摘 要

利用Seebeck效应和Peltier效应实现的热能和电能之间的相互转换，在余热回收和热电制冷等领域有着巨大的应用前景。IV族碲化物(PbTe，SnTe，GeTe)半导体，是具有良好性能的中温(400-700 K)热电材料。GeTe合金作为IV-VI族化合物中的一种，虽然ZT值在0.5左右，但基本无毒性，也不会造成环境污染。GeTe合金具有NaCl型晶体结构，Te元素比较容易挥发，提供了空穴载流子，这些载流子不仅使得GeTe合金具有良好的电导率，同样，Ge空位也会降低其晶格热导率，这使得GeTe合金可以成为通过掺杂改善其热电性能的一种潜在热电材料，目前有关GeTe化合物掺杂Mn的热电材料的研究和报道不多。因此，使用一种能精确控制化合物的化学计量比、高效节能、低成本的制备工艺来制备Ge_1-xMn_xTe成为研究者关注的热点。

本论文针对Ge_1-xMn_xTe热电化合物研究存在的上述问题，以Ge_1-xMn_xTe热电化合物为研究对象，尝试采用熔融退火法结合等离子活化烧结(PAS)技术制备单相Ge_1-xMn_xTe热电材料，同时研究退火工艺对Ge_1-xMn_xTe热电性能的影响，并确定最佳合成工艺。在此基础上研究了不同Mn掺量对Ge_1-xMn_xTe材料热电性能的影响规律。得出如下结论：

Mn掺杂对退火三天的Ge_1-xMn_xTe化合物微结构和热电输运特性的研究表明：当x≤0.09时能制备出单相的Ge_1-xMn_xTe，此时Mn的掺入Ge的位置。当x≥0.12时会出现GeMnTe₂相。从EPMA二次电子像可以看出单相样品的微观形貌没有随着掺杂产生明显的变化。Mn掺杂的样品电导率随温度升高而降低，Seebeck系数随温度的升高而升高。所有样品的Seebeck系数均为正值，显示为p型传导。大于600 K时，Ge_1-xMn_xTe的功率因子均低于GeTe，且在该温度范围内功率因子随着掺杂量的增大而降低。化合物的热导率随着温度的升高逐渐减小，在780 K时该样品x=0获得最大的ZT值1.24。

对单相Ge_1-xMn_xTe和有稳定第二相GeMnTe₂的试样，退火时间对其相组成影响很小；对x=0.12的试样，退火促使Mn析出第二相GeMnTe₂；对于x=0.21的试样，退火三天使Mn析出第三相MnTe₂，退火七天又会使MnTe₂渗入基体。

关键词：Ge_1-xMn_xTe化合物；Mn掺杂；熔融退火法；等离子活化烧结；热电性能

Abstract

With the Seebeck effect and the Peltier effect, the conversion between heat and electricity have great prospects in the recovery of waste heat and the application of thermoelectric refrigeration. Telluride MTe(PbTe, SnTe, GeTe) semiconductors have good performance at medium temperature (400-700 K). As a IV-VI compound, GeTe alloy have a ZT value of ~0.5, but it’s non-toxic and does not cause environmental pollution. GeTe alloy has NaCl type crystal structure, Te element is relatively volatile, provides hole carrier. Not only these carrier makes GeTe alloy has a good electrical conductivity, also the Ge vacancy will reduce its lattice thermal conductivity. These make the GeTe alloy become a potential thermoelectric material through doping to improve its thermoelectric performance. currently about Mn-doped GeTe thermoelectric material is researched and reported not more. Therefore, using a precise control of the compound of stoichiometry, energy efficient, low cost of preparation to prepare the Ge_1-xMn_xTe becomes the focus of researchers.

This paper is aimed at the problem of Ge_1-xMn_xTe thermoelectric compound study mentioned above, decide Ge_1-xMn_xTe thermoelectric compounds as the research object, try using melting and annealing combined with Plasma Activated Sintering(PAS) to prepare the single phase Ge_1-xMn_xTe thermoelectric materials, and study the effect of annealing process on thermoelectric properties of Ge_1-xMn_xTe, and determine the best process. Based on these, research on the effect of Mn content on the thermoelectric properties of Ge_1-xMn_xTe materials were studied. Draw the following conclusions:

For the Ge_1-xMn_xTe annealed for 3 days, the research on the microstructure and the thermoelectric transport properties shows that the single phase Ge_1-xMn_xTe can be prepared when x≤0.09, while Mn are incorporated into Ge position. When x≥0.12 GeMnTe₂ phase occurs. EPMA secondary electrons photos show that morphology of the microstructure of the single phase material is not significantly changed with the increasing doping. With the increasing temperature, the electrical conductivity of Mn-doped samples decreases, and the Seebeck coefficient increases. The Seebeck coefficient of all the samples are positive, appears as a p-type conduction. At the temperature above 600 K, the power factor of Ge_1-xMn_xTe is lower than GeTe. And in this temperature range, power factor decreases as the doping increases. The thermal conductivity decreases with increasing temperature. The sample x=0 gains the highest value of ZT at 780 K, which is about 1.24.

For the single phase Ge_1-xMn_xTe and the samples with stable second phase GeMnTe₂, annealing time had little effect on their phase composition; for the sample x=0.12, annealing will cause the second phase GeMnTe₂; for the sample x=0.21, annealing for 3 days will cause the third phase MnTe₂, annealing for 7 days will lead to the infiltration of the MnTe₂ phase.

Key Words：Ge_1-xMn_xTe compound；Mn-doping；melting and annealing；Plasma Activated Sintering(PAS)；thermoelectric properties

目 录

第1章 绪论 1