Transport properties of the delafossite Rh oxide Cu1-x Agx Rh1-y Mgy O2: Effect of Mg substitution on the resistivity and Hall coefficient

Polycrystalline samples of the delafossite Rh oxide ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ag}}_{x}{\mathrm{Rh}}_{1\ensuremath{-}y}{\mathrm{Mg}}_{y}{\mathrm{O}}_{2}$ were investigated to clarify its transport properties. Mg substitution dramatically decreases the resistivity and the Hall coefficient, whereas it does not change the thermopower and the mobility. As an origin for this, we propose that the holes doped by the Mg ions are spatially segregated in the sample, and move away from the Mg ions to retain high mobility. In the parent oxide $\mathrm{Cu}\mathrm{Rh}{\mathrm{O}}_{2}$, the conductivity in the Cu layer is comparable with that in the $\mathrm{Rh}{\mathrm{O}}_{2}$ layer at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which characterizes this material as a two-hole-band conductor.