Engineering Band Structure via the Site Preference of Pb2+ in the In+ Site for Enhanced Thermoelectric Performance of In6Se7

Although binary In-Se based alloys have in recent years gained interest as thermoelectric (TE) candidates, little attention has been paid to In6Se7-based compounds. Substituting Pb in In6Se7, preference for Pb2+ in the In+ site has been observed, allowing Fermi level (F-r) shift toward the conduction band, where the localized state conduction becomes dominant. Consequently, the Hall carrier concentration (n(H)) has been significantly enhanced with the highest n(H) value being about 2-3 orders of magnitude higher than that of the Pb-free sample. Meanwhile, the lattice thermal conductivity (kappa(L)) tends to be reduced as the n(H) value increases, owing to an increased phonon scattering on carriers. As a result, a significantly enhanced TE performance has been achieved with the highest TE figure of merit (ZT) of 0.4 at similar to 850 K. This ZT value is 27 times that of intrinsic In6Se7 (ZT = 0.015 at 640 K), which proves a successful band structure engineering through site preference of Pb in In6Se7 .