Dual Alloying Strategy to Achieve a High Thermoelectric Figure of Merit and Lattice Hardening in p-Type Nanostructured PbTe

The introduction of an alkaline earth metal telluride as a second phase in PbTe can lead to very high thermoelectric figure of merit, ZT, as a result of hierarchical structuring, e.g., in the PbTe–SrTe system. However, there are two roadblocks to this strategy: poor solubility and occurrence of incoherent nanoprecipitates in the PbTe matrix, e.g., the PbTe–BaTe system. Here we demonstrate a dual alloying approach by simultaneously alloying CaTe and BaTe in the p-type PbTe matrix to achieve ZTmax ranging up to ∼2.2 at high temperatures. Synergistic enhancement of the Seebeck coefficient via favorable band convergence gives rise to higher power factors up to 34 μW cm–1 K–2 and significant suppression of lattice thermal conductivity, κL, down to ∼0.6 W m–1 K–1 results from large multicenter phonon scattering. Additionally, co-inclusion of Ca and Ba causes unanticipated lattice hardening in otherwise brittle PbTe, essential for practical device applications.