  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.
