Fig. 1. (a) Composition-dependent XRD patterns with 2θ=20°-70°, measured at room temperature; corresponding enlarged XRD patterns with (b) 2θ=22°-23° and (c) 2θ=45°-47°. The inverted triangles indicate the secondary phase.

Fig. 2. Temperature-dependent (a1-a10) ε′ and (b1-b10) ε″ of unpoled (colored solid lines) and poled (gray dashed lines) ceramics with x=0-0.16, measured at f=99,997 Hz. The gray, orange, and black arrows in (b1-b10) indicate the anomalies caused by the R-O phase transition, the O-T phase transition, and the space-charge contribution, respectively.

Fig. 3. Phase diagrams of (a) unpoled and (b) poled ceramics. The solid line represents data extracted from the unpoled ceramics, and the dotted line is extracted from the poled ones. TR-O and TO-T values are extracted from ε″-T curves, and Tc value is extracted from ε′-T and εr-T curves. (c) Amplified Rietveld refinement results of the ceramics with x=0.02 via using O phase model, x=0.08 and x=0.12 via using R+O phase model. (d) Variations of the phase fraction.

Fig. 4. Amplified temperature-dependent (a1-a10) ε″, and (b1-b10) tanδ of unpoled ceramics with x=0-0.16. The legend shows the measurement frequency.

Fig. 5. Vogel-Fulcher fitting for unpoled ceramics with x=0, 0.02, 0.04, and 0.06 at TR-O by using data from (a, c, e, f) ε″-T and (b, d) tanδ-T curves.

Fig. 6. PFM and SS-PFM results of the samples with x=0.02, 0.08, 0.12, and 0.14. (a1-a4) Amplitude, (b1-b4) phase, (c1-c4) amplitude and phase of SS-PFM loops; (d) amplitude and (e) |Vc+-Vc-| and |Vc++Vc-| values of SS-PFM loops. Vc+ and Vc- are the coercive biases corresponding to the smallest amplitude in the positive and negative directions, respectively.

Fig. 7. Electrical properties of KNNSx ceramics. (a) d33, (b) kp, (c) εr, (d) Pmax, (e) Pr and Ps, (f) Pbc, (g) εrPr, (h) EC, (i) Suni, (j) Spos and Sneg, (k) Spol, (l) phase angle (θ). All data are abstracted from Figs. S10 and S11.

Fig. 8. (a) Lengths of the six B-O bonds of NbO6 octahedron for 1/12Sb-doped KNN (at Sb, Sb is the center of the octahedron), 1/12Sb-doped KNN (near Sb, Nb that is in the vicinity of Sb is the center of the octahedron) and pure KNN obtained from first-principles calculations; the inset is a schematic diagram of perovskite octahedron. The charge density of (b) optimized KNN and (c) KNN-Sb structures. Red and blue areas indicate large and low charge densities, respectively. The unit is e/Bohr3. Increments between contour lines correspond to 0.01 e/Bohr3. The left of (b, c) is the view along x-direction and the right is the view along z-direction. (d) Composition dependency of v1 shift and FWHM (extracted from Fig. S12). (e) Properties, grain size, domain size, relaxor behavior, and covalency of B-O bond as a function of Sb content; the insets are domain configurations (average grain size and domain size) of the ceramics with increasing content of Sb; Stage I is 0≤x<0.06 with a pure O phase, Stage II 0.06≤x<0.12 with an R-O coexistence phase and Stage II 0.12≤x≤0.16 with a suppressed R-O coexistence phase.