# On the Origin of the Non‐Arrhenius Na‐ion Conductivity in Na3OBr

## TL;DR

This paper investigates why a material called Na3OBr shows unusual sodium ion conductivity, which could help improve solid electrolytes for batteries.

## Contribution

The study identifies the role of poorly crystalline impurities in causing non-Arrhenius conductivity in Na3OBr.

## Key findings

- Crystallographic disorder on anion sites was ruled out as the cause of non-Arrhenius conductivity.
- Poorly crystalline impurities, undetectable by XRD, were found to affect ionic conductivity.
- The findings highlight the importance of processing-structure-properties relationships in NaRAPs.

## Abstract

The sodium‐rich antiperovskites (NaRAPs) with composition Na3OB (B=Br, Cl, I, BH4, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non‐Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature‐resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na3OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing‐structure‐properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high‐performance solid electrolytes.