On the Thermoelectric Properties of Zintl Compounds Mg3Bi2-x Pn x (Pn = P and Sb)

A series of Zintl compounds Mg3Bi2-x Pn (x) (Pn = P and Sb) have been synthesized by the solid-state reaction method. While Sb can be substituted to a level as high as x = 1.0, P can be substituted only up to x = 0.5. The thermoelectric potential of these compounds has been evaluated by measuring resistivity (rho), Seebeck (alpha) and Hall coefficients, and thermal conductivity between 80 K and 850 K. The measured resistivity and Seebeck coefficient values are consistent with those expected for small-bandgap semiconductors. Hall measurements suggest that the carriers are p type with concentration (p) increasing from similar to 10(19) cm(-3) to similar to 10(20) cm(-3) as the Bi content is increased. The Hall mobility decreases with increasing temperature (T) and reaches a more or less similar value (similar to 45 cm(2)/V s) for all substituted compositions at room temperature. Due to mass defect scattering, the lattice thermal conductivity (kappa (L)) is decreased to a minimum of similar to 1.2 W/m K in Mg3BiSb. The power factor (alpha (2)/rho) is found to be rather low and falls in the range 0.38 mW/m K-2 to 0.66 mW/m K-2. As expected, at a high temperature of 825 K, the total thermal conductivity (kappa) of Mg3BiSb reaches an impressive value of similar to 1.0 W/m K. The highest dimensionless figure of merit (ZT) is realized for Mg3BiSb and is similar to 0.4 at 825 K.