Abstract
The broad-based implementation of thermoelectric materials in converting heat to electricity hinges on the achievement of high conversion efficiency. Here we demonstrate a thermoelectric figure of merit ZT of 2.5 at 923 K by the cumulative integration of several performance-enhancing concepts in a single material system. Using non-equilibrium processing we show that hole-doped samples of PbTe can be heavily alloyed with SrTe well beyond its thermodynamic solubility limit of <1 mol%. The much higher levels of Sr alloyed into the PbTe matrix widen the bandgap and create convergence of the two valence bands of PbTe, greatly boosting the power factors with maximal values over 30 μW cm−1 K−2. Exceeding the 5 mol% solubility limit leads to endotaxial SrTe nanostructures which produce extremely low lattice thermal conductivity of 0.5 W m−1 K−1 but preserve high hole mobilities because of the matrix/precipitate valence band alignment. The best composition is hole-doped PbTe–8%SrTe.
Highlights
The broad-based implementation of thermoelectric materials in converting heat to electricity hinges on the achievement of high conversion efficiency
The efficiency of a thermoelectric material is defined by the figure of merit ZT 1⁄4 S2sT/k 1⁄4 S2sT/(kel þ klat), where S is the Seebeck coefficient, s is the electrical conductivity, T is the temperature and k is the thermal conductivity that is comprised of an electronic part and a lattice part
We show that via a non-equilibrium route that involves rapid ice water quenching of the 1,423 K melt followed by annealing at 873 K we can produce hole-doped samples that achieve a 5 mol% solubility of SrTe in bulk PbTe
Summary
The broad-based implementation of thermoelectric materials in converting heat to electricity hinges on the achievement of high conversion efficiency. Band structure (Supplementary Fig. 3) similar to that obtained by molecular beam epitaxy[18,19], which further supports the effectiveness of non-equilibrium synthesis in producing a high degree alloying fraction of SrTe in PbTe. By fitting the lattice parameter as a function of SrTe content (on the basis of Vegard’s law) one can conclude that the achieved solubility limit of SrTe in these samples is around 5 mol%.
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