Intergranular Stress Induced Phase Transition in CaZrO₃ Modified KNN‐Based Lead‐Free Piezoelectrics

Abstract

The phase transition temperatures of CaZrO 3 -doped (Na 0.49 K 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O 3 lead-free piezoelectrics (LKNNT-CZ5) have been studied with X-ray diffraction and Raman scattering. It is found that LKNNT-CZ5 ceramics and powders with the same crystallite size (~2-5 lm) exhibit distinctly different phase transition behaviors versus temperature. The ceramic bulk changes its orthorhombic phase to tetragonal structure abruptly after being pulverized to powders at room temperature(RT), and follows a phase transition sequence with increasing temperature: orthorhombic (RT-65°C), orthorhombic and tetragonal (65°C-105°C), and tetragonal phase (105°C to~220°C). Contrastively, the powders hold a tetragonal structure without any phase transition within the whole temperature region (RT-220°C). These differences might be induced by the existing internal stress or residual strain, which could be released during the grinding process.S. Zhang-contributing editor Manuscript No. 35520.

Multi-scale thermal stability of niobate-based lead-free piezoceramics with large piezoelectricity

“…Raman spectroscopy has been widely used to investigate the phase structure of KNN-based piezoelectric materials. 19,26,27 The evolution of Raman spectra with temperature is depicted in Fig. 2.…”

Diffused Phase Transition Boosts Thermal Stability of High‐Performance Lead‐Free Piezoelectrics

“…It is consistent with the in situ synchrotron X-ray diffraction outcomes as presented in the previous section. The firstprinciples calculations, supported by the experimental determination of field-dependent volume change, unambiguously represent that it is possible to stabilize different polar phases by controlling the applied electric field [5,6] in addition to the well-accepted approaches of composition, [1] stain, [9,10] stress, [31] and pressure. [45] Note that KNN is not a unique system presenting energetically parallel phases; it is frequently observed in many perovskite piezoelectrics because of the flexibility of perovskite structure.…”

“…Intriguingly, current material possesses nearly temperature-insensitive strain behavior up to 140 o C at an electric field of 5 kVmm -1 , the variation of which in the investigated temperature range is within ±10 % of its room-temperature value, being much better than other lead-free systems and also being comparable to the classical PZT4 ceramics (refer to Figure 1(d)). [2,[28][29][30] To uncover the underlying mechanism, herein, we focus on the influence of external justified by the fading of ferroelectric domain contrasts (shown in Figure 3) as well as the reduced lattice displacement [31] (refer to the evolution of (200) pseudocubic reflections with temperature in Figure 4). As outlined above, performance of piezoelectrics is strongly correlated with domain morphologies, particularly among which the nano-domains could extrinsically contribute to the enhanced piezoelectric properties.…”

“…[2, [28][29][30] To uncover the underlying mechanism, herein, we focus on the influence of external justified by the fading of ferroelectric domain contrasts (shown in Figure 3) as well as the reduced lattice displacement [31] (refer to the evolution of (200) pseudocubic reflections with temperature in Figure 4). As outlined above, performance of piezoelectrics is strongly correlated with domain morphologies, particularly among which the nano-domains could extrinsically contribute to the enhanced piezoelectric properties.…”

“…For piezoelectrics, the real-time volume changes V can be resolved by measuring the longitude strain S 33 and transverse strain S 11 simultaneously (V = S 33 +2S 11 ). [28,44] by controlling the applied electric field [5,6] in addition to the well-accepted approaches of composition, [1] stain, [9,10] stress, [31] and pressure. [45] Note that KNN is not a unique system presenting energetically parallel phases; it is frequently observed in many perovskite piezoelectrics because of the flexibility of perovskite structure.…”