1：Experimental Design and Method Selection:

Conventional solid-state sintering route was adopted to synthesize various compositions of BaTiO3-based ceramics with Sr2+ and Ca2+ substitutions. The methodology included powder preparation, calcination, pressing, sintering, and characterization using XRD, SEM, dielectric measurements, ferroelectric testing, and UV-Vis spectroscopy.

2：Sample Selection and Data Sources:

Samples included Ba0.9Sr0.1TiO3, Ba0.7Sr0.3TiO3, Ba0.5Sr0.5TiO3, Ba0.5Ca0.25Sr0.25TiO3, and Ba0.5Ca0.5TiO3. Raw materials were high-purity BaCO3, CaO, SrCO3, and TiO2 in stoichiometric ratios.

3：9Sr1TiO3, Ba7Sr3TiO3, Ba5Sr5TiO3, Ba5Ca25Sr25TiO3, and Ba5Ca5TiORaw materials were high-purity BaCO3, CaO, SrCO3, and TiO2 in stoichiometric ratios. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included ball mill, oven, furnace for sintering, Archimedes method setup for density, X-ray diffractometer (Bruker Advanced D8, Germany), SEM (ZEISS-EVO 18, UK), impedance analyzer (Wayne Kerr 6500B series, UK), multiferroic tester (Radiant Tech. Inc., USA), and UV-Vis spectrophotometer (SHIMADZU UV/Vis-1650 PC, Japan). Materials included ethanol, PVA binder.

4：Experimental Procedures and Operational Workflow:

Powders were ball-milled in ethanol for 20 h, dried at 100°C for 24 h, calcined at 1000°C for 2 h, re-milled, pressed into pellets, sintered at 1150–1250°C for 2 h. Density measured by Archimedes method, XRD for phase identification, SEM for morphology, dielectric properties measured at 20 Hz-5 MHz, P-E loops at 1 Hz, optical band gap by UV-Vis.

5：Data Analysis Methods:

XRD data analyzed with FULLPROF software for Rietveld refinement, grain size by linear intercept method and IMAGE J software, dielectric data analyzed for constant and loss, optical data using Kubelka-Munk function and Tauc plot for band gap.