Strain-driven lone pair electron expression for thermal transport in BiCuSeO
Da Wan, Shulin Bai, Sirui Fan, Xiao Xiang, Zhen Li, Yu Liu, Peng Kang, Lei Zheng, Li‐Dong Zhao, Huibin Xu
Abstract
The stereochemical activity of lone-pair electrons critically influences lattice anharmonicity and thermal transport in crystals. However, traditional chemical substitution methods lack continuity and reversibility. We propose a strain-engineered bond angle distortion strategy in layered BiCuSeO to continuously modulate lone-pair electrons. Theoretically, tensile strain reduces the O-Bi-O bond angle, expands lone-pair electron spatial distribution, and decreases Bi-O bond charge overlap, intensifying Bi atom anharmonic vibrations. Furthermore, tensile strain induces reverse O atom vibrations and strong lattice dynamic disorder, lowering the phonon band gap and enhancing anharmonic phonon-phonon interactions and Umklapp scattering. Importantly, strain modulates lone-pair electron distribution and interaction strength without uniformly weakening long-range interatomic forces. As a result, 4% tensile strain reduces lattice thermal conductivity of BiCuSeO to 0.53 W/mK (54% decrease) at 300 K. This work establishes a multiscale framework linking strain, lone-pair electron behavior, and phonon dynamics, enabling robust and continuous control of thermal transport properties. This study shows that tensile strain continuously tunes lone-pair expression in BiCuSeO, increases lattice disorder and phonon scattering, and lowers thermal conductivity, offering an effective approach to control heat transport in materials.