Diffusion of sodium ions in amorphous<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msub><mml:mi mathvariant="normal">a</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:msub><mml:mi mathvariant="normal">i</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>: Quasielastic neutron scattering and<i>ab initio</i>molecular dynamics simulations
Mayanak K. Gupta, Sanjay K. Mishra, Ranjan Mittal, Baltej Singh, Prabhatasree Goel, Sanghamitra Mukhopadhyay, Rakesh Shukla, Srungarpu N. Achary, Avesh K. Tyagi, Samrath L. Chaplot
Abstract
The dynamics of Na ions in amorphous $\mathrm{N}{\mathrm{a}}_{2}\mathrm{S}{\mathrm{i}}_{2}{\mathrm{O}}_{5}$, a potential solid electrolyte material for Na battery, have been investigated by employing. the quasielastic neutron scattering (QENS) technique in the temperature range 300 to 748 K. To understand the diffusion pathways and relaxation timescales of Na ionic diffusion, the experimental studies are complemented by ab initio and force-field molecular dynamics simulations. The QENS data are fairly well described by a jump-diffusion model with a mean jump length of about 3 \AA{} and residence time about 9 ps. Our molecular dynamics simulations have predicted that the diffusion of $\mathrm{N}{\mathrm{a}}^{+}$ ions occurs in the amorphous phase of $\mathrm{N}{\mathrm{a}}_{2}\mathrm{S}{\mathrm{i}}_{2}{\mathrm{O}}_{5}$ while absent in the crystalline orthorhombic phase even up to 1100 K. The molecular dynamics simulations have revealed that in the amorphous phase, due to different orientations of silicon polyhedral units, several accessible pathways are opened up for $\mathrm{N}{\mathrm{a}}^{+}$ diffusions. These pathways are not available in the crystalline phase of $\mathrm{N}{\mathrm{a}}_{2}\mathrm{S}{\mathrm{i}}_{2}{\mathrm{O}}_{5}$ due to rigid spatial arrangement of silicon polyhedral units.