1：Experimental Design and Method Selection:

The study used the seed-induced method with NaNbO3 crystals as seeds to synthesize NKLN ceramics, employing molten salt synthesis (MSS) for seed preparation and two-step sintering (TSS) for ceramic processing to control phase formation and enhance properties.

2：Sample Selection and Data Sources:

Samples were prepared with varying NaNbO3 seed content (0 to 20 mol%) using analytical-grade metal oxides or carbonates (K2CO3, Na2CO3, Nb2O5, Li2CO3) from specified suppliers.

3：List of Experimental Equipment and Materials:

Equipment included ball mills, furnaces, particle size analyzer (Malvern Zetasizer Nano), X-ray diffractometer (PANalytical X'pert PRO MPD), scanning electron microscope (SEM: JSM-IT300), dielectric measurement systems (Agilent E4980A LCR meter, Agilent 4192A impedance meter), ferroelectric measurement system (Precision Workstation from Radiant Technologies, Inc.), and piezoelectric coefficient meter (KCF S5865 d33 meter). Materials included zirconia grinding media, NaCl salt, ethanol, organic binder (PVA), silver paste, and silicone oil.

4：Experimental Procedures and Operational Workflow:

NaNbO3 seeds were synthesized via MSS by mixing Na2CO3 and Nb2O5 with NaCl (1:6 ratio), heating to 800°C for 4 h, washing with deionized water. NKLN powders were mixed with seeds, ball-milled, calcined at 800-900°C for 10 h, pressed into pellets, sintered using TSS (T1: 1090-1120°C for 10 min, T2: 1050°C for 12 h). Microstructure and phase were analyzed by XRD and SEM. Electrical properties were measured after electrode application and poling at 120°C with 3.5 kV/mm DC field for 30 min.

5：5 kV/mm DC field for 30 min. Data Analysis Methods:

5. Data Analysis Methods: Data were analyzed using particle size distributions, XRD patterns for phase identification, SEM for grain size measurement (linear intercept method), dielectric constant vs. temperature and frequency, P-E hysteresis loops for ferroelectric properties, and d33 measurements for piezoelectric coefficients.