The phase diagram of the BNT–BKT–KNN ternary system near the BNT-rich corner. The four points construct the rhombohedral–tetragonal phase boundary. The compositions reported in this paper are located on the shaded part, showing the MPB region.
(a) XRD profiles at 2θ between 35° and 50° and (b) Raman spectra for y = 0, 0.01, and 0.02 series.
(a) SEM micrographs of the surface of BNT–0.20BKT ceramics, (b) average grain size and relative density as function of BKT and KNN content.
P-E hysteresis loops and bipolar strain responses for BNT–BKT–KNN with (a) y = 0 and (b) y = 0.01 series measured at 10 Hz.
Unipolar S (E) curves of BNT–BKT–KNN ceramics with (a) y = 0 and (b) y = 0.01. Three-dimensional plots of (c) strain and (d) d 33 for all compositions.
(a) P-E hysteresis loops and bipolar strain responses for BNT–BKT–KNN near the MPB, (b) variation of strain and d 33 (inset figure) with the MPB compositions.
Temperature dependence of ε r and tanδ for (a) poled and (b) unpoled BNT-0.20BKT samples, with the measuring frequency from 1 kHz to 1 MHz.
Temperature dependence of ε r, tanδ and j TSDC for poled samples with (a) y = 0 and (b) y = 0.01 series. (c) Three-dimensional plots of the depolarization temperature T d for all compositions (inset shows variation of T d along the MPB location).
(a) Phase diagram of the BNT–BKT–KNN system obtained in this work [d 33* values near the MPB were plotted on the phase diagram], (b) relation between the tolerance factor t and the content of KNN along the MPB line of the system.
Rietveld refinement of a high-resolution XRD pattern of samples with x = 0.20, y = 0.01 showing the observed pattern (□) and the calculated fit (▪). The line below is the difference between the observed and calculated intensities.
TEM bright field images and corresponding diffraction patterns of samples with x = 0.20, y = 0.01 tilted to (a) , (b) , and (c)  zone axis.
(a) In situ X-ray diffraction pattern of [(1 − x)BNT-xBKT]-yKNN (x = 0.20, y = 0.01) ceramics at its virgin state in comparison with that at 60 kV/cm. (b) Pseudo-cubic (200) reflection as a function of electric field from the initial zero field state to an applied field of 60 kV/cm, for [(1 − x)BNT-xBKT]-yKNN (x = 0.12, y = 0; x = 0.20, y = 0; x = 0.20, y = 0.01; and x = 0.17, y = 0.02) compositions.
(a) Raman spectroscopy data for [(1 − x)BNT-xBKT]-yKNN (x = 0.14, y = 0.01) composition with increasing temperature (inset figure shows Raman shift with temperature in the range of 240 to 280 cm−1), (b) P-E hysteresis loops and (c) associated I-V curves for samples at different temperatures, (d) bipolar and (e) unipolar strain curves of the indicated samples at different temperatures.
(a) Temperature dependence of strain and loss tangent for samples with x = 0.12–0.20, y = 0.01, (b) temperature dependence of strain and depolarization current j TSDC for samples with x = 0.12, y = 0–0.04.
(a) P-E hysteresis loops and bipolar strain curves of the indicated samples (x = 0.14, y = 0–0.04) at RT and ∼T d. (b) Three-dimensional plots of for the compositions within the FE phase region at ∼T d.
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