Effect of vacancies on the thermoelectric properties of Mg2Si1-xSbx (0 ≤ x ≤ 0.1)

Mg2Si1-xSbx compositions with x ranging from 0 to 0.1 were prepared by induction melting and compacted by hot uniaxial pressing. The lattice parameter and the positional occupancy at the Mg site as a function of Sb substitution were calculated from Rietveld refinement. A monotonic increase in the a lattice constant value was observed with increasing Sb substitution. Also, a decrease in the Mg site occupancy was observed with increasing Sb substitution and was confirmed by energy dispersive analysis of x-ray measurements. Room temperature carrier concentration (n) measurements show an increase from 1.4 x 10(18) cm(-3) for x = 0 to 1.4 x 10(20) cm(-3) for x = 0.025 followed by a nearly constant n, indicating the influence of vacancy formation. Electrical conductivity (sigma), Seebeck coefficient (S), and thermal conductivity (kappa) values were measured from 300 to 773 K. The observed trends in the absolute values of sigma and S can be explained based on the vacancy formation at the Mg site which counteracts the doping influence of Sb. The kappa(L) (phonon component of the thermal conductivity) values show a significant decrease with increasing Sb substitution. Calculation of the thermoelectric figure of merit (ZT) shows a maximum ZT of 0.55 for x = 0.10 compared to a ZT of similar to 0.05 for x = 0.0.