Synthesis and structural evolution of Ba1-3xLa2xTi1-3xBi4xO3 solid solutions (0.0 ≤ x ≤ 0.05)

In this study, the synthesis and structural evolution of pure BaTiO₃ and BaTiO₃ co-doped with La³⁺ and Bi³⁺, produced using the ball milling method and heat treatment, were analyzed. The starting materials included chemically pure precursor powders of BaCO₃, TiO₂, La₂O_3, and Bi₂O₃. Stoichiometric calculations were performed using the Ba_1-3xLa_2xTi_1-3xBi_4xO₃ mechanism with concentrations x = 0.0, 0.0025, 0.0045, 0.006, 0.01, and 0.05 (mol %). The structural and morphological evolution of the samples was characterized by x-ray diffraction (XRD), Rietveld refinement, and high-resolution scanning electron microscopy (HRSEM-EDS). XRD and Rietveld refinement results indicated a tetragonal ferroelectric phase for samples with x ≤ 0.006. As doping levels increased, a peak disappearance was observed, corresponding to a phase transformation from tetragonal to cubic at x = 0.01. Additionally, a cubic secondary phase, BaBiO₃, was detected at x = 0.05, indicating that the maximum solubility of La³⁺ and Bi³⁺ ions in BaTiO₃ was exceeded at this concentration. The concentration x = 0.0025 was found to exhibit the maximum tetragonality among the samples studied, with a value of 1.0087, greater than the tetragonality for pure BaTiO₃, 1.0083. The HRSEM-EDS analysis revealed that for samples with x ≤ 0.006, the microstructure consisted of faceted shape grains with mean grain size in the range of 362.5 nm-488.3 nm. Punctual microanalysis and elemental distribution mapping of the doped samples showed that the grains were composed of Ba, Ti, O, Bi, and La, which were homogeneously distributed, confirming the incorporation of the dopant elements into the BaTiO₃ structure.