DIELECTRIC RELAXATIONS AND ELECTRICAL TRANSPORT DUE TO NONADIABATIC SMALL POLARONS IN P-TYPE NIO DOPED WITH LI

Dielectric properties and dc-conductivities in p-type NiO doped with Li (1 approximately 10 atomic%) were investigated below 300 K. Around 40 K, a dielectric relaxation peak appeared with an activation energy of 0.051 eV and the intensity of this peak was found to be thermally activated, the activation energy being 0.01 eV. There was a linear relation between log (sigmaT3/2) and 1/T in the range of approximately 45 to approximately 90 K and the activation energy was 0.057 eV. These behaviours have been discussed in terms of hopping process of nonadiabatic small polarons. The theoretical estimates of electron-phonon-coupling constants, lambda, and the changes in spacings between ions, x, associated with formation of a polaron have been carried out. The calculations yield lambda and x between Ni3+ and Ni2+ in [110] directions are -3.48 eV/angstrom and -9.6 x 10(-3) angstrom and these between Ni3+ and O2- in [100] directions are 0.42 eV/angstrom and 5.12 x 10(-2) angstrom. This theoretical calculation provides an evidence on stability of nonadiabatic small polarons in p-type NiO.