La3+/Bi3+ Co-Doping in BaTiO3 Ceramics: Structural Evolution and Enhanced Dielectric Properties

La3+/Bi3+ co-doped BaTiO3 ceramics were synthesized via ball milling followed by heat treatment at 1200 °C according to the Ba1−3xLa2xTi1−3xBi4xO3 formula, with dopant levels ranging from x = 0.0 to 0.006. X-ray diffraction and Rietveld refinement confirmed a ferroelectric tetragonal phase for all compositions, with the highest tetragonality (c/a = 1.009) observed for x = 0.001 exceeding that of pure BaTiO3 (1.0083). High-resolution electron microscopy analysis revealed faceted particles with mean sizes between 362.5 nm and 488.3 nm. Low-doped samples (x = 0.001 and 0.002) exhibited higher permittivity than undoped BaTiO3, with the maximum dielectric constant (εr = 2469.0 at room temperature and 7499.7 at the Curie temperature) recorded for x = 0.001 at 1 kHz. At x = 0.006, minimal permittivity variation indicated a stable dielectric response. A decrease in the Curie temperature was observed with increasing doping levels, indicating a progressive tendency toward the cubic phase. Critical exponent γ values (0.94–1.56) indicated a sharp phase transition for low-doped samples and a diffuse transition for highly doped BaTiO3. These results showed that La3+/Bi3+ co-doping effectively tunes the structural and dielectric properties of BaTiO3 ceramics.