Thermoelectric Transport Properties of RyFe3NiSb12 (RÂ =Â Ba, Nd and Yb)

To evaluate the influence of Ni substitution on electrical transport properties, the thermoelectric transport properties of the p-type skutterudites RyFe3NiSb12 (R = Ba, Nd and Yb) are systematically investigated from 2.5 K to 800 K. By carefully modifying the filling fractions of the three fillers, Ba, Nd and Yb, the carrier concentration is precisely adjusted, which changes proportionally to the nominal value calculated by valence counting rule. The carrier concentration dependences of mobility and Seebeck coefficient represent two band contribution in the valence band, and the optimized carrier concentration for thermoelectric performance is between (5-9) × 1020 cm−3. The lattice thermal conductivity of samples filled with rare-earth elements (Nd and Yb) are significantly lower as compared to Ba-filled, due to the lower resonant frequency and partial filling. Compared with Co substitution, Ni substitution tends to close the band gap, which results in heavier bipolar diffusion at high temperature for RyFe3NiSb12. However, due to the enhancement of the density of state, when the carrier concentrations are similar, RyFe3NiSb12 possess higher thermal power and thus higher power factor than RyFe2Co2Sb12 in the lower temperature range. A ZT value of 0.73 is obtained for Yb0.77Fe3NiSb12 at 600 K.