ELECTRICAL-TRANSPORT PROPERTIES IN LIMN2O4

Bulk conductivity measurements by complex-plane impedance analysis and dielectric measurements have been carried out on LiMn2O4 together wit h four-probe dc conductivity measurements. The electrical conductivity consists of two thermally activated processes: one above 310 K and th e other below 250 K. A dielectric relaxation process shows up at T > 3 10 K with an activation energy nearly equal to that required for the c onduction above 310 K. Below 250 K, a dielectric relaxation also takes place but the activation energy is not available experimentally becau se this relaxation process requires frequencies below the lowest in th e present work. The conduction behaviour is interpreted in terms of a hopping process of small polarons of e, electrons on Mn3+. The transit ion from low-temperature to high-temperature conduction is discussed i n terms of the phase transformation due to the emergence of the I4(1)/ amd phase in the Fd3m matrix caused by the cooperative Jahn-Teller eff ect of the high-spin Mn3+ ions.