1：Experimental Design and Method Selection:

The study used a standard solid-state reaction method to prepare (1-x)BNT-xNN ceramics, with Rietveld refinements of XRD, HR-TEM, Raman spectroscopy, and measurements of dielectric properties and P-E hysteresis loops to investigate phase transitions and energy-storage properties.

2：Sample Selection and Data Sources:

Ceramic samples with x=0 to 0.5 in molar ratio were synthesized using analytical reagents, and data were collected from temperature-dependent permittivity, P-E loops, and structural analyses.

3：5 in molar ratio were synthesized using analytical reagents, and data were collected from temperature-dependent permittivity, P-E loops, and structural analyses. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes a ferroelectric testing system (Precision Multiferroic, Radiant Technologies Inc.), high-temperature probing stage (HFS600E-PB2, Linkam Scientific Instruments), LCR meter (Agilent E4980A), XRD (D/Max2500V, Rigaku), FE-SEM (SU8020, JEOL), FE-TEM (JEM-2100F, JEOL), and Raman spectrometer (LabRam HR Evolution, HORIBA JOBIN YVON). Materials include Na2CO3, Nb2O5, Bi2O3, TiO2, Ba(OH)2·8H2O, CuO, H3BO3, and BCB additive.

4：Experimental Procedures and Operational Workflow:

Powders were mixed, calcined, pressed into disks, sintered, polished, and electrodes applied. Measurements were conducted at various temperatures and frequencies for dielectric and ferroelectric properties, with structural characterization via XRD, TEM, and Raman spectroscopy.

5：Data Analysis Methods:

Data were analyzed using Rietveld refinements with GSAS software, statistical analysis of grain size, and calculation of energy-storage parameters from P-E loops.