Transport properties of the delafossite Rh oxide ${\mathrm{Cu}}_{1-x}{\mathrm{Ag}}_x{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$: Effect of Mg substitution on the resistivity and Hall coefficient

Polycrystalline samples of the delafossite Rh oxide ${\mathrm{Cu}}_{1-x}{\mathrm{Ag}}_x{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$ 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 $300\mathrm{K}$, which characterizes this material as a two-hole-band conductor.

Figure 1

(Color online) Crystal structure of $\mathrm{Cu}\mathrm{Rh}{\mathrm{O}}_2$. Blue (dark gray), gray (light gray), and red (dark gray) spheres represent Cu, Rh, and O atoms, respectively. This material has the $\mathrm{Cd}{\mathrm{I}}_2$-type $\mathrm{Rh}{\mathrm{O}}_2$ layer like the layered Co oxides.

Figure 2

(Color online) (a) XRD patterns of $\mathrm{Cu}{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$ and ${\mathrm{Cu}}_{0.9}{\mathrm{Ag}}_{0.1}\mathrm{Rh}{\mathrm{O}}_2$, and the lattice constants of (b) ${\mathrm{Cu}}_{1-x}{\mathrm{Ag}}_x\mathrm{Rh}{\mathrm{O}}_2$ and (c) $\mathrm{Cu}{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$.

Figure 3

(Color online) (a) Resistivity, (b) thermopower, and (c) Hall coefficient of ${\mathrm{Cu}}_{1-x}{\mathrm{Ag}}_x\mathrm{Rh}{\mathrm{O}}_2$. An arrow indicates the kink in $\rho$ and $S$ (see text).

Figure 4

(Color online) (a) Resistivity, (b) thermopower, and (c) Hall coefficient of $\mathrm{Cu}{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$. Hall mobility $\left({\mu }_H\right)$ of $\mathrm{Cu}{\mathrm{Rh}}_{1-y}{\mathrm{Mg}}_y{\mathrm{O}}_2$ is shown in the inset.

Figure 5

(Color online) (a) Resistivity, (b) thermopower, and (c) Hall coefficient of ${\mathrm{Cu}}_{1-x}{\mathrm{Ag}}_x{\mathrm{Rh}}_{0.8}{\mathrm{Mg}}_{0.2}{\mathrm{O}}_2$.

Figure 6

(Color online) (a) The carrier concentration evaluated from the Hall coefficient and (b) the transport entropy evaluated from the thermopower. The data are taken at $150\mathrm{K}$ to pick up the $\mathrm{Rh}{\mathrm{O}}_2$ contribution.

Figure 7

(Color online) The resistivity $\left({\rho }_{\mathrm{Cu}}\right)$ and thermopower $\left(S_{\mathrm{Cu}}\right)$ in the Cu layer of $\mathrm{Cu}\mathrm{Rh}{\mathrm{O}}_2$ evaluated from the measured data (see text). The Hall coefficient of $\mathrm{Cu}\mathrm{Rh}{\mathrm{O}}_2$ is also plotted for comparison.