Mg substitution in CuCrO 2 delafossite compounds

Abstract

A detailed investigation of the series CuCr 1− x Mg x O 2 ( 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 Mg 2+ for Cr 3+ 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 MgCr 2O 4 spinels as soon as x = 0.005 . The thermopower is discussed in the temperature-independent correlation function 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.