Enhanced thermoelectric properties of the Zintl phase BaGa2Sb2 via doping with Na or K

Na- or K-doped samples of Ba1-x(Na, K)(x)Ga2Sb2 were prepared by ball-milling followed by hot-pressing. The topological analysis of the electron density of BaGa2Sb2 implies a polar covalent nature of the Sb-Ga bonds in which the Sb atoms receive the electrons transferred from Ba rather than the Ga atoms. Successful doping of BaGa2Sb2 with Na or K was confirmed with combined microprobe and X-ray diffraction analysis. Alkali metal doping of BaGa2Sb2 increased the p-type charge carrier concentration to almost the predicted optimum values (similar to 10(20) h(+) cm(-3)) needed to achieve high thermoelectric performance. With increasing alkali metal concentration, electronic transport was shifted from non-degenerate semiconducting behaviour observed for BaGa2Sb2 to degenerate one for Na- or K-doped compounds. Overall, the thermoelectric figure of merit, zT, values reached up to similar to 0.65 at 750 K, considerably higher than the undoped sample (zT similar to 0.1 at 600 K), and a slight improvement relative to previously reported Zn-doped samples (similar to 0.6 at 800 K).