Thermoelectric figure of merit enhancement of intermetallic compound RuGa2 by ball-milling

• RuGa2 powder with the size ranged from 5 to 30 nm were obtained by ball-milling.
• The bulk samples of RuGa2 were synthesized by spark plasma sintering.
• The total thermal conductivity decreased by 31% using ball-milling at 300 K.
• The maximum dimensionless figure of merit was 0.58 at 773 K for milled RuGa2.

The effect of introducing a fine grain boundary using ball-milling to increase phonon scattering on the thermoelectric figure of merit of the binary semiconducting intermetallic compound RuGa2 has been investigated. The studied samples were synthesized by a combination of arc-melting, ball-milling, and spark plasma sintering (SPS). The average grain size of the bulk sample sintered by SPS from milled powder was 10–20 times larger than that of the original nanopowders, which ranged from 5 to 30 nm in size. The total thermal conductivity of the RuGa2, which had a grain size of more than 1 μm, decreased by 31% at room temperature after milling. The maximum dimensionless figure of merit, ZTmax, of milled RuGa2 was 0.58 at 773 K, a 7% and 16% enhancement on the value of 0.54 for unmilled RuGa2 and the highest reported value of 0.50, respectively. Further enhancement in ZT can be expected by preserving the size of the milled nanopowders.