Effects of Mn-substitution for Co on the structure and physical properties of NayCoO2

TL;DR

This study investigates how substituting Mn for Co in NaCoO2 affects its structure, electronic, and magnetic properties, revealing significant lattice changes, a metal-insulator transition at low doping, and valence state variations.

Contribution

It provides new insights into the effects of Mn doping on NaCoO2's structure and properties, including lattice parameter changes and valence state behavior.

Findings

Mn doping decreases lattice parameter a and increases c.

A metal-insulator transition occurs at 3% Mn doping.

Mn valence increases with doping, reaching 3.7 at x=0.5.

Abstract

Structure, transport and magnetic properties have been investigated for layered NaCo1-xMnxO2 materials. With the increase of Mn-doping amount, measurements of x-ray diffraction indicate that the in-plane lattice parameter a decreases progressively, and, conversely, the lattice parameter c increases rapidly. Small amount of Mn doping (i.e. 3% Mn in our work) could result in a metal-insulator transition. Electron energy loss spectroscopy (EELS) measurement shows that the Co valence is about 3.3 and remains unchanged with doping. In contrast, the valence of Mn increases rapidly with doping and reaches 3.7 for the sample with x=0.5. The temperature dependence of magnetization of the samples is found to obey the Curie-Weiss law. Some relevant results have been discussed in terms of the disorder effect induced by doping of magnetic ions.