Raman Spectroscopy Insights into the Reorientational Dynamics of Polyanions in Solid Electrolytes

TL;DR

This study combines ab initio molecular dynamics and Raman spectroscopy to analyze the reorientational behavior of NO2- polyanions in solid electrolytes, revealing how molecular rotation influences spectral features and phase transitions.

Contribution

It introduces a combined computational and experimental approach to characterize polyanion reorientation in solid electrolytes, providing new insights into their dynamic behavior.

Findings

NO2- rotates freely in Na3ONO2

Rotational dynamics are hindered in NaNO2

Temperature affects Raman spectral features and phase transition behavior

Abstract

The interaction between cation diffusion and polyanion rotational dynamics has garnered significant attention, yet characterizing the rotational dynamics of polyanions remains challenging. Previous studies have primarily relied on complex techniques such as Nuclear Magnetic Resonance and Quasi-Elastic Neutron Scattering. In this work, we use ab initio molecular dynamics (AIMD) simulations and temperature-dependent Raman spectroscopy to investigate the reorientational dynamics of the NO2- polyanion in Na3ONO2 and NaNO2. Our findings reveal distinct reorientational behaviors and establish a clear correlation between molecular reorientation and Raman spectral features in polyanion-based solid electrolytes. AIMD simulations show that NO2- rotates easily in Na3ONO2, while its rotational dynamics are hindered in NaNO2. Raman spectroscopy confirms these results, with temperature-dependent shifts in the internal vibrational modes of the polyanion. In Na3ONO2, the full width at half maximum (FWHM) of these modes increases with temperature, while NaNO2 exhibits a constant FWHM until a significant jump at the ordered-disordered phase transition. These insights enhance our understanding of polyanion reorientation and offer a framework for characterizing similar dynamics in other solid electrolytes.