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A Dynamically Induced Phase Transition in Na4P2S6─Ultrafast Na+ Mobility Triggering Rotor Phase Formation
Katharina Hogrefe1, Bernhard Gadermaier1, Christian Schneider2
1Institute of Chemistry and Technology of Materials, Graz University of Technology (NAWI Graz), Stremayrgasse 9, Graz 8010, Austria.
Journal of the American Chemical Society
|July 30, 2025
Summary
Fast ion diffusion in Na4P2S6 initiates structural changes, preceding phase transitions. Sodium ion hopping drives the transformation to a rotor phase, uncoupled from polyanion rotation at high temperatures.
Area of Science:
- Solid-state chemistry
- Materials science
- Crystallography
Background:
- Physical properties of crystalline solids are linked to their structure.
- Changes in ion hopping are typically attributed to structural or defect chemistry changes.
- The relationship between fast ion diffusion and structural phase transitions needs further investigation.
Purpose of the Study:
- To investigate whether fast ionic diffusion can induce structural changes leading to phase transitions.
- To elucidate the mechanism of phase transition in the Na+-conducting compound Na4P2S6.
- To understand the interplay between Na+ diffusion and anionic framework dynamics.
Main Methods:
- High-resolution 23Na and 31P nuclear magnetic resonance (NMR) spectroscopy.
- Variable-temperature studies up to 650 °C.
- Analysis of NMR spectra and relaxation times.
Main Results:
- Changes in the local Na+ environment precede the structural transition from beta-Na4P2S6 to the gamma-phase.
- The gamma-phase exhibits characteristics of a rotor phase with dynamic Na+ cations and anionic framework.
- Na+ diffusion initiates the transformation to the rotor phase, uncoupled from polyanion rotations at high temperatures.
Conclusions:
- Fast Na+ diffusion plays a crucial role in initiating phase transitions in Na4P2S6.
- The study reveals a decoupling of Na+ hopping and polyanion rotation at high temperatures.
- Findings offer new insights into phase transition mechanisms in fast-ion conductors.
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