| Thermoelectric material is a kind of new functional material, which can achieve direct conversion between heat and electricity through the Seebeck effect. Thermoelectric devices are green, safe, and reliable, which has broad application prospects. Improving the figure of merit ZT (an important factor to measure the conversion efficiency) is the major objective pursued by the thermoelectric material science. However, compared with the thermoelectric material science, the slow progress of the thermoelectric material mechanics limits the application of thermoelectric materials in some important areas.Zn4Sb3thermoelectric material is attached great importance to the study of thermoelectric materials in our country and the international community. The crystal structure of Zn4Sb3is very complex, and the disordered structure has always been the research focus and difficulty of this kind of material. The structural disorder of Zn4Sb3is the fundational reason of the low thermal conductivity and excellent thermoelectric properties, an important guarantee for making Zn4Sb3become "electron crystal and phonon glass" thermoelectric material. Meanwhile, the structural disorder of Zn4Sb3is also the foundational reason of the weak mechanics and poor reliability, an important bottleneck for limiting the preparation and application of this kind of material.In view of this, in order to improve the thermo-mechanical performance and its reliability of Zn4Sb3thermoelectric material, based on the key mechanical problems in the design, preparation, and application of Zn4Sb3thermoelectric material, the interatomic potentials and the molecular dynamics theoretical models of various crystal structures of Zn4Sb3are established to study the various disordered structures, the thermal conducticity, and mechanical behavior of Zn4Sb3, revealing the mechanism of the low thermal conductivity and weak mechanical properties and proposing ways to improve the thermo-mechanical performance and reliability of3, which provides an important theoretical basis for the industrial application of thermoelectric material. The interatomic potentials and the molecular dynamics theoretical models of various disordered structures of Zn4Sb3are established, filling the research gaps in the field of interatomic potentials of Zn4Sb3, breaking through the key scientific issues of molecular dynamics study of Zn4Sb3, and laying the solid foundation of molecular dynamics study of Zn4Sb3. Based on the full occupancy model of Zn4Sb3, the bond length, the bond angle, and the structural characteristics of Zn4Sb3are analyzed, and the potential function model of Zn4Sb3is constructed. The cohesive energy, elastic constants, and some ground-state physical properties are calculated by using the first principles calculation. The parameters of interatomic potentials are derived from the fitting of the equations of ground-state properties. Based on different structural features of Zn4Sb3, the interatomic potentials in various models of Zn4Sb3are predicted, and the molecular dynamics theoretical models of various crystal structures of Zn4Sb3are established. Based on those above, the structural and elastic properties in various models of Zn4Sb3by using the molecular dynamics method are investigated. Comparing these properties with the theoretical and experimental values, the feasibility of the interatomic potentials can be verified. Through the verification, the interatomic potentials can be well used to simulate the thermo-mechanical properties of Zn4Sb3thermoelectric material.The equilibrium properties (The energy per unit cell, heat capacity, and thermal conductivity) of Zn4Sb3by using the molecular dynamics method are investigated to study and evaluate the various disordered structures of Zn4Sb3. The research results show that the energies of the three-intersitial model and Mayer’s model are lower and easier to be stable. The calculated heat capacity of the three-interstitial model and full occupancy model agree better with the heat capacity of Zn4Sb3. The calculated thermal conductivity of the three-interstitial model and the vacancy model approximate the theoretical thermal conductivity of Zn4Sb3, and can well explain the reason of the low thermal conductivity of Zn4Sb3. It is found that the three-interstitial model is closer to the actual crystal structure of Zn4Sb3.The thermal conductivity and mechanical behavior of Zn4Sb3by using the molecular dynamics method are investigated to study the thermo-mechanical behavior of Zn4Sb3, revealing the mechanism of the low thermal conductivity and weak mechanical properties. Further more, effects of microscopic defects (the structural disorder, point defects, and nanopores and so on) on thermal-mechanical properties of Zn4Sb3are discussed from the atomic scale to obtain the mechanism understanding, which lays the foundation to improve the thermal-mechanical properties of Zn4Sb3. The research results show that the10%Zn atomic vacancy leads to the low thermal conductivity and weak mechanics of Zn4Sb3.10%Zn atom vacancy dramatically reduces the lattice stability of Zn4Sb3, leading to the unstable crystal structure of Zn4Sb3. The "inserting" of the three-interstitial atoms make up for the defect of vacant atoms, having little influence on the thermal conductivity, and significantly enhancing the lattice stability, also slightly increasing the mechanical properties. The substitution of Zn atoms to Sb(1) atoms can significantly reduce the lattice thermal conductivity, and remarkably increases the lattice stability and mechanical properties of Zn4Sb3.Based on the research results above, the ways to improve the thermodynamic performance and reliability of Zn4Sb3are proposed, which provides an important theoretical basis for the industrial application of Zn4Sb3thermoelectric material.■If the interstitial Zn atoms of Zn4Sb3can be replaced by some atoms which could increase the interaction of neighboring atoms, the low thermal conductivity of Zn4Sb3can be kept unchanged and the lattice stability can be increased. Also, mechanical properties and reliability can be further improved.■If the Sb(1) atoms of Zn4Sb can be replaced by some atoms which could increase the interaction of neighboring atoms, the thermal conductivity of Zn4Sb3can be decreased and the lattice stability can be increased. Also, mechanical properties and reliability can be further improved.■If the site of vacant10%Zn atoms of Zn4Sb can be partly occupancied by some atoms which could compensate the important structural defects, the thermal conductivity of Zn4Sb3will be slightly increased, but the lattice stability can be remarkably increased. Also, mechanical properties and reliability can be further improved. |
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