PbTe掺杂优化及其热电传输特性的理论与实验研究
发布时间：2019-05-16 21:25
【摘要】：碲化铅是目前最重要的中温区热电材料之一,而掺杂则是改善其热电性能的最重要途径。因此,本文主要采用第一性原理计算方法,研究了Pb位单掺杂与阴阳子离子双位掺杂对PbTe能带结构与热电性能的影响。此外,本文采用熔融法与快速感应热压法制备了(Sn, Se)双位掺杂碲化铅材料,以通过实验手段对计算结果进行验证。 1.Ag、Sb共掺杂PbTe (100)表面： 计算表明,重构后的表面晶体结构对PbTe的掺杂稳定性与电子结构特性有着重要影响。由于表面处对称性降低,经充分结构弛豫后出现层内原子波动与原子层间距改变,其幅度随着原子层的深入而减小。Ag、Sb杂质具有向PbTe(100)表面扩散的倾向,且在表面趋于相互靠近而形成Ag-Sb纳米点,波动式的表面结构形成的额外能垒增加了杂质的层间扩散难度,从而可形成较为稳定的掺杂构型。此外,因奇偶原子层的结构弛豫行为相反,Ag、Sb杂质掺杂于奇数层或偶数层时,表面性质随掺杂深度的变化规律也相反。Ag、Sb杂质对表面的作用主要体现在与邻近的基体Te原子间的成键状态上,而元素性质的差异导致Ag-Te与Sb-Te相互作用不同,因此Ag-Sb纳米点的掺杂构型对表面性质也有着至关重要的影响。 2.双位掺杂PbTe： (M, N)(M=K、Ag、Ge、Sn、Sb、Bi,N=S、Se、I)双位杂质在PbTe基体中同样趋于相互靠近,稳定的掺杂构型取决于杂质原子半径与杂质-基体、杂质-杂质相互作用。在双位杂质的作用下,PbTe产生总体晶格畸变与局域原子弛豫两种结构弛豫行为,其中前者减小带隙,而后者则使带隙增加。掺杂引起的结构对称性退化、杂质-杂质与杂质-基体间相互作用,使所有(M,N)双位掺杂情形均在带边产生能带劈裂。阴阳离子双位杂质间的相互作用使得双位掺杂明显区别于单离子位掺杂,例如在S或Se单独掺杂时PbTe的带隙几乎闭合,但与K共掺杂后带隙重新扩张,因同主族元素的性质相似,其双位掺杂效应亦具有相似性。掺杂浓度降低(增大超晶胞尺寸)时,双离子位掺杂(例如(Ag,S))导致的原子局域弛豫程度降低、带隙减小,能带劈裂现象也减弱,但当掺杂浓度提高,杂质形成纳米团簇后,其产生的更强的局域应变场使PbTe带隙增加,能带劈裂程度也加重。尤为重要的是,在(Ag, S)、(Ge, Se)、(Sn, S)与(Sn,Se)双位掺杂情形中,带边产生能带弯曲现象,形成一种多极值驼峰状能带结构。 3.能带弯曲： 这种反常的能带结构可由△k与△E两个相互独立的参数加以描述。基于玻尔兹曼传输定律的计算表明,仅△k对塞贝克系数(S)与电导率(σ)的影响较大：对于n型与p型PbTe,当温度低于本征激发温度时,S在低载流子浓度范围内随Ak增加而降低,而在载流子浓度较高时则随△k增加而增大,而当温度高于本征激发温度时与此相反,σ的变化规律与S相反；对于p型价带顶弯曲与n型导带底弯曲的PbTe,△k较大时,S在低温、高载流子浓度范围内较未弯曲时显著增加,而σ则无明显变化,△k较小时,低温下S同能带未弯曲时相比差别不大,但σ则略有增加,因此能带弯曲能够显著增加PbTe在低温、高载流子浓度区域的功率因子(PF)。S、σ与PF随能带弯曲程度的变化关系,主要是载流子源数量增加的有利效应与载流子谷间散射的不利影响相互竞争的结果。 4.(Sn, Se)双位掺杂PbTe的实验研究： 本文使用熔融法与快速感应热压法制备了高致密度的(Sn, Se)双位掺杂PbTe热电材料。实验结果显示,(Sn, Se)杂质在PbTe基体中的分布规律,以及S、σ与PF随掺杂类型与掺杂浓度的变化规律,均同计算结果十分相符,表明了双位掺杂与能带弯曲相关计算与分析的正确性。 本文(Ⅰ)揭示了银、锑阳离子位杂质在碲化铅(100)表面的分布规律,以及表面结构与掺杂构型对表面性质的影响；(Ⅱ)阐明了阴阳离子双位杂质在碲化铅基体中的分布规律及其对能带结构与热电性能的影响；(Ⅲ)发现选择合适的双位杂质可使碲化铅带边产生能带弯曲,可以有效地改善其在低温、高载流子浓度区域内的热电性能；(ⅣV)并基于熔融法与快速感应热压法制备了高致密度的(Sn, Se)双位掺杂碲化铅材料,通过实验手段证明了计算结果的正确性。本文的相关结果有助于揭示不同掺杂元素对PbTe热电性能的影响机理,对PbTe及类似材料的掺杂优化与热电性能的提高具有一定的参考意义。
[Abstract]:Lead is one of the most important thermoelectric materials in the medium temperature region, and the doping is the most important way to improve its thermoelectric performance. In this paper, the first principle calculation method is used to study the effect of the two-position doping of Pb-position and the two-position doping on the energy band structure and the thermoelectric property of the PbTe. In addition, a two-position doped lead-lead material with (Sn, Se) is prepared by melt-method and rapid induction hot-press method, and the calculation result is verified by means of experimental means. 1. Ag, Sb co-doped PbTe (100) table The results show that the structure of the surface crystal structure after the reconstruction has a focus on the doping stability of PbTe and the characteristics of the electronic structure. If that symmetry of the surface is reduce, the fluctuation of the atomic layer and the spacing of the atomic layer in the layer are changed after the structure relaxation, and the amplitude of the atomic layer increases with the depth of the atomic layer. The Ag and Sb impurities have a tendency to diffuse to the surface of the PbTe (100), and the Ag-Sb nano-dots are formed on the surface of the Ag-Sb nano-dots, and the additional energy barrier formed by the wave-type surface structure increases the inter-layer diffusion difficulty of the impurities, so that a more stable doping can be formed. In addition, due to the structure relaxation behavior of the odd-and-even atomic layer, the variation of the surface property with the doping depth when the Ag and Sb impurities are doped in the odd-numbered or even-numbered layers On the contrary, the effect of Ag and Sb impurity on the surface is mainly reflected in the bonding state with the adjacent matrix Te atom, and the difference of the element property causes the Ag-Te to interact with the Sb-Te, so the doping configuration of the Ag-Sb nano-point is also very important to the surface property. 2.2. Two-position doping The two-position impurities of (M, N) (M = K, Ag, Ge, Sn, Sb, Bi, N = S, Se, I) tend to be close to each other in the PbTe matrix, and the stable doping profile depends on the impurity atom radius and the impurity-matrix, impurities, and under the action of two-position impurities, the PbTe is subjected to two structural relaxation behaviors of total lattice distortion and local atomic relaxation, wherein the former reduces the band gap and then the doping causes the structural symmetry degradation, the impurity-impurity and the impurity-matrix to interact, and all the (m, n) two-position doping cases are in the band, the interaction between the two-position impurities of the anion and the cation makes the two-position doping be obviously different from the single-ion-site doping, for example, the band gap of the pbte is almost closed when the s or se is separately doped, but the band-gap re-expanded after the co-doping with the k, The properties of the element are similar, and the two-position doping effect It should also be similar. When the doping concentration is decreased (for example, the cell size is increased), the local relaxation degree of the atoms caused by the double-ion-position doping (e.g. (Ag, S)) is reduced, the band gap is reduced, and the energy band splitting phenomenon is also reduced, but when the doping concentration is improved, the impurities after the nanoclusters are formed, the stronger local strain field produced by the nanoclusters increases the band gap of the pbte, the energy band, In the case of (Ag, S), (Ge, Se), (Sn, S) and (Sn, Se) two-position doping, the band bending phenomenon is generated by the band edge, and a multi-extreme value is formed. hump-like band structure .3. Energy band bending: This abnormal energy band structure can be composed of two or two of a factor of two to one. The calculation of the Boltzmann's law of transmission shows that only the influence of the factor k on the Seebeck coefficient (S) and the conductivity (S) is large: for n-type and p-type PbTe, when the temperature is lower than the intrinsic excitation temperature, S is at the low carrier concentration. decreases with the increase of the Ak in the range, and increases with the increase of the peak value when the carrier concentration is higher, and when the temperature is higher than the intrinsic excitation temperature, the variation rule of the valence band is opposite to the S; and the PbTe which is bent on the p-type valence band top and the n-type conduction band bottom In the case of large capacity, S is significantly increased in the low temperature and high carrier concentration range, and there is no obvious change in the peak value, but there is no significant difference between the low temperature and the low temperature S when the energy band is not bent, but the energy band is slightly increased, so the energy band bending can A significant increase in the power factor (PF) of PbTe in the low-temperature and high-carrier-concentration region, the change of S, PF and PF with the degree of band bending, is mainly the beneficial effect of the increase of the number of carrier sources and the carrier-valley scattering. unfavorable Impact on competing results. (Sn, Se) In this paper, the high-density (Sn) is prepared by using the melting method and the rapid induction hot-pressing process. The experimental results show that the distribution of the (Sn, Se) impurities in the PbTe matrix and the variation of the doping type and the doping concentration of the (Sn, Se) impurities in the PbTe matrix are in good agreement with the calculation results, and the two-position doping and the doping concentration are shown. The correctness of the calculation and analysis of the energy band bending is presented in this paper. The distribution of silver and antimony cations in the surface of the lead (100) is studied in this paper. The effect of the surface structure and the doping configuration on the surface properties is discussed. (鈪，
本文编号：2478569
[Abstract]:Lead is one of the most important thermoelectric materials in the medium temperature region, and the doping is the most important way to improve its thermoelectric performance. In this paper, the first principle calculation method is used to study the effect of the two-position doping of Pb-position and the two-position doping on the energy band structure and the thermoelectric property of the PbTe. In addition, a two-position doped lead-lead material with (Sn, Se) is prepared by melt-method and rapid induction hot-press method, and the calculation result is verified by means of experimental means. 1. Ag, Sb co-doped PbTe (100) table The results show that the structure of the surface crystal structure after the reconstruction has a focus on the doping stability of PbTe and the characteristics of the electronic structure. If that symmetry of the surface is reduce, the fluctuation of the atomic layer and the spacing of the atomic layer in the layer are changed after the structure relaxation, and the amplitude of the atomic layer increases with the depth of the atomic layer. The Ag and Sb impurities have a tendency to diffuse to the surface of the PbTe (100), and the Ag-Sb nano-dots are formed on the surface of the Ag-Sb nano-dots, and the additional energy barrier formed by the wave-type surface structure increases the inter-layer diffusion difficulty of the impurities, so that a more stable doping can be formed. In addition, due to the structure relaxation behavior of the odd-and-even atomic layer, the variation of the surface property with the doping depth when the Ag and Sb impurities are doped in the odd-numbered or even-numbered layers On the contrary, the effect of Ag and Sb impurity on the surface is mainly reflected in the bonding state with the adjacent matrix Te atom, and the difference of the element property causes the Ag-Te to interact with the Sb-Te, so the doping configuration of the Ag-Sb nano-point is also very important to the surface property. 2.2. Two-position doping The two-position impurities of (M, N) (M = K, Ag, Ge, Sn, Sb, Bi, N = S, Se, I) tend to be close to each other in the PbTe matrix, and the stable doping profile depends on the impurity atom radius and the impurity-matrix, impurities, and under the action of two-position impurities, the PbTe is subjected to two structural relaxation behaviors of total lattice distortion and local atomic relaxation, wherein the former reduces the band gap and then the doping causes the structural symmetry degradation, the impurity-impurity and the impurity-matrix to interact, and all the (m, n) two-position doping cases are in the band, the interaction between the two-position impurities of the anion and the cation makes the two-position doping be obviously different from the single-ion-site doping, for example, the band gap of the pbte is almost closed when the s or se is separately doped, but the band-gap re-expanded after the co-doping with the k, The properties of the element are similar, and the two-position doping effect It should also be similar. When the doping concentration is decreased (for example, the cell size is increased), the local relaxation degree of the atoms caused by the double-ion-position doping (e.g. (Ag, S)) is reduced, the band gap is reduced, and the energy band splitting phenomenon is also reduced, but when the doping concentration is improved, the impurities after the nanoclusters are formed, the stronger local strain field produced by the nanoclusters increases the band gap of the pbte, the energy band, In the case of (Ag, S), (Ge, Se), (Sn, S) and (Sn, Se) two-position doping, the band bending phenomenon is generated by the band edge, and a multi-extreme value is formed. hump-like band structure .3. Energy band bending: This abnormal energy band structure can be composed of two or two of a factor of two to one. The calculation of the Boltzmann's law of transmission shows that only the influence of the factor k on the Seebeck coefficient (S) and the conductivity (S) is large: for n-type and p-type PbTe, when the temperature is lower than the intrinsic excitation temperature, S is at the low carrier concentration. decreases with the increase of the Ak in the range, and increases with the increase of the peak value when the carrier concentration is higher, and when the temperature is higher than the intrinsic excitation temperature, the variation rule of the valence band is opposite to the S; and the PbTe which is bent on the p-type valence band top and the n-type conduction band bottom In the case of large capacity, S is significantly increased in the low temperature and high carrier concentration range, and there is no obvious change in the peak value, but there is no significant difference between the low temperature and the low temperature S when the energy band is not bent, but the energy band is slightly increased, so the energy band bending can A significant increase in the power factor (PF) of PbTe in the low-temperature and high-carrier-concentration region, the change of S, PF and PF with the degree of band bending, is mainly the beneficial effect of the increase of the number of carrier sources and the carrier-valley scattering. unfavorable Impact on competing results. (Sn, Se) In this paper, the high-density (Sn) is prepared by using the melting method and the rapid induction hot-pressing process. The experimental results show that the distribution of the (Sn, Se) impurities in the PbTe matrix and the variation of the doping type and the doping concentration of the (Sn, Se) impurities in the PbTe matrix are in good agreement with the calculation results, and the two-position doping and the doping concentration are shown. The correctness of the calculation and analysis of the energy band bending is presented in this paper. The distribution of silver and antimony cations in the surface of the lead (100) is studied in this paper. The effect of the surface structure and the doping configuration on the surface properties is discussed. (鈪，
本文编号：2478569
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