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<p>Layered oxyselenides are of interest as promising mid- to high-temperature thermoelectric applications due to their tunable electrical properties and intrinsically low lattice thermal conductivity (<i>κ</i>). Understanding microscopic phonon mechanisms driving low-<i>κ</i> in these materials is essential for rational design. Here, we report a layer-differentiated phonon transport in Na<sub>2</sub>CoSe<sub>2</sub>O via solving the Wigner transport equation based on first-principles calculations, where CoSe<sub>6</sub> and Na<sub>6</sub>O octahedra dominate acoustic and low-energy optical phonons, respectively, together inducing acoustic-optical bunching (a typical feature in homo-layered structures such as bilayer graphene and MoS<sub>2</sub>). In addition, Na<sub>6</sub>O generates high-energy flat optical phonons, in contrast to oxide-typical dispersive modes. This phonon dispersion feature, constrained by three-phonon scattering channels, necessitates interpretation via four-phonon processes, which simultaneously enhance wavelike coherent tunneling effects. Consequently, by considering anharmonic phonon renormalization, strong scattering of heat-carrying bunched phonons reduces <i>κ</i> by ~28%, with ~13% compensatory contribution from phonon coherence, yielding a low lattice thermal conductivity of 1.52 W m<sup>−1</sup> K<sup>−1</sup> at 300 K in Na<sub>2</sub>CoSe<sub>2</sub>O. This work provides new insights into the specific vibrational mechanisms, phonon bunching induced strong four-phonon scattering, highlights the critical role of distinct structural layers in governing thermal transport, and enriches the fundamental thermal transport mechanism in layered oxyselenides.</p>

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Phonon bunching induced strong four-phonon scattering for low lattice thermal conductivity in layered Na2CoSe2O

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月8日

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  • Bin Wei,
  • Mengfan Chai,
  • Chang Liu,
  • Junyan Liu,
  • Yongheng Li,
  • Wenyu Zhang,
  • Qing Wang,
  • Erzhen Mu,
  • Binbin Wang,
  • Zhifang Zhou,
  • Changpeng Lin,
  • Xu Chen,
  • Meihua Hu,
  • Yunpeng Zheng,
  • Yuan-Hua Lin

摘要

Layered oxyselenides are of interest as promising mid- to high-temperature thermoelectric applications due to their tunable electrical properties and intrinsically low lattice thermal conductivity (κ). Understanding microscopic phonon mechanisms driving low-κ in these materials is essential for rational design. Here, we report a layer-differentiated phonon transport in Na2CoSe2O via solving the Wigner transport equation based on first-principles calculations, where CoSe6 and Na6O octahedra dominate acoustic and low-energy optical phonons, respectively, together inducing acoustic-optical bunching (a typical feature in homo-layered structures such as bilayer graphene and MoS2). In addition, Na6O generates high-energy flat optical phonons, in contrast to oxide-typical dispersive modes. This phonon dispersion feature, constrained by three-phonon scattering channels, necessitates interpretation via four-phonon processes, which simultaneously enhance wavelike coherent tunneling effects. Consequently, by considering anharmonic phonon renormalization, strong scattering of heat-carrying bunched phonons reduces κ by ~28%, with ~13% compensatory contribution from phonon coherence, yielding a low lattice thermal conductivity of 1.52 W m−1 K−1 at 300 K in Na2CoSe2O. This work provides new insights into the specific vibrational mechanisms, phonon bunching induced strong four-phonon scattering, highlights the critical role of distinct structural layers in governing thermal transport, and enriches the fundamental thermal transport mechanism in layered oxyselenides.