Low thermal conductivity and thermoelectric properties of Si80Ge20 dispersed Bi2Sr2Co2Oy ceramics

Bi2Sr2Co2Oy is a thermoelectric material with low thermal conductivity. The Bi2Sr2Co2Oy/Si80Ge20 composite samples were prepared by solid phase sintering at high temperature to investigate the effects of Si80Ge20 alloys as the second phase on the microstructure and thermoelectric properties of the fabricated composites. An appropriate amount of the dispersed Si80Ge20 in the Bi2Sr2Co2Oy matrix can reduce the resistivity of the composite successfully. In particular, the increase in phonon scattering caused by the second phase leads to a significant decrease in thermal conductivity, which improves the thermoelectric properties of the material significantly. At 923 K, the thermal conductivity of the Bi2Sr2Co2Oy + 0.2 wt% Si80Ge20 sample achieves an ultralow value of 0.58 W/K·m. Its corresponding optimal dimensionless thermoelectric figure of merit value is 0.36, which is 56% higher than that of the pure Bi2Sr2Co2Oy sample.