Microstructures and thermoelectric properties of Fe0.92Mn0.08Six alloys prepared by rapid solidification and hot pressing

Iron disilicide based thermoelectric materials Fe0.92Mn0.08Six (1.9⩽x⩽2.5) were prepared by rapid solidification (melt spinning) and hot uniaxial pressing at 1248 K with 50 MPa for 30 min, followed by annealing at 1073 K for 20 h. X-ray diffraction and scanning electron microscopy showed excess silicon phase for samples with x⩾2.1, and both the configurations and the amounts of secondary silicon particles varied with an increase in x. Hall measurements carried out at room temperature showed that the carrier concentrations for Fe0.92Mn0.08Six (1.9⩽x⩽2.5) were between 2.6×1018 and 5.6×1018 cm−3. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured from room temperature to 973 K. It was found that a little excess silicon in the sample, x=2.1, enhanced the Seebeck coefficient weakly, but was effective for decreasing the thermal conductivity. A maximum figure of merit, ZT=0.17, was obtained for Fe0.92Mn0.08Si2.0 at 973 K.