Effect of Eu and Mn co-doping on temperature dependent dielectric relaxation behaviour and electric conduction mechanisms of bismuth ferrite

Abstract

The temperature dependent microscopic conduction processes and dielectric relaxations in Eu and Mn co-doped multiferroic bismuth ferrite have been examined using complex frequency-dependent ac conductivity, electric modulus and complex impedance examinations. The modified Debye’s function was used to explore the dispersion behaviour of the dielectric constant. The correlated barrier hopping concept is supported by the frequency variation in ac conductivity at various temperatures, which follows Jonscher’s power law. It was observed that when the co-doping concentration is low, the thermally assisted correlated barrier hopping (CBH) conduction model is better suited for the present samples whereas the overlapping large polaron tunnelling (OLPT) conduction model is better suited for higher co-doping concentrations. By looking at scaling curves for imaginary impedance (Z'') and modulus (M''), thermally induced relaxation processes have been demonstrated. It can be shown from a comparison of the Z'' and M'' spectra that charge carrier motion, particularly the dominance of short-range charge carriers which is effective at low temperatures while long-range charge carriers which is effective at high temperatures, leads to dielectric relaxation. By looking at semi-circular arcs on the Nyquist plot, it can be shown that at high temperature the electrical conduction process for the nanocrystalline sample is influenced by both grain and grain boundaries contributions. According to the study of ac conductivity under different temperatures, all compounds transport electricity with the help of electronic hopping, oxygen vacancy movement, or/and the production of the defects.