Chemical Pressure‐Driven Three‐ and Four‐Phonon Scattering in SnTe: Toward Suppressed Lattice Thermal Conductivity and Enhanced Thermoelectric Performance

Abstract Thermoelectric efficiency of SnTe is constrained by high lattice thermal conductivity. This study demonstrates that chemical pressure, engineered via Pb substitution, suppresses phonon propagation by amplifying lattice anharmonicity. Raman and Brillouin spectroscopy reveals that chemical pressure enhances four‐phonon scattering and reduces optical and acoustic phonon lifetimes, while density functional theory (DFT) calculations correlate these effects with a more diffuse phonon dispersion, a broadened phonon density of states, and a distinct 3 THz spectral feature. These modifications elevate three‐ and four‐phonon scattering rates and expand the scattering phase space, reducing lattice thermal conductivity to 0.6 W m −1 K −1 . The resultant peak zT of 1.3 at 873 K underscores chemical pressure as a potent phonon‐engineering strategy. Notably, it is revealed that chemical pressure predominantly mimics the “pressure” effect on phonon dynamics through comparative analysis with physically pressurized SnTe, establishing a universal strategy for thermoelectric optimization by tailoring anharmonic lattice dynamics, with implications for advancing high‐performance energy conversion materials.