Tuning Co valence state in cobalt oxyhydrate superconductor by post reduction

TL;DR

This study demonstrates precise tuning of cobalt valence in cobalt oxyhydrate superconductors through post reduction, revealing a direct correlation between Co valence and superconducting transition temperature within a specific valence range.

Contribution

The paper introduces a straightforward post reduction method using NaOH to accurately control Co valence in cobalt oxyhydrate superconductors, updating the phase diagram.

Findings

Superconducting transition temperature increases with Co valence.

NaOH post reduction effectively suppresses hydronium incorporation.

Updated phase diagram shows monotonic Tc increase with Co valence.

Abstract

We report a successful tuning of Co valence state in cobalt oxyhydrate superconductor via a facile post reduction using NaOH as reducing agent. The change in Co valence was precisely determined by measuring the volume of the released oxygen. The possible hydronium-incorporation was greatly suppressed in concentrated NaOH solution, making the absolute Co valence determinable. As a result, an updated superconducting phase diagram was obtained, which shows that the superconducting transition temperature increases monotonically with increasing Co valence in a narrow range from +3.58 to +3.65.