1：Experimental Design and Method Selection:

The study employed a mechanochemical activation-assisted route to synthesize KNN ceramics, involving high-energy ball milling to reduce particle size and enhance reaction kinetics, followed by calcination and sintering. This method was chosen to overcome limitations of conventional solid-state reactions, such as long milling times and high volatility of alkali elements.

2：Sample Selection and Data Sources:

Raw materials included K2CO3, Na2CO3, and Nb2O5 powders (purity 99.99%) from Sinopharm Chemical Reagent Co., Ltd. Samples were prepared with varying milling times (20-360 min) and compared to a control sample (CKNN) made by conventional method with 24 h milling.

3：99%) from Sinopharm Chemical Reagent Co., Ltd. Samples were prepared with varying milling times (20-360 min) and compared to a control sample (CKNN) made by conventional method with 24 h milling. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a Fritsch Vario-Planetary Mill (pulverisette P7?) for ball milling, zirconia vial/ball set, freeze dryer for drying, calcination furnace, cold isostatic press, sintering furnace in sealed alumina crucible, laser particle size analyzer (Model BI-90Plus, Brookhaven), Field Transmission Electron Microscopy (FTEM; Tecnai G2 F20, FEI), X-ray diffractometer (XRD, Philips), Raman spectrophotometer (in Via Reflex, Renishaw), Field Scanning Electron Microscopy (FE-SEM; SU-8020, Hitachi), LCR meter (TH2818; Tonghui), and ferroelectric analyzer (TF-2000; Aix ACCT). Materials were the chemical reagents mentioned.

4：Experimental Procedures and Operational Workflow:

Powders were weighed stoichiometrically, blended in hyperpure water, and subjected to high-energy ball milling with specific parameters (speed 300/600 rpm, ball-to-powder ratio 8:1, reverse directions every 2 min with 8 min rest). The slurry was freeze-dried, calcined at 700°C or 850°C for 9 h, ball-milled again, dried, pressed into pellets at 200 MPa, and sintered at 1120-1140°C for 2 h. Characterization involved particle size analysis, TEM, XRD, Raman spectroscopy, SEM, dielectric measurements, and ferroelectric property measurements.

5：Data Analysis Methods:

Data were analyzed using software for particle size distribution (nano measurer), XRD peak fitting, Raman spectrum fitting, and calculations for energy storage density (Wtol, Wrec, Wloss) from P-E hysteresis loops using integrals.