Cooperative Suppression Strategy for Dual Thermal Transport Channels in Crystalline Materials

TL;DR

This paper introduces a new structural design principle combining heavy-light and soft-stiff motifs to simultaneously suppress particle-like and wave-like phonon transport, achieving ultralow thermal conductivity in crystalline materials.

Contribution

It presents a novel 'heavy-light and soft-stiff' structural motif for reducing thermal conductivity by suppressing both phonon transport channels, supported by first-principles calculations and high-throughput screening.

Findings

Identified Tl4SiS4 and Tl4GeS4 as materials with ultralow thermal conductivity in both channels.

Demonstrated hierarchical phonon spectrum induced by the structural motif.

Proposed a 1D chain model to generalize the phonon suppression mechanism.

Abstract

We propose a novel design principle for achieving ultralow thermal conductivity in crystalline materials via a "heavy-light and soft-stiff" structural motif. By combining heavy and light atomic species with soft and stiff bonding networks, both particle-like ($\kappa_p$) and wave-like ($\kappa_c$) phonon transport channels are concurrently suppressed. First-principles calculations show that this architecture induces a hierarchical phonon spectrum: soft-bonded heavy atoms generate dense low-frequency modes that enhance scattering and reduce $\kappa_p$, while stiff-bonded light atoms produce sparse high-frequency optical branches that disrupt coherence and lower $\kappa_c$. High-throughput screening identifies Tl$_4$SiS$_4$ ($\kappa_p$ = 0.10, $\kappa_c$ = 0.06 W/mK) and Tl$_4$GeS$_4$ ($\kappa_p$ = 0.09, $\kappa_c$ = 0.06 W/mK) as representative candidates with strongly suppressed transport in both channels. A minimal 1D triatomic chain model further demonstrates the generality of this mechanism, offering a new paradigm for phonon engineering beyond the conventional $\kappa_p$-$\kappa_c$ trade-off.