Enhanced thermopower in an intergrowth cobalt oxide Li₀.₄₈Na₀.₃₅CoO₂

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We report the measurements of thermopower, electrical resistivity and thermal conductivity in a complex cobalt oxide Li₀.₄₈Na₀.₃₅CoO₂, whose crystal structure can be viewed as an intergrowth of the O3 phase of LiₓCoO₂ and the P2 phase of NayCoO₂ along the c axis. The compound shows large room-temperature thermopower of 180 μV/K, which is substantially higher than those of LiₓCoO₂ and NayCoO₂. The figure of merit for the polycrystalline sample increases rapidly with increasing temperature, and it achieves nearly 10⁻⁴ K⁻¹ at 300 K, suggesting that LiₓNayCoO₂ system is a promising candidate for thermoelectric applications.