Thermoelectric Properties Of Chalcopyrite Thermoelectric Materials Tuned By Mechanical Loading

Industrial waste heat not only can cause the environmental pollution, but also waste much energy. Thermoelectric materials can directly convert thermal energy into electric energy without causing environmental pollution. Therefore, thermoelectric materials research has great prospects in terms of energy conversion, which has a very broad application prospects to solve the problem of energy shortage and environmental pollution. The Chalcopyrite system showing advantages of wide distribution, large reserves, non-pollution, and so on, has attracted considerable interest in recent years. Thermoelectric materials with excellent thermoelectric properties usually possess high-symmetry crystal structure. The crystalline symmetry limits the thermoelectric properties of Chalcopyrite thermoelectric materials due to its low-symmetry non-cubic tetragonal crystals, thus their thermoelectric properties can be improved. Therefore, in this thesis, first principle calculations combining with the Semi-classical Boltzmann's theory is used to study the effects of mechanical loading on the electronic structures and thermoelectric properties of chalcopyrite thermoelectric materials. The main works of this thesis are as follows:?1? The effects of pressure on the electronic structures and thermoelectric properties of Chalcopyrite thermoelectric material have been investigated, and the corresponding optimization method on thermoelectric performance is proposed. We calculate the electronic structures and thermoelectric properties of MgSiP₂ under different pressures, it is found that Seebeck coefficients of both p-type and n-type MgSiP₂ decrease with increasing pressure, while the electric conductivity divided by relaxation time increase with increasing pressure, and the enhancement of eletric conductivity in p-type MgSiP₂ is greater than that of n-type, resulting in the power factor of p-type MgSiP₂ higher than that of n-type one. The results indicate that p-type MgSiP₂ possesses high thermoelectric conversion efficiency under pressure, and pressure is an effective ways to improve thermoelectric performance of p-type MgSiP₂.?2? The effects of uniaxial strains on the electronic structure and thermoelectricproperties of Chalcopyrite thermoelectric material have been investigated, and the optimization of Chalcopyrite thermoelectric performance by uniaxial strains is suggestted. Chalcopyrite thermoelectric materials AgAlTe2 under different uniaxial strain has been studied, and it is found that uniaxial strain at 5% can lead to high symmetry of AgAlTe2 with band degeneracy, resulting in enhanced Seebeck coefficient. The results of thermoelectric properties calculations reveals that both the electrical conductivity and power factor are increased by tensile strain, the electrical conductivity with the 8.7% of growth rate under 7% tensile strain, and the power factor has the largest growth rate 27.2% at 6% tensile strain.?3? The effects of biaxial strain on the electronic structures and thermoelectric properties of Chalcopyrite thermoelectric material have been investigated, and the optimization method on thermoelectric performance of Chalcopyrite via biaxial strain is proposed. The electronic structures and thermoelectric properties of Chalcopyrite thermoelectric materials AgGaTe2 and AgAlTe2 have been investigated, the band degeneracy of AgGaTe2 and AgAlTe2 have been achieved at compressive strains-2.32% and-3.3% respectively, around which Seebeck coefficients show peaks.Furthermore, the electrical conductivity of AgGa Te2 and AgAlTe2 gradually increases with respect to increased compressive strain, resulting in the enhanced power factor significantly.