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Ceramic composites of (1‐x)Pb0.99{Nb0.02[(Zr0.57Sn0.43)0.937Ti0.063]0.98}O3 (PNZST)/xZnO were recently reported to exhibit exceptionally high pyroelectric coefficients near human body temperature due to the ferroelectric‐antiferroelectric transition of the matrix grains. In the present work, a comparative study is conducted on two composites of x = 0.1 and 0.4 with in situ heating transmission electron microscopy (TEM). The results verify the presence of strain field in the PNZST grain adjacent to a ZnO particle and the stabilized ferroelectric phase at room temperature in the composite of x = 0.1. During heating, the ferroelectric matrix grain transforms to the antiferroelectric phase, contributing to the pyroelectric effect. In the composite of x = 0.4, high‐angle annular dark‐field imaging combined with energy‐dispersive X‐ray spectroscopy reveal the existence of both ZnO and Zn2SnO4. The formation of Zn2SnO4 indicates that Sn in the PNZST matrix grain is selectively extracted, and decomposition of the perovskite phase has taken place. The decomposition products in the form of fine particles are observed to facilitate the nucleation of the antiferroelectric phase and restrict the motion of the phase boundary during heating. The larger amount of ZnO and Zn2SnO4 and the decomposition of the PNZST perovskite phase are suggested to be responsible for the much lower pyroelectric coefficient in the x = 0.4 composite. [ABSTRACT FROM AUTHOR]

Abstract: The relationship between the piezoelectric properties and the structure/microstructure for 0.05Bi(Mg2/3Nb1/3)O3‐(0.95‐x)BaTiO3‐xBiFeO3 (BBFT, x = 0.55, 0.60, 0.63, 0.65, 0.70, and 0.75) ceramics has been investigated. Scanning electron microscopy revealed a homogeneous microstructure for x < 0.75 but there was evidence of a core‐shell cation distribution for x = 0.75 which could be suppressed in part through quenching from the sintering temperature. X‐ray diffraction (XRD) suggested a gradual structural transition from pseudocubic to rhombohedral for 0.63 < x < 0.70, characterized by the coexistence of phases. The temperature dependence of relative permittivity, polarization‐electric field hysteresis loops, bipolar strain‐electric field curves revealed that BBFT transformed from relaxor‐like to ferroelectric behavior with an increase in x, consistent with changes in the phase assemblage and domain structure. The largest strain was 0.41% for x = 0.63 at 10 kV/mm. The largest effective piezoelectric coefficient (d33*) was 544 pm/V for x = 0.63 at 5 kV/mm but the largest Berlincourt d33 (148 pC/N) was obtained for x = 0.70. We propose that d33* is optimized at the point of crossover from relaxor to ferroelectric which facilitates a macroscopic field induced transition to a ferroelectric state but that d33 is optimized in the ferroelectric, rhombohedral phase. Unipolar strain was measured as a function of temperature for x = 0.63 with strains of 0.30% achieved at 175°C, accompanied by a significant decrease in hysteresis with respect to room temperature measurements. The potential for BBFT compositions to be used as high strain actuators is demonstrated by the fabrication of a prototype multilayer which achieved 3 μm displacement at 150°C. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) is investigated through indirect measurement in two lead-free [Bi1/2(Na,K)1/2]TiO3-based ceramics that were previously reported to display giant electro-strains. In the Nb-doped ceramic, denoted as BNKT-2.5Nb, a decent temperature change of Δ T=1.85 K and an electrocaloric responsivity of Δ T/Δ E=0.37 (10−6Km V−1) are found around room temperature (32°C). While in the Ta-doped ceramic, BNKT-1.5Ta, a wide operation temperature range ( Tspan ~55 K) is observed near room temperature. Additional electrical measurements, as well as transmission electron microscopy experiments, are performed to identify the mechanisms of the ECE in both ceramics. [ABSTRACT FROM AUTHOR]

The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in ( Pb0.94− x La0.04 Ba x)[( Zr0.60 Sn0.40)0.84 Ti0.16] O3 ceramics is investigated through monitoring electric field-induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization ( Pm) and longitudinal strain ( xm). The energy storage density is even increased under the mechanical confinement in compositions x = 0.02 and 0.04. X-ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior. [ABSTRACT FROM AUTHOR]

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 140°C-210°C through solid solution. Remanent polarization ( Pr) tended to decrease with increased content of doping compound, whereas the coercive field ( EC) rose and piezoelectric coefficient ( d33) fell. The highest d33 value in the solid solutions was observed in 0.97 BaTiO3-0.03( Bi1/2 Ag1/2) TiO3 at 90 pC/N. [ABSTRACT FROM AUTHOR]

Since ceramics in the PbZrO3- PbTiO3 binary system display excellent piezoelectric properties and those in BiFeO3- PbTiO3 exhibit high Curie temperatures, morphotropic phase boundary ( MPB) compositions in the BiFeO3- PbZrO3- PbTiO3 ternary solid solution system are investigated for the development of piezoelectric ceramics for high temperature applications. It is found that the MPB compositions in the ternary system deviate away from the mixture of two binary MPB compositions 0.70 BiFeO3-0.30 PbTiO3 and 0.52 PbZrO3-0.48 PbTiO3. With decreasing amount of BiFeO3 in the MPB compositions in the ternary system, the Curie temperature TC is observed to decrease while the piezoelectric coefficient d33 is found to increase. Accompanied with this trend are the decrease in the c/a ratio of the tetragonal phase, the increase in the dielectric constant and the decrease in the loss tangent of the ceramics at room temperature. It is further noticed that the compositions in the rhombohedral-rich side of MPB exhibit slightly better piezoelectric properties. An example of such compositions is 0.511 BiFeO3-0.326 PbZrO3-0.163 PbTiO3, with TC of 431°C, d33 of 101 pC/N, and the electromechanical coupling factor kp of 0.50. [ABSTRACT FROM AUTHOR]

( K,Na) NbO3 ( KNN) lead-free ceramics were fabricated using conventional solid-state reaction method. The domain configurations were studied with transmission electron microscopy and found to be closely related to the sintering temperature and cooling rate. High density ceramics with uniform compositions were obtained when sintered at 1200°C with a slow cooling rate, resulting in the improved piezoelectric properties, with d33 on the order of 150-160 pC/N, which is comparable to the hot pressed KNN ceramics. The microstructures of the ceramics synthesized at various conditions were explained in terms of the solid-solution characteristics of KNN system, based on the high temperature phase diagram. The relationship of processing parameter-microstructure-property established herein will lead to further improvements in the piezoelectric properties of KNN lead-free materials. [ABSTRACT FROM AUTHOR]

The 1:1 structural order and B-site cation order in Pb(Mg1/3Nb2/3)O3 ceramics was significantly enhanced by Zr4+ substituting Nb5+ according to the chemical formula Pb(Mg1/3Zr2 x/3Nb2(1− x)/3)O3− x/3. The enhanced structural and cation order was revealed by both X-ray diffraction and transmission electron microscopy. The increased charge difference and the introduced oxygen vacancies were suggested to account for the observed long-range cation order. Typical relaxor ferroelectric behavior was retained even in the ceramics with a high degree of cation order. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]