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 ZT_max 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, I_L, 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.