Effective Electronic Mechanisms for Optimizing the Thermoelectric Properties of GeTe-Rich Alloys

Most of the recent methods for thermoelectric (TE) enhancement are focused on reduction of the lattice thermal conductivity values, with an only limited success on efficiency enhancement due to an improved electronic doping action. This is attributed partly to the correlation between the involved electronic properties, contradicting each other in terms of the TE efficiency, and partly to the difficulty of effectively doping such alloys in the optimal 10(19) cm(-3) carrier concentration range. Even a positive application of an optimal electronic doping level usually results in a narrow maximal figure of merit (ZT) values range, which is followed by an onset of an intrinsic conduction, degrading these values at higher temperatures. Here, a novel BiTe-and Cu-co-doping of GeTe is reported. Incorporation of Cu electron donors into GeTe-BiTe vacancies results in an effective compensation of the inherent high holes' concentration of GeTe toward the optimal range with pronounced carriers scattering mechanism of ionized impurities, in addition to the known acoustic phonons mechanism, while enhancing of Seebeck coefficient. Adverse high temperature intrinsic conduction effects are suppressed by the rhombohedral-to-cubic phase transition of GeTe, extending the maximal ZTs range of approximate to 1.55 +/- 0.1 over a large temperature range.