In situ Transmission Electron Microscopy Study on the Phase Transitionsin Lead-Free (1−x)(Bi1/2Na1/2)TiO3–xBaTiO3 Ceramics

The phase transitions in unpoled lead-free (1−x)(Bi1/2Na1/2)TiO3–xBaTiO3 (x = 0.06 and 0.11) ceramics are investigated using hot-stage transmission electron microscopy (TEM). It is found that large ferroelectric domains in both ceramics start to disappear around Td, the depolarization temperature. After the transition, both compositions exhibit the P4bm tetragonal symmetry in the form of nanodomains. The structural transition observed by the in situTEM experiments seems to be gradual and occurs within a temperature range of several tens of degrees, in contrast to the sharp anomaly at Td revealed by the dielectric characterization. With further increasing temperature, no structural change was observed for both compositions across TRE, where the dielectric frequency dispersion vanishes, and Tm, where the dielectric permittivity reaches maximum. The tetragonal-to-cubic transition is diffuse and takes place in a broad temperature window well above both TRE and Tm. These results of structural phase transitions are summarized in a phase diagram with its composition range covering the morphotropic phase boundary (MPB)

Morphotropic phase boundary and electrical properties of lead-free (1−x)BaTiO3−xBi(Li1/3Ti2/3)O3 ceramics

Dense polycrystalline ceramics of lead-free perovskitesolid solution(1−x)BaTiO3−xBi(Li1/3Ti2/3)O3 (0.05≤x≤0.20) have been synthesized via the conventional solid state reaction method. A morphotropic phase boundary separating the tetragonal and orthorhombic phases was observed between the compositions x=0.07 and 0.10. With increasing Bi(Li1/3Ti2/3)O3 content, the solid solution displays a stronger frequency dispersion in its dielectric behavior and a significant suppression in the sharp dielectric anomaly at the Curie point as well as the remanent polarization. However, the Curie point of the solid solution is almost independent of x in the composition range studied. These behaviors can be explained by the observed core-shell grain structure. The incorporation of Bi(Li1/3Ti2/3)O3 into BaTiO3 leads to the formation of nanodomains in the shell, which imparts the relaxor characteristics to the dielectric behavior. The core of the grain preserves the large lamellar domains as those in BaTiO3, contributing to the sharp transition at ∼130 °C. The best piezoelectric coefficient was obtained in the composition x=0.07 with d33=110 pC/N

In situ transmission electron microscopy study of the electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic

Electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic was investigated with an electric fieldin situtransmission electron microscopy technique. It is found that the spacing between the (1/x){110}satellite spots and the fundamental reflections do not change with external electric field, indicating that the modulation wavelength stays constant under applied field. The intensity of these satellites starts to decrease when the field level reaches a critical value. Further increase in the field strength eventually leads to the complete disappearance of the satellite reflections. In addition, the 12{111}-type superlattice reflections showed no response to electrical stimuli

Direct observation of the recovery of an antiferroelectric phase during polarization reversal of an induced ferroelectric phase

Electric fields are generally known to favor the ferroelectric polar state over the antiferroelectric nonpolar state for their Coulomb interactions with dipoles in the crystal. In this paper, we directly image an electric-fieldassisted ferroelectric-to-antiferroelectric phase transition during polarization reversal of the ferroelectric phase in polycrystalline Pb0.99{Nb0.02[(Zr0.57Sn0.43)0.92Ti0.08]0.98}O3.With the electric-field in situ transmission electron microscopy technique, such an unlikely phenomenon is verified to occur by both domain morphology change and electron-diffraction analysis. The slower kinetics of the phase transition, compared with ferroelectric polarization reversal, is suggested to contribute to this unusual behavior

Electric-field-induced transformation of incommensurate modulations in antiferroelectric Pb0.99Nb0.02[(Zr1−xSnx)1−yTiy]0.98O3

Most antiferroelectric ceramics are modified from the prototype PbZrO3 by adding Sn and Ti in conjunction with small amount of Nb or La to optimize their properties. These modifiers introduce unique nanoscale structural feature to the ceramics in the form of incommensurate modulations. It was shown previously that the modulation is strongly responsive to a change in chemical composition or temperature. However, its response to an electric field, the driving force in real applications, has not been explored before. In the present work the dynamic evolution of the incommensurate modulation during the electric field-induced antiferroelectric-to-ferroelectric transformation was observed with an in situ transmission electron microscopy (TEM) technique. The results indicate that the incommensurate modulation exists as a transverse Pb-cation displacement wave. The wavelength was found to be quite stable against external electrical stimuli, in sharp contrast to the dramatic change under thermal stimuli reported previously. It is suggested that the appeared incommensurate modulation is an average effect of a mixture of two commensurate modulations. The electric field-induced antiferroelectric-to-ferroelectric transformation proceeds with aligning the Pb-cation displacements, which resembles the process of 90° reorientation and 180° reversal in normal ferroelectrics

Crystal Structure and Electrical Properties of Lead-Free (1-x)BaTiO3–x(Bi1/2A1/2)TiO3 (A = Ag, Li, Na, K, Rb, Cs) Ceramics

Ceramics of solid solutions (1-x)BaTiO3–x(Bi1/2A1/2)TiO3 (A = Ag, Li, Na, K, Rb, Cs, x ≤ 0.20) were prepared and their crystal structures, dielectric, ferroelectric and piezoelectric properties were investigated. It was found that (Bi1/2A1/2)TiO3-type doping compounds broadened the temperature range of the tetragonal phase in BaTiO3 and all the compositions examined displayed a tetragonal structure at room temperature. The Curie temperature (TC) was observed to increase with respect to pure BaTiO3 to the range of 140 to 210 oC through solid solution.Remanent polarization (Pr) tended to decrease with increased content of doping compound, while the coercive field (EC) rose and piezoelectric coefficient (d33) fell. The highest d33 value in the solid solutions was observed in 0.97BaTiO3–0.03(Bi1/2Ag1/2)TiO3 at 90 pC/N

A Comparative Study of the Structure and Properties of Sn-Modified Lead Zirconate Titanate Ferroelectric and Antiferroelectric Ceramics

Comparative studies of the structure and property of a ferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.88Ti0.12]0.98O3 and an antiferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 ceramic were conducted. In addition to their different crystal structures, domain morphologies, Raman modes, and dielectric/ferroelectric properties, distinct fracture behaviors under Vickers indentation are also clearly seen. We propose that the antiferroelectric-to-ferroelectric phase transformation may have been triggered during the fracture process. Supporting evidence for localized phase transformation was provided by an in situ Raman spectroscopic experiment

In-situ TEM study of the aging micromechanisms in a BaTiO3-based lead-free piezoelectric ceramic

Aging and fatigue are the two main concerns regarding the performance reliability of piezoelectric ceramics. Compared with fatigue, less efforts have been made towards clarifying the micromechanisms of aging. In this report, we employ electric field in-situ transmission electron microscopy (TEM) to directly visualize the domain structure evolution during fatigue and the subsequent aging process in the 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) polycrystalline ceramic. The macroscopic aging behaviors, including the development of internal bias field (Ebias) and the degradation in switchable polarization (2Pr), are correlated with the microscopic domain wall clamping and domain disruption resulted from the redistribution of oxygen vacancies driven by depolarization field

High curie temperature ternary piezoelectric ceramics

A preferred piezoelectric ceramic material is a BiFeO3—PbZrO3—PbTiO3 ternary solid solution wherein proportions of the constituent perovskite metal oxides are selected so that the material exhibits relatively high Curie temperatures above 380° C. and useful piezoelectric properties

Giant strain with low cycling degradation in Ta-doped [Bi1/2(Na0.8K0.2)1/2]TiO3 lead-free ceramics

Non-textured polycrystalline [Bi1/2 (Na 0.8K0.2)1/2](Ti1− x Ta x)O3 ceramics are fabricated and their microstructures and electrical properties are characterized. Transmission electron microscopy reveals the coexistence of the rhombohedral R3c and tetragonal P4bm phases in the form of nanometer-sized domains in [Bi1/2 (Na 0.8K0.2)1/2]TiO3 with low Ta concentration. When the composition is x = 0.015, the electrostrain is found to be highly asymmetric under bipolar fields of ±50 kV/cm. A very large value of 0.62% is observed in this ceramic, corresponding to a large-signal piezoelectric coefficient d 33* of 1240 pm/V (1120 pm/V under unipolar loading). These values are greater than most previously reported lead-free polycrystalline ceramics and can even be compared with some lead-free piezoelectric single crystals. Additionally, this ceramic displays low cycling degradation; its electrostrain remains above 0.55% even after undergoing 10 000 cycles of ±50 kV/cm bipolar fields at 2 Hz. Therefore, Ta-doped [Bi1/2(Na 0.8K0.2)1/2]TiO3 ceramics show great potential for large displacement devices