Size effect of Si O 2 on enhancing thermoelectric properties of Cu 1.8 S

Polycrystalline Cu 1.8 S composites dispersed with nanoscale (∼50 nm) and microscale (∼200 µm) SiO 2 were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) method. The average grain size of the host Cu 1.8 S bulk is refined from 700 nm to about 500 and 50 nm by dispersing micro‐ and nano‐SiO 2 along with a fragmented SiO 2 particle itself from the raw size of 200 µm and 50 nm to 2 µm and 20 nm, respectively. The Seebeck coefficient increases by dispersing SiO 2 particles in the whole measuring temperature interval and reaches the peak value 88 µV K −1 at 623 K for the nano‐SiO 2 dispersed sample. The thermal conductivity κ ranges from 1.14 to 1.54 W m −1  K −1 by raising the temperature from 323 to 623 K for the nano‐SiO 2 dispersed sample, which is lower than that of pure Cu 1.8 S owing to the strong phonon scattering. The micro‐SiO 2 dispersed sample has a high κ , ranging from 1.6 to 2.2 W m −1  K −1 at the same temperature range due to the large intrinsic κ of micro‐SiO 2 particles. A maximum thermoelectric figure of merit value of 0.28 was attained at 623 K in the nano‐SiO 2 dispersed sample.