Alkaline-earth elements isovalently substituted into a [Bi2AE2O4][CoO2]y (AE2 = Ca2, Sr2, and CaSr) single crystal with a layered structure were grown by the optical floating zone method. Structural characterization by X-ray diffraction and electron microscopy showed that the layers were oriented perpendicular to the c-axis, as well as the growth of direction was parallel to the ab-plane. The thermoelectric properties, including the Seebeck effect, electrical conductivity and thermal conductivity were investigated. The results of the thermoelectric measurements showed that the full substitution of Ca for Sr in [Bi2Sr2−xCaxO4][CoO2]y has the best overall thermoelectric performance. Compared with the other two cases studied, the full Ca substituted crystal [Bi2Ca2O4][CoO2]y exhibits both reduced resistivity and thermal conductivity, but not a reduced Seebeck coefficient. The enhanced thermoelectric property in [Bi2Ca2O4][CoO2]y is mainly due to lower structural symmetry, which is confirmed by electron microscopy characterization. This work demonstrates that even isovalently substitution can play a crucial role in the thermoelectric effect of layered cobalt oxides.

K0.63RhO2 single crystals were successfully grown by the flux method. Rietveld refinement of power X-ray diffraction patterns suggests that K0.63RhO2 belongs to the monoclinic P63mmc space group. Transport measurements on K0.63RhO2 revealed metallic behavior. The temperature-dependent resistance is well fitted by a different power law in two different temperature ranges. Antiferromagnetic ordering is observed in the ab-plane of K0.63RhO2 below 50 K. The most attractive feature of K0.63RhO2 is its significant Seebeck coefficient at room temperature (46 μV/cm), which is much greater than that of normal metals. Considered all together, the metallic conductivity, the significant Seebeck effect, and the non-hygroscopic properties of K0.63RhO2 make it a promising candidate material for thermoelectric applications