wide sources of raw materials, good thermoelectric properties and affordable price. Compared with traditional thermoelectric material, the low-dimensional nanometer film material has higher thermoelectric properties. Thermoelectric properties are important for the evaluation of energy conversion of thermoelectric devices. In practical application, thermoelectric devices will be subjected to thermal cyclic stress, and the mechanical properties are important indicators of the evaluation of the service behavior of the device. So the thermal and mechanical properties of Mg₂ Si nanometer thin film are studied in this paper. The results can provide theoretical guidance for the design and application of Mg₂ Si thermoelectric devices. At the same time, the research results have important significance for the development of high performance thermoelectric materials.Compared with the experiments, the molecular dynamics simulation method has a great advantage on the nanometer scale of the research object. In this paper, the mechanical and thermal properties of Mg₂ Si bulk and nanometer thin film materials are studied in detail by using molecular dynamics simulation method.Firstly, according to the crystal structure of Mg₂ Si, the Morse potential function and bond angle potential function are chosen in a simulation. After the simulation of equilibrium state, the result is that all atoms in the equilibrium position to do thermal vibration and the total energy of the system unchanged. The results show that the potential functions can be used to describe the material properties of Mg₂ Si. At the same time, the established model and the calculation of the force are correct.Secondly, simulation of stretching process of Mg₂ Si bulk and nanometer thin film. After the simulation, the stress strain diagram and the ultimate stress in each case are counted. The study shows that the mechanical properties of Mg₂ Si bulk decrease with increasing temperature. Mechanical properties of Mg₂ Si nanometer thin film decrease with the increase of temperature, the decrease of film thickness, the increase of Mg atomic vacancy rate. At the same temperature, the mechanical properties of Mg₂ Si nanometer thin film are slightly than the bulk. It is also found that the low dimensional reduces the mechanical properties of the material.At last, the thermal conductivity of Mg₂ Si bulk and nanometer thin film are simulated by using homogeneous non-equilibrium state simulation method. Studies show that the thermal conductivity of the bulk decreases with increasing temperature. And the thermal conductivity of the nanometer thin film decrease with the increase of temperature, the decrease of film thickness, the increase of Mg atomic vacancy rate. The effect of temperature on thermal conductivity is smaller than that several other factors. Under the same condition, the simulation results of the bulk and nanometer thin film are compared, and it is found that the low dimension of the thermoelectric material can effectively reduce the thermal conductivity and improve the thermal performance.Corresponding conclusions obtained by simulation can provide theoretical guidance for the design and application of Mg₂ Si thermoelectric materials. When using Mg₂ Si nanometer thin film to make thermoelectric devices, we should choose a appropriate thickness of the film and a suitable working temperature.