High seebeck coefficient and low thermal conductivity in Bi and In co-doped GeTe thermoelectric material

Pure GeTe shows inferior thermoelectric performance due to the large carrier concentration caused by the intrinsic high concentration of Ge vacancies. In this study, we report improved thermoelectric performance of Bi and In co-doped GeTe based thermoelectric material where a figure of merit, ZT ∼ 1.7 at 623 K was realized through synergetic effect of tuning the carrier concentration, resonant states, and suppression of thermal conduction. In doping induces resonant states in the density of states near the Fermi energy level. Bi sharply reduces lattice thermal conductivity by formation of extensive solid solution point defects. Moreover, Bi and In co-doping decreases the phase transformation temperature to widen the better thermoelectric performance of cubic GeTe at low temperatures. In addition, microstructural characterization showed herringbone structures, high-density of domain boundaries, and twinning. These, together with the point defects, lead to a significantly reduced thermal conductivity.