铌镧共掺钛酸锶陶瓷的制备及热电性能的研究

发布时间：2018-05-05 20:00

本文选题：氧化物 + 简并　；参考：《内蒙古工业大学》2017年硕士论文

【摘要】：近年来,随着工业化的快速发展,能源危机、环境污染等问题日益严峻,如何高效清洁的使用能源逐步得到了人们广泛的关注。热电材料作为一种很有潜力的新型清洁能源转换材料,能够将热能直接转化为电能,且具有无运动部件、安全可靠、不排放燃烧污染物等优点。在n型氧化物热电材料中,钛酸锶(SrTiO_3)是被认为最具有应用潜力的热电材料,但目前钛酸锶基氧化物热电材料的热电性能还较低,不足以达到应用水平,因此针对钛酸锶基氧化物热电材料热电性能提高的研究成为了国内研究的热点。本论文中主要以环境友好型钛酸锶基氧化物热电材料作为主要研究对象,计算了掺杂对能带结构和电子能态密度的影响,研究了不同烧结工艺和掺杂浓度对其热电传输性能的影响,进一步完善了热电体系。具体研究成果如下:1)通过第一性原理计算发现,Nb掺杂浓度越大,体系形成能越大,因而掺杂也越困难,可以通过调整Nb和La掺杂比例来有效的降低掺杂难度。通过对能带结构和态密度分析发现,掺杂后Nb的SrTiO_3体系费米能级进入了导带,掺杂体系变为简并半导体,提高了电导率。2)实验结果表明:水热法制备的铌镧共掺钛酸锶粉体为纳米粉体,通过SEM和TEM分析发现粉体颗粒为片状,平均粒径为15~25 nm。3)经过对热压烧结法制备SrTiO_3陶瓷工艺的探索发现,在烧结时间为2 h,烧结压力为25 MPa,烧结温度为1300℃的条件下能够获得较高的热电性能。4)研究通过热压烧结法制备的铌镧双掺SrTiO_3陶瓷时发现,在所有样品中La10Nb10样品具有高的功率因子,在560 K时达到1.3 mWm-1K-2。La10Nb20样品由于其具有非常低的热导率,在1050 K时低至1.9 Wm-1 K-1,因而得到最高的ZT值0.3。5)对比不同烧结法制备钛酸锶陶瓷的热电输运性质,发现冷压埋烧法制备的SrTiO_3陶瓷得到了较高的ZT值,其中的La10Nb10样品在1050 K时达到0.6,这是目前SrTiO_3块材中的最高值;热压烧结法制备的SrTiO_3陶瓷ZT值并不高,都低于冷压埋烧法;冷压埋烧法制备的SrTiO_3陶瓷晶粒比热压烧结法的小,有利于降低热导率。
[Abstract]:In recent years, with the rapid development of industrialization, energy crisis, environmental pollution and other problems increasingly severe, how to use energy efficient and clean has been gradually paid attention to. As a new type of clean energy conversion material, thermoelectric materials can convert heat energy directly into electric energy, and it has no moving parts, safe and safe. In the n oxide thermoelectric materials, strontium titanate (SrTiO_3) is considered as the most potential thermoelectric material, but at present, the thermoelectric properties of the strontium titanate oxide thermoelectric materials are still low, and the thermoelectric properties of the strontium titanate oxide thermoelectric materials are improved. In this paper, the research focuses on the environment friendly strontium titanate oxide thermoelectric materials as the main research object. The influence of doping on the band structure and the electron state density is calculated. The effects of different sintering processes and doping concentration on the thermoelectric transmission properties are studied, and the thermoelectric system is further perfected. The specific research results are as follows: 1) through the first principle calculation, it is found that the larger the Nb doping concentration is, the greater the formation energy is, the more difficult the doping is, the more difficult it is to reduce the doping degree by adjusting the proportion of Nb and La doping. By analyzing the band structure and the density of States, the Fermi level of the SrTiO_3 system after doping Nb is entered into the guide band. The doping system becomes degenerate semiconductor and improves the conductivity.2. The experimental results show that the lanthanum lanthanum Co doped strontium titanate powder prepared by hydrothermal method is nanometer powder. Through SEM and TEM analysis, the powder particles are flake and the average particle size is 15~25 nm.3). The discovery of the preparation of SrTiO_3 ceramics by hot pressing sintering method is found to be 2 h in the sintering time. When the sintering pressure is 25 MPa and the sintering temperature is 1300 C, the high thermoelectric performance.4 can be obtained. It is found that the La10Nb10 samples in all samples have high power factor in all samples, and the samples of 1.3 mWm-1K-2.La10Nb20 at 560 K have a very low thermal conductivity at the time of 560 K. Rate, low to 1.9 Wm-1 K-1 at 1050 K, thus getting the highest ZT value 0.3.5) to compare the thermoelectric transport properties of strontium titanate ceramics prepared by different sintering methods. It was found that the SrTiO_3 ceramics prepared by the cold compression method obtained a higher ZT value, and the La10Nb10 sample reached 0.6 at 1050 K, which is the highest value in the current SrTiO_3 block; hot pressing sintering method. The ZT value of the prepared SrTiO_3 ceramics is not high, which is lower than the cold pressing method, and the SrTiO_3 ceramics prepared by the cold compression method are smaller than the hot press sintering method, which is beneficial to the reduction of thermal conductivity.

【学位授予单位】：内蒙古工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ174.1

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