Local environment of iron and tin ions, diffuse absorption, and giant dielectric response in BaFe1/2Sn1/2O3-δ prepared by the sol-gel method

Barium ferrostannate BaFe(1/2)Sn(1/2)O(3-delta )was obtained using the sol-gel precursor method and additional annealing in O-2. Phase purity of ceramics was confirmed by x-ray diffraction, the microstructure and microanalysis of grains were investigated by scanning electron microscopy methods, whereas the valence states and co-ordination of tin and iron ions were determined using Mossbauer spectroscopy. We found out that as-sintered and O-2-treated samples contain 27% and 36% of six-coordinated Fe4+ ions, respectively, whereas Fe3+ ions are five-coordinated. Oxygen treatment results in a decrease of the average sizes of coherent scattering regions, increase of the local distortion of [SnO6] octahedra, and significant increase of conductivity. Experiments on diffuse reflection show that the characteristic absorption band is strongly broadened and shifted to the visible and IR regions, which is explained by the formation of a large number of local donor levels in the band gap. Thus, the optical band gap is reduced by Fe-doping as compared to BaSnO3 and can be additionally adjusted by annealing in oxygen. Both as-sintered and O-2-treated BaFe1/2Sn1/2O3-delta ceramics exhibit giant dielectric response in a wide frequency range. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Barium ferrostannate BaFe(1/2)Sn(1/2)O(3-delta) was synthesized using the sol-gel method and annealed in oxygen to improve phase purity. Analysis revealed that oxygen treatment increased conductivity and altered optical properties, narrowing the optical band gap. Additionally, the ceramics exhibited outstanding dielectric response in a wide frequency range.