Unveiling a Novel, Cation-Rich Compound in a High-Pressure Pb-Te Binary System

Because of the common oxidation states of group IV elements (+2 or +4) and group VI elements (-2), 1:1 and 1:2 are two typical stoichiometries found in the IV-VI compounds. Particularly, in the Pb-Te binary system, the 1:1 stoichiometric PbTe is believed to be the only stable compound. Herein, using evolutionary algorithms, density functional theory, a laser-heated diamond anvil cell, and synchrotron X-ray diffraction experiments, we discovered a novel Pb-Te compound with an unexpected stoichiometry of 3:2 above 20 GPa. This tetragonal Pb₃Te₂ is the one of the very few cation-rich compounds that has ever been discovered in the entire IV-VI binary system. Further analyses based on electron density distribution, electron localization function, and Bader charge have shown that this newly discovered compound has a mixed character of chemical bonding with a decreased ionicity. By further calculating the electron-phonon interaction, Pb₃Te₂ is predicted to exhibit a superconducting transition at low temperatures. The discovery of Pb₃Te₂ paves the way for further explorations of other novel cation-rich IV-VI group compounds.