本文關鍵詞：黃銅礦型熱電材料熱電性能的應力應變調控　出處：《湘潭大學》2016年碩士論文　論文類型：學位論文

  更多相關文章： 黃銅礦 熱電性能 外應力 單軸應變 雙軸應變

【摘要】：工業(yè)廢熱不僅造成了環(huán)境污染,同時也浪費了大量熱能,而熱電材料可以直接把這些富余的熱能轉化成電能加以利用,且在使用過程中不會造成環(huán)境污染。因此,熱電材料在廢熱利用方面具有廣闊的應用前景,在應對能源短缺和環(huán)境問題方面存在巨大潛力。黃銅礦體系熱電材料具有無毒無污染、儲量大、分布廣等優(yōu)點,成為了目前熱電材料研究的熱點。通常,材料的對稱度越高,熱電性能越優(yōu)異,但黃銅礦熱電材料是四方相結構,對稱性較低,這使得該體系的熱電性能仍有非常大的提升空間。因此,本論文基于第一性原理和半經典玻爾茲曼理論,以黃銅礦熱電材料體系為研究對象,計算分析了應力、應變對其對稱度和能帶的影響,進而調控優(yōu)化其熱電性能。論文的主要工作如下:(1)探究了外應力對黃銅礦熱電材料性能的影響,提出了外應力對黃銅礦熱電材料的調控優(yōu)化方案。以黃銅礦體系熱電材料MgSiP_2為研究對象,計算其在外應力作用下的電子結構和熱電性能,結果顯示p型和n型MgSiP_2的賽貝克系數隨著外應力的增加均略有減小,電導率與弛豫時間之比均得到了提升,但p型MgSiP_2的電導率增強幅度較n型更大,使p型MgSiP_2的功率因子與弛豫時間比值優(yōu)于n型。這表明外應力使得p型MgSiP_2表現出較優(yōu)的熱電性能,外應力是提高p型MgSiP_2熱電性能的有效途徑。(2)研究了單軸應變對黃銅礦熱電材料電子結構和熱電性能的影響,提出了單軸應變調控其熱電性能的方案。以黃銅礦熱電材料AgAlTe2為研究對象,通過單軸應變提升其晶體對稱性,從而提升其能帶簡并度,促進賽貝克系數的提高。在拉應變?yōu)?%時,AgAlTe2的能帶達到了簡并,此時賽貝克系數最大;電導率與弛豫時間比值在拉應變作用下也有較大的提升,在拉應變?yōu)?%時增長率達到8.7%;功率因子與弛豫時間比值也在拉應變作用下有明顯的增加,在拉應變?yōu)?%時達到最大值,增長率為27.2%。(3)探究了雙軸應變對黃銅礦熱電材料性能的影響,提出黃銅礦熱電材料雙軸應變調控方案。以黃銅礦材料AgAlTe2和AgGaTe2為研究對象,探究雙軸應變對其電子結構和熱電性能的影響,AgGaTe2在壓應變?yōu)?2.32%時能帶達到簡并,AgAlTe2在壓應變?yōu)?3.3%時能帶達到了簡并,兩種情況下材料的賽貝克系數均達到最優(yōu),兩種材料的電導率與弛豫時間的比值也均在壓應變的作用下逐漸增加,因此功率因子與弛豫時間比值在雙軸應變作用下也得到了較大的提高。
[Abstract]:Industrial waste heat not only causes environmental pollution, but also wastes a lot of heat energy. Thermoelectric materials can directly convert these surplus heat energy into electric energy to be used. And the environmental pollution will not be caused in the process of use. Therefore, thermoelectric materials have a broad application prospect in waste heat utilization. There is great potential to deal with energy shortage and environmental problems. Thermoelectric materials of chalcopyrite system have the advantages of non-toxic and pollution-free, large reserves, wide distribution and so on, so it has become a hot spot in the research of thermoelectric materials. The higher the symmetry degree of the material, the better the thermoelectric properties, but chalcopyrite thermoelectric materials are tetragonal phase structure, the symmetry is low, which makes the thermoelectric properties of the system still have a very large room for improvement. Based on the first-principles and semi-classical Boltzmann theory, the effects of stress and strain on the symmetry and band of chalcopyrite thermoelectric material system are calculated and analyzed. The main work of this paper is as follows: 1) the influence of external stress on the properties of chalcopyrite thermoelectric materials is investigated. The optimization scheme of external stress on chalcopyrite thermoelectric material is put forward. The electronic structure and thermoelectric properties of chalcopyrite thermoelectric material MgSiP_2 under external stress are calculated. The results show that the Seebeck coefficient of p-type and n-type MgSiP_2 decreases slightly with the increase of external stress, and the ratio of conductivity to relaxation time increases. But the electrical conductivity of p-type MgSiP_2 is larger than that of n-type. The ratio of power factor to relaxation time of p-type MgSiP_2 is better than that of n-type, which indicates that the external stress makes p-type MgSiP_2 show better thermoelectric performance. The effect of uniaxial strain on the electronic structure and thermoelectric properties of chalcopyrite thermoelectric materials was studied. The uniaxial strain is used to control the thermoelectric properties of chalcopyrite (AgAlTe2). The crystal symmetry is enhanced by uniaxial strain to improve the degeneracy of the band. The energy band of AgAlTe2 reaches degeneracy when the strain is 5, and the Seebeck coefficient is the largest. The ratio of conductivity to relaxation time also increased greatly under tensile strain, and the growth rate reached 8.7 when the tensile strain was 7. The ratio of power factor to relaxation time also increased obviously under tensile strain, and reached the maximum value when tensile strain was 6. The effect of biaxial strain on the properties of chalcopyrite thermoelectric materials was investigated. A biaxial strain control scheme for chalcopyrite thermoelectric materials was proposed. The effects of biaxial strain on the electronic structure and thermoelectric properties of chalcopyrite materials AgAlTe2 and AgGaTe2 were investigated. When the compressive strain of AgGaTe2 is -2.32, the band of AgAlTe2 is degenerate and the band of AgAlTe2 is degenerate when the compressive strain is -3.3. In both cases, the Seebeck coefficient is optimal, and the ratio of conductivity to relaxation time of the two materials increases gradually under the action of compressive strain. Therefore, the ratio of power factor to relaxation time is greatly improved under biaxial strain.
【學位授予單位】：湘潭大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TB34
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本文編號：1388966