Simultaneous optimization of power factor and thermal conductivity via charge transfer effect and enhanced scattering of phonons in Si80Ge20P1/CoSi2 composites

Abstract

SiGe based alloy is a promising medium-high temperature thermoelectric material that has been applied in the field of aerospace exploration. So far, utilizing the second phase to promote the scattering of phonons is a common way to improve the thermoelectric performance of SiGe based alloy, but this often deteriorates the electrical properties. In this study, the Si₈₀Ge₂₀P₁/CoSi₂ composites have been prepared by mechanical alloying and spark plasma sintering, and the content of cobalt silicide (CoSi₂) nanoparticles have been manipulated. Since the CoSi₂ nanoparticles possess higher carrier concentration and smaller work function than the Si₈₀Ge₂₀P₁ matrix, the carrier concentrations of composites have been pushed up due the charge transfer effect. Meanwhile, the formation of nano-sized phase interfaces and stacking faults in the composites has enhanced the scattering of low-frequency phonons. As a result, the optimal power factor of 3.41 mW⋅m⁻¹⋅K⁻² and thermal conductivity of 2.29 W⋅m⁻¹⋅K⁻¹ have been achieved, and the corresponding zT reaches up to 1.3 in the Si₈₀Ge₂₀P₁+0.5% CoSi₂ (in mole) composite at 873 K. This work provides a new idea for developing the performance of SiGe based alloy.