1：Experimental Design and Method Selection:

The study used solid-state reaction technique to prepare BCTS ceramics, with variations in Ca content (x=

2：0 to 1). Methods included XRD for phase analysis, SEM-EDS for microstructure and purity, FE-SEM for morphology, HSM for sintering behavior, DTA for thermal analysis, and electrical measurements for dielectric and piezoelectric properties. Sample Selection and Data Sources:

Samples were prepared from ACS grade reagents (BaCO3, CaCO3, TiO2, SnO2) with purity >99%, mixed in stoichiometric proportions.

3：List of Experimental Equipment and Materials:

Equipment included ball mill, muffle furnace (Nabertherm P330), DTA instrument (DTA 404 PC, Netzsch), XRD (Pan'Analytical), SEM (FEI Inspect, Philips 525), EDS (Quanta 400 FEG, Ametek), FE-SEM, HSM, LCR meter (Hioki 3533-01), piezometer, screen-printing setup, and furnaces. Materials included zirconia balls, ethanol, platinum and alumina crucibles, alumina substrates (ADS-96 R, Coors Tek), platinum conductor paste (ESL 5545, Electro-Science), and organic vehicle (Emflow 227, Emca-Remex).

4：Experimental Procedures and Operational Workflow:

Powders were ball-milled for 24h, dried at 80°C, sieved, calcined at 1050°C or 1200°C for 4h, remilled, dried, sieved, pressed into pellets, sintered at 1300°C or 1400°C for 4h. For humidity sensing, powders were screen-printed onto substrates, dried, and heat-treated. Electrical measurements were conducted after poling.

5：4h. For humidity sensing, powders were screen-printed onto substrates, dried, and heat-treated. Electrical measurements were conducted after poling. Data Analysis Methods:

5. Data Analysis Methods: XRD patterns were indexed using X'Pert Highscore software. EDS and SEM images were analyzed for composition and microstructure. Dielectric and piezoelectric data were analyzed using LCR meter and piezometer.