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采用熔融缓冷技术制备了不同Ag掺杂量的p型Agx(Pb0.5Sn0.5)1-xTe化合物, 系统地研究了Ag掺杂对所得材料的相组成、微结构及其热电传输性能. Ag的掺入显著增加了材料的空穴浓度, 但是材料的空穴浓度远小于Ag作为单电子受主时理论空穴浓度, 且在掺杂量为5%时未出现任何第二相, 这表明Ag在可能进入晶格间隙位置而作为电子施主, 起到补偿作用. 随着Ag掺杂量的增加, 样品的电导率逐渐增加, 而Seebeck系数表现出复杂的变化趋势: 在低于450 K时逐渐增加, 而在温度大于450 K时逐渐降低, 这主要源于材料复杂的价带结构. 由于空穴浓度的优化和重空穴带的主导作用, 1% Ag掺杂样品获得最大的功率因子, 在750 K可达2.1 mWm-1K-2. 此外, Ag的掺入引入的点缺陷大幅散射了传热声子, 使得晶格热导率随着Ag掺量的增加逐渐降低. 结果1% Ag掺杂样品在750 K时获得了最大的热电优值ZT=1.05, 相比未掺样品提高了近50%, 这一数值同商业应用的p型PbTe材料的性能相当. 但是Sn取代显著降低了有毒重金属Pb的用量, 这对PbTe基材料的商业化应用及其环境相适性具有重要意义.A series of Ag-doped p-type Agx(Pb0.5Sn0.5)1-xTe compounds is prepared by melting followed by slow-cooling process, and the phase compositions, microstructures and thermoelectric properties are also systematically investigated. The introduction of Ag in Pb/Sn site effectively increases the hole density which is much lower than the theoretically predicated value in the approximation of complete substitution and single acceptor of Ag, in spite of the fact that all samples show finely single phase for the 5% Ag-doped sample. This implies that part of Ag atoms enter into the interstitial sites acting as electron donor to reduce the hole density. With the increase of Ag content, the electrical conductivity increases gradually and the Seebeck coefficient shows an opposite variation tendency, mainly owing to the variation of hole density. Interestingly, the anomalous crossover of Seebeck coefficient at about 450 K indicates the transition of dominating valence valley from light-band to heavy-band while temperature is higher than 450 K. Consequently, due to the optimization of hole density and the domination of heavy band with large effective mass, 1% Ag-doped sample obtains a highest power factor of 2.1 mWm-1K-2 at 750 K, which results in a highest ZT of 1.05 combined with the suppressed lattice thermal conductivity via intensifying point defect phonon scattering. This high ZT is ～ 50% higher than that of Ag-free sample and also higher than commercial p-type PbTe material. Further, the 50% substitution of toxic and heavy Pb by Sn is beneficial for the practical application and environmental sustainability of PbTe-based materials.
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Keywords:
- Ag-doping /
- Sn-alloying /
- hole density /
- thermoelectric properties
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[1] Tritt T M, Bottner H, Chen L D 2008 MRS Bull. 33 366
[2] Tang X F, Chen L D, Goto T, Hirai T, Yuan R Z 2001 Acta Phys. Sin. 50 1560 (in Chinese) [唐新峰, 陈立东, 後藤孝, 平井敏雄, 袁润章 2001 50 1560]
[3] Li H, Tang X F, Cao W Q, Zhang Q J 2009 Chin. Phys. B 18 287
[4] Heremans J P, Jovovic V, Toberer E S, Saramat A, Kurosaki K, Charoenphakdee A, Yamanaka S, Snyder G J 2008 Science 321 554
[5] Pei Y Z, Shi X Y, LaLonde A, Wang H, Chen L D, Snyder G J 2011 Nature 473 66
[6] Biswas K, He J Q, Zhang Q C, Wang G Y, Uher C, Dravid V P, Kanatzidis M G 2011 Nature Chem. 3 160
[7] Jaworski C P, Wiendlocha B, Jovovic V, Heremans J P 2011 Energy Environ. Sci. 4 2085
[8] Yadav G G, Susoreny J A, Zhang G Q, Yang H R, Wu Y 2011 Nanoscale 3 3555
[9] Vaqueiro P, Powell A V 2010 J. Mater. Chem. 20 9577
[10] Joffe A F, Stil'bans L S 1959 Rep. Prog. Phys. 22 167
[11] Dimmock J O, Melngailis I, Strauss A J 1966 Phys. Rev. Lett. 16 1193
[12] Arachchige I U, Kanatzidis M G 2009 Nano Lett. 9 1583
[13] Snyder G J, Toberer E S 2008 Nat. Mater. 7 105
[14] Ravich Y I, Efimova B A, Smirnov I A 1970 Semiconducting Lead Chalcogenides (New York, London: Plenum Press)
[15] Bozin E, Malliakas C D, Souvatzis P, Proffen T, Spaldin N A, Kanatzidis M G, Billinge S J L 2010 Science 330 1660
[16] Androulakis J, Todorov I, He J Q, Chung D Y, Dravid V, Kanatzidis M G 2011 J. Am. Chem. Soc. 133 10920
[17] Pei Y Z, LaLonde A, Iwanaga S, Snyder G J 2011 Energy Environ. Sci. 4 2085
[18] Pei Y Z, May A F, Snyder G J 2011 Adv. Energy Mater. 1 291
[19] Androulakis J, Lee Y, Todorov I, Chung D Y, Kanatzidis M 2011 Phys. Rev. B 83 195209
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[23] Du B L, Xu J J, Yan Y G, Tang X F 2011 Acta Phys. Sin. 60 018403 (in Chinese) [杜保立, 徐静静, 鄢永高, 唐新峰 2011 60 018403]
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