Thermoelectric figure of merit of bulk FeSi_2-Si_(0.8)Ge_(0.2) nanocomposite and a comparison with β-FeSi_2

摘要

Among various thermoelectric (TE) materials, iron disilicide (FeSi_2) has relatively low cost and non-toxic characteristics which make it appropriate for large scale applications. To enhance the dimensionless figure of merit (ZT) of this material, a composite of FeSi_2-Si_(0.8)Ge_(0.2) with high fraction of α-FeSi_2 was prepared by mechanical alloying and sintering. The process was followed by thermal annealing to transform α to β phase FeSi_2 through a slow peritectoid reaction (several hours). The thermoelectric properties were significantly improved upon the completion of the phase transformation. At temperatures above 900 ℃, FeSi_2 component rapidly changed from β to α phase (several minutes) leading to sudden increase of the thermal conductivity. For comparison, the thermoelectric alloy of β-FeSi_2 was prepared through a similar process. The effect of sintering conditions and annealing time were studied and a comparison was drawn between the thermoelectric properties of β-FeSi_2 and FeSi_2-Si_(0.8)Ge_(0.2) nanocomposite. Overall, (FeSi_2)_(0.75)(Si_(0.8)Ge_(0.2))_(0.25) showed 170% enhancement in ZT compared with β-FeSi2 making it suitable for medium to high temperature applications (500 ℃ -850 ℃).