1：Experimental Design and Method Selection:

The study focuses on fabricating 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 (BCT–BMT) lead-free relaxor ferroelectric thin films using a sol–gel method on Pt(111)/TiOx/SiO2/Si substrates. The experimental design includes structural characterization, dielectric property measurements, and electrocaloric effect evaluation to understand the phase transition and its role in the negative EC effect.

2：5(Ba8Ca2)TiO3–5Bi(Mg5Ti5)O3 (BCT–BMT) lead-free relaxor ferroelectric thin films using a sol–gel method on Pt(111)/TiOx/SiO2/Si substrates. The experimental design includes structural characterization, dielectric property measurements, and electrocaloric effect evaluation to understand the phase transition and its role in the negative EC effect. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The thin film samples are prepared with specific chemical compositions, including excess Bi and Mg to avoid pyrochlore phases. Data are sourced from various characterization techniques applied to these films.

3：List of Experimental Equipment and Materials:

Equipment includes X-ray diffractometer (Rigaku 9 KW Smartlab), scanning electron microscope (FEI Sirion 200), transmission electron microscopes (Titan Cubed Themis G2300, JEOL JEM-2100F), scanning probe microscopes (Bruker Multimode 8, Asylum Research MFP-3D), Raman spectrometer (Horiba HR800), impedance analyzer (Agilent E4980A), ferroelectric tester (Radiant Technologies Precision Premier II), signal source (Agilent 81150A), digital oscilloscope (LeCroy HDO4104), and thermal controller (Linkam THMSG600). Materials include precursor chemicals like Bi(CH3COO)3, Ca(CH3COO)2, Ba(CH3COO)2, Mg(OC2H5)2, Ti(OCH(CH3)2)4, and substrates.

4：0). Materials include precursor chemicals like Bi(CH3COO)3, Ca(CH3COO)2, Ba(CH3COO)2, Mg(OC2H5)2, Ti(OCH(CH3)2)4, and substrates. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The fabrication involves dissolving precursors, mixing solutions, spin-coating on substrates, drying, pyrolyzing, and annealing. Characterization steps include XRD for crystallinity, SEM and TEM for morphology, AFM and PFM for surface and domain analysis, Raman spectroscopy for phase identification, dielectric measurements, P–E loop measurements, and energy storage tests. Electrical properties are measured with top electrodes deposited by sputtering.

5：Data Analysis Methods:

Data analysis involves fitting dielectric permittivity with Lorentz-type relations, analyzing Raman spectra with multi-peak fitting, calculating EC effects using Maxwell relations, and evaluating energy density from P–E loops. Statistical models are used for relaxor behavior, and thermodynamic potentials are applied to understand phase transitions.