# $\mbox{Rb}_{2}\mbox{Ti}_2\mbox{O}_{5-\delta}$: A superionic conductor with colossal dielectric constant

## TL;DR

This study reports a novel ionic conductor with an exceptionally high dielectric constant and ionic conductivity, demonstrating ion migration-induced colossal polarization, which challenges the traditional view that high conductivity and dielectric properties are mutually exclusive.

## Contribution

The paper introduces $ ext{Rb}_2 ext{Ti}_2 ext{O}_{5- ext{delta}}$ as a superionic conductor with colossal dielectric constant, highlighting its ionic conduction and giant polarization due to ion migration.

## Key findings

- Colossal dielectric constant up to 10^9 observed.
- High ionic conductivity of 10^-3 S/cm at room temperature.
- Material exhibits giant polarization, acting like a 'ferro-ionet'.

## Abstract

Electrical conductivity and high dielectric constant are in principle self-excluding, which makes the terms insulator and dielectric usually synonymous. This is certainly true when the electrical carriers are electrons, but not necessarily in a material where ions are extremely mobile, electronic conduction is negligible and the charge transfer at the interface is immaterial. Here we demonstrate in a perovskite-derived structure containing five-coordinated Ti atoms, a colossal dielectric constant (up to $\mbox{10}^9$) together with very high ionic conduction $\mbox{10}^{-3}\mbox{S.cm}^{-1}$ at room temperature. Coupled investigations of I-V and dielectric constant behavior allow to demonstrate that, due to ion migration and accumulation, this material behaves like a giant dipole, exhibiting colossal electrical polarization (of the order of $\mbox{0.1\,C.cm}^{-2}$). Therefore, it may be considered as a "ferro-ionet" and is extremely promising in terms of applications.