Microstructure and thermoelectric properties of WSi2-added CrSi2 composite

CrSi2-based composite materials with submicrometer-sized grains were fabricated by the powder metallurgical process using ball-milling and pulse-current sintering. By the solid-state reaction of submicrometer-sized fine powders of CrSi2 and WSi2 during the sintering, the composites consisting of Cr-rich hexagonal (Cr,W)Si2 phase and W-rich tetragonal (W,Cr)Si2 phase were obtained. The grain size of CrSi2 phase was effectively reduced by the WSi2 addition because of the suppression of grain growth during sintering. Thermal conductivity was then decreased with the WSi2 content by the enhancement of phonon scattering resulting from the reduction of grain size, the introduction of the CrSi2/WSi2 interface and the crystal lattice distortion induced by the W substitution for CrSi2 phase. Seebeck coefficient and electrical resistivity were also decreased due to the addition of metallic WSi2 phase and the deformation of CrSi2 electronic structure resulting from the W substitution. The WSi2 addition had then little effect on the thermoelectric power factor. Consequently, the thermoelectric figure-of-merit, ZT, was enhanced by the reduction of thermal conductivity and reached 0.3 around 700 K.