Temperature‐Insensitive (K,Na)NbO₃‐Based Lead‐Free Piezoactuator Ceramics

Abstract

The development of lead‐free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead‐free (K,Na)NbO3 (KNN)‐based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd33 of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field‐induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field‐induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature‐dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature‐insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.

Fatigue-free unipolar strain behavior in CaZrO3 and MnO2 co-modified (K,Na)NbO3-based lead-free piezoceramics

“…To improve the general piezoelectric performance and the temperature stability of KNN ceramics, various attempts through manipulation of crystallographic structure 4,5 or refined processing techniques 6 have been published. Especially, CaZrO 3 and MnO 2 co-modified (K,Na,Li)(Nb,Ta)O 3 (CZ5) lead-free piezoceramics have high potential, since they show a large normalized strain d 33 * of 300-350 pm/V, which is extremely stable in the temperature range from room temperature up to 175 C. 7 However, practical applications demand not only outstanding piezoelectric properties but also the reliability and long term stability during cyclic electric loading to ensure successful industrial implementation. 8 The most common electric loading scenario for piezoelectric elements in actuator applications is the unipolar driving mode, where an electric signal is cycled between zero and a maximum field without reversing polarity.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The term incipient denotes "beginning to happen or develop". This indicates that at zero bias-field these materials depict an ergodic relaxor state with negligible 33 , whereas under electric field they develop a ferroelectric state and a reversible induced giant strain [121][122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137][138][139] and 33 values 121 , as schematically introduced in Figure 2.14. Research on these materials has focused on understanding their strain mechanism in order to further enhance it.…”

“…Since then, several binary and ternary BNT-based incipient piezoelectrics were shown to present giant strains. [121][122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137][138][139]258,[275][276][277][278] The KNN-based family of materials is also widely considered as a potential candidate to replace PZT. 10,29,154,279 pm/V at 2 kV/mm.…”

“…These exceptional properties were achieved through a complex texturing process. In subsequent investigations it was demonstrated that KNN-based materials depict promising small [280][281][282][283] and large 136 signal properties with conventional solid state synthesis. However, this family of materials presents major synthesis difficulties that need to be overcome for entering a reliable large scale production.…”

PMN-PT based quaternary piezoceramics with enhanced piezoelectricity and temperature stability

“…Of particular interest is that high d 33 * value with a minimal temperature-dependent variation is obtained for x ¼ 0.33, in the temperature range of 25-165 C. Fig. 3(c) that the variation of d 33 * for PMN-PFN-PZ-PT ceramics with x ¼ 0.33 is less than 8% in the investigated temperature range, much lower than those of commercial PZT5H (>20%) 35 and PZT4 ($15%) 36 ceramics, and outperforms slightly compared with BMT-PT 25 and BST-PT 26 which possess much higher Curie temperature of >300 C. In addition, (Na 0.49 K 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O 3 -0.05CaZrO 3 (NKL-NT-CZ) 37 lead-free ceramics exhibit a comparable d 33 * variation of $10% in the studied temperature range, however, the value of d 33 * is 320 pm/V, being only half of that of x ¼ 0.33; while Ba(Ti 0.8 Zr 0.2 )O 3 -50(Ba 0.7 Ca 0.3 )TiO 3 (BZT-50BCT) 38 has much lower Curie temperature and its d 33 decreases to nearly 60% of the room temperature value when temperature increases to 70 C. The high field-induced piezoelectric strain coefficient and excellent temperature stability of x ¼ 0.33 make it promising for temperature-insensitive actuator devices.…”