Polaronic conduction of electrons in α-Mn 3O 4 slightly doped with Li

Abstract

Dielectric properties and d.c. conductivities of α-Mn 3O 4 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 ~200 K with an activation energy of ~0.3eV and the other is at ~320K with an activation energy of ~0.65eV. Though the low temperature relaxation follows Debye's theory, the high temperature relaxation is thermally activated. There were linear relationships in Arrhenius plots of σ T and 1 T with an activation energy of ~0.75 eV above ~220K, while conductivities below ~ 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 +-Mn 2+ at low temperatures to a hopping process of free small polarons between Mn 3+ and Mn 2+ at octahedral sites as the temperature increases.