Effect of the composition and structure on the optical properties of Ba1-xLaxTi1-xFexO3 (0 ≤ x ≤ 1) solid solution: Correlation study using Rietveld refinement

In this work, X-ray diffraction assisted with Rietveld refinement method was used to study the effect of the composition on the structural transitions and the optical properties of perovskite ABO(3)-type, prepared using the conventional solid state reaction technique. X-ray analysis indicates the ability of BaTiO3 to accommodate different percentages of La3+ cation in A-sites and Fe3+ cation in B-sites while maintaining the ABO(3)-type structure. Rietveld refinement method showed the existence of several phase transitions: a first from tetragonal (0 <= x <= 0.25) to cubic (0.3 <= x <= 0.6) and a second from cubic (0.3 <= x <= 0.6) to orthorhombic (0.7 <= x <= 1), with one tetragonal sub-transition (P4mm -> P4/mmm) and one orthorhombic sub-transition (Pnma -> Pbnm). The UV-vis analysis showed that BaTiO3 absorption band undergoes an expansion up to 592 nm as the amount of La3+ and Fe3+ increases. The structural investigation revealed that B-O-B bond angle has an effect on the band gap values as small values were found for bonds angles close to 180 degrees. As the amount of the substitution increases, a shift of both the conduction band minimum and valence band maximum was observed for all the compositions, which is consistent with the band gap values obtained.