Electrical transports and stability of small polarons of O 2p holes in LixCo1-xO

In order to disentangle the confused arguments as to whether a band conduction or a hopping conduction dominates the electrical transport in LixCo1-xO, dielectric properties, dc and ac conductivities, and thermopowers were investigated. Positive thermopowers indicated the major carriers of holes. Two dielectric relaxations appeared in the loss tangent, a very weak peak at a low temperature (similar to 170 K) and a rather strong one at a high temperature (similar to 240 K). The activation energy required for the high temperature relaxation was nearly equal to that obtained in Arrhenius plots of sigma . T and 1/T. The temperature-dependence of ac conductivities corresponded well to that of loss tangent. The results are explained in terms of small polarons of O 2p holes hopping between oxygen sites. The reorientation of holes bound to Li+ ions gives rise to the low temperature relaxation. A theoretical calculation provides a direct evidence for stability of small polarons of O 2p holes in CoO.