Transport properties of La-doped Mn–Zn ferrite

A doped MnxZn1 − xLa0.1Fe1.9O4; 0 ≤ x ≤ 1 Mn–Zn ferrite was prepared by using the standard ceramic technique. The dielectric constant ɛ′, dielectric loss factor ɛ″ and the a.c. conductivity (ln σ) were measured as a function of temperature at different frequencies. Different polarization mechanisms appeared responsible for the variation in the dielectric constant. The polarization process is favored at low frequency, whereas at high frequency alignment of dipoles is disturbed. The decrease in the internal viscosity of the system allows the dipoles to dissipate the thermal energy produced from their friction. The variation of the electrical conductivity is mainly attributed to thermally activated mobility and not to thermal creation of charge carriers. The existence of more than one straight line on the conductivity data indicates the concurrence of several conduction mechanisms. The value of the calculated activation energy indicates the semiconducting behaviour of the investigated materials. Seebeck voltage coefficients measurements indicate that electrons and holes as well as small polarons are responsible for the conduction, where in some samples the electronic conduction predominates.