Effects of precipitation treatment and oxygen dispersions on thermoelectric properties of CoSi

Abstract Effects of a precipitation treatment on the thermoelectric properties in a CoSi thermoelectric material are investigated by scanning and transmission electron microscopy. The Seebeck coefficient and electrical conductivity are explained based on electron-phonon scattering by considering relaxation time approximation and its electronical structure in the framework of the Boltzmann transport equation in the as-sintered (AS) sample fabricated by spark plasma sintering. A precipitation treatment at 1073 K for 30 min is applied to the AS sample. The high Seebeck coefficient and electrical conductivity are obtained, while low thermal conductivity is achieved by dispersing metallic Co2Si phases and insulating amorphous SiO2 nanoparticles in addition to small grain size of ≈3 μm due to enhancement in phonon scattering. The dispersion of the amorphous SiO2 is also beneficial in reducing the matrix grain size by the Zener drag.