Design, structural evolution, optical, electrical and dielectric properties of perovskite ceramics Ba1-xBixTi1-xFexO3 (0 <= x <= 0.8)

International audienceThe ceramics with perovskite structure of the compositions Ba1-xBixTi1-xFexO3 (x = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized through the conventional solid-state reaction route. All prepared samples were characterized by X-ray diffraction, Raman spectroscopy, UV-visible spectroscopy and impedance spectroscopy. The X-ray diffraction characterization at room temperature indicated the formation of perovskite phase in all the samples. The X-ray diffraction data refined by Rietveld technique revealed two phase transitions with the increase of BiFeO3 content, the first structural transformation from tetragonal (P4mm) to cubic (Pm (3) over barm) and the second from cubic (Pm (3) over barm) to rhombohedral (R3c), which were confirmed by Raman spectroscopy. UV-vis absorption spectra of doped compounds indicated the presence of four electronic transitions in octahedrally coordinated Fe3+ ions from their fundamental (6)A(1g) (S) level to different excited levels. The co-doping of Bi3+ and Fe3+ ions from 0% to 80 mol% leads to a decrease of the direct band gap energy from 3.29 to 1.91 eV, and a shift of the band gap edges, namely the conduction band minimum and valence band maximum. The impedance results suggest that both grain (G) and grain boundary (GB) contribute to the total conductivity and the effect of this latter increases with (Bi, Fe) content. Additionally, the Nyquist plots showed the negative temperature coefficient of resistance (NTCR) and the temperature-dependent dc electrical conductivity demonstrated the semiconducting nature for all samples. The sample x = 0.4 exhibited the highest dc electrical conductivity. The activation energy values revealed that the conduction mechanism is dominated by ionized oxygen vacancies. The changes of dielectric properties at room temperature with increasing BiFeO3-doping amount are discussed