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Abstract:
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).
