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Lead-based piezoelectric materials cause many environmental problems, regardless of their exceptional performance. To overcome this issue, a lead-free piezoelectric composite material was developed by incorporating different percentages of carbon fiber (CF) into the ceramic matrix of Bismuth Sodium Titanate (BNT) by employing the microwave sintering technique. The aim of this study was also to evaluate the impact of microwave sintering on the microstructure and the electrical behavior of the carbon-fiber-reinforced Bi0.5Na0.5TiO3 composite (BNT-CF). A uniform distribution of the CF and increased densification of the BNT-CF was achieved, leading to improved piezoelectric properties. X-ray diffraction (XRD) showed the formation of a phase-pure crystalline perovskite structure consisting of CF and BNT. A Field Emission Scanning electron microscope (FESEM) revealed that utilizing microwave sintering at lower temperatures and shorter dwell times results in a superior densification of the BNT-CF. Raman Spectroscopy confirmed the perovskite structure of the BNT-CF and the presence of a Morphotropic Phase Boundary (MPB). An analysis of nanohardness indicated that the hardness of the BNT-CF increases with the increasing amount of CF. It is also revealed that the electrical conductivity of the BNT-CF at a low frequency is significantly influenced by the amount of CF and the temperature. Moreover, an increase in the carbon fiber concentration resulted in a decrease in dielectric properties. Finally, a lead-free piezoelectric BNT-CF showing dense and uniform microstructure was developed by the microwave sintering process. The promising properties of the BNT-CF make it attractive for many industrial applications. [ABSTRACT FROM AUTHOR]

High‐performance dielectric ceramic capacitors for automotive applications require high operation temperature, thermal stability, and reliability for dielectric ceramics. A broad composition search has been carried out to replace the existing BaTiO3‐based dielectrics having limited upper operating temperature due to the relatively low Curie temperature at around 120°C. However, most of the developed compositions are too complicated and compositionally sensitive, making them difficult to commercialize. This study introduces a dielectrically reliable ceramic system based on Bi1/2Na1/2TiO3 (BNT) with a wide operation temperature range simply by adding paraelectric CaZrO3 (CZ). At 15 mol% addition of CZ to BNT, the permittivity variation within ±15% from −55 to 280°C was achieved, which surpasses the EIA‐X9R standard. Moreover, the dielectric reliability was shown with low dielectric loss (tanδ < 0.02) for the aforementioned temperature range and remarkable dielectric breakdown strength (∼260 kV/cm) at room temperature. Along with the proposal of a promising high‐performance dielectric material, structural analysis and dielectric behavior investigation as a function of CZ contents were presented. [ABSTRACT FROM AUTHOR]

In this study, lead-free bismuth sodium titanate (BNT; Bi0.5Na0.5TiO3) powder was synthesized using wet precipitation. The sintering behavior and dielectric properties of the BNT ceramics were investigated in terms of the sintering temperature. Titanium isopropoxide, sodium nitrate, and bismuth nitrate were used as starting materials. A titanium peroxo complex (TPC) solution was synthesized using titanium hydroxide, nitric acid, and hydrogen peroxide. A clear Bi-Na-Ti precursor solution was obtained by mixing the TPC, sodium, and bismuth nitrate solutions. The pH of the precursor solution was increased to 9 using NaOH and a white powder was precipitated. A spherical and pyrochlore phase-free BNT powders were obtained by calcining the white precipitate above 600°C for 3 h. Particle size analysis and SEM observations revealed that the BNT powder calcined at 700°C exhibited homogeneous distribution with particle size less than 300 nm. The sinterability of the BNT ceramic prepared through wet precipitation was significantly enhanced compared to that of the BNT powder prepared via the solid-state reaction of sodium carbonate, bismuth oxide, and titanium oxide powders.

Lead-based piezoelectric materials cause many environmental problems, regardless of their exceptional performance. To overcome this issue, a lead-free piezoelectric composite material was developed by incorporating different percentages of carbon fiber (CF) into the ceramic matrix of Bismuth Sodium Titanate (BNT) by employing the microwave sintering technique. The aim of this study was also to evaluate the impact of microwave sintering on the microstructure and the electrical behavior of the carbon-fiber-reinforced Bi0.5Na0.5TiO3 composite (BNT-CF). A uniform distribution of the CF and increased densification of the BNT-CF was achieved, leading to improved piezoelectric properties. X-ray diffraction (XRD) showed the formation of a phase-pure crystalline perovskite structure consisting of CF and BNT. A Field Emission Scanning electron microscope (FESEM) revealed that utilizing microwave sintering at lower temperatures and shorter dwell times results in a superior densification of the BNT-CF. Raman Spectroscopy confirmed the perovskite structure of the BNT-CF and the presence of a Morphotropic Phase Boundary (MPB). An analysis of nanohardness indicated that the hardness of the BNT-CF increases with the increasing amount of CF. It is also revealed that the electrical conductivity of the BNT-CF at a low frequency is significantly influenced by the amount of CF and the temperature. Moreover, an increase in the carbon fiber concentration resulted in a decrease in dielectric properties. Finally, a lead-free piezoelectric BNT-CF showing dense and uniform microstructure was developed by the microwave sintering process. The promising properties of the BNT-CF make it attractive for many industrial applications.

Structural and electric characteristics of Gd, Li and Sr modified Bismuth Sodium Titanate i.e. (Bi0.5Na0.5)0.6(Gd0.5Li0.5)0.2Sr0.2TiO3 (BNGLST) composition is demonstrated. BNGLST was synthesized by the solid-state mixed oxide method using the stoichiometrically weighed constituent oxides and carbonates. The homogenously wet mixed powder was calcined at 1000 °C for 12h and compressed pellets were sintered at 1250 °C for 2h. X-ray diffraction was carried out to confirm the phase formation. Crystallographic information was extracted from the Rietveld refinement of the XRD data. Dielectric measurement was carried out from room temperature to 300 °C at 1 kHz − 1 MHz frequencies. The a.c. conductivity associated with oxygen ion conduction is discussed in detail as a function of temperature and frequency. [ABSTRACT FROM AUTHOR]

In this study, lead-free bismuth sodium titanate (BNT; Bi0.5Na0.5TiO3) powder was synthesized using wet precipitation. The sintering behavior and dielectric properties of the BNT ceramics were investigated in terms of the sintering temperature. Titanium isopropoxide, sodium nitrate, and bismuth nitrate were used as starting materials. A titanium peroxo complex (TPC) solution was synthesized using titanium hydroxide, nitric acid, and hydrogen peroxide. A clear Bi-Na-Ti precursor solution was obtained by mixing the TPC, sodium, and bismuth nitrate solutions. The pH of the precursor solution was increased to 9 using NaOH and a white powder was precipitated. A spherical and pyrochlore phase-free BNT powders were obtained by calcining the white precipitate above 600°C for 3 h. Particle size analysis and SEM observations revealed that the BNT powder calcined at 700°C exhibited homogeneous distribution with particle size less than 300 nm. The sinterability of the BNT ceramic prepared through wet precipitation was significantly enhanced compared to that of the BNT powder prepared via the solid-state reaction of sodium carbonate, bismuth oxide, and titanium oxide powders. [ABSTRACT FROM AUTHOR]

In order to realize the preparation of environmentally friendly piezoelectric ceramic coatings on the surface of metallic materials, sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT) ceramic coatings were prepared by supersonic plasma spraying. The surface morphology, cross-sectional morphology, phase structure, and elemental valence variations of the BNT coating were examined, as well as the dielectric and ferroelectric properties of the BNT coating. The results show that the coating has a good quality and a single perovskite structure. The dielectric constant was stable at about 425 and the dielectric loss was stable at about 0.06 when the test frequency reached 200 kHz. The coating exhibits good hysteresis lines under different applied electric fields. When the applied electric field was 40 kV/cm, the remnant polarization value of the prepared coating was 11.47 mC/cm². It can be seen that the BNT piezoelectric coating prepared by supersonic plasma spraying has good ferroelectric and dielectric properties, which lays a solid foundation for in-situ monitoring of environmentally friendly lead-free BNT piezoelectric coating. [ABSTRACT FROM AUTHOR]

Lead-free (Bi 0.5 Na 0.5)TiO 3 (BNT)-based piezoelectric materials, have a great potential for high-precision actuators' applications. In this work, the high-quality (0.94- x %)(Bi 0.5 Na 0.5)TiO 3 -0.06BaTiO 3 - x %NaNbO 3 (x = 2–10, BNT-6BT- x NN) thin films have been successfully deposited on Pt/TiO 2 /SiO 2 /Si substrates by sol-gel method. An ultra-high poling strain S pol value of 1.7% with a unipolar strain S uni value of 1.47% was reported in the BNT-6BT-6NN thin films. The coexistence of the ferroelectric phase and relaxor state was observed in the compositions of x = 2–8. Furthermore, the BNT-6BT-6NN thin films show more active domain switching compared to other compositions. It is demonstrated that the optimized strain responses in the BNT-6BT-6NN are attributed to a synergistic reaction of active domain switching and reversible electric-field-induced phase transition between the ferroelectric phase and relaxor state. Our systematic study demonstrates that the BNT-6BT- x NN thin films with an improved strain response are promising candidates for the applications of miniaturized actuators. [ABSTRACT FROM AUTHOR]

Depolarization temperature, or T d , in ferroelectric materials limits the high temperature operation regime as the long range dipolar ordering could not be maintained beyond T d during zero field heating. Therefore, the control of T d has been always drawing the attention of the ferroelectric/piezoelectric community. Some particular issues include: Which point defect is more responsible for the change of T d ? What is the phase equilibrium as a function of T d ? In this paper, our goal is to elaborate the correlation between T d and defect chemistry in 85% (Bi 0.5 Na 0.5)TiO 3 -15% BaTiO 3 (BNT-15BT) ferroelectric ceramics. Various experimental tools are employed and cross referenced, including dielectric measurements, thermal stimulated depolarization current, impedance spectroscopy, scanning transmission electron microscopy and in-situ transmission electron microscopy. Collectively this study generates a more insightful understanding of T d in BNT-based ferroelectrics. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight. [ABSTRACT FROM AUTHOR]

Bi 0.5 Na 0.5 TiO 3 (BNT)-based complexes, one of the most promising piezoelectric materials, have been recently raised as potential ionic conductors. Although the property modification of BNT-based materials was studied intensively, the influence of the preparation process on the structure and conduction mechanism has not received the attention it deserves since its particular sensitivity to the conductive performance. Herein, (Bi 0.44 Nd 0.01 Sr 0.02 Ca 0.02)Na 0.5 TiO 2.965 (BNSCNT) ceramics were prepared by tape-casting (TC) and conventional solid-state reaction (SR) method, respectively. Despite the pure perovskite phase with rhombohedral distortion of BNSCNT ceramics prepared by SR, the rutile titanium dioxide phase can be identified for TC. The ac impedance spectra reveal a discernible bulk response with appreciable oxide ion conductive capacity in SR, while the contribution from each physical origin becomes obscure due to the superposition in the Nyquist plots of TC. Combined with the activation energy deduced from the thermally dependent conductivity, which is significantly less than the dielectric BNTs, the dominated ionic conductive nature with non-negligible electron contribution is proposed. The grain boundary and electrodes/interfaces response, and their conduction mechanism in the intermediate frequencies range are disclosed by employing the dc bias field and atmospheres. The field-induced inverse variation is recognized of which the dissociation of defect clusters is responsible for SR, whereas the trapping of conduction electrons on the sample surface and the second phase will play the key role for TC, in determining their impedance. This work raises the great importance of the preparation route on the structure and conduction mechanisms of BNT-based oxide ionic conductive materials. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)–based thin films have attracted large attention for the production of modern precise micro–devices due to their outstanding strain responses. However, obtaining good electrical properties and low leakage current in BNT-based thin films is still a great challenge. In this work, 0.945(Bi0.5Na0.5)TiO3–0.055BaZrO3 (BNT–5.5BZ) thin films were deposited by the chemical solution deposition (CSD) method and annealed under two different conditions. This work describes a careful research study on the influence of the annealing conditions on the crystalline structure, morphology, and electrical performance of the BNT–5.5BZ thin films. The films exhibited a dense structure and excellent electrical properties following an optimized thermal treatment process. An ultra–high strain response of 1.5% with a low dielectric loss of ~0.03 was obtained in the BNT–5.5BZ thin films after post-annealing in an O2 atmosphere. The results of this work show that the enhanced strain response was mainly due to a reversible field-induced phase transition between the ferroelectric phase and the relaxation state. The post-annealing treatment is an effective method to optimize the electrical properties of BNT–based films, providing many opportunities for the application of ferroelectric devices. [ABSTRACT FROM AUTHOR]

Off-stoichiometry of perovskite structural Bi0.5Na0.5TiO3 (BNT) ferroelectrics can give rise to considerable oxide-ion conductivity. The inherent structural characteristics are urgent to be resolved due to its particular sensitivity of the conduction mechanism to the nominal composition and synthesis process. Herein, a thorough study of the temperature-dependent neutron, X-ray diffraction and Raman spectrum is carried out on a series of equivalently substituted A-site deficient non-stoichiometric and pristine BNT. Phase transition and defect association are systemically investigated in these dominated rhombohedral phases at room temperature, associated with well saturated ferroelectric states. Significant structural evolution identified by Rietveld refinements and the origin of the electrical performance are clarified at elevated temperatures, focusing on the subtle distortions of ionic displacements, oxygen octahedral tilts and local chemical environments for oxygen vacancies. The ion migration ability mediated by oxygen vacancies that are not energetically favorable in BNT mainly depends on the external substitutional disorder, and is strongly affected by the dopant concentration. Together with the lone pair substitution concept, superior oxide ionic conductivity is achieved, and an alternative strategy is provided in designing BNT based oxide ion conductors.

Changes in the relaxation state can greatly affect the electric-field induced strain response in bismuth sodium titanate-based materials. In this work, the strain performances from nonergodic relaxation (NER) to ergodic relaxation (ER) phase transition are investigated by introducing SrTiO 3 in (Bi 0·5 Na 0.5) 0.98 (La 0·5 Li 0.5) 0.02 TiO 3. The solid solutions of perovskite are achieved in all compositions. The ferroelectric to the relaxation phase transition is revealed based on the characteristic peak shape in XRD and temperature dependence of the dielectric properties. The weakened hysteresis of electric-field induced polarization and strain curves results from the creation of localized random fields due to the coexistence of multiple A-site ions, disrupting the ferroelectric long-range ordering at a higher SrTiO 3 dopant. The formation of polar nanodomain is promoted and accompanied by the transition from the NER to the ER state. Meanwhile, chemical inhomogeneity is deduced by the anomalous variation in the conduction mechanism and surface state of elemental environments. Asymmetric strain behavior is obtained upon reducing the sample thickness to 0.2 mm, especially pronounced in components with stronger ferroelectricity, where highly asymmetric strain is dominated by surface effect and generated by the non-180° domain switching of the upper and lower surface layers. These features provide insights into the design of strain properties in lead-free piezoelectric ceramics. • The strain performance is studied by modulating A-site ions of Bi 0·5 Na 0·5 TiO 3 -based materials. • The asymmetric strain is mainly dominated by the surface effect and becomes more pronounced with stronger ferroelectricity. • The electrical inhomogeneities and local random fields are discussed from nonergodic to ergodic state. • This work provides insights and significance into the strain design of lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Lead-free relaxor ferroelectric ceramics are attracting attention due to their fast charge/discharge and environmentally friendly properties. In this work, the bismuth sodium titanate-barium titanate-barium zirconate titanate [(0.94Bi 0 · 51 Na 0 · 47 TiO 3 -0.06BaTiO 3) -x BaZr 0.3 Ti 0 · 7 O 3 , abbreviated as BNBT-100 x BZT] relaxor ferroelectric ceramics were synthesized by the solid-state reaction technique. The microstructure, energy storage properties, and conductivity mechanism of BNBT-100 x BZT were analyzed as the barium zirconate titanate doping content changed. All BNBT-100 x BZT have a single perovskite structure by XRD. The BNBT-5BZT ceramics was found to be tetragonal by Rietveld refinement. Moreover, the doping of BZT is beneficial to optimize the breakdown strength (BDS). Owing to the higher BDS, an effective energy storage density of 1.457 J/cm3 was obtained under 122 kV/cm in BNBT-5BZT with an energy storage efficiency (η) of 81.9%. In addition, BNBT-5BZT has outstanding temperature and cycling stability. The results indicate that BNBT-5BZT ceramics is excellent candidates for energy storage devices. A new relaxor ferroelectric bismuth sodium titanate-barium titanate-barium zirconate titanate synthesized with a tetragonal phase shows an energy storage density of 1.457 J/cm3 at 122 kV/cm and energy storage efficiency of 81.9%. [Display omitted] [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight.

Here, the phase structure, microstructure, and electrical and luminescent properties of 0.93(Na 0.5 Bi 0.5) 1- x TiO 3 -0.07BaTiO 3 - x Eu3+ (BNBT- x Eu, 0.000≤ x ≤ 0.020) ceramics were investigated. Coexisting rhombohedral (R) and tetragonal (T) phases were obtained in all ceramics. As the Eu3+ content increased, the phase structure changed from a mixture of R - T phases to a main T phase with a minor R phase, along with a decreased grain size. The T m of the BNBT- x Eu ceramics increased from 283 °C to 302 °C upon increasing the Eu3+ content, and the permittivity curve became broader, especially at a high doping content. The ferroelectric and piezoelectric properties were enhanced due to appropriate ratio of R and T phases, increased density, reduced T d , reduced E C , and reduced current density caused by Eu3+ doping. The maximum remnant polarization of P r = 35.5 μC/cm2 and piezoelectric constant of d 33 = 214 pC/N were achieved for the x = 0.010 ceramic. Eu3+ doped BNBT ceramics exhibited red fluorescence at 614 nm derived from the 5D 0 →7F 2 transition of Eu3+ under 466 nm excitation. These results demonstrate the potential applications of the Eu3+ doped BNBT ceramics for novel integrated electronic devices. [ABSTRACT FROM AUTHOR]

Lead‐free (1−x)Bi0.5(K0.15Na0.85)0.5TiO3‐xSr(Ti0.85Zr0.15)O3 ((1−x)BKNT‐xSTZ, x = 0.1–0.4) ceramics are synthesized by citrate combustion method. The grain size is reduced, and the high‐temperature shoulder dielectric peak (Tm) shifts toward low temperature, while the low‐temperature shoulder dielectric peak (Ts) shifts toward high temperature as x increases. The remnant polarization decreases and slimmer hysteresis loops are realized with x increasing. The optimal energy density (Wre ≈2.85 J cm−3) with high efficiency (η ≈ 81%) is obtained for 0.7BKNT‐0.3STZ at 160 kV cm−1. More importantly, excellent frequency stability and enhanced temperature‐dependent energy properties (Wre ≈ 1.12 J cm−3 and η ≈ 94%) of 0.7BKNT‐0.3STZ ceramic are obtained at 100 kV cm−1 and 120 °C. [ABSTRACT FROM AUTHOR]

Lead‐free (1−x)Bi0.5(K0.15Na0.85)0.5TiO3‐xSr(Ti0.85Zr0.15)O3 ((1−x)BKNT‐xSTZ, x = 0.1–0.4) ceramics are synthesized by citrate combustion method. The grain size is reduced, and the high‐temperature shoulder dielectric peak (Tm) shifts toward low temperature, while the low‐temperature shoulder dielectric peak (Ts) shifts toward high temperature as x increases. The remnant polarization decreases and slimmer hysteresis loops are realized with x increasing. The optimal energy density (Wre ≈2.85 J cm−3) with high efficiency (η ≈ 81%) is obtained for 0.7BKNT‐0.3STZ at 160 kV cm−1. More importantly, excellent frequency stability and enhanced temperature‐dependent energy properties (Wre ≈ 1.12 J cm−3 and η ≈ 94%) of 0.7BKNT‐0.3STZ ceramic are obtained at 100 kV cm−1 and 120 °C. [ABSTRACT FROM AUTHOR]

In this review, the evolution of high strain Na0.5Bi0.5TiO3-based lead-free piezoceramics and their multilayer actuators has been explored. First, in terms of Na0.5Bi0.5TiO3-based ceramic materials, the origin of high strain, the typical chemical modification methods of obtaining large strain and extrinsic factors affecting the large strain are discussed. Then it briefly summarizes the problems existing in Na0.5Bi0.5TiO3-based ceramics for multilayer actuator applications. Strategies to optimize strain performance by means of microstructure control and phase structure design are also discussed. Thereafter, in terms of multilayer actuator, we describe its characteristics, applications and preparation process systematically, as well as the recent development of Na0.5Bi0.5TiO3-based multilayer actuator. At last, perspectives on directions of following work and promising fields for the applications of the materials and their devices are presented.

Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)–based thin films have attracted large attention for the production of modern precise micro–devices due to their outstanding strain responses. However, obtaining good electrical properties and low leakage current in BNT-based thin films is still a great challenge. In this work, 0.945(Bi0.5Na0.5)TiO3–0.055BaZrO3 (BNT–5.5BZ) thin films were deposited by the chemical solution deposition (CSD) method and annealed under two different conditions. This work describes a careful research study on the influence of the annealing conditions on the crystalline structure, morphology, and electrical performance of the BNT–5.5BZ thin films. The films exhibited a dense structure and excellent electrical properties following an optimized thermal treatment process. An ultra–high strain response of 1.5% with a low dielectric loss of ~0.03 was obtained in the BNT–5.5BZ thin films after post-annealing in an O2 atmosphere. The results of this work show that the enhanced strain response was mainly due to a reversible field-induced phase transition between the ferroelectric phase and the relaxation state. The post-annealing treatment is an effective method to optimize the electrical properties of BNT–based films, providing many opportunities for the application of ferroelectric devices.

• The stoichiometry of BNT based ceramics was shown to be achieved by intentionally introduced Na deficiency. • The origin of the exponentially increasing dielectric loss in BNT at elevated temperatures was identified. • The kinetically frozen-in oxygen vacancies are shown to be effectively removed by a thermal annealing at and above 700 ℃. Dielectrics for automobile applications generally require high temperature reliability. Bi 1/2 Na 1/2 TiO 3 -based materials are excellent high-temperature dielectric candidates with relatively large temperature-insensitive dielectric responses and a maximum dielectric permittivity temperature as high as 300 °C. However, they suffer from a high dielectric loss that increases exponentially above 200 °C due to ionic conduction from thermally activated oxygen vacancy migration. Here, we demonstrate that the impact of ionic conduction on dielectric loss can be effectively suppressed by introducing a sodium deficiency and thermal annealing An appropriate combination of both treatments elevated the temperature insensitivity of the dielectric loss up to ∼ 300 °C. A systematic investigation using impedance spectroscopy correlated with microstructure analysis revealed that the sodium deficiency and thermal annealing affected the mobile oxygen vacancy concentration differently. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics with the composition of (1-x)[Bi0.5Na0.5TiO3-0.06BaTiO3]-xBa(Ti0.90Sn0.10)O3 or (1-x)[BNT-0.06BT]-xBTS ternary system (where x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05 mol fraction) have been synthesized by a conventional mixed-oxide method. The optimum sintering condition for all samples was found to be 1125 °C/2 h with a heating/cooling rate of 5 °C/min. The relative densities of all samples were ∼98% with the accompanying linear shrinkage of ∼18%. The XRD patterns of all samples showed no detected impurity phase. It was found that the composition of x = 0.03 exhibited optimum electrical properties (εr = 1895, tan δ = 0.0355 and d33 = 255 pC/N at room temperature), suggesting that this composition had potential to be a promising lead-free piezoelectric candidate compound for dielectric and piezoelectric applications. [ABSTRACT FROM AUTHOR]

In the present work, the nature of phase evolution of (1−x)(Na0.5Bi0.5)TiO3-xSrTiO3 (NBT-xST) solid solutions with x of 0–0.6 is revealed by characterizing the dielectric and ferroelectric properties. Two unique dielectric anomalies associated with high-temperature nanoregions (PNRs) in the ergodic relaxor (ER) state and low-temperature PNRs in the nonergodic relaxor (NR) state are identified. Characteristic temperatures, including TB, TRT∗, Tm, Td and TT∗, are determined in fresh and poled states on the basis of the characteristics of the evolution of these two dielectric anomalies. The whole evolution of the transition from the NR state to the ER state is reflected by the temperature-dependent polarization versus electric field (P-E) hysteresis loops, i.e., from the square loops, via the double-like loops, to the slim loops. The characteristic temperatures, including TP-N, TN-R and TR-dis, are determined by the characteristics of the evolution of P-E loops. Accordingly, a phase diagram of NBT-xST was constructed according to these characteristic temperatures. Most importantly, the relationship between polarization responses and heterogeneous polar phase coexistence has been established and a schematic diagram is given. This work will help to understand the phase evolution and its impact on the macroscopic properties of NBT and the associated NBT-based solid solutions.

This work reports a detailed study of the crystal structure and electrical properties of a potential lead-free piezoelectric Bi 0.5 Na 0.5 TiO 3 co-doped with Ba2+ and Fe3+ sintered at relatively low temperature (900 °C). The effect that co-dopants have over the electric properties in (Bi 0.5 Na 0.5) 1-x Ba x Ti 1-y FeyO 3-0.5y , varying x from 0 to 0.075, Δx = 0.025, and y from 0 to 0.075, Δy = 0.025, was evaluated. XRD analysis showed a successful synthesis of co-doped BNT ceramics with a rhombohedral structure for samples with x < 0.075. In contrast, the sample with x = 0.075 exhibited the coexistence of the rhombohedral and tetragonal structures, confirmed by Rietveld refinement. The co-doping promotes the grain size growth and increase the pellets' density from 93 % to 98 %. Dielectric spectroscopy analysis, conducted in the range from 25 to 500 °C, showed an increase in the relative permittivity with the dopant concentration, specifically at high temperatures. Electric analysis validate the piezoelectric behavior and the electric polarization of the co-doped BNT ceramics, unveiling a maximum remnant polarization (P r) of 25.6 μC/cm2 and, a maximum piezoelectricity coefficient of 53 pC/N, which varied depending on the composition. The obtained results demonstrate that co-doping BNT ceramics with Ba2+ and Fe3+ cations lower the sintering temperature typically used in the solid-state reaction to obtain pure BNT, showing similar properties compared to those of the same material sintered at higher temperatures and longer times. • All samples obtained by high-energy milling exhibiting a rhombohedral structure. • The Bi 0.5 Na 0.5 TiO 3 co-doped with Ba–Fe was sintered at low temperature (900 °C). • Dopants Ba–Fe enhance atomic diffusion at 900 °C, resulting in high-density pellets. • With dopant concentrations exceeding 0.025 mol, the ε r increase from 400 to 1200. • The sample BNT-0.05B-0.075F exhibit a maximum polarization of 31 μC/cm2. [ABSTRACT FROM AUTHOR]

0.7(Na0.5Bi0.5)TiO₃-0.26SrTiO₃-0.04BaTiO₃ (0.7NBT-0.26ST-0.04BT) ceramics was chosen as the base material, and x mol% MnCO₃ (x=0, 0.1, 0.3, 0.5, 0.7) was externally introduced to investigate its effect on the phase structure, microstructure, dielectric and ferroelectric properties for energy storage. X-ray diffraction (XRD) analysis revealed that no diffraction peak location shifting but intensity weakening can be observed with manganese doping amount, indicating manganese did not enter the crystal lattice but form glass phases and/or impurities. Scanning electron microscopy (SEM) analysis showed that manganese doping promoted grain growth, and some liquid or precipitated impurity particles were found at grain boundaries, which was consistent with the results of XRD. Manganese doping can effectively suppress the dielectric loss near room temperature of the ceramics. When the doping amount of MnCO₃ was 0.5 mol% and the applied electric field was only 60 kV/cm, the optimal recoverable energy density and efficiency of the ceramics were 0.63 J/c³ and 65% respectively, presenting a valuable solid state energy storage ceramic capacitor material

Bi 0·5 Na 0·5 TiO 3 -based relaxor ferroelectric ceramics have recently gained increasing attention due to their outstanding energy storage properties. However, the trade-off between the recoverable energy storage density/efficiency and discharge rate resulted from the hysteresis of domain switching process, severely limits their applications. Herein, a strategy realizing synergistic excellent energy storage properties and fast discharge rate is proposed through regulating relaxation temperature. The relaxation temperature was decreased to below room temperature by introducing Sr 0·85 Bi 0·1 TiO 3 into Bi 0·5 Na 0·5 TiO 3 [(1- x)Bi 0·5 Na 0·5 TiO 3 - x Sr 0.85 Bi 0·1 TiO 3 , x = 0.5–0.7)], enabling the small size and weak correlation polar nanoregions (PNRs) with relatively high polarization. The trade-off was overcome by reducing the hysteresis of electrical switching of weak correlation PNRs. Thus, large recoverable energy storage density of 2.32 J/cm3 and high efficiency of 80.1% (250 kV/cm) were achieved simultaneously for x = 0.7 ceramics. Meanwhile, extremely rapid discharge rate (<30 ns) and remarkable power density of 63.7 MW/cm3, which were superior to the previously reported lead-free ceramics were realized. Besides, the 0.3BNT-0.7SBT ceramics also possess good thermal stability over 25 °C–115 °C at 100 kV/cm and good frequency stability (5–100 Hz). These properties make the 0.3BNT-0.7SBT ceramic an ideal candidate for energy storage applications. [ABSTRACT FROM AUTHOR]

Lead-free bismuth sodium titanate piezoceramics were processed by a solid-state route with a novel precursor approach. By carefully controlling the processing parameters and sintering atmospheres, translucent ceramics with pore-free, homogeneous microstructures with exceptionally low dielectric loss at elevated temperatures. The pore-free microstructure can influence the operating life of a dielectric device positively, since pores and other microstructural defects are usually responsible for material failures within devices. Synchrotron and surface X-ray diffraction experiments revealed a clear dependence of the crystal structure on sintering parameters and defect chemistry. Microstructural analysis showed a dependency of a secondary phase on the sintering atmosphere. The grain size could be adjusted using a shortened grinding process instead of using the common methods like increasing calcining or sintering temperature. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate Bi0.5Na0.5TiO3 (BNT) is a lead‐free piezoelectric ceramic material with high Curie temperature. The effect of substitution of the smaller ion Li+ for the larger ion Na+ in Bi0.5(Na1‐xLix)0.5TiO3 (0 ≤ x ≤ 0.20) on the structure of BNT is studied using powder X‐ray diffraction (XRD) and Raman spectroscopy. The Rietveld refinement analysis of the powder XRD patterns showed that all the compositions formed under the monoclinic Cc space group, with the lattice parameters showing minor changes above x > 0.08. Raman spectral parameters such as position and intensity of a peak also showed a similar trend in the same Li concentration range with increasing Li content. A corresponding change in the variation of the dielectric constant with increasing Li content is also observed, suggesting a close correlation between the crystal structure and dielectric properties of the different compositions in the Bi0.5(Na1‐xLix)0.5TiO3 solid solution series. [ABSTRACT FROM AUTHOR]

We report the effect of various Bi:Ti ratios x:1 (x = 0.5–3) on the phase formation of sodium-bismuth titanate Na0.5Bi0.5TiO3 (NBT) during hydrothermal synthesis (230°С, 3 MPa, 96 h) from titanium oxide and bismuth hydroxide in 20 M NaOH solution. It was shown that single-phase ceramics with perovskite structure could be obtained at x = 0.5–0.9 using the hot-pressing technique (1025°С, 60 MPa, 1 h). At x = 1, hydrothermal synthesis results in single-phase samples, while, after sintering, the admixture of Na2Ti3O7 was detected. At x = 2 and 3, samples contained admixtures after hydrothermal synthesis. The x–value does not significantly affect the composition of perovskite-like products despite the excess of bismuth in the system. The chemical composition of the samples with x = 0.5–0.9 corresponds to the general formula Na0.60–0.69Bi0.40–0.31TiO2.9–2.81δ0.10–0.19 (where δ represents vacancies in oxygen sublattice). The Bi3+ content in the samples is underestimated due to the solubility of its hydroxide in a 20 M alkali solution. The properties of ceramics are not significantly affected by x values, and materials exhibit following average characteristics: electrical resistivity 1.3 × 109 Ohm∙cm, tanδ = 0.15, Кр = 0.1, d31 = 6.7 and d33 = 9.5 pC/N, g31 = 2.34 and g33 = 3 mV∙m/N. [ABSTRACT FROM AUTHOR]

We use a strategy to reduce the driving electric field of the relaxor 0.72Bi 1/2 Na 1/2 TiO 3 –0.28SrTiO 3 (BNT–28ST) by introducing ferroelectric plate–type Bi 1/2 (Na 0.78 K 0.22) 1/2 TiO 3 (BNKT) particles. Consequently, 10 vol.% BNKT added BNT–28ST/BNKT (relaxor/ferroelectric) composite has delivered large normalized strain (S max / E max = 650 pm/V) under relatively low applied field of 2.5 kV/mm with the reduction in the poling field value to 36% compared to that of pure BNT–28ST ceramics. We demonstrated that such behavior comes from the stress induced effect at the boundary of the ferroelectric and relaxor materials due to their different nature (relaxor/ferroelectric). The generation of stress is expected from the ferroelectric (BNKT) to the relaxor (BNT–28ST) at the boundary. Thereby, field–dependent stress at relaxor/ferroelectric phase boundary is monitored proposing the reduction of the poling field due to the strain coupling mechanism. Our findings provide a pathway for reducing the poling field in BNT–based incipient piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

An inherent conflict of (Bi 0.5 Na 0.5)TiO 3 -based (BNT) lead-free piezoelectric ceramics is the optimizing piezoelectric response (d 33) with deteriorating depolarization temperature (T d), which severely restricts the further achievements of BNT-based ceramics. A new strategy is proposed in this work to simultaneously realize high piezoelectric property (d 33 = 140 pC/N) and thermal stability (T d = 232 °C) in BNT-based ceramics by integrating layered composite structure of 0.89(Bi 0.5 Na 0.5)TiO 3 -0.11BaTiO 3 with high T d and 0.87(Bi 0.5 Na 0.5)TiO 3 -0.11BaTiO 3 -0.02(Sm 0.5 K 0.5)TiO 3 with large d 33 (BNT1/BNT2) and thermal treatment processes. In the layered composite ceramics, the composition difference induces a built-in field (E b) that promotes the diffusion of ferroelectric-relaxor (FE-RE) phase transition in the ceramics, delaying the T d to 185 °C. In addition, the thermal treatment processes facilitate both the E b expansion, stabilize the d 33 over a wide temperature range, as well as enlarge the grain size to elevate the d 33 from 133 pC/N to 145 pC/N. Hence, the strategy we proposed is promising to offer a new paradigm for designing piezoelectric materials with high piezoelectric response over a wide temperature range. [Display omitted] • An innovative solution was proposed to significantly mitigate the conflict between d 33 and T d. • BNT-based piezoceramics not only achieve large d 33 over the temperature interval of -45 ℃-244 ℃ but also improve temperature stability of d 33. • The incompatibility between d 33 and T d in bilayer structured ceramic composites at elevated temperature is resolved. [ABSTRACT FROM AUTHOR]

A systematic study of pseudo-isovalent B site co-substitution of Ti4+ by Mg2+ and Nb5+ in bismuth sodium titanate is presented. A complete solid solution in the Bi 0.5 Na 0.5 Ti 1− x (Mg 1/3 Nb 2/3) x O 3 system is formed. With increasing level of substitution, dielectric anomalies associated with depoling and maximum permittivity temperatures (T d and T m , respectively) are suppressed and shift to lower temperatures. Variable temperature X-ray powder diffraction on the x = 0.2 composition reveals a non-linear thermal expansion at temperatures below T m. B-site co-substitution by Mg and Nb has the effect of interrupting the long-range ferroelectric ordering in the system, resulting in lower saturation and remnant polarizations. A maximum energy storage density of 4.14 J cm−3 with a recoverable energy density of 2.35 J cm−3 was obtained for the x = 0.1 composition, while the x = 0.5 composition appears to have the best balance between energy storage and energy efficiency. • B-site co-substitution of (Bi 0.5 Na 0.5)TiO 3 relaxor ferroelectrics. • Depoling and maximum permittivity temperatures shift to lower temperature. • Mg and Nb interrupt long-range ferroelectric ordering. • The balance of energy storage density and energy loss shows compositional dependence. [ABSTRACT FROM AUTHOR]

Achieving good piezoelectric properties, such as the widely reported d33 charge coefficient, is a good starting point in establishing the potential applicability of piezoceramics. However, piezoceramics are only completely characterized by consistent piezoelectric-elastic-dielectric material coefficient matrices in complex form, i.e., including all losses. These matrices, which define the various alternative forms of the constitutive equations of piezoelectricity, are required for reliable virtual prototyping in the design of new devices. To meet this need, ten precise and accurate piezoelectric dielectric and elastic coefficients of the material, including all losses, must be determined for each alternative. Due to the difficulties arising from the coupling of modes when using the resonance method, this complete set of parameters is scarcely reported. Bi0.5Na0.5TiO3-based solid solutions are already commercially available in Europe and Japan. Here, we report a case study of the determination of these sets of material coefficients (diα, giα, eiα and hiα; sE,Dαβ and cE,Dαβ; εTik and εSik; and βTik and βSik), including all losses, of the commercial PIC700 eco-piezoceramic. Plate, disk, and cylinder ceramic resonators of a manageable aspect ratio were used to obtain all the material coefficients. The validation procedure of the matrices is also given by FEA modeling of the considered resonators.

The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks are investigated under biaxial loading on unpoled and poled samples. The bending strength of unpoled samples was higher than those of poled ones. Fatigue tests were conducted under a load ratio of 10 at a frequency of 20 Hz with a sinusoidal waveform. The curve fitting for the S-N fatigue diagram is used to predict the lifetime of these eco-piezoceramics and describe their fatigue behavior. It was also found that the unpoled samples exhibited higher fatigue resistance than the poled ones. The fatigue limit of maximum load for ten million cycles of unpoled and poled samples was estimated to be 160 and 135 MPa, respectively. The detailed observations of the fatigue fracture surfaces by scanning electron microscopy (SEM) indicated that a wavy surface with a mixture of transgranular and intergranular fractures occurred preferentially in the case of the poled material. On the other hand, transgranular fractures seem to be predominant in the unpoled samples. It appears that the poling process causes the change in failure characteristics due to domain orientation that leaves an anisotropic stress field in the material. The poled ceramics possess a local stress concentration created by the orientation under the electric poling field of the 90° ferroelectric–ferroelastic domains. Under this local stress concentration, a microstructural degeneration is induced by domain switching under the cyclic load that accelerates crack growth, thereby reducing fatigue lifetime.

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics (1−x)Bi0.5Na0.5TiO3−xBaTiO3 (BNT−xBT, x=0, 0.02, 0.04, 0.06, 0.08 and 0.10). The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed. Three dielectric anomalies with pronounced frequency dispersion at Td, a maximum dielectric with variable frequency-dispersion at Tm and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed. The significant dielectric thermal hysteresis, low barrier energy, high freezing temperature in heating process and the maximum dielectric tunability appeared in x=0.4 ceramic.

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics (1 − x) Bi 0. 5 Na 0. 5 TiO 3 − x BaTiO3 (BNT − x BT, x = 0 , 0.02, 0.04, 0.06, 0.08 and 0.10). The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed. Three dielectric anomalies with pronounced frequency dispersion at T d , a maximum dielectric with variable frequency-dispersion at T m and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed. The significant dielectric thermal hysteresis, low barrier energy, high freezing temperature in heating process and the maximum dielectric tunability appeared in x = 0. 4 ceramic. [ABSTRACT FROM AUTHOR]

Doping in bismuth sodium titanate (BNT)-based ceramic is often intended to realize excellent direct piezoelectric responses mainly through A-site substitution and generate ultrahigh strain behaviors mainly by B-site doping, which indicate the different effects of the doping on direct and converse piezoelectricity. Here, we reported simultaneous occurrences of anomalies in electric field and temperature dependence of direct/converse piezoelectric responses of 0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 (BNT-BT6) ceramics by detailed analyses of the weak-field piezoelectric coefficient d 33 , high-field piezoelectric coefficient d 33 ∗ , and small signal bias-field piezoelectric coefficient d 33 ∗ (E = 0). The multiple piezoelectric responses presented similar anomalies at critical field E p = 20 kV/cm and critical temperature T f = 120 °C. The analogous changes in direct/converse piezoelectric behaviors are highly related to the electric-field/temperature-driven phase transformation, which could boost polarization reorientation and domain switching to a lager extent. Particularly, the phase transition resulted in an obvious increase in high-field piezoelectric coefficient d 33 ∗ , and so offer a potential strategy for further development of high-performance lead-free piezoelectric materials. Image 1 • Simultaneous enhancement in multi-piezoelectric responses was achieved. • The analogous changes in direct/converse piezoelectric behaviors took placed. • Electric-field-driven phase transformation resulted in obvious increases of d 33 ∗ . [ABSTRACT FROM AUTHOR]

Oxide ion-conducting solid electrolytes are of considerable importance as fuel cell component. Recently, Bi0.5Na0.5TiO3 (BNT)-based perovskite-structured oxides become a new hotspot of solid electrolyte since it has potential in oxygen ion conduction. Considerable ionic conductivity is achieved in a Bi deficient or an acceptor doping composition. In this work, the role of Sm content without lone pair electrons substituted for isovalent Bi is studied on the electrical properties of non-stoichiometric (Bi0.45Ca0.04)Na0.5TiO2.965 (BCNT). In the solid solution range, a transformation from resistive BCNT to dominated oxide ionic conductive process is revealed despite no additional designed vacancies involved. Interestingly, employment of smaller Sm cations by doping favors the plateau formation of dielectric permittivity at higher frequencies. Lone pairs substitution conception and shrinkage of lattice parameters are proposed to be responsible for the anomalous dielectric relaxation. [ABSTRACT FROM AUTHOR]

Abstract The electrocaloric effects (ECE) in the composites consisting of ferroelectric (FE) copolymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) and (Bi 0.5 Na 0.5)TiO 3 - x BaTiO 3 nanoparticles (BNT-xBT, x = 0, 0.06, 1.0) are investigated. The anti-ferroelectric (AFE) nanofillers are found to affect more significantly than the FE nanofillers on the order-to-disorder phase transition near 60 °C in the copolymer matrix, as revealed by differential scanning calorimetry. Nevertheless, the influences of AFE nanofillers on the negative ECE are much weaker than that of FE nanofillers, suggesting that the negative ECE observed might not be associated with the AFE states in the composites. Instead, based on the dynamic mechanical analyses on the effects of nanofillers on the order-to-disorder phase transition in the copolymer matrix, the structural glassy states induced by the interaction between the nanofillers and the copolymer matrix are proposed to account for the negative ECE in the composite. This work provides an effective approach in enhancing the negative ECE, which is of technological importance to the implementation of electrocaloric refrigeration. Highlights • The anti-ferroelectric nanofillers are found to affect more significantly than the ferroelectric nanofillers on the order-to-disorder phase transition in P(VDF-TrFE) copolymer. • The structural glassy states induced by the interaction between the nanofillers and the copolymer matrix are proposed to account for the negative electrocaloric effect in the composite. • This work provides an effective approach in enhancing the negative electrocaloric effect, which is of technological importance to the implementation of electrocaloric refrigeration. [ABSTRACT FROM AUTHOR]

Graphical abstract (a) Electric field amplitude (E 0) dependence of P - E hysteresis loops measured at 0.1 Hz. The inset (b) shows hysteresis area < A > of the hysteresis loops with variation E 0. (c), (d) are the plots of ln P r , ln E c , ln< A > and dln< A >/dln E 0 versus ln E 0. Here, the polarization reversal and dynamic hysteresis were investigated in (Bi 1/2 Na 1/2)TiO 3 (BNT) ceramics. The scaling behaviors were presented by studying the dependence of hysteresis loops on the field amplitude E 0. New feature of polarization responses and scaling behaviors were obtained. The exponent α in an equation of the hysteresis loop area < A >∝ E 0 α displayed large values in high- E 0 stage. Highlights • The exponent α in the hysteresis loop area < A >∝ E 0 α equation shown large values in high- E 0 stage. • The < A > displayed abnormal increase with temperature. • A near frequency-invariant coercive field E C , accompanied by a weakly dependent P r and < A > was observed. Abstract The excellent electrical properties and potential applications of ferroelectric ceramics are intrinsically correlated with the dynamic polarization response under applied electric field. However, the lack of clarity with regard to global polarization reversal process has hindered the understanding of the functional properties. Here, the polarization reversal and dynamic hysteresis were investigated in (Bi 1/2 Na 1/2)TiO 3 (BNT) ceramics. The scaling behaviors were presented by studying the field amplitude E 0 , frequency f 0 and temperature T 0 dependence of hysteresis loops. Three new features of polarization responses and scaling behaviors were obtained. First, the exponent α in the hysteresis loop area < A >∝ E 0 α equation displayed large values in high- E 0 stage. Then, the < A > displayed an abnormal increase with increasing temperature. Finally, a near frequency-invariant coercive field E C , accompanied by a weak dependent P r and < A >, was observed. The correlation between these new features and polarization extension/rotation as well as complex domain structure and field-induced phase transition was demonstrated. [ABSTRACT FROM AUTHOR]

The ban of lead in many electronic products and the expectation that, sooner or later, this ban will include the currently exempt piezoelectric ceramics based on Lead-Zirconate-Titanate has motivated many research groups to look for lead-free substitutes. After a short overview on different classes of lead-free piezoelectric ceramics with large strain, this review will focus on Bismuth-Sodium-Titanate and its solid solutions. These compounds exhibit extraordinarily high strain, due to a field induced phase transition, which makes them attractive for actuator applications. The structural features of these materials and the origin of the field-induced strain will be revised. Technologies for texturing, which increases the useable strain, will be introduced. Finally, the features that are relevant for the application of these materials in a multilayer design will be summarized.

Novel high temperature ceramic capacitors (1−  x )(Na 0.5 Bi 0.5 TiO 3 − 0.15Ba 0.8 Ca 0.2 Ti 0.8 Zr 0.2 O 3 )−  x K 0.5 Na 0.5 NbO 3 were synthesized in the solid-state reaction route. The influence of K 0.5 Na 0.5 NbO 3 modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x  = 0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (< 0.05) over a relatively broad temperature range (66–230 °C). A variation in permittivity within ± 15% can be observed over a pretty wide temperature range of 66–450 °C. Beyond that, this ceramic shows enhanced energy-storage properties with the density ( W rec ) of 0.52 J/cm 3 and efficiency (η) of 80.3% at 110 kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy. [ABSTRACT FROM AUTHOR]

In this work, an ink-jet printing process based on the sol-gel route was applied to prepare lead-free ferroelectric Na 0.5 Bi 0.5 TiO 3 (BNT) thin films for the first time. Dense and crack-free films with perovskite structure were obtained from a modified precursor solution through multiple printing and pyrolysis processes. The ferroelectric, dielectric and electrical properties were significantly affected by the annealing temperature and atmosphere. The film annealed at 670 °C in wet air showed a high remnant polarization of 24.7 μC/cm 2 with a low coercive field of 263 kV/cm, the dielectric constant and loss were 185 and 0.1 at 10 kHz, respectively. It was found that wet air was an alternative to reduce oxygen vacancies and enhance properties of ferroelectric films, which can be explained by the defect chemical reaction between water and oxygen vacancies. X-ray photoelectron spectroscopy(XPS) confirmed the decrease of oxygen vacancies after annealing with water presence, with a formation of Ohmic conduction mechanism dominated by charged hydroxyl groups. [ABSTRACT FROM AUTHOR]

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(Bi0.5Na0.5)0.94Ba0.06TiO3 dense ceramics were obtained from autocombustion sol-gel synthesized nanopowders and sintered at 1050 °C for 1-2 h for the study of the electromechanical anisotropy. Measurement of the complex impedance spectrum was carried out on thin ceramic disks, thickness-poled, as a function of the temperature from 16 °C up to the vanishing of the electromechanical resonances at the ferroelectric to relaxor transition near 100 °C. The spectrum comprises the fundamental radial extensional mode and three overtones of this, together with the fundamental thickness extensional mode, coupled with other complex modes. Thermal evolution of the spectrum shows anisotropic behavior. Piezoelectric, elastic, and dielectric material coefficients, including all losses, were determined from iterative analysis of the complex impedance curves at the planar, thickness, and shear virtually monomodal resonances of disks and shear plates, thickness-poled. d33 was measured quasi-statically at 100 Hz. This set of data was used as the initial condition for the optimization of the numerical calculation by finite elements of the full spectrum of the disk, from 100 kHz to 1.9 MHz, to determine the thermal evolution of the material coefficients. An appropriate measurement strategy to study electromechanical anisotropy of piezoelectric ceramics has been developed. [ABSTRACT FROM AUTHOR]

The features of the crystal structures and spontaneous polarization (Ps) under an electric field (E) have been reviewed for (1 − x)(Bi0.5Na0.5)TiO3–xBaTiO3 (BNT–BT). In-situ measurements of high-resolution synchrotron radiation X-ray diffraction (SR-XRD) under electric fields show that single crystals with x = 0 (BNT) and 5% have a monoclinic distortion in space group Cc at 25 °C. The SR-XRD study combined with density functional theory (DFT) calculations demonstrates that BNT–5%BT exhibits a rotation of Ps in the monoclinic a–c plane by 2° under an E of 70 kV/cm along the pseudo-cubic direction, which is much larger than BNT.

Highly uniform lead-free piezoelectric bismuth sodium titanate (Bi 0.5 Na 0.5 TiO 3 , BNT) nanowires were successfully synthesized via a hydrothermal method. Synthesized at a stirring speed range of 300–1000 rpm, the compositions and orientations of BNT nanowires were well controlled. The effects of stirring speeds on the formation of BNT nanoparticles and nanowires in the hydrothermal processes were systematically investigated. The BNT nanowires with a high aspect ratio were proven to be single crystals with [110] growth direction from high-resolution TEM analysis. The mechanism of growth of BNT nanowires out of nanoparticles in the hydrothermal processes was proposed. [ABSTRACT FROM AUTHOR]