Effect of 3d-transition metal substitution on the thermoelectric properties of the misfit-layered cobalt oxide [Ca2CoO3]pCoO2
Y. Miyazaki, Y. Suzuki, T. Miura, Y. Ono, T. Kajitani
Department of Applied Physics, Graduate School of Engineering, Tohoku University/ Aramaki Aoba, Aoba-ku, Sendai 980-8579, Japan
The 3d-transition metal (M) substitution has been performed on the cobalt site in the rock-salt (RS)-type [Ca2CoO3] subsystem of the misfit-layered cobalt oxide [Ca2(Co1-xMx)O3]pCoO2. Except for M = Ni and Zn, the solid solution has been prepared up to x ~ 0.10, when the mixed powders of starting materials were sintered at 920 degree C. In the case of M = Cu, the solubility limit expands up to x ~ 0.20. The Cu-substituted samples exhibit larger thermoelectric power (S) and lower resistivity (r) relative to the non-doped one. For example, the sample with x = 0.15 shows S = 160 mV/K and r = 8.6 mWcm at 300 K and the resulting thermoelectric power factor reaches S2/r = 3.0 x 10-4 W/mK2, being almost three times larger than that of [Ca2CoO3]pCoO2.