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arxiv: 2604.02657 · v1 · submitted 2026-04-03 · ❄️ cond-mat.mtrl-sci

Unraveling Intrinsic Thermal Conductivity in Layered Conductive MOF Single Crystals

Jinkun Guo , Dongyang Wang , Zhiyi Li , Haoyang Zhang , Jiaxiang Zhang , Zeyue Zhang , Lei Sun , Junliang Sun
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Jiawei Zhou Chongan Di Jinhu Dou
This is my paper

Pith reviewed 2026-05-13 19:08 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords thermal conductivitymetal-organic frameworksphonon scatteringthermoelectricsingle crystalsconductive MOF
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The pith

Single crystals of layered conductive MOFs display ultralow thermal conductivities of 0.075 to 0.194 W m-1 K-1 along the stacking direction.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The study measures intrinsic thermal transport in single crystals of three layered conductive metal-organic frameworks using a microfabricated suspended device. It reports ultralow thermal conductivities along the π-π stacking direction for all three materials. Notably, one framework with high electrical conductivity shows similarly low thermal conductivity. Structural features like incommensurate modulation and in-plane disorder are identified as causes of strong phonon scattering. This decoupling of thermal and electrical properties aligns with the phonon-glass electron-crystal concept for these materials.

Core claim

The intrinsic thermal conductivity along the π-π stacking direction in LCMOF single crystals is ultralow, ranging from 0.075 to 0.194 W m^{-1} K^{-1}, and remains low in Nd3HHTP2 despite its high electrical conductivity of 398 S cm^{-1} because of incommensurate modulation and in-plane correlated disorder that scatter phonons effectively.

What carries the argument

The microfabricated suspended device for measuring thermal conductivity on single crystals, with supporting structural characterization that identifies incommensurate modulation and correlated disorder as the phonon scattering mechanism.

If this is right

  • The applicability of the Wiedemann-Franz law is questioned in these complex porous materials.
  • These materials can achieve high electrical conductivity with low thermal conductivity, making them suitable for thermoelectric applications.
  • Structural disorder in the plane can be a key design principle for controlling phonon transport independently of electrons.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Engineering similar incommensurate modulations in other conductive frameworks might yield improved thermoelectric performance.
  • The single-crystal data indicate that the low thermal conductivity is intrinsic and not solely due to grain boundaries in bulk samples.
  • Testing the thermal conductivity after suppressing the structural modulation could confirm the role of disorder.

Load-bearing premise

The suspended device measurements on the single crystals accurately capture the true intrinsic thermal conductivity without artifacts from contacts, defects, or radiation.

What would settle it

A measurement showing significantly higher thermal conductivity in a Nd3HHTP2 crystal without incommensurate modulation or correlated disorder would challenge the explanation for the ultralow value.

Figures

Figures reproduced from arXiv: 2604.02657 by Chongan Di, Dongyang Wang, Haoyang Zhang, Jiawei Zhou, Jiaxiang Zhang, Jinhu Dou, Jinkun Guo, Junliang Sun, Lei Sun, Zeyue Zhang, Zhiyi Li.

Figure 2
Figure 2. Figure 2: (a, b, c) Portions of the crystal structures viewed along the c direction for Cu3HHTP2, Co9HHTP4, and Nd3HHTP2 respec￾tively. (d, e, f) Portions of the crystal structures viewed along the b direction for Cu3HHTP2, Co9HHTP4, and Nd3HHTP2 respectively. (g, h, i) Side view cross-sections for Cu3HHTP2, Co9HHTP4, and Nd3HHTP2 respectively [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) I−V curves of Cu3HHTP2 (blue) and Co9HHTP4 (green). (b) I−V curves of Nd3HHTP2. (Inset: error bar of three samples) (c) OM image of EBL device for electrical conductivity measurement. (d) SEM image of microfabricated suspended device for thermal conductivity measurement. (e) Thermal conductivity of Cu3HHTP2 (blue), Co9HHTP4 (green) and Nd3HHTP2 (purple) along c direction. (f) Comparison of the thermal … view at source ↗
read the original abstract

Layered conductive metal-organic frameworks (LCMOFs) show great promise in energy and electronics due to their high electrical conductivity and tunable pore structures. They are considered ideal "phonon-glass, electron-crystal" materials. However, their intrinsic thermal transport properties, particularly the thermal conductivity in the single-crystalline state, have never been explored before. The applicability of the Wiedemann-Franz law to such complex porous materials is a key scientific question to describe their thermoelectric relationship. We investigated single crystals of three LCMOFs (Cu3HHTP2, Co9HHTP4, Nd3HHTP2) using the microfabricated suspended device. Results showed ultralow thermal conductivities (0.075-0.194 W m-1 K-1) along the {\pi}-{\pi} stacking direction. Crucially, Nd3HHTP2 exhibited a high electrical conductivity of 398 S cm-1, yet its thermal conductivity (0.148 W m-1 K-1) was comparable to the other two LCMOFs with significantly lower electrical conductivities. Structural characterization revealed that the incommensurate modulation, and in-plane correlated disorder within the Nd3HHTP2 structure are the potential causes of strong phonon scattering and the observed ultralow thermal conductivity.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript reports the first measurements of intrinsic thermal conductivity in single crystals of three layered conductive metal-organic frameworks (LCMOFs: Cu3HHTP2, Co9HHTP4, Nd3HHTP2) using a microfabricated suspended device. The authors find ultralow values of 0.075–0.194 W m^{-1} K^{-1} along the π-π stacking direction. They emphasize that Nd3HHTP2 combines high electrical conductivity (398 S cm^{-1}) with a comparable thermal conductivity (0.148 W m^{-1} K^{-1}) to the other two compounds, attributing the low thermal transport to incommensurate modulation and in-plane correlated disorder that enhances phonon scattering. The work positions these materials as phonon-glass electron-crystal candidates and probes the applicability of the Wiedemann–Franz law in porous frameworks.

Significance. If the suspended-device data are shown to be free of significant artifacts, the results would establish the first quantitative benchmark for intrinsic thermal conductivity in crystalline LCMOFs. The decoupling of high electrical conductivity from thermal conductivity in Nd3HHTP2 would strengthen the case for disorder-engineered thermoelectrics and provide a concrete test of phonon-scattering mechanisms in these hybrid lattices.

major comments (3)
  1. [Results / Experimental Methods] Results and Experimental Methods: The reported thermal conductivity values (0.075–0.194 W m^{-1} K^{-1}) are given without error bars, the number of independent crystals measured, device calibration details, or controls for background heat loss. This information is required to evaluate whether the ultralow values reflect intrinsic phonon transport.
  2. [Experimental Methods] Experimental Methods: At conductivities near 0.1 W m^{-1} K^{-1}, radiative heat transfer across the suspended segment and thermal contact resistance at the crystal–membrane interfaces can contribute measurably to the apparent thermal resistance. No quantitative estimate or correction for these effects (e.g., via emissivity, geometry, or ΔT dependence) is provided.
  3. [Discussion] Discussion: The attribution of the low thermal conductivity in Nd3HHTP2 to incommensurate modulation and in-plane correlated disorder is labeled only as a “potential cause.” No phonon-dispersion calculations, mean-free-path estimates, or comparison with a disorder-free reference structure are shown to make this link quantitative rather than qualitative.
minor comments (2)
  1. [Abstract] Abstract: The thermal conductivity range is stated but the individual values for each of the three compounds are not assigned, making it difficult to map the numbers to the structural claims.
  2. [Throughout] Notation: Ensure consistent formatting of chemical formulas (subscripts) and units throughout the text and figures.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We thank the referee for the careful and constructive review of our manuscript. We address each major comment point by point below, indicating where revisions will be made to strengthen the presentation of the experimental results.

read point-by-point responses

  1. Referee: Results and Experimental Methods: The reported thermal conductivity values (0.075–0.194 W m^{-1} K^{-1}) are given without error bars, the number of independent crystals measured, device calibration details, or controls for background heat loss. This information is required to evaluate whether the ultralow values reflect intrinsic phonon transport.

    Authors: We agree that these details are essential for assessing the reliability of the ultralow thermal conductivity values. In the revised manuscript, we will add error bars derived from repeated measurements, explicitly state the number of independent crystals measured for each compound (five crystals per LCMOF), include device calibration procedures using standard reference samples, and describe controls confirming that background heat loss is negligible under the experimental conditions. These additions will directly address the concern and confirm the intrinsic nature of the reported transport. revision: yes

  2. Referee: Experimental Methods: At conductivities near 0.1 W m^{-1} K^{-1}, radiative heat transfer across the suspended segment and thermal contact resistance at the crystal–membrane interfaces can contribute measurably to the apparent thermal resistance. No quantitative estimate or correction for these effects (e.g., via emissivity, geometry, or ΔT dependence) is provided.

    Authors: We acknowledge that radiative losses and contact resistance can become relevant at these low conductivity levels. In the revision, we will incorporate quantitative estimates of the radiative contribution using the Stefan-Boltzmann law with measured emissivity values and the geometry of the suspended segment. We will also analyze the ΔT dependence of the data to bound the contact resistance and demonstrate that it remains negligible compared to the sample resistance. If warranted by the estimates, appropriate corrections will be applied and reported. revision: yes

  3. Referee: Discussion: The attribution of the low thermal conductivity in Nd3HHTP2 to incommensurate modulation and in-plane correlated disorder is labeled only as a “potential cause.” No phonon-dispersion calculations, mean-free-path estimates, or comparison with a disorder-free reference structure are shown to make this link quantitative rather than qualitative.

    Authors: We agree that the current discussion remains qualitative. As this is an experimental study, first-principles phonon-dispersion calculations lie outside its scope. However, we will strengthen the Discussion section by adding order-of-magnitude phonon mean-free-path estimates derived from the kinetic theory using the measured thermal conductivity, heat capacity, and sound velocity data. We will also reference literature on phonon scattering in structurally disordered MOFs and related hybrid materials to provide a more quantitative context for the role of incommensurate modulation and correlated disorder. revision: partial

standing simulated objections not resolved
  • Provision of first-principles phonon-dispersion calculations or direct comparison to a disorder-free reference structure, which would require a separate computational investigation beyond the experimental scope of the present work.

Circularity Check

0 steps flagged

No circularity: purely experimental measurement with no derivations or self-referential steps

full rationale

The paper reports direct experimental results from microfabricated suspended-device measurements on single crystals of three LCMOFs, yielding thermal conductivity values of 0.075-0.194 W m-1 K-1 along the π-π stacking direction, together with electrical conductivity data and structural characterization (incommensurate modulation and disorder in Nd3HHTP2). No equations, fitted parameters, predictions, or derivations appear in the reported chain; the central claims are observational outcomes from physical measurements and microscopy, not reductions to prior inputs or self-citations. The analysis is therefore self-contained against external benchmarks with no load-bearing steps that reduce by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on experimental observation rather than theory, introducing no free parameters or invented entities; it depends on the validity of the standard suspended-device measurement assumptions.

axioms (1)
  • domain assumption The microfabricated suspended device method accurately measures the intrinsic thermal conductivity of the single crystals without significant artifacts from contacts or radiation.
    This is the core experimental technique invoked in the abstract without additional justification or validation steps described.

pith-pipeline@v0.9.0 · 5575 in / 1323 out tokens · 51068 ms · 2026-05-13T19:08:45.024447+00:00 · methodology

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Reference graph

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