Bond weakening and strong anharmonicity driven ultralow thermal conductivity in monolayer CdIn2Se4

Abstract

Two-dimensional (2D) materials with ultralow lattice thermal conductivity (kl) are crucial for high-efficiency thermoelectrics. Herein, we investigate the thermal transport properties of monolayer CdIn2Se4 using first-principles calculations combined with the phonon Boltzmann transport equation. An exceptionally low kl of 0.28 W m−1 K−1 is predicted at 300 K. This ultralow kl originates from the synergistic effect of strong lattice anharmonicity and weakened chemical bonds. The strong anharmonicity induces intense phonon scattering, and an extremely strong intraband and interband scattering in the out-of-plane acoustic branch is identified beyond expectation, leading to extremely short phonon relaxation times. Chemical bonding analysis reveals that the filling of antibonding states below the Fermi level weakens the Se–Cd bonds, which significantly reduces the phonon group velocities. Further scattering channel analysis confirms that the strong acoustic–acoustic and acoustic–optical phonon scatterings are the key factors suppressing kl. Our findings not only pinpoint the dual origins of ultralow kl in a promising 2D thermoelectric material but also provide a mechanistic framework for designing materials with engineered thermal transport properties.