Chemical bonding manipulation unlocks high performance ionic-bonded thermoelectrics

Developing a strategy to enhance the thermoelectric performance of ionic semiconductors is challenging because of the pronounced electron localization inherent to the bonding nature. Herein, we demonstrate a bond manipulation approach in ionic-bonded compound MnTe achieved by the introduction of diverse atomic species, which effectively delocalizes electrons and modifies phase composition, leading to a comprehensive optimization in thermoelectric performance. As a result, we realize a peak zT value of ~1.6 at 773 K and an average zT value of ~0.9 from 300 K to 773 K. In addition, this chemical bonding engineering induces bond softening and forms multiscale hierarchical structures, resulting in a significant reduction in lattice thermal conductivity. Consequently, the segmented module fabricated from this p-type MnTe-based material achieves a thermoelectric conversion efficiency of 11% at a temperature difference ∆T = 473 K. Our findings establish bond engineering as an effective paradigm for enhancing the thermoelectric performance of ionic compounds.