<p>Barium titanate (BT) and calcium-doped barium titanate BCT (BaCa_xTi_1-xO₃), <i>x</i> = 0.0, 0.025, 0.050, and 0.075, and perovskite powders nanostructures, were manufactured by the solid-state reaction (SSR) route and analyzed using X-ray diffraction (XRD) at (20–90) degrees to investigate the crystallite phases and geometric limits for the synthesized powders. The XRD peaks revealed a narrowing and a shift toward higher angles for <i>X</i>_Ca (0, 0.025, and 0.050), and a shift to lower angles for <i>X</i>_Ca (0.075), due to Ca²⁺ substitution or interstitial sites in the BaTiO₃ lattice. The impact of Ca²⁺ substitution or interstitial insertion into the BaTiO₃ lattice was investigated using X-ray diffraction, as well as strain analysis via the Williamson–Hall and Scherrer equations. In addition, stress, Young’s modulus, and energy density have been valued for the perovskite structure. Moreover, the lattice parameter has been estimated according to Vegard’s law with fitted plots and goodness of fit R² close to 1. The reflectance curves exhibit red-shifted reflectivity peaks for Ca-doped BaTiO₃, especially at 0.075, dopant; moreover, the c/a ratio of the tetragonality degree greatly influences the Curry temperature (Tc). It was observed that Tc shifts toward room temperature with increasing Ca ion content. The surface morphology was measured using scanning electron microscopy (SEM), which shows a dense microstructure and an increase in roughness during grain growth.</p>