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

Abstract

Abstract:High piezoelectricity of (K,Na)NbO 3 (KNN) lead-free materials benefits from a polymorphic phase transition (PPT) around room temperature, but its temperature sensitivity has been a bottleneck impeding their applications. We find that good thermal stability can be achieved in CaZrO 3 -modified KNN lead-free piezoceramics, in which the normalized strain d 33 * almost keeps constant from room temperature up to 140 o C. In situ synchrotron X-ray diffraction experiments combined with permitivity measurements disclose the occurrence of a new phase transformation under an electrical field, which extends the transition range between tetragonal and orthorhombic phases. It is revealed that such an electrically-enhanced diffused 2 polymorphic phase transition (EED-PPT) contributed to the boosted thermal stability of KNN based lead-free piezoceramics with high piezoelectricity. The present approach based on phase engineering should also be effective in endowing other lead-free piezoelectrics with high piezoelectricity and good temperature stability. IntroductionPiezoelectricity, a phenomenon whereby materials become electrically polarized upon the application of stress or deform in response to electrical stimuli, has been an active research topic since its discovery in 1880 by Pierre and Jacques Curie, because of its scientific interests and abundant applications. For the last half-century, the lead-contained materials, e.g., Pb(Zr,Ti)O 3 (PZT) and Pb(Mg,Nb)O 3 -PbTiO 3 (PMN-PT), have been the icons of piezoelectrics, exhibiting a morphotropic phase boundary (MPB), where plural phases with negligible difference in free energy coexist and strongly enhanced functional properties arise.[1] However, a possible toxicity of lead in PZT and PMN-PT has been raising intense health and environmental concerns; thus, the last decade has witnessed the surging dedication to viable lead-free alternatives. [2][3][4][5] Resembling the principle characteristics of MPB, [4][5][6][7][8][9][10] polymorphic phase transition (PPT) boundary has also been extensively pursued. [2, 11,12] Unfortunately, contrary to the nearly vertical MPB in the well-known PZT and PMN-PT systems, [1] the PPT in lead-free piezoelectrics is always tilted, resulting in unavoidable thermally unstable electromechanical properties. [13][14][15] Weak thermal stability is unacceptable for many industrial applications, even though lead-free piezoelectrics have competitive performance at ambient conditions. To address the issue, two approaches have been adopted so far, i.e., fabricating textured samples, [2] or shifting the PPT temperature T O-T well below room temperature. [13] However, the former confronts the poor reproducibility due to an excessively complex synthesis procedure; while the latter would inevitably sacrifice a large 3 portion of piezoelectric activity. Consequently, a barrier still exists in developing reliable lead-free piezomaterials as alternatives to currently market-dominating lead-based materials.Inspired by the nature of MPB in PZT and PMN-PT...

Piezoelectric properties of (K0.5Na0.5)NbO3-BaTiO3lead-free ceramics prepared by spark plasma sintering

“…[2][3][4] Up to present, a lot of research papers on KNNbased lead-free piezoelectric ceramics have been published, including the piezoelectric properties, [5][6][7] the energy-storage properties, 8 etc. In order to further improve the piezoelectric properties of KNN, engineering of the polymorphic phase transition (PPT) between tetragonal and orthorhombic phases, i.e., shifting downward the PPT point T OÀT to ambient temperature through chemical modifications, 9 has been employed, represented by the formation of pseudobinary solid solutions between KNN and one additional component, e.g., KNN-LiTaO 3 , 10-14 KNN-LiSbO 3 15-17 KNN-BiFeO 3 18 and so on.…”

Modifying Temperature Stability of (K,Na)NbO3 Ceramics through Phase Boundary

“…Although shifting phase boundaries away from room temperature will inevitably reduce the initial S uni value measured at room temperature, a relatively high S uni value of 0.148% was still obtained in the ceramics with x = 0.03 at T = 20 °C, which was comparable to those of other KNN-based ceramics at the same electric field. [25] Thus, a simple mode was proposed to show how the locations of phase boundaries affected the temperature stability (Figure 5b). Shifting the locations of phase boundaries from room temperature to higher temperature will generate an arch-shaped variation of S uni , resulting in the relatively high normalized S uni values at high temperature, as shown in the variations of black, red, and blue lines (Figure 5b).…”

“…Shifting the locations of phase boundaries from room temperature to higher temperature will generate an arch-shaped variation of S uni , resulting in the relatively high normalized S uni values at high temperature, as shown in the variations of black, red, and blue lines (Figure 5b). Furthermore, if one can broaden the temperature range of the phase boundaries, such as by applying high electric field and optimizing composition design, [25,26] not only the highly initial S uni but also the smooth variation can be obtained, producing an ideal temperature stability for piezoelectric actuator applications, as shown in the variation of green line (Figure 5b). We compared the temperature stability of (0.99-x)KNNS-0.01SZ-xBNZ ceramics and other representative lead-free piezoceramics (Figure 5c).…”

Giant Electrostrictive Responses and Temperature Insensitive Strain in Barium Titanate‐Based Ceramics

“…[1][2][3][4] The searches for new high-performance piezoelectric materials, exhibiting high performance and temperature stability, continue to boost considerable interest. [1][2][3][4] The searches for new high-performance piezoelectric materials, exhibiting high performance and temperature stability, continue to boost considerable interest.…”