1：Experimental Design and Method Selection:

A chemical method similar to the St?ber process was used to coat BaTiO3 nanoparticles with TiO2, with thickness controlled by tetrabutyl titanate volume. Compositions with different TiO2 contents (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt.%) were prepared. Annealing in O2 was performed to study defect engineering effects.

2：2, 4, 6, 8, 0 wt.%) were prepared. Annealing in O2 was performed to study defect engineering effects. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Commercial BaTiO3 nanoparticles (average size 200 nm) and analytical-reagent materials (TBT, acetic acid, ethanol, ammonia water, acetylacetone) were used. Samples were sintered and annealed.

3：List of Experimental Equipment and Materials:

Equipment includes X-ray diffractometer (Philips PW3050/60), TEM (JEM-2100F STEM/EDS), SEM (JSM-5610LV), LCR meter (Agilent E4980A), quasi-static d33 meter (ZJ-3D), impedance analyzer (Agilent HP4294A), ferroelectric test system (HVI0403-239). Materials include BaTiO3 nanoparticles, TBT, acetic acid, ethanol, ammonia water, acetylacetone, PVA binder.

4：9). Materials include BaTiO3 nanoparticles, TBT, acetic acid, ethanol, ammonia water, acetylacetone, PVA binder. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: BaTiO3 nanoparticles were activated with acetic acid, coated with TiO2 via sol synthesis, dried, pressed into pellets with PVA binder, debindered at 600°C, sintered at 1270°C in air, and some annealed in O2 at 1100°C. Electrical properties were measured after poling with silver electrodes.

5：Data Analysis Methods:

XRD for phase structure, TEM and SEM for microstructure, LCR meter for dielectric properties, d33 meter for piezoelectric constant, impedance analyzer for electromechanical factors, ferroelectric test system for hysteresis loops. Impedance spectra were fitted with RC-branch equivalent circuits.