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1. Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides

   https://doi.org/10.1038/s41467-021-22999-z  

   Aryana, Kiumars; Stewart, Derek A.; Gaskins, John T.; Nag, Joyeeta; Read, John C.; Olson, David H.; Grobis, Michael K.; Hopkins, Patrick E. (December 2021, Nature Communications)

   Abstract 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 frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network. 

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2. Organic cross-linking decreases the thermal conductivity of calcium silicate hydrates

   https://doi.org/10.1016/j.cemconres.2023.107324  

   Moshiri, Amir; Morshedifard, Ali; Stefaniuk, Damian; El Awad, Santiago; Phatak, Tejasree; Krzywiński, Kamil J.; Rodrigues, Debora Frigi; Qomi, Mohammad Javad; Krakowiak, Konrad J. (December 2023, Cement and Concrete Research)

   We study the conductive heat transport through calcium silicate hydrate (C-S-H) and organically cross-linked C-S-H via experiments, micromechanical homogenization theory, and molecular simulations. We find that C-S-H's intrinsic thermal conductivity falls below its amorphous limit when cross-linked with short-chain organosilanes. The observed reduction correlates with the alkyl chain length of the bis-organosilane molecule. To understand the underlying fundamental molecular processes accountable for such a reduction, we construct realistic molecular structures of cross-linked C-S-H and validate them against the spectroscopic and pycnometery measurements. The atomistic simulations indicate that the reduction in the contribution of propagons (propagating heat carriers) and diffusons (diffusive heat carriers) to heat transport, and the amplification of locons (localized vibrational modes), are the main driving factors allowing to limit the heat conduction in C-S-H. Presented findings offer new potential directions to nanoengineering novel admixtures for cement composites and resilient lightweight cementitious mesostructures for thermally efficient building envelopes. 

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3. Significant ballistic thermal transport across graphene layers: Effect of nanoholes and lithium intercalation

   https://doi.org/10.1063/5.0275738  

   Crosby, John; Cui, Haoran; Wang, Yan (August 2025, Applied Physics Letters)

   Porous graphene and graphite are increasingly utilized in electrochemical energy storage and solar-thermal applications due to their unique structural and thermal properties. In this study, we conduct a comprehensive analysis of the lattice thermal transport and spectral phonon characteristics of holey graphite and multilayer graphene. Our results reveal that phonon modes propagating obliquely with respect to the graphene basal planes are the primary contributors to cross-plane thermal transport. These modes exhibit a predominantly ballistic nature, resulting in an almost linear increase in cross-plane thermal conductivity with the number of layers. The presence of nanoholes in graphene induces a broadband suppression of cross-plane phonon transport, whereas lithium-ion intercalation shows potential to enhance it. These findings provide critical insights into the mechanisms governing cross-plane heat conduction in key graphene-based structures, offering valuable guidance for thermal management and engineering of van der Waals materials. 

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4. Pushing the Limits of Heat Conduction in Covalent Organic Frameworks Through High‐Throughput Screening of Their Thermal Conductivity

   https://doi.org/10.1002/smll.202401702  

   Thakur, Sandip; Giri, Ashutosh (April 2024, Small)

   Abstract Tailor‐made materials featuring large tunability in their thermal transport properties are highly sought‐after for diverse applications. However, achieving `user‐defined’ thermal transport in a single class of material system with tunability across a wide range of thermal conductivity values requires a thorough understanding of the structure‐property relationships, which has proven to be challenging. Herein, large‐scale computational screening of covalent organic frameworks (COFs) for thermal conductivity is performed, providing a comprehensive understanding of their structure‐property relationships by leveraging systematic atomistic simulations of 10,750 COFs with 651 distinct organic linkers. Through the data‐driven approach, it is shown that by strategic modulation of their chemical and structural features, the thermal conductivity can be tuned from ultralow (≈0.02 W m⁻¹K⁻¹) to exceptionally high (≈50 W m⁻¹K⁻¹) values. It is revealed that achieving high thermal conductivity in COFs requires their assembly through carbon–carbon linkages with densities greater than 500 kg m⁻³, nominal void fractions (in the range of ≈0.6–0.9) and highly aligned polymeric chains along the heat flow direction. Following these criteria, it is shown that these flexible polymeric materials can possess exceptionally high thermal conductivities, on par with several fully dense inorganic materials. As such, the work reveals that COFs mark a new regime of materials design that combines high thermal conductivities with low densities. 

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5. Mechanism of Charge Transport in Mixed-Valence 2D Layered Hybrid Organic–Inorganic Bronze Materials

   https://doi.org/10.1021/acs.jpcc.5c01250  

   Akter, Suchona; Momeni, Mohammad R (May 2025, The Journal of Physical Chemistry C)

   Two-dimensional layered hybrid organic–inorganic bronze (HOIB) materials are a new class of mixed-valence hybrid metal-oxides that demonstrate great potential as advanced functional materials for next-generation electronics. Recently, new hybrid vanadium bronze materials, (EV)V8O20 and (MV)V8O20, EV = ethyl viologen and MV = methyl viologen, have been introduced, with EV having ≈3 orders of magnitude higher electrical conductivity than the MV system. Given their stoichiometrically similar inorganic V–O layers and close reduction potentials, the observed significant difference in electrical conductivities is puzzling. Here, through accurate first-principles electronic structure calculations coupled with MACE machine learning molecular dynamics (MD) simulations validated by accurate ab initio MD data, we provide mechanistic molecular-level insights into dominant charge transport and electrical conductivity pathways in these materials. Our detailed structural and electronic properties data identify factors contributing to this significant difference in the electrical conductivity of these materials. Our findings in this work offer clues and provide valuable insights into improving the electrical conductivity of hybrid bronze and similar materials, suggesting new ways to guide the design of next-generation materials with enhanced properties for electronic and energy conversion applications. 

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