Host-guest crystalline materials with strong anharmonicity exhibiting long-range order and local disorder offer a paradigm for ideal thermoelectric model known as the “phonon-glass electron-crystal” (PGEC), which ensures efficient electrical conduction characteristic of crystals while suppressing thermal transport in a glasslike manner. It is widely accepted that guest atoms introduce low-frequency low-lying optical phonons (referred to as rattling modes), which intensely scatter the acoustic phonons, thereby drastically reducing lattice thermal conductivity (${\kappa }_L$). In quasi-one-dimensional (Q-1D) thermoelectrics, this mechanism is conceptualized as covalent 1D chains forming the host framework, with isolated interchain ions acting as charge-balancing rattlers to further dampen ${\kappa }_L$. However, our first-principles studies of the Q-1D perovskite $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$ reveal that the covalent 1D chains serving as host frames also produce low-lying optical phonons, which introduce additional three-phonon scattering channels. Utilizing self-consistent phonon theory and Wigner transport formalism, we capture phonon frequency renormalization and wavelike coherent scattering. This approach uncovers an ultralow ${\kappa }_L$ with weak temperature dependence, consistent with the results from homogeneous nonequilibrium molecular dynamics. Furthermore, based on a low-order expansion of electron-phonon coupling, we estimate a thermoelectric figure of merit $\mathit{ZT}$ up to 0.53 (0.92) at 300 (425) K for $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$. Notably, we identify the low-lying optical branches originating from the antiparallel sliding of the host 1D chains, offering additional phonon scattering channels for damping phonon transport. These findings offer new microscopic insights into Q-1D thermoelectric transport and provide a viable material platform and a design scheme to explore PGEC behavior in anisotropic systems.

Close

PrevNext

View figure in article

• Anharmonic lattice dynamics
• Lattice thermal conductivity
• Phonons
• 1-dimensional systems
• Thermoelectrics
• Density functional theory
• First-principles calculations