Evidence for polaron conduction in nanostructured manganese ferrite

Abstract

Nanoparticles of manganese ferrite were prepared by the chemical co-precipitation technique.\nThe dielectric parameters, namely, real and imaginary dielectric permittivity (ε and ε ),\nac conductivity (σac) and dielectric loss tangent (tan δ), were measured in the frequency range\nof 100 kHz–8MHz at different temperatures. The variations of dielectric dispersion (ε ) and\ndielectric absorption (ε ) with frequency and temperature were also investigated. The variation\nof dielectric permittivity with frequency and temperature followed the Maxwell–Wagner\nmodel based on interfacial polarization in consonance with Koops phenomenological theory.\nThe dielectric loss tangent and hence ε exhibited a relaxation at certain frequencies and at\nrelatively higher temperatures. The dispersion of dielectric permittivity and broadening of the\ndielectric absorption suggest the possibility of a distribution of relaxation time and the\nexistence of multiple equilibrium states in manganese ferrite. The activation energy estimated\nfrom the dielectric relaxation is found to be high and is characteristic of polaron conduction in\nthe nanosized manganese ferrite. The ac conductivity followed a power law dependence\nσac = Bωn typical of charge transport assisted by a hopping or tunnelling process. The\nobserved minimum in the temperature dependence of the frequency exponent n strongly\nsuggests that tunnelling of the large polarons is the dominant transport process