Cyclic properties and impedance analysis of (Li,Na,K)NbO₃-based multilayered piezoceramics

Abstract

(Li,Na,K)NbO3-based multilayered piezoceramics were characterized by performing unipolar polarization electric field measurements and impedance spectroscopy. Subjecting an as-poled sample to up to 107 cycles in an applied 4 kV mm−1 unipolar cyclic field at 100 °C reduced its polarization by 8.9%. The impedance spectra of as-sintered, as-poled, and fatigued samples were acquired and analyzed. Two relaxation processes reported to occur in single-layered (Na,K)NbO3-based ceramics were identified. They occurred at inner domains and interfaces, including domain walls (DWs) and grain boundaries, below the Curie temperature (TC, 450 °C). The electrical properties of the samples were evaluated by two resistance-constant phase element (2 R-CPE) equivalent circuit analysis. The results indicated that DW pinning was the primary cause of unipolar fatigue.

Influence of Oxygen Vacancies on the Impedance Spectrum of Al2O3–Na0.5K0.5NbO3 Composites

“…The activation energy for the bulk response increased from 0.87 ± 0.06 eV to approximately 1.12 ± 0.03 eV, with the most significant change occurring at 5 vol%. As previous studies suggested, the predominant conductive process in NKN is through oxygen vacancy migration at temperatures above 400 • C, with an activation energy between 0.98 and 1.41 [20,55,56]. The findings of the current study correspond well with these values.…”

“…At 0 vol%, the activation energies for the bulk and grain boundary are 0.87 ± 0.06 eV and 1.26 ± 0.09 eV, respectively. Similar values have been calculated for similar materials and have been linked to the motion of ionized oxygen vacancies [20,40,52]. It should be noted that in oxide ceramics, background impurities are present, leading to intrinsic defects that contribute to the overall concentration of oxygen vacancies [40,53].…”

“…Similar results were measured for Tb-and Tm-doped NKN [19]. However, the activation energy can also be changed during fatigue, as shown by Nishiyama et al [20] in Li-modified NKN. Here, the changes were attributed to the anisotropic character of the ion conductivity of the lattice; due to an increase in the c-axis orientation along the measurement direction during fatigue, the ion conductivity increased macroscopically.…”

“…Impedance spectroscopy is a versatile tool that can be used to characterize the electrical properties of polycrystalline microstructures [17]. In addition to the possibility of gathering information on the dielectric and conductive properties of grains, grain boundaries, and interfaces, changes in the domain structure and oxygen vacancies can be measured [18][19][20][21]. For instance, Zeng et al showed that the activation energy evaluated by the temperature-dependent conductivity could be decreased by doping 0.3Pb(Zn 1/3 Nb 2/3 )O 3 -0.7Pb(Zr 0.49 Ti 0.51 )O 3 with LiF, as the number of oxygen vacancies increased [18].…”

Ferroelectric polarization of tetragonal BiFeO3—an approach from DFT calculations for BiFeO3–BaTiO3 superlattices—

“…10,[13][14][15][16][17][18][19][20][21][22] To establish an MBP similar to the PZT system, various lead-free solid solution systems have been investigated and composition-driven variations of crystal structure and properties have been studied. Since the discovery of (K, Na)NbO 3 -based ceramics with properties comparable to PZT, 23) (K, Na)NbO 3 [24][25][26][27][28][29][30] and its related Nb-based materials [31][32][33][34][35][36] have intensively studied with the aim of developing lead-free piezoelectric devices.…”