Abstract
Bulk conductivity measurements by complex-plane impedance analysis and dielectric measurements have been carried out on LiMn2O4 together with four-probe dc conductivity measurements. The electrical conductivity consists of two thermally activated processes: one above 310 K and the other below 250 K. A dielectric relaxation process shows up at T > 310 K with an activation energy nearly equal to that required for the conduction above 310 K. Below 250 K, a dielectric relaxation also takes place but the activation energy is not available experimentally because this relaxation process requires frequencies below the lowest in the present work. The conduction behaviour is interpreted in terms of a hopping process of small polarons of eg electrons on Mn3+. The transition from low-temperature to high-temperature conduction is discussed in terms of the phase transformation due to the emergence of the I41/amd phase in the Fd3m matrix caused by the cooperative Jahn-Teller effect of the high-spin Mn3+ ions.