Mg substitution in CuCrO2 delafossite compounds

A detailed investigation of the series CuCr1−xMgxO2 (x=0.0–0.05x=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∼0.02–0.03x∼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=0.005x=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.

► The transport and structure of CuCrO2 are strongly affected by substituting Cr by Mg. ► A theory of the high-temperature thermopower is presented to analyze the reported measurements. ► A microstructure characterization for a series of doping values is presented. ► The effective charge carrier density is smaller than the nominal Mg content. ► We obtain a solubility limit close to 1.1% Mg in this delafossite.