Influence of Ba-doping on the structural and physical properties of Sr2−xBaxFeVO6 double perovskites

The influence of A-site Ba-doping on the structural, dielectric, magnetic, and optical properties of double perovskite (Ba x Sr 2-x )FeVO 6 (BSFV(x): x = 0.0 - 2.0) ceramics prepared by solid-state reaction method, is reported. X-ray diffraction patterns and Rietveld refinements revealed that the BSFV (x) samples with x = 0.0 - 1.0 crystallized in a cubic crystal structure with an Fm 3 ̅ m symmetry whereas the samples with x = 1.5 and 2.0 crystallized in a hexagonal crystal structure with R 3c symmetry. Their unit cell volumes increased progressively with the Ba-doping content due to the steric effect generated by the progressive increase of the average ionic radius at A-site, 〈r A 〉. SEM images revealed the BSFV(x) samples were highly dense with ceramic grains of polyhedral morphology. Their average grain sizes increased from 2.0(2) μm (x = 0.0) to 5.0(3) μm (x = 2.0). X-ray energy dispersive spectroscopy data gave out the chemical compositions of these samples, which were close to the nominal stoichiometric values. FTIR spectra verified the vibrating modes of the [FeO 6 ] and [VO 6 ] octahedrons in the present samples. XPS spectra confirmed dual chemical valence states of Fe element (Fe 2+ and Fe 3+ ) and a triple oxidation states of V element (V 3+ , V 4+ and V 5+ ) as well as two species of oxygens in the BSFV(x) samples. The BSFV ceramics exhibited a strongly frequency-dependent dielectric behavior and a diffuse phase transition, which were resulted from the dielectric response of oxygen vacancies and the electron hopping between the variable cations at B-site as well as the B-site cationic random occupancy. Magnetic Curie temperature ( T C ) and effective magnetic moment ( μ eff ) decreased as increasing the Ba-doping content due to the weakening of superexchange magnetic interactions between the Fe and V ions. The optical band gaps ( E g ) of the BSFV(x) samples extracted from UV-Visible spectra, were in the range of 1.94 – 2.42 eV, exhibiting a blue shift towards semiconductor range as increasing the Ba-doping content. The overlapping between the O-2 p and Fe/V-3 d orbitals contributes to the E g in the BSFV samples. • (Ba x Sr 2-x )FeVO 6 (x = 0.0 - 2.0) ceramics were synthesized by solid-state reaction method. • Microstructures and chemical valence state of the elements were investigated. • The ceramic samples exhibit strongly frequency-dependent dielectric behavior. • T C and μ eff of the ceramic samples decreased with increasing the Ba-doping content. • E g values of the ceramic samples were in the range of 1.94 – 2.42 eV.