Ultralow thermal conductivity via topological network control of vibrational localization in amorphous chalcogenides (original) (raw)
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Nature Communications, 2021
Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10 ± 0.01 W m−1 K−1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower f...
Nature Communications, 2020
Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS3, despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomi...
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The thermal transport in amorphous/crystalline silicon superlattices with means of molecular dynamics is presented in the current study. The procedure used to build such structures is discussed. Then, thermal conductivity of various samples is studied as a function of the periodicity of regular superlattices and of the applied temperature. Preliminarily results show that for regular amorphous/crystalline superlattices, the amorphous regions control the heat transfer within the structures. Secondly, in the studied cases thermal conductivity weakly varies with the temperature. This, points out the presence of a majority of non-propagating vibrational modes in such systems.
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We present a theoretical study of the thermal conductivity ͑͒ of amorphous silicon ͑a-Si͒ based on molecular and lattice dynamics. We find that the majority of heat carriers are quasi-stationary modes; however the small proportion ͑Ӎ3%͒ of propagating vibrations contributes to about half of the value of . We show that in bulk samples the mean free path of several long-wavelength modes is on the order of microns; this value may be substantially decreased either in thin films or in systems with etched holes, resulting in a smaller thermal conductivity. Our results provide a unified explanation of several experiments and show that kinetic theory cannot be applied to describe thermal transport in a-Si at room temperature.
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Journal of Non-crystalline Solids, 2022
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arXiv (Cornell University), 2023
Materials with low thermal conductivity usually have complex crystal structures. Herein we experimentally find that a simple crystal structure material AgTlI 2 (I4/mcm) owns an extremely low thermal conductivity of 0.25 W/mK at room temperature. To understand this anomaly, we perform in-depth theoretical studies based on molecular dynamics simulations and anharmonic lattice dynamics. We find that the unique atomic arrangement and weak chemical bonding provide a permissive environment for strong oscillations of Ag atoms, leading to a considerable rattling behavior and giant lattice anharmonicity. This feature is also verified by the experimental probability density function refinement of single-crystal diffraction. The particularly strong anharmonicity breaks down the conventional phonon gas model, giving rise to non-negligible wavelike phonon behaviors in AgTlI 2 at 300 K. Intriguingly, unlike many strongly anharmonic materials where a small propagative thermal conductivity is often accompanied by a large diffusive thermal conductivity, we find an unusual coexistence of ultralow propagative and diffusive thermal conductivities in AgTlI 2 based on the thermal transport unified theory. This study underscores the potential of simple crystal structures in achieving low thermal conductivity and encourages further experimental research to enrich the family of materials with ultralow thermal conductivity.
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