p型BiCuSeO基硒氧化物热电传输特性研究

发布时间：2018-03-02 19:00

本文选题：BiCuSeO硒氧化物　切入点：塞贝克系数　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：热电材料能够直接将废热转化为电能,受到广泛的关注。由于高温下优良的热稳定性和化学稳定性、低成本及无毒性,氧化物热电材料有着潜在的应用价值。其中,具有独特晶体结构的BiCuSeO基硒氧化物成为当前的研究热点。BiCuSeO晶格由绝缘的(Bi2O2)2~+氧化物层和导电的(Cu2Se2)2-硒化物层沿四方晶体c轴交替堆叠而成,其中含有离子键的(Bi2O2)2~+层充当电荷存储器,具有共价键的(Cu2Se2)2_层为载流子传输提供导电通道。此外,BiCuSeO层间弱结合键、重组成元素和独特的晶体结构可引起声子的强烈散射,从而导致本征较低的热导率。在本文中,结合传统的两步固态反应和感应热压烧结工艺,制备了Bi1-xSbxCuSe1-yTeyO、Bi1-xZnxCuSeO1-xSx、BiCu1-xAgxSeO 和 Bi1-2xMgxPbxCuSeO等化合物,并系统研究了不同掺杂或替换方法对BiCuSeO基硒氧化物热电传输特性的影响。尽管BiCuSeO具有特殊的层状晶体结构,然而其热电传输特性可以假设为各向同性的。Sb替换增加了载流子浓度,而Te替换引起了相反的变化,因此所有的等价替换均对电学传输特性有着显著的影响,Bi_(0.98)Sb0.02CuSeO在750K时取得最大的功率因子3.8 μWcm-1K-2。此外,等价替换对于总热导率的降低无显著作用。750 K时,BiCuSe0.975Te0.025O具有最大的ZT值0.56,为相同条件下BiCuSeO 的 1.44 倍。通过Zn和S双位替换,温度为750 K时,电导率从BiCuSeO的28.9 S/cm增加到 Bi0.975Zn0.025CuSeO0.975S0.025的43.3 S/cm,且 Bi0.95Zn0.05CuSeO0.95S0.05具有最高的塞贝克系数360 μV/K。Bi0.95Zn0.05CuSeO0.95S0.05适中的电导率和高的塞贝克系数,使其在750 K时获得最大的最大功率因子4.6μWcm-1K-2。由于提高的功率因子抵消了总热导率的轻微增加,因此,Bi0.95Zn0.05CuSeO0.95S0.05在750 K时取得最大的ZT值0.68,与BiCuSeO相比,提升了约70%。Ag~+替换Cu~+之后,BiCu_(0.98)Ag0.02SeO和BiCu0.92Ag0.08SeO分别具有最高的电导率36.6 Scm-1和最大的塞贝克系数350 μVK-1。然而,由于适中的电导率和塞贝克系数,BiCu0.95Ag0.05SeO在750K时具有最大的功率因子3.67 μWcm-1K-2。同时,BiCu0.95Ag0.05SeO在750 K时的热导率低至0.38 Wm-1K-1,最大的ZT值达到0.72,此值是相同条件下未掺杂BiCuSeO的1.85倍。计算结果表明,Ag掺杂BiCuSeO热电性能的提升主要归因于带隙的减少和费米面附近态密度的增加。Bi1-2xMgxPbxCuSeO硒氧化物均由单一的BiCuSeO相组成,且晶体中的取向生长可以忽略不计。X射线光谱(XPS)结果表明,掺杂样品中Mg和Pb杂质均为2~+氧化态,然而除了预期的Bi3~+之外,较高氧化态的Bi离子也存在于原始态和掺杂BiCuSeO化合物中。Mg和Pb双掺杂显著增加了电导率,并使样品具有适中的塞贝克系数。750K时,功率因子从原始态BiCuSeO的2.54μWcm-1K-2显著提高到Bi0.88Mg0.06Pb0.06CuSeO的11.1μWcm-1K-2。由于Mg和Pb杂质引入的声子点缺陷散射,双掺杂进一步降低了晶格热导率。因此,Bi0.88Mg0.06Pb0.06CuSeO在750 K时取得最大的ZT值1.19,该值是相同条件下未掺杂BiCuSeO的3.1倍。
[Abstract]:Thermoelectric materials can convert waste heat directly into electric energy, which has attracted wide attention. Because of its excellent thermal and chemical stability at high temperature, low cost and non-toxicity, oxide thermoelectric materials have potential application value. The BiCuSeO based selenium oxide with unique crystal structure has become a hot research topic. The BiCuSeO crystal lattice is composed of the insulating Bi2O2O2-oxide layer and the conductive Cu2Se2Se2-selenide layer alternately stacked along the c-axis of the tetragonal crystal, in which a layer of Bi2O2Se containing ionic bonds acts as a charge storage. In addition, the weak binding bond between BiCuSeO layers, which recombines into elements and unique crystal structures, can cause strong scattering of phonons, resulting in lower intrinsic thermal conductivity. Bi1-xSbxCuSe1-yTeyOU Bi1-xZnxCuSeO1-xSxSxSiCuCuSe1-xSxSeO and Bi1-2xMgxPbxCuSeO were prepared by conventional two-step solid-state reaction and induction hot-pressing sintering process. The effects of different doping or substitution methods on the thermoelectric transport properties of BiCuSeO based selenium oxides were studied systematically. Although BiCuSeO has a special layered crystal structure, However, its thermoelectric transport properties can be assumed that the isotropic Sb substitution increases the carrier concentration, while the Te substitution causes the opposite change. Therefore, all equivalent substitutions have a significant effect on the electrical transmission characteristics. The maximum power factor of 3.8 渭 Wcm-1K-2 is obtained at 750K. Equivalent substitution has no significant effect on the decrease of total thermal conductivity. BiCuSe0.975Te0.025O has the largest ZT value of 0.56, which is 1.44 times of that of BiCuSeO under the same conditions. The conductivity of Bi0.95Zn0.05CuSeO0.95S0.05 increased from 28.9S / cm of BiCuSeO to 43.3s / cm of Bi0.975Zn0.025CuSeO0.975S0.025, and Bi0.95Zn0.05CuSeO0.95S0.05 had the highest Sebek coefficient of 360 渭 V / K.Bi0.95Zn0.05CuSeO0.95S0.05 and high Sebeck coefficient. The maximum power factor is 4.6 渭 Wcm-1K-2 at 750K. Because the increase of power factor counteracts the slight increase in total thermal conductivity, Bi0.95Zn0.05CuSeO0.95S0.05 obtains the largest ZT value of 0.68 at 750K, compared with BiCuSeO. The highest conductivity of 36.6 Scm-1 and the maximum coefficient of Saebeck of 350 渭 VK-1 were obtained for BiCuO 0.98 Ag0.02SeO and BiCu0.92Ag0.08SeO, respectively. At 750K, BiCu0.95Ag0.05SeO has the maximum power factor 3.67 渭 Wcm-1K-2.The thermal conductivity of BiCu0.95Ag0.05SeO at 750K is as low as 0.38Wm-1K-1SeO, and the maximum ZT value is 0.72, which is 1.85 times that of undoped BiCuSeO under the same conditions. The results show that the improvement of BiCuSeO thermoelectric properties is mainly due to the decrease of band gap and the increase of density of states near Fermi surface. The selenium oxide of Bi _ (1-2) x mg _ (x) Pb _ (xCuSeO) is composed of a single BiCuSeO phase. The orientation growth in the crystal can be neglected. The results of X-ray spectroscopy show that the mg and Pb impurities in the doped samples are both 2-oxidation states, but in addition to the expected Bi _ 3 ~, The higher oxidation state Bi ions also exist in the original state and the doped BiCuSeO compounds, which increase the conductivity of the samples significantly, and make the samples have moderate Seebeck coefficient (.750K). The power factor increased significantly from 2.54 渭 Wcm-1K-2 of the original BiCuSeO to 11.1 渭 Wcm-1K-2 of Bi0.88Mg0.06Pb0.06CuSeO. Due to the phonon defect scattering induced by mg and Pb impurities, Bi0.88Mg0.06Pb0.06CuSeO obtained the largest ZT value of 1.19 at 750K, which is 3.1 times of that of undoped BiCuSeO under the same condition.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB34

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