Origin of the large strain response in (K0.5Na0.5)NbO3-modified (Bi0.5Na0.5)TiO3–BaTiO3 lead-free piezoceramics

Abstract

Origin of the large strain response in "K 0.5 Na 0.5 …NbO 3 -modified "Bi 0.5 Na 0.5 …TiO 3 -BaTiO 3 lead-free piezoceramics The mechanism of the giant unipolar strain recently observed in a lead-free piezoceramic, 0.92͑Bi 0.5 Na 0.5 ͒TiO 3 − 0.06BaTiO 3 − 0.02͑K 0.5 Na 0.5 ͒NbO 3 ͓S.-T. Zhang, A. B. Kounga, E. Aulbach, H. Ehrenberg, and J. Rödel, Appl. Phys. Lett. 91, 112906 ͑2007͒ was investigated. The validity of the previously proposed mechanism that the high strain comes both from a significant volume change during the field-induced phase transition, from an antiferroelectric to a ferroelectric phase and the domain contribution from the induced ferroelectric phase was examined. Monitoring the volume changes from the simultaneously measured longitudinal and transverse strains on disk-shaped samples showed that the phase transition in this specific material does not involve any notable volume change, which indicates that there is little contribution from a volume change due to the phase transition to the total strain response. Temperature dependent hysteresis measurements on unpoled samples of a nearby ferroelectric composition, 0.93͑Bi 0.5 Na 0.5 ͒TiO 3 − 0.06BaTiO 3 − 0.01͑K 0.5 Na 0.5 ͒NbO 3 demonstrated that the origin of the large strain is due to the presence of a nonpolar phase that brings the system back to its unpoled state once the applied electric field is removed, which leads to a large unipolar strain.

Dramatic Influence of A-Site Nonstoichiometry on the Electrical Conductivity and Conduction Mechanisms in the Perovskite Oxide Na0.5Bi0.5TiO3

“…[1][2][3][4] The perovskite oxide Na 0.5 Bi 0.5 TiO 3 (NBT) is one of the favoured candidates to replace PZT and various solid solutions with other ferroelectric materials such as BaTiO 3 and K 1-x Na x NbO 3 have been studied both for piezoelectric and high temperature capacitor (dielectric) applications. [5][6][7][8][9][10][11][12][13][14][15][16][17] NBT has a complex crystal structure. [18][19][20][21][22][23][24][25] Early neutron powder diffraction studies proposed NBT to exhibit a rhombohedral (space group R3c) structure at room temperature (RT).…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The origin of the large electromechanical response of incipient piezoelectrics is generally attributed to an electric field induced phase transition. [140][141][142][143][144][145][146][147] Figure 2.14 at point displays an ergodic relaxor state, as previously discussed. For BNT-based lead-free incipient piezoelectrics, it was demonstrated that the electric field induced phase transition coincides with the inflection point of the strain output 148 and the transformation is followed by switching of the newly created domains.…”

“…However, it should be pointed out that the reversibility of the polarization and strain outputs in the Hz range was proved (Appendix IV). 140 Several BNT-based materials feature a similar electric field induced phase transition. 125,130,[138][139][140]275,434 Further details that point towards certain unique features of the BNT-ST system, will be discussed in the subsequent paragraphs.…”

“…This strain mechanism is qualitatively similar as proposed for other BNT-based materials. 140,141 However, Krauss et al 258 proposed that the electric field induced phase transition is from an antiferroelectric state to a ferroelectric state.…”

“…454,455 Despite the specifics described for the phase transition of BNT-based materials with a crystallographic dependence, it has been generally recognized that the electric field induced phase transformation in BNT-based materials occurs due to an average non-polar to polar phase or phases, indicating a FD longitudinal instability of . 140 Nonetheless, these materials may also feature AFD distortions considering that this is a feature of pure BNT. 367 Generally covalency 70 and anionic radii 152 determine the prevailing type of instability.…”