High temperature electrical conductivity and thermoelectric power of NaxCoO2

Layered cobalt oxides, NaxCoO2, with the density of sodium ions, x, ranging from 0.65 to 0.85, were prepared by rapid heat-up method. The determination by X-ray diffraction pattern of crystal structure and the grain morphology studied by scanning electron microscopy were reported. The measurements of electrical conductivity and thermoelectric power were carried out between 300 K and 1100 K. It has been found that the concentration of sodium ions sandwiched between two neighboring CoO2 layers plays a crucial role in transport properties.