Cr3+/Er3+ Co-Doped BaTiO3 Ceramics: Structural Evolution, Microstructural Development, and Dielectric Response

Cr3+/Er3+ co-doping was investigated as a strategy to modify the structural, microstructural, and dielectric response of BaTiO3 ceramics. Ba1−3xCr2xTi1−3xEr4xO3 compositions (x = 0, 0.001, 0.0015, and 0.002) were prepared by mechanical milling followed by high-temperature sintering. X-ray diffraction and Rietveld refinement confirmed a single tetragonal BaTiO3 perovskite phase without detectable secondary crystalline phases. Co-doping slightly increased the tetragonality ratio from 1.0083 to approximately 1.0098, while the lattice microstrain decreased markedly from 2.34 × 10−3 for undoped BaTiO3 to 8.37 × 10−5 for x = 0.002, with the crystallite size remaining nearly constant at approximately 29–30 nm. FE-SEM analysis revealed a non-monotonic microstructural evolution, with x = 0.001 exhibiting the largest average grain size (3.881 ± 1.479 µm), highest relative density (97.97%), and lowest apparent porosity (0.21%). Dielectric measurements revealed a strongly composition- and frequency-dependent response, with x = 0.0015 exhibiting the highest maximum relative permittivity (εr,max ≈ 12,457) at 1 kHz and 114 °C. However, this composition also exhibited a pronounced decrease in permittivity with increasing frequency and appreciable dielectric loss upon heating, indicating that its enhanced low-frequency response should not be interpreted solely as an intrinsic dielectric effect. Possible non-intrinsic polarization mechanisms may be involved in this behavior, although their individual contributions cannot be distinguished from the present measurements. Overall, the results demonstrate that Cr3+/Er3+ co-doping produces composition-dependent modifications in the structural, microstructural, and dielectric response of BaTiO3 ceramics, with enhanced relative permittivity under specific conditions accompanied by significant frequency dependence and dielectric loss.