Mg substitution in CuCrO2 delafossite compounds

TL;DR

This study investigates Mg substitution in CuCrO2 delafossite compounds, revealing a low solubility limit of about 1.1% Mg and its effects on electrical resistivity and thermopower through experimental and theoretical analyses.

Contribution

It provides a detailed experimental and theoretical analysis of Mg substitution effects and identifies the solubility limit in CuCrO2 delafossite compounds.

Findings

Mg substitution decreases resistivity and thermopower up to a certain limit.

MgCr2O4 spinels form at low Mg concentrations.

The solubility limit of Mg in CuCrO2 is approximately 1.1%.

Abstract

A detailed investigation of the series CuCr(1-x)MgxO2 (x = 0.0 - 0.05) has been performed by making high-temperature resistivity and thermopower measurements, and by performing a theoretical analysis of the latter. Microstructure characterization has been carried out as well. Upon Mg2+ for Cr3+ substitution, a concomitant decrease in the electrical resistivity and thermopower values is found, up to x ~ 0.02 - 0.03, indicating a low solubility limit of Mg in the structure. This result is corroborated by scanning electron microscopy observations, showing the presence of MgCr2O4 spinels as soon as x = 0.005. The thermopower is discussed in the temperature-independent correlation functions ratio approximation as based on the Kubo formalism, and the dependence of the effective charge carrier density on the nominal Mg substitution rate is addressed. This leads to a solubility limit of 1.1% Mg in the delafossite, confirmed by energy dispersive X-ray spectroscopy analysis.