Development of environmental conservation type thermoelectric device of silicide compounds and their power generation modules

近年来，热电材料作为一种直接在热能和电能之间进行能量转换的技术而受到人们的关注，它可以利用低品位的能源，即中低温的余热。目前主要研究和应用的是Bi_2Te_3、CoSb_3和SiGe。然而，这些化合物是由有毒的、资源有限的和/或昂贵的元素组成的。因此，限制这些材料的应用，并在不久的将来控制这些材料的使用，以减少对环境的污染。本研究开发了由有毒元素和资源丰富元素组成的热电材料，并研究了掺杂剂对热电性能的影响。本研究得到的结果如下：1。在掺Al的Mg_2Si化合物中，对于标称Al含量为0.15 at%的样品，在856 K时获得了0.67×10^<-3> K^<-1>的最大优值。结果表明，Al掺杂Mg_2Si是中温范围热电能量转换的良好候选材料。Fe_2VAl_<0.95>Si_<0.05>化合物显示出较高的功率因数值3.1×10^<-3> Wm^<-1>K^<-2>。这一数值与在低温范围内被称为最佳热电材料的Bi_2Te_3相当。这表明在低温范围内，Si掺杂Fe_2VAl化合物是一种很好的候选热电材料。al掺杂Mg_2Si和Si掺杂Fe_2VAl化合物为n型。需要开发高效p型热电材料。

Recently, thermoelectric materials are attracted as an energy-conversion technology between thermal energy and electric energy directly, and are possible to utilize low-grade energy, i.e. waste heat at middle- and the low-temperature. At present, Bi_2Te_3, CoSb_3 and SiGe are principally investigated and applied. These compounds, however, are composed of poisonous, limit in resource, and/or expensive elements. Therefore, the application of these materials is restricted, and also the use of these materials will be controlled in the near future in order to the pollution abatement of environment. In this study, thermoelectric materials composed of atoxic and resource-rich elements were developed, and investigated the effect of the dopant on the thermoelectric properties. The results obtained in this study are as follows.1. In Al-doped Mg_2Si compounds, the maximum figure of merit of 0.67×10^<-3> K^<-1> was obtained at 856 K for the specimen with nominal Al content of 0.15 at%. The obtained figure of merit is comparable to that reported for Si-Ge, suggests that Al doped Mg_2Si is a good candidate material for thermoelectric energy conversion in the middle-temperature range.2. Fe_2VAl_<0.95>Si_<0.05> compound showed a high power factor value of 3.1×10^<-3> Wm^<-1>K^<-2>. This value is comparable that of Bi_2Te_3 known as the best thermoelectric materials in the low-temperature range. This suggests that Si doped Fe_2VAl compounds is a good candidate thermoelectric material in the low-temperature range.3. Al-doped Mg_2Si and Si doped Fe_2VAl compounds are n type. The development of highly efficiency p type thermoelectric materials is needed.