Binrong Huang, Dasol Kim, Yuan Yu, Jinxuan Zhong, Jianbo Zhu, Yaoling Shen, Yu Guo, Moran Wang, Jiawei Huang, Tu Lyu, Nan Lin, Yongsheng Zhang, Matthias Wuttig, Lipeng Hu
Abstract Tailoring chemical bonds offers an innovative way to design materials for a wide range of applications. Metavalent bonding is conducive to excellent thermoelectric performance in p‐bonded chalcogenides with octahedral coordination. However, the requirement to form a bond through only a single p‐electron between adjacent atoms (half of an electron pair), such as in PbTe and Bi 2 Te 3 , limits the number of possible materials. Here, it is shown that the essence of metavalent bonding is a half‐filled single‐electron σ‐bond, which can also be formed with a significant s‐orbital contribution. This is illustrated for AgBiSe 2 , which crystallizes in three different phases: hexagonal, rhombohedral, and cubic. Quantum chemical calculations and bond‐breaking behavior reveal that all three octahedrally coordinated AgBiSe 2 phases utilize metavalent bonding. In addition, PbTe alloying is used to tune the chemical bonding and Br doping to optimize the carrier concentration. With these modifications, a record‐high zT max value of 1.1 is achieved in n‐type cubic (AgBiSe 2 ) 0.75 (PbTe) 0.25 −0.01BiBr 3 at 798 K. The understanding and tailoring of chemical bonds achieved in AgBiSe 2 can be easily extended to other AgVVI 2 compounds.