Thermoelectric properties of Sc- and Y-doped Mg2Si prepared by field-activated and pressure-assisted reactive sintering

Highlights: → Yttrium and scandium-doped Mg2Si (Sc: 1000-4000 ppm and Y: 1000-3000 ppm) was fabricated by the FAPAS process. → The incorporation of Sc and Y into Mg2Si resulted in an increase in the lattice parameter up to 2500 ppm for Sc and 2000 ppm for Y. → The addition of these elements resulted in a smaller grain size relative to pure Mg2Si. The average grain size of Mg2Si doped with 2000 ppm Y was 1.5-2 μm. → The thermoelectric properties of the RE-doped Mg2Si were improved relative to that of the pure silicide. - Abstract: Sc- and Y-doped-Mg2Si samples were reactively sintered by the field-activated and pressure-assisted synthesis (FAPAS) method. The incorporation of these rare-earth elements in this silicide resulted in an n-type semiconductor. The addition of Sc and Y had no discernable effect on the lattice constant of Mg2Si. The average grain size of the Y-doped Mg2Si was about 2 μm, which was smaller than that of the sintered pure Mg2Si. The power factor of samples doped with 2500 ppm Sc was consistently higher than that of pure Mg2Si in the temperature range of 300-550 K. Similarly, the power factor of 2000 ppm Y doped Mg2Si samples was higher than that of pure Mg2Si over the temperature range of 300-675 K; the highest value being about 2.2 x 10-3 W m-1 k-2 at 468 K. This value is about two times that of the undoped Mg2Si at the same temperature. The thermal conductivity of Mg2Si doped with 2000 ppm Y was 80% of that of pure Mg2Si. The highest figure of merit (ZT) for the Y doped (2000 ppm) samples was 0.23 at 600 K which was higher by a factor of 1.6 than the corresponding value of pure Mg2Si at the same temperature. The results demonstrate the benefits of doping of Mg2Si with Sc and Y in enhancing its thermoelectric properties.