[Paper Review] Anharmonic lattice dynamics study of phonon transport in layered and molecular-crystal indium iodides

Takuma Shiga, Yoshikazu Mizuguchi+1 more|arXiv (Cornell University)|Jan 5, 2026

Thermal properties of materials0 citations

TL;DR

The paper uses first-principles anharmonic lattice dynamics to quantify phonon transport in InI and low-pressure InI3, finding ultralow lattice thermal conductivities (<1 W/mK) with distinct roles for particle-like and wave-like phonon transport across compositions and high-pressure phases.

ABSTRACT

Indium iodides, which adopt layered or molecular-crystal-like arrangements depending on composition, are expected to exhibit low lattice thermal conductivity because of their heavy constituent atoms and weak In-I bonding. In this work, we employed first-principles anharmonic lattice dynamics calculations to systematically investigate phonon transport in indium iodides from particle- and wave-like perspectives. The calculated lattice thermal conductivities of both materials remained below 1 W/m-K over a broad temperature range. Notably, the influence of wave-like phonon transport differed by composition: in InI3, the wave-like contribution became comparable to the particle-like Peierls contribution, whereas it remained negligible in InI. We also investigated the thermal transport properties of the experimentally reported high-pressure phase of InI3. Motivated by experimental indications of stacking faults and partial disorder in indium site occupancy within the rhombohedral phase, we constructed several ordered structural models with different stacking sequences. These stacking sequences exhibited no significant energetic preference and had similar lattice thermal conductivities, suggesting that in-plane thermal transport is largely governed by the vibrational properties of the In2I6 layers themselves rather than by the specific stacking sequence. These findings provide insight into phonon transport in layered and molecular-crystal systems with structural complexity and contribute to a broader understanding of thermal transport mechanisms in layered and molecular-crystal-like materials.

Motivation & Objective

• Investigate phonon transport mechanisms in layered InI and molecular-crystal-like InI3 from particle- and wave-like perspectives.
• Quantify lattice thermal conductivities and phonon lifetimes using anharmonic lattice dynamics with three- and four-phonon scatterings.
• Assess the impact of high-pressure phases and stacking disorder in InI3 on thermal transport.
• Explore how in-plane vibrational properties of In2I6 layers govern thermal transport in high-pressure phases.

Proposed method

• Perform DFT optimizations with optB88-vdW corrections for InI and low-pressure InI3.
• Compute harmonic IFCs with Phonopy and include nonanalytic corrections for LO-TO splitting.
• Solve the Peierls–Boltzmann transport equation in the single-mode RTA, including three- and four-phonon scatterings and phonon–isotope scattering.
• Estimate four-phonon contributions via a sampling-based approach to reduce computational cost.
• Apply third- and fourth-order IFCs using specified cutoffs (NN interactions for 4th order; 3rd-order radii 5.5 Å for InI, 4.3 Å for InI3).
• Evaluate wave-like contributions to κ using interband tunneling formalism and compare to κPB.

Experimental results

Research questions

• RQ1 What are the lattice thermal conductivities of InI and low-pressure InI3 across a broad temperature range?
• RQ2 How do particle-like (κPB) and wave-like (κC) phonon transport contributions compare for InI and InI3, and how do they depend on composition and temperature?
• RQ3 How does high-pressure InI3 with various ordered stacking models affect phonon transport and thermodynamic properties?
• RQ4 Is the in-plane thermal transport of high-pressure InI3 dominated by In2I6 layer vibrations, and how does monolayer behavior compare to bulk/heavy-stack structures?

Key findings

• κtot for InI and low-pressure InI3 remains well below 1 W m−1 K−1 over a wide temperature range.
• For InI, κC (wave-like) is about 10% of κPB (particle-like) and does not dominate temperature trend deviations, with τ generally exceeding the Ioffe–Regel limit.
• Low-pressure InI3 exhibits strong anharmonicity where including four-phonon scattering reduces lifetimes and κ by roughly a factor of five compared to three-phonon only results; κC becomes comparable to κPB above ~270 K.
• High-pressure InI3 models (R̄3, P̄31c, P312, P̄31m) are energetically similar (differences <30 meV per f.u.) and yield similar in-plane κtot and spectral features, suggesting stacking sequence plays a minor role in-plane heat transport.
• An isolated In2I6 monolayer shows in-plane κtot ~0.6 W m−1 K−1 at 300 K, with four-phonon scattering significantly influencing τ and emphasizing layer-intrinsic vibrational properties over stacking alone.
• Overall, stacking confinement within layers and weak interlayer interactions can stabilize phonon modes and influence thermal transport in these complex layered/molecular-crystal systems.