【作者】 李静；

【导师】 蔡伟； Nita DRAGOE；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2015， 博士

【摘要】 BaCu₂Se₂和BiCuSeO具有较低的热导率和较高的Seebeck系数,是两种极具应用潜力的p型铜硫族化合物热电材料,但这两种材料电导率较低,导致ZT值较小,因而提高ZT值成为其实际应用的关键。本文主要采用元素掺杂和织构化提高BaCu2Se2和BiCuSeO的电导率,提高ZT值。采用X射线衍射仪、扫描电子显微镜、透射电子显微镜、Hall效应测试仪、Seebeck系数/电导率综合测试系统和激光热导仪等研究BaCu₂Se₂中Na掺杂和Ag掺杂以及BiCuSeO中Ba掺杂、S掺杂和热锻织构化对微观组织结构、输运特性和热电性能的影响规律和机制。采用Na和Ag掺杂分别提高BaCu₂Se₂的载流子浓度和迁移率,以提高电导率,提高ZT值。随Na掺杂量增加,Ba1-xNaxCu2Se2的载流子浓度大幅度增大,电导率（σ）显著提高,Seebeck系数（S）减小,导致功率因子（PF=S2σ）先升高后降低,在x=0.075时达到最高,773K时为8.1μWcm-1K-2。随Na掺杂量增加,晶格热导率（κlat）略有降低,电导率的提高使电子热导率（κele）增大,导致总热导率（κtot）增大。根据ZT=（S2σ/κtot）T,ZT值先升高后降低,在x=0.075时达到最大,773K时为1。适量Ag等电位取代BaCu₂Se₂中的Cu提高了载流子迁移率,提高电导率和功率因子,改善其热电性能,使室温ZT值由0.018提高至0.034。采用Ba掺杂提高BiCuSeO的载流子浓度,以提高电导率,提高ZT值。Ba掺杂量增加,Bi1-xBaxCu Se O的载流子浓度大幅度增加,使电导率显著提高,而Seebeck系数减小,导致功率因子在Ba掺杂量为x=0.125时出现峰值,在923K为6.33μWcm-1K-2。电导率的提高使电子热导率增大;同时Bi与Ba的原子质量和离子尺寸波动加重晶格畸变,增强声子散射,使晶格热导率减小,并且κele增加幅度大于κlat,因此总热导率增大。最终,随Ba掺杂量增加,ZT值先升高后降低,x=0.125时ZT值在923K达1.1。Bi1-xBaxCu Se O经923K保温1周后热电性能无变化,呈现出良好的稳定性。在Ba重掺杂改性BiCuSeO基础上,利用其各向异性特点,通过热锻构建织构,提高载流子迁移率,提高电导率（σ=nμe）,进一步改善热电性能。随热锻次数增加,垂直于压力方向的载流子迁移率（μ⊥）、电导率（σ⊥）和热导率（κ⊥）升高,而平行于压力方向的对应值均降低。特别指出,Seebeck系数不因热锻次数增加而改变。随热锻次数增加,σ⊥/κ⊥增大,σ∥/κ∥减小,因此三次热锻后ZT⊥值提高,923K时达1.4。采用S掺杂,降低BiCuSeO的成本,同时降低热导率。在x=0¹范围内,Bi Cu Se1-xSxO可形成近纯相固溶体。随着S替代量增加,Bi Cu Se1-xSxO的晶格常数线性减小,符合Vegard定律。第一原理计算表明,在Bi Cu Ch O（Ch=S、Se）中,Cu-Ch键的共价性较强,连接（Bi2O2）2+层与（Cu2Ch2）2-层的Bi-Ch键离子性较强,经S取代Se后,二者的离子性均变强。S部分取代Se时,S与Se离子半径差加重了晶格畸变,增强声子散射,导致热导率明显低于BiCuSeO和Bi Cu SO。更多还原

【Abstract】 BaCu₂Se₂ and Bi CuSe O, as two kinds of promising p-type copper-chalcogenide based thermoelectric materials, have low thermal conductivity and high Seebeck coefficient. But the low electrical conductivity results in low ZT value. Therefore, improvement of electrical conductivity is the key issue for their practical application. In this thesis, doping was carried out to increase electrical conductivity of BaCu₂Se₂ and Bi Cu SeO, and further improve their ZT value. Influence of doping on the microstructure, transport behavior and thermoelectric properties of BaCu₂Se₂ and Bi Cu SeO was investigated by XRD, SEM, TEM, Hall measurement, ZEM-3 and laser flash diffusivity apparatus. Meanwhile, the related mechanism was also investigated.In order to improve electrical conductivity and ZT value, Na doping and Ag doping were developed to increase carrier concentration and mobility of BaCu₂Se₂, respectively. As Na doping content increased, carrier concentration of Ba1-xNaxCu2Se2 increased obviously, electrical conductivity（σ） and Seebeck coefficient（S） was increased and decreased, respectively. The maximum power factor（PF） of 8.1μWcm-1K-2 at 773 K was obtained when x=0.075. Lattice thermal conductivity（κlat） decreased slightly as Na doping increasing, while electronic thermal conductivity（κele） increased due to the improved electrical conductivity. According to the equation ZT=（S2σ/κtot）T, ZT first increased and then decreased with the increasing Na doping amount. Maximum ZT of 1 at 773 K was obtained when x=0.075. Proper amount of Ag substitution in the BaCu₂Se₂ increased the carrier mobility. Therefore, the electrical conductivity and PF was improved. Room temerpature ZT was enhanced from 0.018 to 0.034.Ba doping was chosen in BiCuSeO to increase the carrier concentration, thus improve the electrical conductivity and ZT. As Ba doping concentration increased, carrier concentration of Bi1-xBaxCu SeO increased remarkably, leading to electrical conductivity and Seebeck coefficient increase and decrease, respectively. Therefore, the maximum PF of 6.33μWcm-1K-2 at 923 K was obtained when x=0.125. Electronic thermal conductivity was increased because of the improved electrical conductivity after Ba doping, while lattice thermal conductivity was decreased due to enhanced phonon scattering by the fluctuation of atomic mass and size between Ba and Bi. The increase of κele surpassed reduction of κlat, so κtot increased after Ba doping. As a concequence, ZT first increased and then decreased. The maximum ZT of 1.1 at 923 K was obtained when x=0.125. The thermoelectric properties of Bi1-xBaxCuSe O showed no change after annealing at 923 K for one week, displaying their good thermal stability.Taking the advantage of the anisotropic characteristics of BiCuSeO, hot forging method was applied on the Ba heavily doped BiCuSeO to induce texture and improve the carrier mobility and electrical conductivity. For the direction perpendicular to the pressure, with the increase of hot forging times, carrier mobility（μ⊥）, electrical conductivity（σ⊥） and thermal conductivity（κ⊥） increased. In contrast, transport behavior showed a reverse regulation in the direction parallal to the pressure. Seebeck coefficient and carrier concentration were still unchanged after hot forging. σ⊥/κ⊥ increased while σ∥/κ∥ decreased as increasing hot forging times, consequently, ZT⊥ was boosted to 1.4 at 923 K after three times hot forging.S doping was applied to decrease the cost and thermal conductivity of BiCuSeO. Nearly pure phase Bi Cu Se1-xSxO solid solution can be formed within x=0¹. Lattice parameters of Bi Cu Se1-xSxO decreased linearly as increasing S content, obeying the Vegard’s law. Ab initio calculation for Bi Cu Ch O（Ch=S, Se） indicated that Cu-Ch bonding had strong covalent characteristic, while Bi-Ch bonding that connected（Bi2O2）2+ layer with（Cu2Ch2）2- layer had strong inoic characteristic. When Se was partially substituted by S, atomic mass and size difference between Se and S induced lattice distortion and intensified phonon scattering, so their thermal conductivity was lower than those of Bi CuSe O and Bi Cu SO.更多还原