Electrochemical De-intercalation, Oxygen Non-stoichiometry, and Crystal Growth of NaxCoO2-d

TL;DR

This study investigates the electrochemical de-intercalation of sodium from NaxCoO2-d, revealing stable phases, oxygen non-stoichiometry, and crystal growth methods, with implications for understanding its magnetic and structural properties.

Contribution

It provides detailed insights into sodium de-intercalation, oxygen deficiencies, and crystal growth techniques for NaxCoO2-d, highlighting stable phases and oxygen non-stoichiometry.

Findings

Stable Na content phases near 1/3, 1/2, 5/8, 2/3, 3/4 identified.

Oxygen deficiencies present in powder samples but not in single crystals.

Oxygen deficiencies persist after electrochemical de-intercalation.

Abstract

We report a detailed study of de-intercalation of Na from the compound NaxCoO2-d using an electrochemical technique. We find evidence for stable phases with Na contents near the fractions ~1/3, 1/2, 5/8, 2/3, and 3/4. Details regarding the floating-zone crystal growth of Na0.75CoO2 single crystals are discussed as well as results from magnetic susceptibility measurements. We observe the presence of significant oxygen deficiencies in powder samples of Na0.75CoO2-d prepared in air, but not in single crystal samples prepared in an oxygen atmosphere. The oxygen deficiencies in a Na0.75CoO2-d sample with d ~ 0.08 remain even after electrochemically de-intercalating to Na0.3CoO2-d.