# Virtual cathode induced in Rb2Ti2O5 solid electrolyte

## TL;DR

This study investigates the charge distribution in Rb2Ti2O5 solid electrolyte, revealing negative charge accumulation near the anode and explaining its colossal capacitance through a virtual cathode effect.

## Contribution

It introduces a pressure-wave-propagation method to analyze charge distribution in Rb2Ti2O5, uncovering the virtual cathode phenomenon as a key to colossal capacitance.

## Key findings

- Negative charges accumulate near the anode in RTO.
- Electric field near the cathode remains zero.
- Colossal capacitance is due to a virtual cathode effect.

## Abstract

Rb2Ti2O5 (RTO) has recently been demonstrated to be a solid electrolyte, producing colossal capacitance when interfaced with metals. In order to understand the mechanisms leading to such colossal equivalent permittivity (up to four orders of magnitude above state-of-the-art values), the charge distribution in RTO is a key feature to be investigated. In the present article, this charge distribution is probed using the pressure-wave-propagation method, in devices made of RTO single crystals or polycrystals sandwiched between two metallic electrodes. Remarkably enough, in both types of samples, negative charges are found to accumulate inside RTO, near the anode, while the electric field near the cathode remains zero. This proves that the ionic carriers are majoritarily negatively charged and provides an explanation for the colossal capacitance. The latter takes place only at the anode while the cathode is virtually shifted into the solid electrolyte.