Structural characterization, dielectric, magnetic and optical properties of double perovskite Bi2FeMnO6 ceramics

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Double perovskite Bi2FeMnO6 (BFMO) oxides are promising candidate for single-phase multiferroic system. However, up to date only a limited works are carried out to synthesize the BFMO ceramics, and most of them have the issues of impure phases. In this work, we report on the structural, dielectric, magnetic, and optical properties of single-phase BFMO ceramics synthesized by solid-state reaction method. The BFMO ceramics crystallized in a rhombohedral structure with R3c space group, and their grains exhibited polyhedron morphology with average size of 15.0 µm. X-ray energy dispersive spectroscopy revealed the ceramic grains with atomic ratio of Bi:Fe:Mn equal to 2.0:1.16:0.90. XPS spectra of Fe 2p and Mn 2p core levels confirm the mixed chemical valence states of Fe (Fe2+ and Fe3+) and Mn (Mn3+ and Mn4+) in the BFMO ceramics. O 1s XPS spectra reveal the oxygen existing in the forms of lattice oxygen and oxygen vacancies while bismuth is present as Bi3+. Dielectric measurements demonstrate that the BFMO ceramics have much high dielectric constant (in the order of 104) in the frequency below 102 Hz but decrease fast with increasing the frequency. The same phenomenon appeared for the dielectric loss. A dielectric relaxation behavior with activation energy of 0.34 eV was observed in the BFMO ceramics, which was due to the thermal motion of the oxygen vacancies. The BFMO ceramics exhibit antiferromagnetic nature but a weak ferromagnetic behavior at 2 K. Sharp cusp peaks were observed in the zero-field-cooling (ZFC) curves and bifurcations between the field-cooling (FC) and ZFC curves were observed. Both of them shifted to low temperature as increasing the external applied magnetic field, indicating a spin-glass like behavior in the system. UV–Vis absorption spectra demonstrated a broad absorption peak in the wavelength range of 300–800 nm and a direct optical band gap of ~1.23 eV for the BFMO ceramics. Such narrow optical band gap as well as the high dielectric constant at room temperature enable the BFMO ceramics to be promising candidate used for solar cells, sensors, bolometer and optoelectronic devices.