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

Abstract

A series of Zintl compounds Mg3Bi2-xPnx (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 (ρ), Seebeck (α) 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 ~1019 cm−3 to ~1020 cm−3 as the Bi content is increased. The Hall mobility decreases with increasing temperature (T) and reaches a more or less similar value (~45 cm2/V s) for all substituted compositions at room temperature. Due to mass defect scattering, the lattice thermal conductivity (κL) is decreased to a minimum of ~1.2 W/m K in Mg3BiSb. The power factor (α2/ρ) is found to be rather low and falls in the range 0.38 mW/m K2 to 0.66 mW/m K2. As expected, at a high temperature of 825 K, the total thermal conductivity (κ) of Mg3BiSb reaches an impressive value of ~1.0 W/m K. The highest dimensionless figure of merit (ZT) is realized for Mg3BiSb and is ~0.4 at 825 K.