Preparation of the composite thermoelectric materials with small particles dispersion by MA

Abstract

We have prepared the thermoelectric materials, where the small particles are dispersed in the matrix, by mechanical grinding (MG) or alloying (MA). Si and C powders were added to the p-type Fe 0.92 Mn 0.08 Si 2 or n-type Fe 0.98 Co 0.02 Si 2 powders, and they were mechanically milled followed by being hot-pressed. The amounts of the β-phase, ε-phase, α-SiC and C in the sintered samples depend on the amount of the added (Si+C) and Si/C molar ratio, which affect the values of the Seebeck coefficient and electrical resistivity of the samples. A lot of fine α-SiC particles around 20nm were dispersed in the samples, which decreases the thermal conductivity of the samples. The maximum figure of merit values appear at Si/C=1.5 for p-type Fe 0.92 Mn 0.08 Si 2 containing 4 mass% (Si+C) and Si/C=1.75 for n-type Fe 0.98 Co 0.02 Si 2. We have also prepared the CoSb 3 -FeSb 2 composite where the FeSb 2 particles are dispersed in the CoSb 3 matrix. The dispersed FeSb 2 particles contributed to decreasing the thermal conductivity and maintaining the moderate Seebeck coefficient and electrical resistivity of the samples. As a result, the composite whose molar ratio CoSb 3 /FeSb 2 is 0.7/0.3 and milling time is 25h has a maximum value of figure of merit of 6.1×10 −4 K −1 at 756K, which is much larger than that of 3.2×10 −4 K −1 for CoSb 3.