Thermoelectric properties of epitaxial Li$_{x}$CoO$_{2}$ thin films .

We have studied the thermoelectric properties of layered cobaltate Li$_{x}$CoO$_{2}$ since the similar compound Na$_{x}$CoO$_{2}$ has shown exceptionally high thermoelectric power. Both \textit{in situ} epitaxial grown and topotaxial Li$_{x}$CoO$_{2}$ films have been achieved. Epitaxial films were grown by pulsed-laser deposition technique and topotaxial films were prepared by converting an epitaxial Co$_{3}$O$_{4}$ film to Li$_{x}$CoO$_{2 }$by annealing in Li vapor. X-ray diffraction analysis showed the films are $c$-axis oriented. For topotaxial Li$_{x}$CoO$_{2 }$the largest thermoelectric power of the samples is found to be around 380 $\mu $V/K at room temperature, while\textit{ in situ} films show thermopower of 100 $\mu $V/K. Both show semiconducting behaviors. The difference on the thermopower of the two types of samples will be discussed.