Anomalous high ZT above 2.2 in light element dominated compound Li4OTe due to low thermal conductivity

Thermoelectric materials usually contain heavy metal elements to ensure low lattice thermal conductivity κl. However, such elements like Pb, Bi and Sb have the expenses of high prices and potential risks of pollution. Herein, we propose a novel design strategy for thermoelectrics by constructing new light element dominated materials, such as quasi-antifluorite Li4OTe, with a high figure of merit surpassing 2.2. The introduction of O atom in Li4OTe crystal causes optical phonon softening and large phase space for three-phonon scattering processes, leading to much lower κl (<1 W m−1 K−1) than antifluorite Li2X (X=O, Te). This picture can be extended to other quasi-antifluorites, which will stimulate intense interests in the exploration of the light element dominated compounds, as new environmentally friendly and low-cost thermoelectric materials.