Structural and optical properties of Bi1−xAxFeO3 (A = Sr, Ca; 0.40 ⩽ x ⩽ 0.55)

The effect of Sr2+ and Ca2+ cation substitution on BiFeO3-type (Bi1−xAxFeO3; A = Sr, Ca; 0.40 ⩽ x ⩽ 0.55) ceramics are investigated for structural and optical properties. X-ray diffraction patterns confirmed that Ca2+/Sr2+ substitution facilitates the formation of tetragonal phase instead of rhombohedral phase as observed in undoped BiFeO3 (BFO). The iodometric titration results show that substitution of Sr2+ has higher tendency to form oxygen vacancies than Ca2+ substituted samples. On the other hand, Ca2+ substitution shows opposite trend. The FT-IR and Raman spectra show shift in the peak positions towards higher wavenumber and diffused bands with the increasing concentration of substituent. The parameters like band gap energy, Urbach energy has been calculated from the UV–visible spectra. Sr2+ substituted samples show higher structural distortion and low optical band gap values which can be correlated to the higher oxygen vacancies and low Fe4+ content as compared to Ca2+ substituted samples.