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Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite Ag8SnSe6

Nature Materials (2023)Cite this article

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Abstract

Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite Ag8SnSe6 using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed ‘liquid-like thermal conduction’ picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (<0.5 W m−1 K−1) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.

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Fig. 1: Crystal structures and phase transition in Ag8SnSe6.
Fig. 2: Lattice and diffusive dynamics across the superionic transition.
Fig. 3: Phonon dispersions and coupled vibrations of the Ag and free Se atoms.
Fig. 4: Dramatic phonon broadening without energy softening at low temperature.

Data availability

Data that support the plots within this paper and other findings of this study are available from the corresponding authors upon request. Source data are provided with this paper.

Code availability

The input files including structure and neural network potential files used for calculating the thermal conductivity using LAMMPS are provided with this paper. The codes that support other findings of the study are available from the corresponding authors on request.

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Acknowledgements

J.M. thanks the National Science Foundation of China for the financial support (grant no. U1732154). Q.R. thanks the Guangdong Basic and Applied Basic Research Foundation (grant no. 2021B1515140014), the National Natural Science Foundation of China (grant no. 52101236), the Institute of High Energy Physics, Chinese Academy of Science (grant no. E15154U110) and the Open Project of Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education; grant no. 2020-05). J.D. and O.D. were supported by the US National Science Foundation DMREF award (no. DMR-2119273). Y.P. thanks the National Science Foundation of China for support (no. T2125008). M.J. thanks the National Science Foundation of China for financial support (grant no. 52272006) and the ‘Shuguang Program’ from the Shanghai Education Development Foundation and Shanghai Municipal Education Commission. Z. Cheng thanks the Australia Research Council for support (no. DP210101436). X.T. acknowledges the financial support from the Guangdong Basic and Applied Basic Research Foundation (grant no. 2019B1515120079). Q.R. thanks Y. Guo and H. Su from ShanghaiTech University for the help on crystal alignment, and S. Danilkin, D. Yu and C.-W. Wang from the Australian Nuclear Science and Technology Organisation for the assistance with neutron data collection. We all acknowledge the beam time granted by Institut Laue-Langevin (proposal nos 5-14-263 and 5-14-268), Heinz Maier-Leibnitz (proposal no. 14754), J-PARC (proposal nos 2018B0262 and 2020A0228) and the Australian Nuclear Science and Technology Organisation (proposal no. P7875), and the technical support from Q. Gu during the experiments at the Australian Synchrotron.

Author information

Author notes

  1. These authors contributed equally: Qingyong Ren, Mayanak K. Gupta.

Authors and Affiliations

  1. Key Laboratory of Artificial Structures and Quantum Control, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China

    Qingyong Ren, Jiangtao Wu, Guohua Wang & Jie Ma

  2. Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China

    Qingyong Ren & Xin Tong

  3. Spallation Neutron Source Science Center, Dongguan, China

    Qingyong Ren & Xin Tong

  4. Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, USA

    Mayanak K. Gupta, Jingxuan Ding & Olivier Delaire

  5. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, India

    Mayanak K. Gupta

  6. College of Materials, Shanghai Dianji University, Shanghai, China

    Min Jin & Siqi Lin

  7. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    Jingxuan Ding

  8. Interdisciplinary Materials Research Center, School of Materials Science and Engineering, Tongji University, Shanghai, China

    Zhiwei Chen, Siqi Lin & Yanzhong Pei

  9. Institut Laue-Langevin, Grenoble, France

    Oscar Fabelo & Jose Alberto Rodríguez-Velamazán

  10. J-PARC Center, Japan Atomic Energy Agency, Tokai, Japan

    Maiko Kofu & Kenji Nakajima

  11. Technische Universität München, Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany

    Marcell Wolf

  12. Jülich Centre for Neutron Science (JCNS), Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich, Garching, Germany

    Fengfeng Zhu

  13. College of Physics, Jilin University, Changchun, China

    Jianli Wang

  14. Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong, North Wollongong, NSW, Australia

    Jianli Wang & Zhenxiang Cheng

  15. Physics Department, Duke University, Durham, NC, USA

    Olivier Delaire

  16. Chemistry Department, Duke University, Durham, NC, USA

    Olivier Delaire

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  1. Qingyong Ren
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  3. Min Jin
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Contributions

Q.R., O.D. and J.M. conceived the project. M.J., Z. Chen, S.L. and Y.P. prepared the single-crystal samples, and Q.R. aligned the crystals with help from G.W.; J. Wang and Z. Cheng performed the SXRD measurements, and Q.R. analysed the results. Q.R. carried out the SCND measurements and structural analyses with help from J. Wu, O.F. and J.A.R.-V. Neutron scattering measurements were conducted by Q.R., M.K., K.N., M.W., F.Z. and J. Wu and were analysed by Q.R. with assistance from X.T. and J.M.; M.K.G., J.D. and O.D. performed the first-principles and MLMD simulations. Q.R., O.D. and J.M. drafted the manuscript. All authors edited and finalized the manuscript.

Corresponding authors

Correspondence to Yanzhong Pei, Olivier Delaire or Jie Ma.

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Supplementary information

Supplementary Information

Supplementary Sections 1–6, Figs. 1–24, Tables 1 and 2 and refs. 1–7.

Reporting Summary

Supplementary Code 1

The initial structure file in LAMMPS format, neural network force-field file generated using DeePMD-kit code, LAMMPS input file, Fortran script and input file for lattice thermal conductivity calculations using time dependence heat flux.

Source data

Source Data Fig. 1

SXRD data plotted in Fig. 1a,b; and the lattice parameters as a function of temperature plotted in Fig. 1c.

Source Data Fig. 2

INS data plotted in Fig. 2a–c; INS data and QENS analysis plotted in Fig. 2d; and S(Q,E) data from MLMD simulations plotted in Fig. 2e.

Source Data Fig. 3

INS data plotted in Fig. 3a–d; partial phonon DOS from MLMD simulations plotted in Fig. 3e,f; and MSD values from MLMD simulations plotted in Fig. 3g,h.

Source Data Fig. 4

INS data plotted in Fig. 4a–c; Bose-factor-corrected dynamic structure factor plotted in Fig. 4d; and neutron-weighted DOS over energy transfer from MLMD simulations plotted in Fig. 4e.

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Ren, Q., Gupta, M.K., Jin, M. et al. Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite Ag8SnSe6. Nat. Mater. (2023). https://doi.org/10.1038/s41563-023-01560-x

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