Impedance spectroscopy of Bi-rich BiFeO3: Twin thermal-activations

Transport measurements data are presented on bismuth-rich BiFeO3 ceramic, synthesized by a solid state method. Conductivity isotherms were analyzed using Jonscher’s empirical power-law frequency dependence. Monotonically increasing frequency-exponent n(T) over 413–593 K indicates a small polaron tunnelling mechanism for the charge transport. Distinct linear regimes observed in the Arrhenius σdc vs. T−1 plot suggest that two different charge-carriers/conductivity-relaxations prevail above and below ∼490 K. Twin Arrhenius regimes of ac-conductivity also exhibit a sharp “transition” at 510 K, from the pinned-dipole/hopping-anion dynamics to the free-dipole/oscillating-ions response at higher temperatures. Furthermore, a concurrent behavior-change of the locus traced out by the charge-hopping frequency ωh [with σ(ωh) = 2σdc] also designates 510 K as delineating two different transport characteristics in the adjacent temperature regimes.