Exploring the dielectric behaviour of nano-structured Al3+ doped BiFeO3 ceramics synthesized by auto ignition process

Dielectric relaxation and electrical properties of Al doped polycrystalline bismuth ferrite (BAFO) nano-structured ceramics (13–20 nm having composition Bi1−xAl2xFe1−xO3 (0.0 ≤ x ≤ 0.3) were investigated over a wide range of frequency and temperature. Relaxation peaks were obtained in low as well as high frequency regions for all samples which are explained on the basis of Debye-type relaxation model. The replacement of Fe3+ and Bi3+ by Al3+ ions in the BFO system creates oxygen vacancies and hence Schottky barriers, which are responsible for the anomalous behaviour in the dielectric properties. Debye relaxation model and Maxwell–Wagner charge carriers hopping were utilized in overall estimation of the dielectric behaviour of the system. The values of dielectric constant and loss tangent were found to decrease with the increase in frequency, while these parameters increase with the increase in temperature as well as dopant concentration. The a.c. conductivity has a general decreasing trend as a function of composition while it increases with the increase in frequency. The temperature dependence of a.c. conductivity and relaxation time follow well-defined Arrhenius behaviour. The calculated values of activation energies are in the order of 0.54 eV–0.73 eV (<1.0 eV) which are indicative of the conduction by means of space charge carriers and O2− vacancies.

► The values of dielectric constant and loss tangent were observed to decrease with the increase in frequency, while these parameters increase with the increase in temperature as well as dopant concentration.
► The a.c. conductivity has a general decreasing trend as a function of composition while it increases with the increase in frequency.
► The temperature dependence of a.c. conductivity and relaxation time follow well-defined Arrhenius behaviour.
► The calculated values of activation energies are in the range of 0.54 eV–0.73 eV (<1.0 eV) which are indicative of the conduction by means of space charge carriers.