Abstract
The ionic materials and are both based on the same building blocks of the dimer ions (. Motivated by new experimental structural and ion conductivity studies, we computationally examine this family of materials, finding and its modification to be promising Na ion electrolytes. Using first-principles calculations based on density functional theory and density functional perturbation theory within the harmonic phonon approximation, we show that vibrational effects provide nontrivial contributions to the structural stabilization of these materials. Computed nonresonant Raman phonon spectra and temperature-dependent ionic conductivity for are both found to be in reasonable agreement with experiment. First-principles analysis of ionic conductivity in both and indicates that Na ions move primarily within the interlayer region between the ( layers, efficiently proceeding via direct or indirect hops between vacancy sites, with indirect processes involving intermediate interstitial sites.
8 More- Received 28 January 2020
- Accepted 24 March 2020
DOI:https://doi.org/10.1103/PhysRevMaterials.4.045406
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