Fig. 1. Schematic diagram showing the increase of W_rec through decreasing the grain size by doping BMT in KNN ceramics.

Fig. 2. Circuit diagram of direct test system.

Fig. 3. XRD patterns of (1–x)KNN-xBMT ceramics.

Fig. 4. SEM images of the (1–x)KNN-xBMT ceramics with their grain size distribution and average grain size inserted: (a) x = 0.05; (b) x = 0.10; (c) x = 0.15; (d) x = 0.20.

Fig. 5. (a) Dielectric constant as a function of temperature in a temperature range of –150 ℃ to 300 ℃ for (1 – x)KNN-xBMT ceramics and 25 ℃ to 500 ℃ for pure KNN ceramics; (b) plots of ln(1/ε_r–1/ε_m) versus ln(T–T_m) of the (1–x)KNN-xBMT ceramics.

Fig. 6. P-E loop and I-E curves under 60 kV·cm^–1 electric field of the (1–x)KNN-xBMT ceramics: (a) x = 0; (b) x = 0.05; (c) x = 0.10; (d) x = 0.15; (e) x = 0.20.

Fig. 7. (a) P-E loops, (b) W_rec and η of (1–x)KNN-xBMT ceramics at the maximum applied electric fields; (c) P-E loops, (d) W_rec and η of (1–x)KNN-xBMT ceramics under 200 kV·cm^–1 electric fields.

Fig. 8. (a) P-E loops and (b) W_rec and η under different electric fields, (c) P-E loops and (d) W_rec and η at different frequencies, (e) P-E loops and (f) W_rec and η at different temperatures of 0.85KNN-0.15BMT ceramics.

Fig. 9. (a) Pulsed discharge current curves, (b) discharge energy density W_dis and discharge time t₉₀, and (c) comparative figures of W_dis and W_rec under breakdown electric field of the (1–x)KNN-xBMT ceramics; (d) pulsed discharge current curves, (e) discharge energy density W_dis, and (f) the comparative figures of W_dis and W_rec under different electric fields of the 0.85KNN-0.15BMT ceramic