Design of High‐Performance Cubic N‐Type AgBiSe2 Guided by Metavalent Bonding Mechanism

Abstract

AbstractAgBiSe2 undergoes two structural transitions in its service temperature range. Increasing entropy by alloying is considered an effective solution for modulating phase transition, but the efficacy of increasing entropy is limited by solubility and the selection of alloying components depends on trial and error. This study first confirmes that trigonal AgBiSe2 is metavalently bonded and searches metavalent PbTe as the alloying material based on the 2D map spanned by quantitative chemical bonding descriptors of electrons transferred (ET) and electrons shared (ES). The large solubility can be explained by the same bonding mechanism. PbTe alloying successfully stabilizes cubic AgBiSe2 to room temperature. Further, by optimizing the carrier concentration, the average ZT value from 300 to 773 K of (AgBiSe2)0.7(PbTe)0.3Cu0.02 reaches 0.42, which is 40% higher than that of pristine AgBiSe2. Simultaneously, heavy alloying leads to solid solution strengthening with enhanced hardness. This study not only paves the way for practical applications of AgBiSe2‐based materials but also provides an effective strategy for screening potential alloying candidates to solve the structure‐transition issue from the viewpoint of chemical bonding.