Immittance Studies of Bi₆Fe₂Ti₃O₁₈ Ceramics

Results of studies focusing on the electric behavior of Bi₆Fe₂Ti₃O₁₈ (BFTO) ceramics are reported. BFTO ceramics were fabricated by solid state reaction methods. The simple oxides Bi₂O₃, TiO₂, and Fe₂O₃ were used as starting materials. Immittance spectroscopy was chosen as a method to characterize electric and dielectric properties of polycrystalline ceramics. The experimental data were measured in the frequency range Δν = (10^-1-10⁷) Hz and the temperature range ΔT = (-120-200) °C. Analysis of immittance data was performed in terms of complex impedance, electric modulus function, and conductivity. The activation energy corresponding to a non-Debye type of relaxation was found to be E_A = 0.573 eV, whereas the activation energy of conductivity relaxation frequency was found to be E_A = 0.570 eV. An assumption of a hopping conductivity mechanism for BFTO ceramics was studied by 'universal' Jonscher's law. A value of the exponents was found to be within the "Jonscher's range" (0.54 ≤ n ≤ 0.72). The dc-conductivity was extracted from the measurements. Activation energy for dc-conductivity was calculated to be E_DC = 0.78 eV, whereas the dc hopping activation energy was found to be E_H = 0.63 eV. The obtained results were discussed in terms of the jump relaxation model.