Dielectric and conductivity spectroscopy of Li1-xNi1+xO2 in the range of 10-1010 Hz:: polaron hopping

Dielectric and conductivity spectra of the compound Li1-xNi1+xO2 (x = 0.03) are reported and analysed. The spectra were recorded for compacted powders within the broad frequency range 10-10(10) Hz at temperatures varying between 210 and 300 K. The evolution of the spectra of the sample with respect to the damage under air allows us to define two regimes: the first one is an interfacial regime and the second a bulk regime. The frequency of crossover (nu(co)) between the two regimes lies in the interval 1 x 10(9) and 2 x 10(9) Hz at room temperature. At frequencies below nu(co), the spectral analysis shows dielectric relaxations due to interfacial polarization phenomena in the sample. The complex resistivity plots (for nu < nu(co)) allowed the determination of the dc conductivity of Li1-xNi1+xO2 versus temperature. At frequencies greater than nu(co), one dielectric relaxation corresponding to small-polaron hopping has been observed. The corresponding relaxation frequency is thermally activated with an activation energy of 0.15-0.16 eV and a pre-exponential factor nu(0) approximate to 3 x 10(12)-4 x 10(12) Hz, which is of the order of the longitudinal-optical-phonon frequency nu(LO). The conduction behaviour is interpreted in terms of hopping of small polarons (holes) on an oxygen network.