Chemical Instability of the Cobalt Oxyhydrate Superconductor under Ambient Conditions

TL;DR

This study reveals that the sodium cobalt oxyhydrate superconductor is highly sensitive to ambient temperature and humidity, leading to dehydration and loss of superconductivity, with implications for its stability and superconducting mechanism.

Contribution

It demonstrates the instability of Na0.3CoO2*1.4H2O under ambient conditions and identifies the critical layer spacing for superconductivity in this system.

Findings

Superconductor dehydrates to a lower hydrate under ambient conditions.

Superconductivity depends on CoO2 layer spacing between 6.9 and 9.9 angstroms.

Hydration state affects the material's superconducting properties.

Abstract

The layered sodium cobalt oxyhydrate superconductor Na0.3CoO2*1.4H2O is shown through X-ray diffraction and thermogravimetric studies to be one of a series of hydrated phases of Na0.3CoO2. Further, it is shown that the material is exceptionally sensitive to both temperature and humidity near ambient conditions, easily dehydrating to a non-superconducting lower hydrate. The observation of this stable lower hydrate with c=13.8 angstroms implies that the superconductivity turns on in this system between CoO2 layer spacings of 6.9 and 9.9 angstroms at nominally constant chemical doping.