本文選題：BiCuSeO硒氧化物　切入點：塞貝克系數(shù)　出處：《中國科學技術大學》2017年博士論文　論文類型：學位論文

【摘要】：熱電材料能夠直接將廢熱轉化為電能,受到廣泛的關注。由于高溫下優(yōu)良的熱穩(wěn)定性和化學穩(wěn)定性、低成本及無毒性,氧化物熱電材料有著潛在的應用價值。其中,具有獨特晶體結構的BiCuSeO基硒氧化物成為當前的研究熱點。BiCuSeO晶格由絕緣的(Bi2O2)2~+氧化物層和導電的(Cu2Se2)2-硒化物層沿四方晶體c軸交替堆疊而成,其中含有離子鍵的(Bi2O2)2~+層充當電荷存儲器,具有共價鍵的(Cu2Se2)2_層為載流子傳輸提供導電通道。此外,BiCuSeO層間弱結合鍵、重組成元素和獨特的晶體結構可引起聲子的強烈散射,從而導致本征較低的熱導率。在本文中,結合傳統(tǒng)的兩步固態(tài)反應和感應熱壓燒結工藝,制備了Bi1-xSbxCuSe1-yTeyO、Bi1-xZnxCuSeO1-xSx、BiCu1-xAgxSeO 和 Bi1-2xMgxPbxCuSeO等化合物,并系統(tǒng)研究了不同摻雜或替換方法對BiCuSeO基硒氧化物熱電傳輸特性的影響。盡管BiCuSeO具有特殊的層狀晶體結構,然而其熱電傳輸特性可以假設為各向同性的。Sb替換增加了載流子濃度,而Te替換引起了相反的變化,因此所有的等價替換均對電學傳輸特性有著顯著的影響,Bi_(0.98)Sb0.02CuSeO在750K時取得最大的功率因子3.8 μWcm-1K-2。此外,等價替換對于總熱導率的降低無顯著作用。750 K時,BiCuSe0.975Te0.025O具有最大的ZT值0.56,為相同條件下BiCuSeO 的 1.44 倍。通過Zn和S雙位替換,溫度為750 K時,電導率從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具有最高的塞貝克系數(shù)360 μV/K。Bi0.95Zn0.05CuSeO0.95S0.05適中的電導率和高的塞貝克系數(shù),使其在750 K時獲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總熱導率的輕微增加,因此,Bi0.95Zn0.05CuSeO0.95S0.05在750 K時取得最大的ZT值0.68,與BiCuSeO相比,提升了約70%。Ag~+替換Cu~+之后,BiCu_(0.98)Ag0.02SeO和BiCu0.92Ag0.08SeO分別具有最高的電導率36.6 Scm-1和最大的塞貝克系數(shù)350 μVK-1。然而,由于適中的電導率和塞貝克系數(shù),BiCu0.95Ag0.05SeO在750K時具有最大的功率因子3.67 μWcm-1K-2。同時,BiCu0.95Ag0.05SeO在750 K時的熱導率低至0.38 Wm-1K-1,最大的ZT值達到0.72,此值是相同條件下未摻雜BiCuSeO的1.85倍。計算結果表明,Ag摻雜BiCuSeO熱電性能的提升主要歸因于帶隙的減少和費米面附近態(tài)密度的增加。Bi1-2xMgxPbxCuSeO硒氧化物均由單一的BiCuSeO相組成,且晶體中的取向生長可以忽略不計。X射線光譜(XPS)結果表明,摻雜樣品中Mg和Pb雜質均為2~+氧化態(tài),然而除了預期的Bi3~+之外,較高氧化態(tài)的Bi離子也存在于原始態(tài)和摻雜BiCuSeO化合物中。Mg和Pb雙摻雜顯著增加了電導率,并使樣品具有適中的塞貝克系數(shù)。750K時,功率因子從原始態(tài)BiCuSeO的2.54μWcm-1K-2顯著提高到Bi0.88Mg0.06Pb0.06CuSeO的11.1μWcm-1K-2。由于Mg和Pb雜質引入的聲子點缺陷散射,雙摻雜進一步降低了晶格熱導率。因此,Bi0.88Mg0.06Pb0.06CuSeO在750 K時取得最大的ZT值1.19,該值是相同條件下未摻雜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.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TB34

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