Title: Anharmonic lattice dynamics and superionic transition in AgCrSe ₂

Abstract

Intrinsically low lattice thermal conductivity ( ${\kappa }_{lat}$) in superionic conductors is of great interest for energy conversion applications in thermoelectrics. Yet, the complex atomic dynamics leading to superionicity and ultralow thermal conductivity remain poorly understood. Here, we report a comprehensive study of the lattice dynamics and superionic diffusion in ${\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{r}\mathrm{S}\mathrm{e}}_2$from energy- and momentum-resolved neutron and X-ray scattering techniques, combined with first-principles calculations. Our results settle unresolved questions about the lattice dynamics and thermal conduction mechanism in ${\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{r}\mathrm{S}\mathrm{e}}_2$. We find that the heat-carrying long-wavelength transverse acoustic (TA) phonons coexist with the ultrafast diffusion of Ag ions in the superionic phase, while the short-wavelength nondispersive TA phonons break down. Strong scattering of phonon quasiparticles by anharmonicity and Ag disorder are the origin of intrinsically low ${\kappa }_{lat}$. The breakdown of short-wavelength TA phonons is directly related to the Ag diffusion, with the vibrational spectral weight associated to Ag oscillations evolving into stochastic decaying fluctuations. Furthermore, the origin of fast ionic diffusion is shown to arise from extended flat basins in the energy landscape and collective hopping behavior facilitated by strong repulsion between Ag ions. These findings offer fundamental insights into the complex atomic dynamics of superionic conductors.

Authors:

Ding, Jingxuan; Niedziela, Jennifer L.; Bansal, Dipanshu; Wang, Jiuling; He, Xing; May, Andrew F.; Ehlers, Georg; Abernathy, Douglas L.; Said, Ayman; Alatas, Ahmet; Ren, Yang; Arya, Gaurav; Delaire, Olivier

Publication Date:

2020-02-06

Research Org.:

Duke Univ., Durham, NC (United States); Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of California, Berkeley, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; USDOE Office of Science (SC), Basic Energy Sciences (BES)

Contributing Org.:

Oak Ridge National Laboratory Spallation Neutron Source; National Energy Research Scientific Computing Center

OSTI Identifier:

1598367

Alternate Identifier(s):

OSTI ID: 1598277; OSTI ID: 1607011; OSTI ID: 1632173

Grant/Contract Number:  

SC0019299; SC0016166; AC02-06CH11357; AC02-05CH11231; AC05-00OR22725

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 117 Journal Issue: 8; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Superionic conductor; Thermoelectrics; Thermal transport; Phonons; Diffusion; Anharmonic lattice dynamics; anharmonic lattice dynamics; superionic conductor; thermal transport; thermoelectrics