Symmetry-Breaking Amplifies Lone Pair Expression and Orbital Splitting for Promising Chain-Like Thermoelectrics
Shulin Bai, Yixuan Hu, Shaoping Zhan, Tian Gao, Bingchao Qin, Li‐Dong Zhao
Abstract
The relative impact of electronic instability and quantum confinement on lattice dynamics and transport properties remains elusive. Here, we demonstrate that the influence of lone-pair electrons (LPEs) expression on phonon dissipation surpasses that of dimensional reduction using a quasi-low-dimensional Pb-Sn-S-Se system as a prototype. We experimentally observe that quasi-one-dimensional (1D) PbSnS 3 exhibits higher thermal transport than quasi-two-dimensional (2D) PbSnS 2, attributed to the loss of LPEs. Therefore, we attempt a symmetry-breaking strategy to amplify the expression of LPEs in 1D-Pb 2 Sn 2 S 5 Se. Using first-principles calculations and Boltzmann transport theory, we reveal that amplified LPEs expression in 1D-systems induces more diffuson-like vibrations, as well as enhanced Umklapp and Normal processes. Moreover, phase transition and thermal transport analysis in 2D-PbSnS 2 reveals a stronger correlation between LPEs expression and phonon dissipation compared to the 1D-systems, regardless of variations on structure symmetry and dimension. Apart from the LPEs expression amplification, the symmetry-breaking strategy substantially facilitates orbital splitting in 1D-systems, leading to effective electron-phonon decoupling for promising thermoelectric efficiency. Consequently, our proposed strategy can be extended to optimize other quasi-low-dimensional systems containing LPEs, offering novel physical and chemical insights into the design of advanced thermoelectrics and thermal management materials.