Sb基Zintl相化合物的结构与热电性能研究

发布时间：2018-03-19 05:01

本文选题：结构　切入点：掺杂半导体　出处：《山东大学》2017年博士论文　论文类型：学位论文

【摘要】：含有磷族元素(第十五主族)的化合物,由于其数目繁多,表现出非常丰富的结构类型和多样的性质,引起了人们的广泛研究。由于环境污染、能源短缺等现实问题的加剧,能将废热转换成电能回收再利用的热电材料逐渐受到人们的重视并得到不断的发展。Zintl相化合物由于其复杂的晶体和电子结构,被认为是极具潜力的热电材料。本论文主要开展了 Zintl相中9-4-9体系和1-1-1体系结构相关热电材料的制备、结构与性能优化工作。1、Ca9Zn4+xSb9化合物合成及热电性质研究9-4-9体系中Ca9Zn4+xSb9结构化合物,具有较大的单胞和复杂的晶体结构,从而具有较低的晶格热导率,进而展现出较好的热电性质。通过无机固相的方法,我们得到了 Ca9Zn4.5Sb9的纯相,其ZT值大约在0.37左右。在测试中得知,较高的电阻率是阻碍其热电性质提升的主要原因,因此在之后的工作中,我们通过部分取代来提升材料的电学性能,从而得到更优的热电性质。2、Ca9Zn4+xSb9合物间隙原子位置掺杂改性为了进一步对Ca9Zn4+xSb9进行进行研究,我们选择用Al代替部分的Zn原子,并得到了这几种化合物的纯相Ca9Zn4.5-xAl2x/3Sb9(x=0,0.5,1),然后对其热电性质进行了研究。在该体系研究中发现,通过用Al取代Zn原子,可以使间隙位置的缺陷浓度增加,体系的迁移率大幅下降,材料的导电性能明显降低,不利于热电性能的提升。通过实验与理论计算的分析,我们进一步设计并得到了掺Cu的化合物Ca9Zn4.5-xCuxSb9(x=0.05,0.1,0.15,0.2),在保证间隙原子浓度的情况下,显著提升了材料的电导率,并使得功率因子大幅度提高,最终优化了热电性能。在873K时,Ca9Zn4.35Cu0.15Sb9的热电优值达到了 0.72,是未掺杂前Ca9Zn4.5Sb9的两倍。之后我们又选择了原子半径更大的Ag原子来进行掺杂,得到了一系列化合物Ca9Zn4.5-xAgxSb9(x=0.05,0.1,0.15,0.2),并对其进行了相应热电性质的测试,最终也优化了热电性能。3、阳离子"尺寸效应"对Ca9Zn4+xSb9化合物热电性质的影响为了继续研究阳离子掺杂对Ca9Zn4+xSb9结构化合物热电性质的影响,我们选择用尺寸更大的Eu原子来取代部分Ca。在后续对其进行的霍尔性能测试中发现,载流子浓度随着Eu掺杂浓度的增加略微减小,但是迁移率显著增大的趋势更加明显。这也表明在阳离子位置掺杂半径更大的Eu,有利于间隙原子位置"容纳"更多的Zn原子,这点可以由掺杂后变大的晶胞参数来证实,而间隙原子位置中更多的Zn,带来了迁移率的明显提高。在后续的电学性质及热学性质的测试中,也得到了相符的变化规律。在测试的基础上,通过对其有效质量及洛伦兹常数等的计算,进一步对其物理性质进行了研究。最终综合考虑了材料的各种相关性质,获得的Ca8.2Eu0.8Zn4.5Sb9热电材料,在873K时具有较高的热电优值ZT～0.81。4、几种新晶体的发现并对其热电性质进行研究我们采用金属助熔剂法通过在YbAgSb中掺杂稀土元素引入缺陷,得到了两种新的晶体,并通过单晶衍射确定其结构式为Yb1.76La0.24Ag1.79Sb2和Yb1.67Ce0.33Ag1.74Sb2。根据其元素比例,采用高温熔炼炉的方法快速而又方便地制得了一系列新的化合物Yb0.85RE0.15Ag0.85Sb(RE=La,Ce,Pr,Nd,Sm),并对对其行了热电性质测试,Yb0.85Ce0.15Ag0.85Sb的ZT值在1023K时达到0.4。经过分析得知,是由于该体系化合物的载流子浓度过高,所以为了降低p型掺杂半导体的载流子浓度,继续在Yb的位置上掺入Ca,得到一系列新的化合物Yb0.85-xCaxCe0.15Ag0.85Sb(x=0.1,0.2,0.3,0.4,0.5,0.6),并提升了材料的热电性能。
[Abstract]:Contains pnicogen (fifteenth main group) of the compound, due to its large number of exhibit structural type is very rich and diverse properties, have been widely researched. Due to environmental pollution, energy shortages and other problems intensified, waste heat can be converted into electrical energy thermoelectric materials recycling by people gradually attention to and the development of.Zintl phase compounds because of the crystal and electronic structure of the complex, is considered to be a potential thermoelectric material. This paper carried out the Zintl phase of 9-4-9 system and 1-1-1 system structure and thermoelectric material preparation, structure and performance optimization of.1, synthesis and thermoelectric properties of Ca9Zn4+xSb9 compounds with Ca9Zn4+xSb9 structure the 9-4-9 system has a large compound, single cell and complex crystal structure, which has a lower lattice thermal conductivity, and show good thermoelectric properties Through the method of inorganic solid matter. And we got the pure phase Ca9Zn4.5Sb9, the ZT value is about 0.37. In that test, high resistivity is the main reason to hinder its thermoelectric properties improve, so after work, we replace the electrical properties to enhance the material through the part, so as to get the.2 the thermoelectric properties better, Ca9Zn4+xSb9 complexes of Ca9Zn4+xSb9 were studied in order to change the position of interstitial doping, we choose to use Al instead of part of Zn atoms, and these compounds pure phase Ca9Zn4.5-xAl2x/ 3Sb9 (x=0,0.5,1), and then studied on the thermoelectric properties. Found in the system research. By replacing Zn atoms with Al, can increase the defect concentration gap position, system migration rate fell sharply, the electric conductivity of the materials is significantly reduced, is not conducive to the promotion. The thermoelectric properties Experimental analysis and theoretical calculation, we further design and obtained the Cu doped compound Ca9Zn4.5-xCuxSb9 (x=0.05,0.1,0.15,0.2), in order to ensure the interstitial concentration conditions, significantly improve the conductivity of the material, and the power factor is improved greatly, to optimize the thermoelectric properties. At 873K, ZT value reached 0.72 Ca9Zn4.35Cu0.15Sb9 that is two times larger than that of the undoped Ca9Zn4.5Sb9. Then we choose the atomic radius larger Ag atoms are doped, obtained a series of compounds Ca9Zn4.5-xAgxSb9 (x=0.05,0.1,0.15,0.2), and has carried on the corresponding thermal properties test, finally optimize the thermoelectric properties of.3. The effect of cationic "size effect" on thermoelectric properties Ca9Zn4+xSb9 compounds in order to continue to influence of cation doping on the structure of Ca9Zn4+xSb9 compound thermoelectric properties, we choose the larger size of the original Eu To replace Ca. Holzer found in the performance test for subsequent, the carrier concentration with the increase of Eu doping concentration decreased slightly, but significantly increased the migration rate trend is more obvious. It also shows that the larger cation sites in the radius of doped Eu, is conducive to the clearance of atomic positions "accommodating" more Zn atoms. This can be changed by doping after the cell parameters of the confirmed and interstitial position more Zn, brought increased mobility. The electrical properties and thermal properties of the follow-up tests, also obtained consistent. On the basis of test, through the calculation of the effective mass and Lorenz constant, further the physical properties were studied. Finally considering the various properties of materials, Ca8.2Eu0.8Zn4.5Sb9 thermoelectric materials obtained, ZT is high in 873K when the value of ZT to 0 .81.4, several new crystals were studied by us found in YbAgSb doped rare earth metal flux method by introducing defects on the thermoelectric properties, two new crystals were obtained, and the structural formula of Yb1.76La0.24Ag1.79Sb2 and Yb1.67Ce0.33Ag1.74Sb2. according to the proportion of elements by single crystal diffraction determined by method of high temperature smelting furnace and quickly got to form a series of new compounds Yb0.85RE0.15Ag0.85Sb (RE=La, Ce, Pr, Nd, Sm), and the line of the thermoelectric properties test, Yb0.85Ce0.15Ag0.85Sb ZT value reached 0.4. after analysis showed that in 1023K, is due to the high carrier concentration of compound system, so in order to reduce the carrier concentration of P type doped semiconductor to continue, the incorporation of Ca in the position of Yb, obtained a series of new compounds Yb0.85-xCaxCe0.15Ag0.85Sb (x= 0.1,0.2,0.3,0.4,0.5,0.6), and enhance the material. The thermoelectric properties of materials.

【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB34

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