Fig. 1. (a-c) Room-temperature XRD patterns of (KxNa1-x)NS-BAZ ceramics with 2θ=22-23°, 31°-32.5°, and 45°-47°; (d) the position, (e) the difference in the position (Δ2θ), and (f) intensity ratio of (200)pc and (002)pc peaks. The diffractions are indexed according to the pseudo-cubic (pc) unit cell.

Fig. 2. (a) ε′-T, (b) ε″-T, and (c) tan δ-T curves of unpoled (colored solid lines) and poled (black dashed lines) (KxNa1-x)NS-BAZ ceramics. The white and green areas respectively indicate the increase and decrease of values after poling, and RT in (b) is the abbreviation of room temperature.

Fig. 3. (a) Δε′-T, (b) Δε″-T, and (c) Δtan δ-T curves of (KxNa1-x)NS-BAZ ceramics, measured at f=9997 Hz.

Fig. 4. Variations of TR-O&O-T and TC of unpoled and poled samples.

Fig. 5. (a) Composition-dependent Raman spectra of (KxNa1-x)NS-BAZ ceramics; schematic diagrams of (b) A1g(υ1) and (c) Eg(υ2) modes; Raman shift of (d) A1g(υ1) and (e) Eg(υ2) modes. The inset in (a) shows the Lorentz fitting for the Raman spectrum of samples with x=0.35.

Fig. 6. V-PFM and SS-PFM measurements for samples with x=0.35 (a1-a3), x=0.45 (b1-b3), x=0.55 (c1-c3), and x=0.65 (d1-d3); variations of (e) amplitude and (f) VC with x. The scanning area of (a1-d2) is 3 μm × 3 μm.

Fig. 7. (a) P-E loops and (b) S-E curves of samples with x=0.35 measured during first and second electric cycles; (c-h) variations of Pmax, Pr, (Pmax-Pr), Ec, Sp, Sneg, and Spos as a function of x. The data in (c-h) are extracted from Fig. S10.

Fig. 8. (a-c) Variations of d33, kp, εr, tan δ, phase angle, and εrPr of poled samples as a function of x, measured at room temperature. εr and tan δ are measured at f=10 kHz. The phase angle is obtained from Fig. S12.

Fig. 9. Contour maps of normalized Suni (SuniT/SuniRT) measured at different temperatures and electric fields for samples with x=0.35 (a), x=0.50 (b), and x=0.65 (c).

Fig. 10. (a) Schematic diagrams of the lattice structure of KxNa1-xNS-BAZ ceramics with different K/Na ratio; (b) composition-dependent tan δ-T curves of unpoled and poled samples. The Bi3+ ions are off-centered along the <001> directions, and the Na+ ions are off-centered along the <011> directions [58,60]. Note that the off-centering of the Bi3+ and Na+ ions is overstated to offer a better understanding. The real off-centering is much small (e.g., approximately 0.4 ? for the Bi3+ ions and less 0.35 ? for the Na+ ions) [58,60].