Dynamics of Na Ion in the Amorphous Na2Si2O5 Using Quasielastic Neutron Scattering and Molecular Dynamics Simulations

TL;DR

This study combines quasielastic neutron scattering and molecular dynamics simulations to explore Na ion diffusion in amorphous Na2Si2O5, revealing diffusion pathways and relaxation times relevant for solid electrolyte applications.

Contribution

It provides new insights into Na-ion diffusion mechanisms in amorphous Na2Si2O5 using combined experimental and simulation approaches, highlighting differences from crystalline phases.

Findings

Na ions diffuse in amorphous Na2Si2O5 with a mean jump length of ~3 Å

Diffusion pathways are accessible in the amorphous phase but not in the crystalline phase

Diffusion occurs up to 748 K in the amorphous phase, not observed in the crystalline phase up to 1100 K

Abstract

We have investigated the dynamics of Na ions in amorphous Na2Si2O5, a potential solid electrolyte material for Na-battery. We have employed quasielastic neutron scattering (QENS) technique in the amorphous Na2Si2O5 from 300 to 748 K to understand the diffusion pathways and relaxation timescales of Na atom dynamics. The microscopic analysis of the QENS data has been performed using ab-initio and classical molecular dynamics simulations (MD) to understand the Na-ion diffusion in the amorphous phase. Our experimental studies show that the traditional model, such as the Hall and Ross (H-R) model, fairly well describe the diffusion in the amorphous phase giving a mean jump length of ~3 {\AA} and residence time about 9.1 picoseconds. Our MD simulations have indicated that the diffusion of Na+ ions occurs in the amorphous phase of Na2Si2O5 while that is not observed in the crystalline orthorhombic phase even up to 1100 K. The MD simulations have revealed that in the amorphous phase, due to different orientations of silicon polyhedral units, accessible pathways are opened up for Na+ diffusions. These pathways are not available in the crystalline phase of Na2Si2O5 due to rigid spatial arrangement of silicon polyhedral units.