Association of microstructure and electric heterogeneity in BiFeO3

BiFeO₃ ceramics was synthesized by solid state reaction technique. Synchrotron X-ray diffraction analysis was employed to investigate the phase formation and structure determination. Rietveld refinement of the diffracted data confirmed the rhombohedrally distorted perovskite structure with space group R3c. Localized atomic structure determined from fitted X-ray data showed off centered displacement of Fe³⁺ cations with a magnitude of 0.397 Å along c-axis. The FeO₆ octahedron comprised of two types of Fe–O bonds with bond lengths of ∼1.935 Å and ∼2.131 Å. Impedance spectroscopic data collected in wide temperature (300–400 K) and frequency (200 Hz–2 MHz) ranges, demonstrated two relaxation phenomena corresponding to two heterogeneous phases. The best fits to the collected impedance data were achieved by employing an equivalent circuit model R_g(R_gbC_gb)(R_eQ_e). Grain boundaries showed only p-type small polaronic hopping conduction process assisted with the oxidation of Fe³⁺ to Fe⁴⁺ in measured temperature range of 300–400 K. Grains exhibited p-type small polaronic hopping conduction mechanism up to 375 K; however, above 375 K electronic conduction becomes prominent. Conduction is dominated by short range hopping of the polarons among Fe³⁺ and Fe⁴⁺ or through the first ionized oxygen vacancy bridge between Fe³⁺ and Fe²⁺ cations.