Electrical Transports and Stability of Small Polarons of O2pHoles in LixCo1 -xO

Abstract

In order to disentangle the confused arguments as to whether a band conduction or a hopping conduction dominates the electrical transport in Li x Co 1- x O, 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 (∼170 K) and a rather strong one at a high temperature (∼240 K). The activation energy required for the high temperature relaxation was nearly equal to that obtained in Arrhenius plots of σ· 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 2 p 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 2 p holes in CoO.