Si基和Ge基笼合物热电材料的高压制备和性能优化

发布时间：2018-01-03 15:24

本文关键词：Si基和Ge基笼合物热电材料的高压制备和性能优化　出处：《吉林大学》2017年博士论文　论文类型：学位论文

【摘要】：本论文采用高温高压制备技术成功制备了系列Si基和Ge基笼合物热电材料,深入研究了合成压力、微观组织结构和掺杂对该体系热电材料电声输运性质的影响机制。主要研究成果如下:(1)在3GPa,840℃的压力和温度条件下,首次采用Ba(N_3)_2和Si在高温高压下的化学反应成功制备出常压方法难易制备的Ⅰ型Si基笼合物Ba_8Si_(46),发现其具有超导特性,超导转变温度Tc=8.3K;另外,在相同的合成条件下,我们以Ba Si2和Si为初始原料,也成功制备出了Ⅰ型Si基笼合物Ba_8Si_(46)。(2)采用高温高压制备技术成功制备了系列Cu掺杂的Si基笼合物热电材料Ba8Cux Si46-x(x=1,2,3,4,5)。随着Cu掺杂量的增加,合成样品的Seebeck系数和功率因子显著提高。进一步,我们在3GPa的合成压力下成功制备了不同Ge掺杂量的系列Cu、Ge双掺杂块体Si基笼合物热电材料Ba_8Cu_5Ge_(8x) Si_(41-8x)(x=0,1,2,3)。研究发现,随着Ge元素掺杂量的增加,合成样品的Seebeck系数大幅度提高,热导率明显降低,ZT值显著提高。其中Ba_8Cu_5Ge_(24)Si_(17)样品的最大Seebeck系数达到-141.2μV/K@673K,最小热导率为0.91Wm~(-1)K~(-1)@573K,最大ZT值为0.42@673K。(3)研究了合成压力对高温高压制备的Cu、Ge双掺杂Si基笼合物热电材料Ba_8Cu_5Ge_(24)Si_(17)电声输运性质的影响机制。研究发现,在5GPa的合成压力范围内,随着合成压力的升高,合成样品的电阻率明显降低;同时,随着合成压力的升高,样品中的纳米晶、位错、晶格扭曲、黑白条纹等微观结构显著增多,声子散射增强,热导率明显降低,5GPa压力下合成的样品获得了最低热导率0.76Wm~(-1)K~(-1)@573K。4GPa压力下合成的样品获得最大ZT值0.55@673K。(4)在不同合成压力(2GPa,3GPa,4GPa,5GPa)条件下成功制备出ZT值大于1的高性能n-型块体多晶Ge基笼合物热电材料Ba_8Ga_(16)Ge_(30)。研究发现,高温高压合成的该体系样品内部存在多尺度的微纳米结构,如纳米球、局域非晶区、晶格畸变(位错、晶格局部扭曲等),有效增强了声子散射,降低了材料的热导率。另外,随着合成压力的升高,所合成样品的电阻率显著降低,功率因子明显增大。在5GPa压力下合成的Ba_8Ga_(16)Ge_(30)样品获得最大ZT值1.14@773K,这比常压下合成的同类样品ZT值提高了大约30%。综上研究表明,高温高压制备技术可成功制备出常压方法难易制备的具有多尺度微观组织结构的Si基和Ge基笼合物热电材料,并部分截获其高温高压下的优异热电性能。
[Abstract]:In this paper, a series of Si based and Ge based clathrate thermoelectric materials prepared by technology successfully prepared by high temperature high pressure system, in-depth study of the synthesis of pressure, structure and doping microstructure lose influence mechanism of the transport properties of the system thermoelectric materials electro acoustic. The main results are as follows: (1) in 3GPa, 840 DEG C and pressure the temperature conditions, for the first time by using Ba (N_3) type Si base cage _2 and Si chemical reaction was successfully prepared under high temperature and high pressure pressure method difficult preparation of complexes of Ba_8Si_ (46), has found that the superconducting properties, the superconducting transition temperature Tc=8.3K; in addition, the synthesis conditions of the same. We use Ba Si2 and Si as the raw material, but also successfully prepared type Si based clathrates Ba_8Si_ (46). (2) to prepare a series of Cu doped Si based cage complexes Ba8Cux Si46-x thermoelectric materials were successfully prepared by high temperature high pressure system (x=1,2,3,4,5). With the increase of the concentration of Cu and synthetic samples Seebeck coefficient and power factor is improved significantly. Further, we in the synthesis of 3GPa under pressure for Cu series of different amount of Ge doped by Ge double doped Si based clathrate thermoelectric materials Ba_8Cu_5Ge_ (8x) Si_ (41-8x) (x=0,1,2,3). The study found that with the increase of Ge element doping amount Seebeck, greatly improve the coefficient of synthetic samples, the thermal conductivity decreased significantly, ZT increased significantly. The Ba_8Cu_5Ge_ (24) Si_ (17) Seebeck coefficients of the samples reached -141.2 mu V/K@673K, the minimum thermal conductivity is 0.91Wm~ (-1) K~ (-1) @573K, the maximum ZT value of 0.42@673K. (3) studied the synthesis the pressure of high temperature and high pressure produced by Cu, Ge double doped Si based clathrate thermoelectric materials Ba_8Cu_5Ge_ (24) Si_ (17). The influence mechanism of the transport properties of electro acoustic. The study found that in the synthesis of 5GPa pressure range, with the increase of synthesis pressure, the resistivity of synthetic samples decreased significantly; at the same time, with the Increased synthesis pressure, nanocrystalline, samples of dislocations, lattice distortion, black and white striped microstructure significantly increased, enhanced phonon scattering, thermal conductivity decreased, samples synthesized under the pressure of 5GPa for the low conductivity of 0.76Wm~ (-1) K~ (-1) @573K.4GPa samples synthesized under pressure to obtain the maximum value of ZT 0.55@673K. (4) under different synthesis pressure (2GPa, 3GPa, 4GPa, 5GPa) under the conditions of preparation of high performance ZT value is greater than 1 n- of bulk polycrystalline Ge based clathrate thermoelectric materials Ba_8Ga_ (16) Ge_ (30). The study found that micro nano structure has multi scale internal high pressure synthesis the system samples, such as nanoparticles, localized amorphous region, lattice distortion (dislocations, lattice distortion, local) effectively enhance the phonon scattering, reducing thermal conductivity. In addition, with the increase of synthesis pressure, the resistivity of the samples decreased significantly, the power factor is increased obviously. Under the pressure of 5GPa synthesis of Ba_8Ga_ (16) Ge_ (30) ZT samples to obtain the maximum value of 1.14@773K, the synthesis of similar samples than under normal pressure and ZT value increased by about 30%. in conclusion, high temperature and high pressure preparation technology can be successfully prepared by atmospheric pressure method easily prepared with multi-scale micro structure Si based and Ge based clathrate thermoelectric materials, and excellent thermoelectric properties to intercept the part under high temperature and pressure.

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

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