Abstract
Al-doped higher manganese silicides (HMS), MnSi1.75-δ:Alx were synthesized by solid state reaction and hot pressing. Through X-ray diffraction analysis of the synthesized HMS, the optimum conditions for solid state reaction were determined to be 1273 K for 6 h. Phase fractions of HMS with compositional variation (δ) had no significant difference, but the MnSi1.75:Al0.005 specimen had the highest fraction of HMS at approximately 98.36%. All specimens showed p-type conduction at all temperatures examined, and exhibited degenerate semiconductor characteristics, in that the electrical conductivity decreased and the Seebeck coefficient increased with increasing temperature. Al doping shifted the onset temperature of intrinsic conduction to higher temperature. Thermoelectric figure of merit (ZT) of HMS increased with increasing temperature, and further improvement was achieved by Al doping. The maximum ZT was obtained as 0.41 at 823 K for MnSi1.73:Al0.005.
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