热电材料可以实现热能和电能之间的直接转换，而且热电材料的使用不受限于使用环境，但是目前突出的问题是大多数传统热电材料转化效率低且含有有毒元素。近年来化石能源逐渐枯竭伴随着自然环境的恶化，如何利用自然含量丰富的资源以简便低成本的方式获取高转化效率的热电材料逐渐成为研究的重点。硒化锡（SnSe）是一种简单含量丰富且不含有毒元素的二元化合物，作为一种新发现的热电材料具有最高的热电优值ZT值，这主要来源于其自身存在的层状结构导致其具有极低的热导率，是近年来的研究热点。本文主要的研究工作是通过水热方法结合放电等离子烧结（SPS）制备出了纯相p型具有织构化特征的块体SnSe多晶，通过优化水热制备工艺，利用SnSe自身层状结构调节微观形貌，调控载流子浓度和迁移率等方法，来进一步提高热电性能。本文首先探索了水热法制备粉体SnSe，成功制备了纯相且存在取向性的二元SnSe化合物。根据SnSe多晶具有典型的层状结构，所以采用SPS烧结的方法制备块体SnSe多晶，分别在120℃，140℃和160℃水热温度下制备了粉体SnSe，SPS烧结成块体SnSe多晶，分别命名为SS120，SS140和SS160，分析了热电性能。结果显示块体SnSe多晶样品的载流子浓度得到大幅度提高并且随温度变化不明显，SS140块体样品载流子浓度最高达到2.58×1019 cm-3；温度低于500 K时，载流子迁移率主要由晶界势垒散射机制控制；SS140电导率最高达到62 Scm-1；SS160功率因子最高达到6.22 μWcm-1K-2。因为纳米尺寸晶粒显著降低了热导率，SS160最低热导率为0.45 Wm-1K-1，最高ZT值达到0.57。本文还研究了在水热过程中通过改变NaOH加入量对烧结后块体SnSe多晶微观形貌和热电性能的影响。结果发现不同NaOH加入量制备的SnSe多晶都是纯相且存在一定取向性，增加NaOH加入量强烈的改变了粉体SnSe的微观形貌，块体SnSe多晶的电导率不断增加，最高值达到70.1 Scm-1。
Thermoelectric materials, a medium to convert heat and electricity directly, have attracted much attention in the modern society of energy crisis and natural environment deterioration. But most traditional thermoelectric materials have low conversion efficiency and contain toxic elements. High conversion efficiency thermoelectric materials with earth abundant elements through a simple and low cost way become the focus.Tin selenide (SnSe), a simple abundant binary compound without any toxic elements, is a promising thermoelectric material achieved the highest ZT, which caused by intrinsically ultralow lattice thermal conductivity due to layered structure, in the last few years. Here in this work p-type polycrystalline SnSe samples with high phase purity and enhanced texture were synthesized by a combination of hydrothermal synthesis and spark plasma sintering (SPS). The thermoelectric prosperities of SnSe were enhanced by the method of optimizing hydrothermal process, microstructure designing based on the layered structure of SnSe and optimizing the carrier concentration and the carrier mobility.At first, hydrothermal SnSe powders with purely phase and preferred orientation were synthesized. Fomer researches show that SnSe polycrystals exibit layered structure and to further investigate the thermoelectric properties SPS densification of the hydrothermal powders synthesized in different temperatures were conducted. Bulk samples denoted as SS120, SS140 and SS160 according to the preparation of the corresponding powders at different hydrothermal temperature of 120℃, 140℃ and 160℃. The carrier concentrations were greatly enhanced and have weak temperature dependence. SS140 sample reachs the maximum carrier concenctration of 2.58×1019 cm-3. The carrier transport below 500 K is mainly dominated by grain boundry potential barrier scattering. SS140 sample reaches the maximum electrical conductivity of 62 Scm-1. SS160 sample reaches the maximum power factor of 6.22 μWcm-1K-2. And lower thermal conductivity was obtained due to the nanograined structure. As a result, SS160 sample reaches the minimam thermal conductivity of 0.45 Wm-1K-1 and the maximum ZT value was 0.57.In addition, SnSe bulk samples were synthesized with different amount of sodium hydroxide (NaOH) in the hydrothermal process to investigate the microstructure and thermoelectric properties. The results show that in case of different amount of NaOH in the hydrothermal process the bulk samples were with purely phase and textured structure. The microstructure of bulk samples changed strongly gaining the amount of NaOH and the maximum electrical conductivity was 70.1 Scm-1.
