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

Highlights: • Synthesis and characterization of Ba_1-xLa_xTi_1-xFe_xO₃ (0≤x≤1) solid solution. • Demonstration of two main structural phase transition in BLTF (0≤x≤1) system. • Observation of the optical absorption expansion from the UV domain up to 592 nm of the visible domain. • The reveal of B-O-B bond angle parameter effect on the decrement of the optical band gap. • Visualization of a downward shift of the CBM and upward shift of the VBM. 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 ABO₃-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 ABO₃-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 BOB bond angle has an effect on the band gap values as small values were found for bonds angles close to 180°. 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.