Simultaneous suppression and temperature-driven crossover of particle-like and wave-like thermal transport in trigonal CsAg3S2
Abstract
The simultaneous suppression of particle-like (κp ) and wave-like (κc) thermal transport channels in crystalline materials remains a challenging problem, as reducing one channel can enhance the other. Here, we investigate the thermal transport in trigonal PBar3m1 CsAg3S2 using self-consistent phonon theory with cubic and quartic anharmonicity and the unified theory of thermal transport. Our calculations predict an ultralow lattice thermal conductivity of 0.222 W m−1 K−1 at 300 K, featuring simultaneously low κp and κc with a weak temperature dependence of ∼T−0.42, which deviates significantly from the conventional ∼T−1 behavior. This simultaneous suppression arises from localized Cs modes, which enhance anharmonic scattering, and the softer Ag-S framework, which reduces phonon group velocities, together suppressing κp, in conjunction with sparse, well-separated high-frequency S-derived optical modes that suppress κc by limiting the coherent coupling between the phonon modes. Furthermore, the dominant transport channel exhibits a temperature-dependent crossover, with κp contributing ∼74 \% of total lattice thermal conductivity at 300~K and κc contributing ∼63 \% at 700~K. Combining the ultralow thermal conductivity with electrical transport calculated within the momentum relaxation time approximation (MRTA), we obtain a ZT of 1.28 for n-type doping at 700 K. The present work not only clarifies the microscopic mechanism of ultralow thermal conductivity in trigonal CsAg3S2 but also identifies the covalent M-Ch framework modification within the AM3Ch2 family of ternary chalcogenides as an additional tuning parameter for further reducing κp within the bonding-hierarchy design principle.
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BibTeX
@misc{gusain2026simultaneous,
title = {{Simultaneous suppression and temperature-driven crossover of particle-like and wave-like thermal transport in trigonal CsAg$_3$S$_2$}},
author = {Vivek Gusain and B K Mani},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35360},
eprint = {2610.35360},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35360},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Simultaneous suppression and temperature-driven crossover of particle-like and wave-like thermal transport in trigonal CsAg_3S_2
AU - Vivek Gusain
AU - B K Mani
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.35360
UR - https://arxiv.org/abs/2610.35360
AB - The simultaneous suppression of particle-like (κ_p ) and wave-like (κ_c) thermal transport channels in crystalline materials remains a challenging problem, as reducing one channel can enhance the other. Here, we investigate the thermal transport in trigonal PBar3m1 CsAg_3S_2 using self-consistent phonon theory with cubic and quartic anharmonicity and the unified theory of thermal transport. Our calculations predict an ultralow lattice thermal conductivity of 0.222 W m^−1 K^−1 at 300 K, featuring simultaneously low κ_p and κ_c with a weak temperature dependence of ∼T^−0.42, which deviates significantly from the conventional ∼T^−1 behavior. This simultaneous suppression arises from localized Cs modes, which enhance anharmonic scattering, and the softer Ag-S framework, which reduces phonon group velocities, together suppressing κ_p, in conjunction with sparse, well-separated high-frequency S-derived optical modes that suppress κ_c by limiting the coherent coupling between the phonon modes. Furthermore, the dominant transport channel exhibits a temperature-dependent crossover, with κ_p contributing ∼74 \% of total lattice thermal conductivity at 300~K and κ_c contributing ∼63 \% at 700~K. Combining the ultralow thermal conductivity with electrical transport calculated within the momentum relaxation time approximation (MRTA), we obtain a ZT of 1.28 for n-type doping at 700 K. The present work not only clarifies the microscopic mechanism of ultralow thermal conductivity in trigonal CsAg_3S_2 but also identifies the covalent M-Ch framework modification within the AM_3Ch_2 family of ternary chalcogenides as an additional tuning parameter for further reducing κ_p within the bonding-hierarchy design principle.
ER -