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High-efficiency thermoelectric conversion is achieved by using materials with a maximum figure of merit Z = S2σ/κ, where S is the Seebeck coefficient, and σ and κ are the electrical conductivity and thermal conductivity, respectively, over a wide temperature range. Lead telluride alloys were some of the first materials investigated and commercialized for generators; however, their full potential for thermoelectrics has only recently been revealed to be greater than commonly believed. The maximal value of Z, as a function of electron density, is attained only for a specific location of the Fermi level EF relative to the conduction band edge EC. A systematic study of structural, microstructural, and thermoelectric properties of bulk PbTe doped with indium is presented. Samples were prepared by the pulsed electric current sintering technique. The high dimensionless figure of merit ZT ≈ 0.8 over 200–500 °C temperature range for PbTe doped with 0.05–0.1 at. % of In was obtained. Moreover, ZT is practically the same for Pb0.9995In0.0005Te and Pb0.99In0.01Te compounds at high temperature. Therefore, indium dopant in PbTe stabilizes the optimal location of the Fermi level. The effect of the negative process of indium diffusion into the matrix during the long service time of the TE generator could be avoided by doping heavily with indium the hot side of n-type functionally graded PbTe:In leg.
Parashchuk et al. (Tue,) studied this question.