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Study on Pressure Sintering of beta-FeSi_2 with highly Efficient Thermoelectric Properties

高效热电性能β-FeSi_2的压力烧结研究

基本信息

批准号：
06555266
负责人：
SHIMADA Masahiko
金额：
$ 8.64万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

beta-Fe_<1-x>Ru_xSi_2 solid solution was synthesized by solid state reaction at 1100ﾟC for 48h and subsequect annealing at 850ﾟC for 168h in an evacuated silica tube. Single phase solid solution was obtained in the composition range 0*x*0.1. The thermal stability range of the beta-phase extended to higher temperature region by partial substitution of Ru atom. The thermoelectric properties of Cr or Co-doped B-Fe_<1x>Ru_xSi_2 strongly depend on the sinthering conditions. The samples with optimum thermoelectric properties are obtaind by high-pressure sintering at 3 GPa and 800ﾟC for 1h. Seebeck coefficient for X-axis perpendicular to applied pressure was superior to that for Z-axis parallel to applied pressure. The anisotropy of electrical conductivity was opposite tendency comparing with the results of Seebeck coefficient. The optimum compositions are found to be Fe_<0.92>Ru_<0.05>Cr_<0.03>Si_2 and Fe_<0.92>Ru_<0.05>Co_<0.03>Si_2 for p-type and n-type materials, respectively. The power factors (sigmaalpha_2) of these materials are higher than that of beta-FeSi_2 based materials. The mechanism for the anisotropy of thermoelectric properties was examined. As a result, it is considered that the model of oriented-grain microstructure is most possible factor to introduce the anisotropy of thermoelectric properties. In this model, a very few amounts of impurities (FeSi, amorphous Si etc.) were located at grain boundaries. Both oriented-grains and impurities in microstructure play an important role to introduce the anisotropy of thermoelectric properties.

用1100ﾟC固相反应48h，然后在真空硅管中850ﾟC热处理168h，合成了β-Fe_&lt；1-x&gt；Ru_xSi_2固溶体。在成分为0*x*0.1的范围内，获得了单相固溶体。Ru原子的部分取代使β相的热稳定性范围向高温区扩展。铬或钴掺杂的B-Fe_&lt；1x&Gt；Ru_xSi_2的热电性能强烈地依赖于晶化条件。在3 GPa800ﾟC下高压烧结1h，可获得热电性能最佳的样品。垂直于外压的X轴的Seebeck系数优于平行于外压的Z轴的Seebeck系数。电导率的各向异性与Seebeck系数的结果相反。对于p型和n型材料，最佳成分分别为Fe_&lt；0.92&gt；Ru_&lt；0.05&gt；Cr_&lt；0.03&gt；Si_2和Fe_&lt；0.92&gt；Ru_&lt；0.05&gt；Co_&lt；0.03&gt；Si_2。这些材料的功率因数(σα_2)高于β-FeSi_2基材料。对热电性能各向异性的机理进行了探讨。因此，取向晶微结构模型是引入热电性能各向异性的最有可能的因素。在这个模型中，只有极少量的杂质(FeSi、非晶态Si等)。位于晶界。取向晶和显微组织中的杂质都是导致热电性能各向异性的重要因素。