(a) SEM micrographs of the surface of BNKT20–xLN ceramics. (b) Average grain size and relative density of BNKT20–xLN ceramics as a function of LN content (inset of this figure shows the variation of optimum sintering temperature with LN content).
(a) X-ray diffraction patterns of the crushed bulk samples for BNKT20–xLN with different LN content, (b) Raman spectroscopy data for BNKT20–xLN ceramics at room temperature. Spectral deconvolution was performed according to eight Gaussian-Lorentzian modes based on literature. 15,30 The assignment of spectral modes to specific vibrations in the crystal lattice is superimposed on the graph.
Lattice constant a, c, and tetragonality (c/a) as a function of x in BNKT20–xLN ceramics.
TEM bright field images and corresponding diffraction patterns of BNKT20–0.025LN samples tilted to (a) , (b) , and (c)  zone axis.
(a) The selected area electron diffraction pattern along  axis and (b) the corresponding TEM bright field image and of BNKT20–0.025LN ceramics.
(a) P–E hysteresis loops and (b) bipolar strain curves of BNKT20–xLN with different LN content measured at 10 Hz, respectively [inset of Figure 6(a) is the current-electric filed curves for the indicated composition].
(a) Unipolar strain curves of BNKT20–xLN with different LN content, (b) unipolar strain (S uni) and negative strain (S neg) values for BNKT20–xLN as a function of LN content, respectively (the inner schematic indicates the definition of S neg in the present study). (c) Compositional dependence of normalized strain d 33 * (S max/E max) and piezoelectric constant d 33 for BNKT20–xLN (the inset figures illustrate variation of planar electromechanical coupling factor k p with LN content).
In situ measurements of dielectric constant ε r under bias field at 10 kHz (solid line: first cycle, dotted line: second cycle).
Temperature dependence of dielectric permittivity and loss tangent for poled BNKT20–xLN samples, with the measuring frequency from 1 kHz to 1 MHz.
(a) Temperature dependence of dielectric permittivity and loss tangent for poled BNKT20–xLN samples at a measuring frequency of 1 kHz, (b) the enlarged view of Figure 10(a) in the temperature below 150 °C, (c) Temperature dependence of depolarization current j TSDC for poled BNKT20–xLN samples, (d) Compositional dependence of T d, T F-R, and T m as a function of x for BNKT20–xLN.
Temperature dependence of (a) calculated P loss (=P r) and (b) measured k p for poled BNKT20–xLN samples, (c) annealing temperature dependence of d 33 for poled BNKT20–xLN samples.
(a) Raman spectroscopy data for BNKT20 composition with increasing temperature. (b) Raman spectra of BNKT20 at RT and 250 °C, respectively. The open circles are plotted for the experimental data, the red solid lines show the calculated fits, and dotted lines display the spectral deconvolution.
Temperature dependence of selected modes of the BNKT20 spectrum. (a) The peak position and intensity of the A-site-mode centered at ∼120 cm−1, (b) The peak positions and intensities for the B-site selected modes, centered at 260 cm−1, 520 cm−1, and 610 cm−1, respectively.
Temperature-dependent P–E hysteresis loops and bipolar strain curves for (a), (d) 0LN; (b), (e) 0.01LN; and (c), (f) 0.02LN, respectively.
In situ measurements of ε r under bias field for (a) 0.01LN and (b) 0.02LN at different temperatures.
Variations of S uni and S neg values for BNKT20–xLN ceramics with temperature.
(a) Temperature dependence of d 33 * (S max/E max) and ε r for BNKT20 samples (inset figure shows temperature dependence of d 33 * and j TSDC for this sample), (b) Influence of bias field on permittivity ε r (at 10 kHz) of poled BNKT20 samples.
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