Development of the discrete electric power-generator from exhaust or waste heat sources using ecologically friendly semiconductors

利用垂直布里奇曼法在石英、氧化铝、SiNx涂层石英、CVD热解石墨、CVD碳化硅涂层石墨等材料中生长了镁硅晶体，以减少生长过程中熔体的反应和粘结。同量结晶来自化学计量比的镁硅熔体，非化学计量比熔体产生不均匀结晶，镁硅比为85：15、70：30和60：40。用X射线衍射和电子探针对生长样品进行了表征从室温到773K测量了它们的Seebeck系数和电导率，并计算了它们的功率因数。从化学计量比熔体中获得的样品的Seebeck系数为-470 mV/K，而从镁硅比为70：30的不均匀熔体中获得的样品在373K时的最高功率因数为1.1×10-5W/cmK2。使用热解石墨和碳化硅涂层石墨等石墨基熔体使生长的晶体中含有碳，导致Seebeck系数和电导率增加。

Mg2Si, an ecologically friendly semiconductor, is a promising thermoelectric material at temperatures ranging 'rom 500 to 800 K.Mg2Si crystals were grown by the vertical Bridgman method in various crucibles made of quartz, alumina, SiNx-coated quartz, CVD pyrolytic graphite, CVD SiC-coated graphite in order to minimize the reaction and sticking of molten Mg-Si during growth.Congruent crystallization was derived from a stoichiometric melt of Mg2Si and incongruent crystallization was derived from nonstoichiometric melts having Mg : Si ratios of 85 : 1 5, 70:30, and 60:40.Grown samples were characterizedby x-ray diffraction and electron-probe microanalysis, and their power factors were calculated from the Seebeck coefficients and electrical-conductivities measured from room temperature to 773 K.The grown crystals were single crystal and showed n-type conductivity in undoped condition. A sample derived from a stoichiometric melt had a Seebeck coefficient of -470 mV/K, while the highest power factor, 1.1x10-5 W/cmK2 at 373 K, was obtained for the sample derived from an incongruent melt with an Mg : Siratio of 70:30.The use of the graphite based crucibles such as pyrolytic and SiC coated graphites caused the carbon incorporati in the grown crystals, resulting in an increase in the Seebeck coefficient and the electrical conductivity.