PbTe摻雜優(yōu)化及其熱電傳輸特性的理論與實驗研究
發(fā)布時間：2019-05-16 21:25
【摘要】：碲化鉛是目前最重要的中溫區(qū)熱電材料之一,而摻雜則是改善其熱電性能的最重要途徑。因此,本文主要采用第一性原理計算方法,研究了Pb位單摻雜與陰陽子離子雙位摻雜對PbTe能帶結(jié)構(gòu)與熱電性能的影響。此外,本文采用熔融法與快速感應(yīng)熱壓法制備了(Sn, Se)雙位摻雜碲化鉛材料,以通過實驗手段對計算結(jié)果進行驗證。 1.Ag、Sb共摻雜PbTe (100)表面： 計算表明,重構(gòu)后的表面晶體結(jié)構(gòu)對PbTe的摻雜穩(wěn)定性與電子結(jié)構(gòu)特性有著重要影響。由于表面處對稱性降低,經(jīng)充分結(jié)構(gòu)弛豫后出現(xiàn)層內(nèi)原子波動與原子層間距改變,其幅度隨著原子層的深入而減小。Ag、Sb雜質(zhì)具有向PbTe(100)表面擴散的傾向,且在表面趨于相互靠近而形成Ag-Sb納米點,波動式的表面結(jié)構(gòu)形成的額外能壘增加了雜質(zhì)的層間擴散難度,從而可形成較為穩(wěn)定的摻雜構(gòu)型。此外,因奇偶原子層的結(jié)構(gòu)弛豫行為相反,Ag、Sb雜質(zhì)摻雜于奇數(shù)層或偶數(shù)層時,表面性質(zhì)隨摻雜深度的變化規(guī)律也相反。Ag、Sb雜質(zhì)對表面的作用主要體現(xiàn)在與鄰近的基體Te原子間的成鍵狀態(tài)上,而元素性質(zhì)的差異導(dǎo)致Ag-Te與Sb-Te相互作用不同,因此Ag-Sb納米點的摻雜構(gòu)型對表面性質(zhì)也有著至關(guān)重要的影響。 2.雙位摻雜PbTe： (M, N)(M=K、Ag、Ge、Sn、Sb、Bi,N=S、Se、I)雙位雜質(zhì)在PbTe基體中同樣趨于相互靠近,穩(wěn)定的摻雜構(gòu)型取決于雜質(zhì)原子半徑與雜質(zhì)-基體、雜質(zhì)-雜質(zhì)相互作用。在雙位雜質(zhì)的作用下,PbTe產(chǎn)生總體晶格畸變與局域原子弛豫兩種結(jié)構(gòu)弛豫行為,其中前者減小帶隙,而后者則使帶隙增加。摻雜引起的結(jié)構(gòu)對稱性退化、雜質(zhì)-雜質(zhì)與雜質(zhì)-基體間相互作用,使所有(M,N)雙位摻雜情形均在帶邊產(chǎn)生能帶劈裂。陰陽離子雙位雜質(zhì)間的相互作用使得雙位摻雜明顯區(qū)別于單離子位摻雜,例如在S或Se單獨摻雜時PbTe的帶隙幾乎閉合,但與K共摻雜后帶隙重新擴張,因同主族元素的性質(zhì)相似,其雙位摻雜效應(yīng)亦具有相似性。摻雜濃度降低(增大超晶胞尺寸)時,雙離子位摻雜(例如(Ag,S))導(dǎo)致的原子局域弛豫程度降低、帶隙減小,能帶劈裂現(xiàn)象也減弱,但當(dāng)摻雜濃度提高,雜質(zhì)形成納米團簇后,其產(chǎn)生的更強的局域應(yīng)變場使PbTe帶隙增加,能帶劈裂程度也加重。尤為重要的是,在(Ag, S)、(Ge, Se)、(Sn, S)與(Sn,Se)雙位摻雜情形中,帶邊產(chǎn)生能帶彎曲現(xiàn)象,形成一種多極值駝峰狀能帶結(jié)構(gòu)。 3.能帶彎曲： 這種反常的能帶結(jié)構(gòu)可由△k與△E兩個相互獨立的參數(shù)加以描述。基于玻爾茲曼傳輸定律的計算表明,僅△k對塞貝克系數(shù)(S)與電導(dǎo)率(σ)的影響較大：對于n型與p型PbTe,當(dāng)溫度低于本征激發(fā)溫度時,S在低載流子濃度范圍內(nèi)隨Ak增加而降低,而在載流子濃度較高時則隨△k增加而增大,而當(dāng)溫度高于本征激發(fā)溫度時與此相反,σ的變化規(guī)律與S相反；對于p型價帶頂彎曲與n型導(dǎo)帶底彎曲的PbTe,△k較大時,S在低溫、高載流子濃度范圍內(nèi)較未彎曲時顯著增加,而σ則無明顯變化,△k較小時,低溫下S同能帶未彎曲時相比差別不大,但σ則略有增加,因此能帶彎曲能夠顯著增加PbTe在低溫、高載流子濃度區(qū)域的功率因子(PF)。S、σ與PF隨能帶彎曲程度的變化關(guān)系,主要是載流子源數(shù)量增加的有利效應(yīng)與載流子谷間散射的不利影響相互競爭的結(jié)果。 4.(Sn, Se)雙位摻雜PbTe的實驗研究： 本文使用熔融法與快速感應(yīng)熱壓法制備了高致密度的(Sn, Se)雙位摻雜PbTe熱電材料。實驗結(jié)果顯示,(Sn, Se)雜質(zhì)在PbTe基體中的分布規(guī)律,以及S、σ與PF隨摻雜類型與摻雜濃度的變化規(guī)律,均同計算結(jié)果十分相符,表明了雙位摻雜與能帶彎曲相關(guān)計算與分析的正確性。 本文(Ⅰ)揭示了銀、銻陽離子位雜質(zhì)在碲化鉛(100)表面的分布規(guī)律,以及表面結(jié)構(gòu)與摻雜構(gòu)型對表面性質(zhì)的影響；(Ⅱ)闡明了陰陽離子雙位雜質(zhì)在碲化鉛基體中的分布規(guī)律及其對能帶結(jié)構(gòu)與熱電性能的影響；(Ⅲ)發(fā)現(xiàn)選擇合適的雙位雜質(zhì)可使碲化鉛帶邊產(chǎn)生能帶彎曲,可以有效地改善其在低溫、高載流子濃度區(qū)域內(nèi)的熱電性能；(ⅣV)并基于熔融法與快速感應(yīng)熱壓法制備了高致密度的(Sn, Se)雙位摻雜碲化鉛材料,通過實驗手段證明了計算結(jié)果的正確性。本文的相關(guān)結(jié)果有助于揭示不同摻雜元素對PbTe熱電性能的影響機理,對PbTe及類似材料的摻雜優(yōu)化與熱電性能的提高具有一定的參考意義。
[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，
本文編號：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，
本文編號：2478569
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