Thermoelectric properties of Fe-substituted layered compound, LiCo1-x Fex O2

The layered compound LiCoO2 belonging to the ABO(2) class exhibits a variety of interesting behaviors, and substitution adds a twist to the properties. Hence, the effect of partial substitution of Co+3 with Fe+3 on the high-temperature thermoelectric properties has been studied in detail. The X-ray diffraction patterns together with Rietveld refinement indicate formation of a single phase conforming to Rm space group in all the three cases, LiCo1-x Fe O-x(2) with x = 0.01, 0.02, and 0.08. The electrical resistivity in all the compounds decreases by four orders of magnitude with increasing temperature from 300 to 1000 K, a semiconducting behavior. The Seebeck coefficient is found to be very high, > 700 mu V K-1 in all the cases, and increases with increasing temperature and Fe+3 substitution. The thermal conductivity, on the other hand, has been found to decrease with temperature in all the compounds from 3.5 W m(-1) K-1 at room temperature to 1 W m(-1) K-1 at 973 K, a consequence of phonon-phonon scattering. High resistivity of the compounds limits power factor indicating that carrier concentration and mobility need to be increased to realize a high figure-of-merit.