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.

GeTe, as a p-type semiconductor, has been intensively studied in recent years as a promising lead-free midtemperature-range thermoelectric (TE) material. Herein, we report an improved energy conversion efficiency (η) using a two-step TE properties optimization in Mn−Sb co-doped GeTe by engineering electronic structure and lattice dynamics. Mn−Sb co-doping enhances the TE properties of GeTe, as evidenced from both experiments and first-principles-based theoretical calculations. The density functional theory (DFT) calculations indicate that Mn−Sb co-doping improves the band convergence and optimizes the Fermi level position. This in turn helps in enhancing the Seebeck coefficient (α). As a result of the optimized Seebeck coefficient and electrical conductivity (σ), an enhanced power factor (α 2 σ) is obtained for the Mn−Sb co-doped system. Moreover, a significant reduction in the phonon (lattice) thermal conductivity (κ ph ∼ 0.753 W/mK) at 748 K is observed for Ge 0.87 Mn 0.05 Sb 0.08 Te, attributed to the point-defect scattering and reduced phonon group velocity. The synergistic improvement in α and reduction in κ ph result in a maximum figure-of-merit (zT) of 1.67 at 773 K, with an average zT (zT av ) of ∼ 0.9 for Ge 0.87 Mn 0.05 Sb 0.08 Te over a temperature range of 300−773 K, leading to an η of ∼12.7%.

Lead telluride is one of the most attractive state-of-the-art thermoelectric (TE) materials. Therefore, any improvement of its average thermoelectric figure of merit (ZT)av over a broad temperature range is a...

In this work, we show the simultaneous enhancement of electrical transport and reduction of phonon propagation in p-type PbTe codoped with Tl and Na. The effective use of advanced electronic structure engineering improves the thermoelectric power factor S 2 σ over the temperature range from 300 to 825 K. A rise in the Seebeck coefficient S was obtained due to the enhanced effective mass m*, coming from the Tl resonance state in PbTe. Due to the presence of additional carriers brought by Na codoping, electrical conductivity became significantly improved. Furthermore, Tl and Na impurities induced crystal lattice softening, remarkably reducing lattice thermal conductivity, which was confirmed by a measured low speed of sound v m and high internal strain Cε XRD . Eventually, the combination of both the attuned electronic structure and the lattice softening effects led to a very high ZT value of up to ∼2.1 for the Pb 1−x−y Tl x Na y Te samples. The estimated energy conversion efficiency shows the extraordinary value of 15.4% (T c = 300 K, T h = 825 K), due to the significantly improved average thermoelectric figure of merit ZT ave = 1.05. This work demonstrates that the combination of impurity resonance scattering and crystal lattice softening can be a breakthrough concept for advancing thermoelectrics.