Thermoelectric transport in the layered Ca$_3$Co$_{4-x}$Rh$_x$O$_9$ single crystals

摘要: We have examined an isovalent Rh substitution effect on the transport properties of thermoelectric oxide Ca$_3$Co$_{4}$O$_9$ using single-crystalline form. With increasing content $x$, both electrical resistivity and Seebeck coefficient change systematically up to $x=0.6$ for Ca$_3$Co$_{4-x}$Rh$_{x}$O$_9$ samples. In Fermi-liquid regime where behaves as $\rho=\rho_0+AT^2$ around 120 K, $A$ value decreases with content, indicating that correlation is weakened by $4d$ electrons extended orbitals. find that, in contrast such a weak observed Rh-substituted samples, low-temperature increased which explained possible enhancement pseudogap associated short-range order spin density wave. high-temperature range above room temperature, we show largely suppressed while becomes almost temperature-independent, leading significant improvement power factor This result also discussed terms differences orbital size state between Co $3d$ electrons.