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Anharmonic Lattice Dynamics in Sodium Ion Conductors
Thomas M Brenner1, Manuel Grumet2, Paul Till3
1Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
The Journal of Physical Chemistry Letters
|June 22, 2022
Summary
Sodium ion conductors Na3PS4 and Na3PSe4 show anharmonic lattice dynamics. Coupled ion and lattice vibrations drive phase transitions, differing in character between the two materials.
Area of Science:
- Solid-state chemistry
- Materials science
- Condensed matter physics
Background:
- Sodium ion conductors are crucial for next-generation energy storage.
- Understanding lattice dynamics is key to optimizing ion transport.
- Anharmonicity plays a significant role in phase transitions and ionic conductivity.
Purpose of the Study:
- To investigate the lattice dynamics of Na3PS4 and Na3PSe4.
- To elucidate the role of anharmonic effects in their tetragonal-to-cubic phase transitions.
- To correlate lattice dynamics with ionic conductivity.
Main Methods:
- Terahertz-range temperature-dependent Raman spectroscopy.
- First-principles lattice dynamical calculations.
- Analysis of soft modes and their behavior across phase transitions.
Main Results:
- Both Na3PS4 and Na3PSe4 exhibit anharmonic lattice dynamics.
- Anharmonic effects involve coupled host lattice and Na+ ion dynamics.
- Na3PSe4 shows a displacive transition, while Na3PS4 exhibits an order-disorder transition.
Conclusions:
- Coupled host lattice-mobile ion dynamics are critical for vibrational instabilities.
- These instabilities are linked to the exceptional ionic conductivity of these materials.
- Qualitative differences in anharmonicity explain distinct phase transition behaviors.
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