The results of the effect of the three Ba:Ti molar ratios (MR) (1:1, 2:1, 4:1) and four sintering temperatures (1250, 1275, 1300, 1325 °C) on the structural and electrical properties of BaTiO₃ (BT)-type ceramics synthesized by the hydrothermal method are shown. The BT phase formed was analyzed by x-ray diffraction (XRD), Raman spectroscopy (RS), dielectric and ferroelectric measurements and high-resolution scanning electron microscopy (HRSEM). For the samples synthesized using a Ba:Ti MR of 4:1 and at all sintering temperatures analyzed, XRD results confirmed the presence of the tetragonal ferroelectric phase, BT. In the same way, these results corroborated the results obtained by the RS technique. Dielectric properties measured at 100 kHz and 1 MHz over a temperature range of 30 °C–200 °C indicated a relative permittivity value of 4280 at 1 MHz and 4200 at 100 KHz at a Curie temperature of 110 °C in both cases for the sample synthesized at with a Ba:Ti MR ratio of 4:1 and sintered at 1300 °C. Ferroelectric measurements for the samples showed a best remnant polarization (Pr) of 3.5 µC/cm² for the sample synthesized with a Ba:Ti MR ratio of 4:1 and sintered at 1325 °C. The HRSEM results showed grains composed of Ba, Ti, and O homogeneously distributed in the BT structure, and a trend of increasing average grain size with increasing sintering temperature was observed.

Cr³⁺/Er³⁺ co-doping was investigated as a strategy to modify the structural, microstructural, and dielectric response of BaTiO₃ ceramics. Ba_1−3xCr_2xTi_1−3xEr_4xO₃ 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 (ε_r,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.