Comparing the Descriptors for Investigating the Influence of Lattice Dynamics on Ionic Transport Using the Superionic Conductor Na<sub>3</sub>PS<sub>4- x</sub>Se <sub>x</sub>.

TitleComparing the Descriptors for Investigating the Influence of Lattice Dynamics on Ionic Transport Using the Superionic Conductor Na3PS4- xSe x.
Publication TypeJournal Article
Year of Publication2018
AuthorsT Krauskopf, S Muy, SP Culver, S Ohno, O Delaire, Y Shao-Horn, and WG Zeier
JournalJournal of the American Chemical Society
Volume140
Issue43
Start Page14464
Pagination14464 - 14473
Date Published10/2018
Abstract

Recent work on superionic conductors has demonstrated the influence of lattice dynamics and the softness of the lattice on ionic transport. When examining either the changes in the acoustic phonon spectrum or the whole phonon density of states, both a decreasing activation barrier of migration and a decreasing entropy of migration have been observed, highlighting that the paradigm of "the softer the lattice, the better" does not always hold true. However, both approaches to monitor the changing lattice dynamics probe different frequency ranges of the phonon spectrum, and thus, it is unclear if they are complementary. In this work, we investigate the lattice dynamics of the superionic conductor Na<sub>3</sub>PS<sub>4- x</sub>Se <sub>x</sub> by probing the optical phonon modes and the acoustic phonon modes, as well as the phonon density of states via inelastic neutron scattering. Notably, Raman spectroscopy shows the evolution of multiple local symmetry reduced polyhedral species, which likely affect the local diffusion pathways. Meanwhile, density functional theory and the ionic transport data are used to compare the different approaches for assessing the lattice dynamics. This work shows that, while acoustic and inelastic methods may be used to experimentally assess the overall changing lattice stiffness, calculations of the average vibrational energies between the mobile ions and the anion framework are important to assess and computationally screen for ionic conductors.

DOI10.1021/jacs.8b09340
Short TitleJournal of the American Chemical Society