Tunneling conductivity in lithiated transition metal oxide cathode Li_0.9 [Ni_1/3Mn_1/3Co_1/3]O_1.95

Abstract

Electrical complex ac conductivity of the compound Li_0.9[Ni_1/3Mn_1/3Co_1/3]O_1.95 has been studied in the frequency range 10 Hz-2 MHz and in the temperature range 93-373 K. It has been observed that the frequency dependence of the ac conductivity obeys a power law and the temperature dependence of the ac conductivity is quite weak. The experimental data have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping over barriers. It has been observed that the electron tunneling is dominant in the temperature range from 93 K to 193 K. A crossover of relaxation mechanism from electron tunneling to polaron tunneling is observed at 193 K. Out of the several models discussed, the electron tunneling and the polaron tunneling models are quite consistent with the experimental data for the complex ac conductivity. The various parameters obtained from the fits of the experimental results for the real and imaginary parts of the conductivity to the predictions of these models are quite reasonable.