Size effect of SiO2 on enhancing thermoelectric properties of Cu1.8S

Polycrystalline Cu1.8S composites dispersed with nanoscale (approximate to 50nm) and microscale (approximate to 200 mu m) SiO2 were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) method. The average grain size of the host Cu1.8S bulk is refined from 700nm to about 500 and 50nm by dispersing micro- and nano-SiO2 along with a fragmented SiO2 particle itself from the raw size of 200 mu m and 50nm to 2 mu m and 20nm, respectively. The Seebeck coefficient increases by dispersing SiO2 particles in the whole measuring temperature interval and reaches the peak value 88 mu VK-1 at 623K for the nano-SiO2 dispersed sample. The thermal conductivity ranges from 1.14 to 1.54Wm(-1)K(-1) by raising the temperature from 323 to 623K for the nano-SiO2 dispersed sample, which is lower than that of pure Cu1.8S owing to the strong phonon scattering. The micro-SiO2 dispersed sample has a high , ranging from 1.6 to 2.2Wm(-1)K(-1) at the same temperature range due to the large intrinsic of micro-SiO2 particles. A maximum thermoelectric figure of merit value of 0.28 was attained at 623K in the nano-SiO2 dispersed sample.