# Unconventional and Powerful Ion Sources for Solid-State Ion Exchange, Cu2SO4 and Cu3PO4: Exemplified by the Synthesis of Metastable β-CuGaO2 from Stable β-LiGaO2

## TL;DR

This paper introduces new ion sources for creating metastable materials, enabling the synthesis of β-CuGaO2 from β-LiGaO2.

## Contribution

The study identifies Cu2SO4 and Cu3PO4 as powerful Cu+ ion sources for solid-state ion exchange, surpassing traditional CuCl.

## Key findings

- Cu2SO4 and Cu3PO4 provide a higher thermodynamic driving force for ion exchange than CuCl.
- Experimental ion exchange from β-LiGaO2 to β-CuGaO2 was successfully demonstrated.
- Simple compounds can act as powerful ion sources, previously overlooked in material synthesis.

## Abstract

This study introduces a new method for synthesizing Cu+-containing metastable phases through ion exchange. Traditionally,
CuCl has been used as a Cu+ ion source for solid-state
ion exchanges; however, its thermodynamic driving force is often insufficient
for complete ion exchange with Li+-containing precursors.
First-principles calculations have identified Cu2SO4 and Cu3PO4 as more powerful alternatives,
providing a higher driving force than CuCl. It has been experimentally
demonstrated that these ion sources can open up new reaction pathways
through experimental ion exchanges, such as from β-LiGaO2 to β-CuGaO2, which were previously unattainable.
An important perspective provided by this study is that the potential
of such simple compounds to act as powerful ion sources has been overlooked
and that they were identified through straightforward first-principles
calculations. This work presents the initial strategic design of an
ion-exchange reaction by exploring suitable ion sources, thereby expanding
the potential for synthesizing metastable materials.