POLARONIC CONDUCTION OF ELECTRONS IN ALPHA-MN3O4 SLIGHTLY DOPED WITH LI

Dielectric properties and d.c. conductivities of alpha-Mn3O4 ceramic specimens slightly doped with Li were measured as a function of temperature between 80 and 373 K to investigate transport mechanisms of electrons compensating Li+ ions at interstitial sites. The specimens were quenched to room temperature after the final sintering at 1673 K. The tetragonally-distorted spinel structure was confirmed by an X-ray diffraction pattern. Two apparent dielectric relaxations appear in loss tangent, one is at approximately 200 K with an activation energy of approximately 0.3 eV and the other is at approximately 320 K with an activation energy of approximately 0.65 eV. Though the low temperature relaxation follows Debye's theory, the high temperature relaxation is thermally activated. There were linear relationships in Arrhenius plots of sigmaT and 1/T with an activation energy of approximately 0.75 eV above approximately 220 K, while conductivities below approximately 220 K are independent of temperature. These results can be explained self-consistently in terms of small polaron hopping, which undergoes a progressive transformation from a reorientation of a dipole of Li+-Mn2+ at low temperatures to a hopping process of free small polarons between Mn3+ and Mn2+ at octahedral sites as the temperature increases.