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 (BaxSr2-x)FeVO6 (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 Fm3m symmetry whereas the samples with x = 1.5 and 2.0 crystallized in a hexagonal crystal structure with R3c 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) mu m (x = 0.0) to 5.0(3) mu m (x = 2.0). X-ray energy dispersive spectroscopy data gave out the chemical composi-tions of these samples, which were close to the nominal stoichiometric values. FTIR spectra verified the vibrating modes of the [FeO6] and [VO6] octahedrons in the present samples. XPS spectra confirmed dual chemical valence states of Fe element (Fe2+ and Fe3+) and a triple oxidation states of V element (V3+, V4+ and V5+) 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 di-electric 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 (TC) and effective magnetic moment (mu 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 (Eg) of the BSFV(x) samples ex-tracted 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-2p and Fe/V-3d orbitals contributes to the Eg in the BSFV samples. (c) 2022 Published by Elsevier B.V.