黄铜矿型热电材料热电性能的应力应变调控

发布时间：2018-01-06 18:25

  本文关键词：黄铜矿型热电材料热电性能的应力应变调控　出处：《湘潭大学》2016年硕士论文　论文类型：学位论文

  更多相关文章： 黄铜矿 热电性能 外应力 单轴应变 双轴应变

【摘要】：工业废热不仅造成了环境污染,同时也浪费了大量热能,而热电材料可以直接把这些富余的热能转化成电能加以利用,且在使用过程中不会造成环境污染。因此,热电材料在废热利用方面具有广阔的应用前景,在应对能源短缺和环境问题方面存在巨大潜力。黄铜矿体系热电材料具有无毒无污染、储量大、分布广等优点,成为了目前热电材料研究的热点。通常,材料的对称度越高,热电性能越优异,但黄铜矿热电材料是四方相结构,对称性较低,这使得该体系的热电性能仍有非常大的提升空间。因此,本论文基于第一性原理和半经典玻尔兹曼理论,以黄铜矿热电材料体系为研究对象,计算分析了应力、应变对其对称度和能带的影响,进而调控优化其热电性能。论文的主要工作如下:(1)探究了外应力对黄铜矿热电材料性能的影响,提出了外应力对黄铜矿热电材料的调控优化方案。以黄铜矿体系热电材料MgSiP_2为研究对象,计算其在外应力作用下的电子结构和热电性能,结果显示p型和n型MgSiP_2的赛贝克系数随着外应力的增加均略有减小,电导率与弛豫时间之比均得到了提升,但p型MgSiP_2的电导率增强幅度较n型更大,使p型MgSiP_2的功率因子与弛豫时间比值优于n型。这表明外应力使得p型MgSiP_2表现出较优的热电性能,外应力是提高p型MgSiP_2热电性能的有效途径。(2)研究了单轴应变对黄铜矿热电材料电子结构和热电性能的影响,提出了单轴应变调控其热电性能的方案。以黄铜矿热电材料AgAlTe2为研究对象,通过单轴应变提升其晶体对称性,从而提升其能带简并度,促进赛贝克系数的提高。在拉应变为5%时,AgAlTe2的能带达到了简并,此时赛贝克系数最大;电导率与弛豫时间比值在拉应变作用下也有较大的提升,在拉应变为7%时增长率达到8.7%;功率因子与弛豫时间比值也在拉应变作用下有明显的增加,在拉应变为6%时达到最大值,增长率为27.2%。(3)探究了双轴应变对黄铜矿热电材料性能的影响,提出黄铜矿热电材料双轴应变调控方案。以黄铜矿材料AgAlTe2和AgGaTe2为研究对象,探究双轴应变对其电子结构和热电性能的影响,AgGaTe2在压应变为-2.32%时能带达到简并,AgAlTe2在压应变为-3.3%时能带达到了简并,两种情况下材料的赛贝克系数均达到最优,两种材料的电导率与弛豫时间的比值也均在压应变的作用下逐渐增加,因此功率因子与弛豫时间比值在双轴应变作用下也得到了较大的提高。
[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.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB34
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本文编号：1388966