1992 Volume 61 Issue 9 Pages 3385-3393
Dielectric properties and dc-conductivities in p-type NiO doped with Li (1∼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 (σT3⁄2) and 1⁄T in the range of ∼45 to ∼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, λ, and the changes in spacings between ions, x, associated with formation of a polaron have been carried out. The calculations yield λ and x between Ni3+ and Ni2+ in 〈110〉 directions are −3.48 eV/Å and −9.6×10−3 Å and these between Ni3+ and O2− in 〈100〉 directions are 0.42 eV/Å and 5.12×10−2 Å. This theoretical calculation provides an evidence on stability of nonadiabatic small polarons in p-type NiO.
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