Effect of 3d-transition metal substitution on the thermoelectric properties of the misfit-layered cobalt oxide [Ca2CoO3]pCoO2

The 3d-transition metal (M) substitution has been performed on the cobalt site in the rock-salt (RS)-type [Ca₂CoO₃] subsystem of misfit-layered cobalt oxide [Ca₂(Co_1-xM_x)O₃]pCoO₂. Except for M = V, Ni and Zn, the solid solution has been prepared up to x ∼ 0.10, when the mixed powders of starting materials were sintered at 1193 K. The Cu-substituted samples exhibit larger thermoelectric power (S) and lower resistivity (ρ) relative to the non-doped one. For example, the sample with x = 0.10 shows S = 160 μVK^-1 and ρ = 9.1 mΩcm at 290 K and the resulting thermoelectric power factor reaches S²/ρ = 2.8 x 10^-4 Wm^-1K^-2, being almost twice larger than that of [Ca₂CoO₃]_pCoO₂.