Low-Temperature Magnetic and Thermoelectric Properties of Layered Ca0.33CoO2 Crystals

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Ca0.33CoO2 crystals have been prepared by a low-temperature ion-exchange technique from layered Na0.50CoO2 precursor crystals and characterized by X-ray diffraction, magnetic susceptibility, and ab-plane thermoelectric property measurements. Ca0.33CoO2 is isostructural to Na0.50CoO2 with a layered triangular structure. Its magnetic susceptibility shows a Curie--Weiss behavior at temperatures above 50 K. With decreasing temperature, a crossover from a metallic behavior to a semiconducting behavior is observed at about 36 K. The Seebeck coefficient increases monotonically with increasing temperature and reaches 81 μV/K at 300 K. The maximum power factor is 9.0\times 10^{-4} W m-1 K-2 at 300 K, which is about 25% higher than that of Ca3Co4O9. The thermal conductivity at room temperature is 11 W m-1 K-1, which is lower than that for NaxCoO2-\delta single crystals.
2011-07-15