Structural, magnetic, dielectric and optical properties of double-perovskite Bi2FeCrO6 ceramics synthesized under high pressure

We report on double-perovskite Bi2FeCrO6 ceramics synthesized by solid-state reaction under high pressure of 6 GPa and temperature of 1000 degrees C. Its crystal structure was refined by X-ray powder diffraction data, and the Bi2FeCrO6 ceramics crystallized in rhombohedral structure with R3c space group. The ceramic grains exhibited polyhedron morphology with average size of 2.80 mu m. The atomic ratio of Bi:Fe:Cr was determined to be 2.04:1.00:1.00, close to the nominal value. X-ray photoelectron spectra confirmed the dual oxidation states of ion (Fe2+ and Fe3+) and chromium (Cr3+ and Cr6+) in the Bi2FeCrO6 ceramics and oxygen in the forms of lattice oxygen and oxygen vacancies. Bi2FeCrO6 ceramics exhibits both antiferromagnetic and ferromagnetic orders, which are reflected in the unique temperature dependent magnetization curves. In addition, Bi2FeCrO6 ceramics also have large dielectric constant (similar to 508 at 1 kHz) and small dielectric loss (0.38 at 1 MHz) at room temperature. The direct band gap of the Bi2FeCrO6 ceramics deduced from their UV-Vis-NIR absorption spectra, was similar to 1.50 eV, which was small enough to absorb the sunlight at wavelengths below 829 nm. A strong absorption peak was also observed at 600 nm in the absorption spectra of the Bi2FeCrO6 ceramics. These findings demonstrate that the Bi2FeCrO6 ceramics with a narrow direct band gap can effectively absorb the main portion of the sunlight spectrum (i.e., visible lights) and have promising applications in the fields of photoelectrochemical devices and photovoltaic devices. (C) 2019 Elsevier B.V. All rights reserved.