Electric field‐induced irreversible relaxor to ferroelectric phase transformations in Na_0.5Bi_0.5TiO₃‐NaNbO₃ ceramics

Abstract

(1‐x)Na0.5Bi0.5TiO3‐xNaNbO3 (x = 0.02, 0.04, 0.06, and 0.08) ceramics were fabricated by solid‐state reaction. High‐resolution synchrotron x‐ray powder diffraction (SXPD) data, coupled with macroscopic electromechanical measurements, reveal the occurrence of an electric field‐induced irreversible crystallographic transformation for x = 0.02 and 0.04, from a pseudo‐cubic non‐ergodic relaxor to a rhombohedral or coexisting rhombohedral‐tetragonal long range‐ordered ferroelectric phase, respectively. The highest unipolar electrostrain, corresponding to an effective longitudinal piezoelectric strain coefficient of approximately 340 pm V−1, was obtained for x = 0.04; this effect is attributed to enhanced domain switching as a result of the co‐existing rhombohedral and tetragonal phases for this composition, which is critical for piezoelectric actuator applications.

Origin of the large electrostrain in BiFeO3-BaTiO3 based lead-free ceramics

“…For example, an irreversible phase transition from RFE cubic to metastable FE rhombohedral/tetragonal phase can be induced in NBT-based materials which subsequently exhibit FE behaviour after removing the external electric field. [57][58][59][60] It is evident from the in-situ data presented here that the BF-BT based compositions investigated during the present study do not follow this general trend and no long-range FE state is induced during or after application of the applied electric field.…”

Fatigue resistant lead-free multilayer ceramic capacitors with ultrahigh energy density

“…A sudden decrease in grain size with dopants is common in solid solutions and may be attributed to an increase of grain boundary drag, related to the incorporation of a high valence species such as Nb. 47,48,77,78 The similar grain size for all subsequent compositions for x > 0.05 indicates that it is not a critical factor in optimising the energy density in ceramics as x increases. However, for multilayers with $8 mm layer thickness the decrease from $8 to $1-2 mm is important as it ensures there are multiple grains rather than a single grain separating the electrodes and thereby eliminating the potential of short circuit conduction pathways and maintaining a high BDS.…”

Microstructural, structural, dielectric, piezoelectric and energy storage properties of 0.2 wt% MnO2 doped (0.94-x)Na0.5Bi0.5TiO3–0.06BaTiO3-xK0.5Na0.5NbO3 ceramics (0 ≤ x ≤ 0.08)

“…This indicates that for compositions till 4KNN, application of strong electric field leads to a structural transformation from the high symmetry pseudo-cubic phase to a lower symmetry structure/phase. For compositions above 4KNN the inability of the electric field to force a structural/phase transformation, indicates the dominance of chemical/structural disorder in the ferroelectric matrix [52,66].…”