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Improvement of Thermoelectric Properties of Iron Disilicide by Plasma Processing and Its Relation with Microstructure

等离子体处理改善二硅化铁热电性能及其与微观结构的关系

基本信息

批准号：
07680534
负责人：
MIKI Toshikatsu
金额：
$ 1.47万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

To improve the thermoelectric figure-of-merit of FeSi_2 and SiGe ceramics, we have employed rf-plasma processing of micrograins prior to sintering. Either SiH_4 or GeH_4 were used as plasma gas for processing. The plasma processed grains were sintered by the ordinary method and the thermoelectric properties of the resultant ceramic specimens were measured. The experimental results are shown in the followings :(1) Plasma-processed ceramics shows electrical conductivity higher than non-processed ceramics. This conductivity increase occurs by either SiH_4 or GeH_4 plasma processing. The Hall measurements revealed that the conductivity increase is mainly due to the increase of carrier mobility.(2) Electron paramagnetic resonance study indicates that some paramagnetic centers are annihilated by plasma processing. The conductivity increase is probably due to the decrease of potential barrier height at grain boundaries.(3) In case of SiH_4 plasma processing, no significant change was oberved in thermal conductivity. However, GeH_4 plasma processing reduces the thermal conductivity.(4) The effect of plasma procesisng on Seebeck coefficient is somewhat complicated, but in most cases plasma processing increases the Seebeck.(5) The effects of plasma processing described above are observed not only for FeSi_2 but also SiGe ceramics.On the basis of these experimental results, we can summarize the effect of plasma processing on FeSi_2 and SiGe ceramics as follows.(1) Plasma processing and resulting microstructure modification improve the thermoelectric properties of FeSi_2 and SiGe ceramics by factor 2 or 3.(2) SiH_4 plasma processing is effective to the electrical conductivity improvement, but GeH_4 plasma processing primarily contributes to the decrease of thermal conductivity. Therefore, it is expected that plasma processing with suitably mixed SiH_4 and GeH_4 gases further improves the themoelectric properties.

为了提高FeSi_2和SiGe陶瓷的热电性能，我们在烧结前对微颗粒进行了射频等离子体处理。采用SiH_4或GeH_4作为等离子体气体进行处理。采用普通方法对等离子体处理后的晶粒进行烧结，并对所得陶瓷试样的热电性能进行了测量。实验结果表明：(1)等离子体处理陶瓷的电导率高于未处理陶瓷。这种电导率的增加发生在SiH_4或GeH_4等离子体处理中。霍尔测量表明，电导率的增加主要是由于载流子迁移率的增加。(2)电子顺磁共振研究表明一些顺磁中心被等离子体处理湮灭。电导率的增加可能是由于晶界势垒高度的降低。(3)在SiH_4等离子体处理下，导热系数没有明显变化。然而，GeH_4等离子体处理降低了热导率。(4)等离子体处理对塞贝克系数的影响比较复杂，但在大多数情况下，等离子体处理增加了塞贝克系数。(5)等离子体处理不仅对FeSi_2有影响，对SiGe陶瓷也有影响。根据这些实验结果，我们可以总结出等离子体处理对FeSi_2和SiGe陶瓷的影响如下：(1)等离子体处理和由此产生的显微结构改性使FeSi_2和SiGe陶瓷的热电性能提高了2或3倍。(2) SiH_4等离子体处理对电导率的提高是有效的，而GeH_4等离子体处理对电导率的降低起主要作用。因此，期望通过适当混合SiH_4和GeH_4气体的等离子体处理进一步改善热电性能。