Raman and infrared spectroscopy of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> - BaTiO<Subscript>3</Subscript> ceramics

Lead-free Na_0.5Bi_0.5TiO₃ -BaTiO₃ ceramics have been prepared in the whole range of concentrations and studied at room-temperature by means of X-ray, Raman scattering and infrared techniques. X-ray measurements revealed rhombohedral, rhombohedral-tetragonal boundaries and tetragonal modifacations depending on the contents of BaTiO₃. The distinct changes of the Raman and infrared spectra with increasing of BaTiO₃ content, which were correlated with X-ray results, were observed. The broad phonon spectra indicated the disorder in the A site of Na_0.5Bi_0.5TiO₃ -BaTiO₃ system.     

High piezoelectricity associated with crossover from nonergodicity to ergodicity in modified Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> relaxor ferroelectrics

The structural origin of high piezoelectricity in perovskite-type relaxor ferroelectrics is a fundamental issue that remains elusive for decades. In this study, high and unstable piezoelectricity for the poled ceramics, accompanied with a crossover from a nonergodic relaxor to an ergodic relaxor state at room temperature, has been observed for 0.95(Bi_0.5Na_0.5)_1-x (Li_0.5Sm_0.5) _x TiO₃–0.05BaTiO₃ ceramics with x = 0.06. The result suggests that the high piezoelectric activity origins from the electric field-induced-ordered nanodomains. The rapid loss of piezoelectricity stems from the reversibility of the ordered nanodomains after removing applied electric field.     

Lead-free K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>Li<Subscript>0.5</Subscript>ZrO<Subscript>3</Subscript>–BiAlO<Subscript>3</Subscript> ternary ceramics: Structure and piezoelectric properties

Lead-free perovskite (0.995–x)(K_0.5Na_0.5)NbO₃–x(Bi_0.5Li_0.5)ZrO₃–0.005BiAlO₃ ternary piezoelectric ceramics were projected and prepared by a conventional solid-state method. A research was conducted on the effects of (Bi_0.5Li_0.5)ZrO₃ content on the structure and piezoelectric properties of the ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, a rhombohedral–orthorhombic–tetragonal phase coexistence was identified for the ceramics with 0.02 ≤ x ≤ 0.025, and a rhombohedral–tetragonal phase boundary was determined in the composition x = 0.03. Upon further increasing the (Bi_0.5Li_0.5)ZrO₃ content, the rhombohedral–tetragonal phase boundary transformed to a single rhombohedral structure with x ≥ 0.035. An obviously improved piezoelectric activity was obtained for the ceramics with compositions in and around the rhombohedral–tetragonal phase boundary, among which the composition x = 0.025 exhibited the maximum values of piezoelectric constant d ₃₃, and planar and thickness electromechanical coupling coefficients (k _p and k _t), of 252 pC/N, 0.366, and 0.466, respectively. In addition, the ceramic with x = 0.025 was found to possess a relatively high Curie temperature of 368 °C, suggesting it may have a prospect for applications at elevated ambient temperatures.     

Effects of MnO<Subscript>2</Subscript> addition on microstructure and electrical properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>) <Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.     

Dielectric and Piezoelectric Properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-NaNbO<Subscript>3</Subscript>Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 – x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃] – xNaNbO₃(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant _r and dissipation factor tan measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures T_d and T_m are lowered due to introduction of NaNbO₃. P-E hysteresis loops show that 0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃ ceramics has the maximum P_r and E_c corresponding to the maximum values of electromechanical coupling factor K_p and piezoelectric constant d_33. The piezoelectric constant d₃₃ and electromechanical coupling factor K_p decrease a little, while the dielectric constant ₃₃^T/₀ improves much more when the concentration of NaNbO₃ is 8 mol%.     

Effects of co-doped CaO/MnO on the piezoelectric/dielectric properties and phase transition of lead-Free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

The piezoelectric properties of (1?x)(Bi_0.5Na_0.5)TiO₃-xBaTiO₃ ceramics were reported and their piezoelectric properties reach extreme values near the MPB (about x?=?0.06). The X-ray analysis of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics for all compositions exhibited a pure perovskite structure without any secondary phase. Within a certain ratio of contents, the co-doped ceramics enhanced piezoelectric coefficient (d ₃₃ ), lowered the dielectric loss, and increased the sintered density. The temperature dependence of relative dielectric permittivity (K ₃₃ ^T ) reveals that the solid solutions experience two phase transitions, ferroelectric to anti-ferroelectric and anti-ferroelectric to relaxor ferroelectric, which can be proven by P-E hysteresis loops at different temperatures. In addition, the specimen containing 0.04/0.01 wt.% CaO/MnO showed that the coercive field E _c was a minimum value of 26.7 kV/cm, while the remnant polarization P _r was a maximum value of 38.7 μC/cm², corresponding to the enhancement of piezoelectric constant d₃₃ of 179 pC/N, electromechanical coupling factor k _p of 37.3%, and relative dielectric permittivity K ₃₃ ^T of 1137. (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics co-doped with CaO/MnO were considered to be a new and promising candidate for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties, which are superior to an un-doped BNBT system.     

Effect of BiAlO3 concentration on the dielectric and piezoelectric properties of lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

In this paper, lead-free (1-x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-xBiAlO₃ (BNBT-BA, x?=?0, 0.010, 0.015, 0.020, 0.025, and 0.030) piezoelectric ceramics were synthesized using a conventional solid-state reaction method. The effect of BiAlO₃ concentration on dielectric, ferroelectric and piezoelectric properties were investigated. The ferroelectric and piezoelectric properties of BNBT ceramics are significantly influenced by the presence of BA. In the composition range studied, X-ray diffraction revealed a perovskite phase with the coexistence of rhombohedral and tetragonal phases. The temperature dependence of dielectric properties showed that the depolarization temperature (T _d) shifted towards lower temperatures and that the degree of diffuseness of the phase transition around T _d and T _m became more obvious with increasing BiAlO₃ content. The remanent polarization increased with increasing BA, and reached a maximum value of 30 μC/cm² at x?=?0.020. As a result, at x?=?0.020, the piezoelectric constant (d ₃₃) and the electromechanical coupling factor (k _p) of the ceramics attained maximum values of 188 pC/N and 34.4 %, respectively. These results indicate that BNBT-BA ceramics is a promising candidate for lead-free piezoelectric materials.     

Effect of Ca substitution on microwave dielectric properties of BaV<Subscript>2</Subscript>O<Subscript>6</Subscript> ceramics

Effects of Ca substitution for Ba on the phase composition, microstructure, sintering behavior and microwave dielectric properties of nominal ceramics Ba_1-xCa_xV₂O₆ (0.2?≤?x?≤?0.5) were investigated. The XRD, Raman and SEM results revealed that BaV₂O₆ and CaV₂O₆ composite ceramics were formed. Nominal ceramics Ba_1-xCa_xV₂O₆ could be well densified at about 550 °C via a solid-state reaction method. The microwave dielectric properties exhibited strong dependence on the composition and microstructure. Typically, the Ba_0.7Ca_0.3V₂O₆ ceramics sintered at 550 °C exhibited excellent microwave dielectric properties: ε_r?=?10.9, Qxf?=?17,100 GHz (at 9.9 GHz), and τ_f?=?4 ppm/°C. Meanwhile, Ba_0.7Ca_0.3V₂O₆ ceramics also showed good chemical compatibility with Al electrode. These results indicated that the Ba_0.7Ca_0.3V₂O₆ ceramics could be a promising candidate for the ULTCC technology.     

Piezoelectric ceramics of (Bi1/2Na1/2)TiO3-PbTiO3-BaTiO3 system

Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi_1/2Na_1/2)TiO₃(BNT)-based solid solution, that is, (Bi_1/2Na_1/2)(_1-x)(Pb_a Ba_b)_xTiO₃(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(F_a-tetragonal (F_β) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi_1/2Na_1/2)TiO₃[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε₃₃Tε₀, and a high electromechanical coupling factor k₃₃, along with a high mechanical strength.     

Structure and piezoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript> based lead-free piezoceramics with slight deviation from A-site K or Na stoichiometry

The dependence of structure and piezoelectric response d₃₃ on individual excess A-site K or Na in K_0.5Na_0.5NbO₃ based lead-free piezoceramics is reported. The coexistence of orthorhombic, tetragonal, and monoclinic phases at room temperature is observed in the investigated 0.94K_0.5+xNa_0.5NbO₃–0.06LiNbO₃ and 0.94K_0.5Na_0.5+yNbO₃–0.06LiNbO₃ ceramics (x, y = 0–0.025). The weight ratio of three phases, orthorhombic-tetragonal phase transition temperature, and d₃₃ value are highly sensitive to A-site K or Na nonstoichiometry. A-site Na nonstiochiometry plays a dominant role in enhancing the electrical properties of KNN by significantly reducing the weight ratio percentage of monoclinic phase and shifting the orthorhombic-tetragonal phase transition temperature to lower temperatures.     

Dielectric,ferroelectric and bipolar electric field induced strain properties of MPB composition of NBT-xKNN system

(1-x) (Na_0.5Bi_0.5TiO₃)-xK_0.5Na_0.5NbO₃/NBT-xKNN [x?=?0.07, 0.06, 0.05] ferroelectric ceramics were prepared by solid state synthesis route (SSSR). The effects of KNN contents on the microstructure, dielectric, piezoelectric and ferroelectric properties of the NBT-xKNN system were investigated in detail. For single perovskite phase formation, the calcination temperature was optimized at 800 °C for 6 h. From the XRD study, the morphotropic phase boundary (MPB) was confirmed for x?=?0.07 composition. For better densification, the sintering temperature was optimized for 1150 °C for 4 h. SEM micrographs illustrate the closely packed and non-uniform distribution of grains. Diffusive type of behaviour was observed in all the ceramics. Polarization (P) vs. electric field (E) study confirmed the ferroelectric nature of the NBT-xKNN ceramics. The bipolar field-induced strain measurement for all the ceramic samples showed butterfly-shaped loops indicating their piezoelectric nature. Among all the different compositions in MPB region, high dielectric constant (ε_r) of?~?3011, high remnant polarization (P _r ) of 17.88μC/cm² and high strain % of 0.41, were obtained in NBT-xKNN system with x?=?0.07 confirming the existence of MPB at this composition.     

Microstructure and electrical properties of the rare-earth doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 piezoelectric ceramics

Phase structure, microstructure, piezoelectric and dielectric properties of the 0.4 wt% Ce doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (Ce-BNT6BT) ceramics sintered at different temperatures have been investigated. The powder X-ray diffraction patterns showed that all of the Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The morphologies of inside and outside of the bulk indicated that the different sintering temperatures did not cause the second phase on the inside of bulk. However, the TiO₂ existed on the outside of the bulk due to the Bi₂O₃ and Na₂O volatilizing at higher temperature. The ceramics sintered at 1,200 °C showed a relatively large remnant polarization (P _r) of about 34.2 μC/cm², and a coercive field (E _c) of about 22.6 kV/cm at room temperature. The permittivity ? _r of the ceramics increased with the increasing of sintering temperature in antiferroelectric region, the depolarization temperature (T _d) increased below 1,160 °C then decreased at higher sintering temperature. The resistivity (ρ) of the Ce-BNT6BT ceramics increased linearly as the sintering temperature increased below 1,180 °C, but reduced as the sintering temperature increased further. A maximum value of the ρ was 3.125?×?10¹⁰ ohm m for the Ce-BNT6BT ceramics sintered at 1,180 °C at room temperature.     

Structure and properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-0.38PbTiO<Subscript>3</Subscript> ceramics with MPB composition

0.62Bi(Mg_1/2Ti_1/2)O₃-0.38PbTiO₃-xwt%Bi₂O₃ (BMT-0.38PT-xBi₂O₃) ceramics were prepared by conventional powder-processing method. It indicated that the morphotropic phase boundary (MPB) region located in 0.0?≤?x?≤?0.3. For x?=?0.3, it exhibited good piezoelectric properties, d₃₃ ~245pC/N and k_p ~40 %. With the increase of Bi₂O₃ content, the Curie temperature (T_c) was found to increase, and the dielectric loss was found to decrease above 200 °C compared with BMT-0.38PT sample. Finally, it can be found that depolarization temperature was around 350 °C by thermal depoling method.     

Synthesis and piezoelectric properties of [Bi1-z(Na1-x-y-zKxLiy)]0.5BazTiO3 lead-free piezoelectric ceramics

[Bi_1-z(Na_1-x-y-zK_xLi_y)]_0.5Ba_zTiO₃ lead-free piezoelectric ceramics were fabricated by ordinary ceramic technique and the piezoelectric and ferroelectric properties of the ceramics were studied. The ceramics can be well sintered at 1,100–1,150 °C for 2 h. X-ray diffraction (XRD) analysis shows that K⁺, Li⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a single-phase perovskite structure. The introduction of K⁺, Li⁺ and Ba²⁺ into Bi_0.5Na_0.5TiO₃ significantly decreases the coercive field E _c but maintains the large remanent polarization P _r of the materials. The ceramics provide piezoelectric constant d ₃₃ of 205 pC/N, electromechanical coupling factor k _p of 0.346, remanent polarization P _r of 31.7–38.5 μC/cm², and coercive field E _c of 3.18–5.16 kV/mm.     

Studies on new systems of BNT-based lead-free piezoelectric ceramics

Several new systems of Bi_0.5Na_0.5TiO₃-based lead-free piezoelectric ceramics were proposed based on the design of the multiple complex in the A-site of ABO₃ compounds. These ceramics were prepared by conventional ceramic techniques. The comparison of the piezo- and ferroelectric properties of these ceramics with those of the best properties of the Bi_0.5Na_0.5TiO₃-based lead-free piezoelectric ceramics published recently shows that these ceramics of the new systems have better ferroelectric and piezoelectric performance, and better temperature characteristic of the properties. Among these materials, Bi_0.5(Na_1?x?y K _x Li _y )_0.5TiO₃ possesses higher piezoelectric constant (d ₃₃?=?230.8 pC/N), higher electromechanical couple factor (k _p?=?0.41), larger remanent polarization (P _r?=?40 μC/cm²) and a better P–E hysteresis loop below 200 °C. Practical devices such as ceramic middle frequency filters and buzzers have been made by using these lead-free piezoelectric ceramics.     

Dielectric properties and defect mechanisms of (1-<Emphasis Type="Italic">x</Emphasis>)Ba(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> -<Emphasis Type="Italic">x</Emphasis>BiYbO<Subscript>3</Subscript> ceramics

(1-x)Ba(Fe_0.5Nb_0.5)O₃ -xBiYbO₃ (BFN-xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN-xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law.     

Excellent dielectric constants observed in heterogeneous conduction Ba(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> ceramics doped with Sr(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>

The (1-x)Ba(Zr_0.25Ti_0.75)O₃-xSr(Fe_0.5Nb_0.5)O₃ or (1-x)BZT-xSFN ceramics have been fabricated via a solid-state reaction technique. All ceramics exhibit a pure phase perovskite with cubic symmetry. The addition of a small amount of SFN (x?=?0.1) produces an obvious change in dielectric behavior. Very high dielectric constants (ε_r?>?164,000 at 1 kHz and temperature?>?150°C) are observed and the value is obviously higher than dielectric constants for Ba(Zr_0.25Ti_0.75)O₃ and Sr(Fe_0.5Nb_0.5)O₃ ceramics. The ferroelectric measurement data suggests that the unmodified sample exhibited a ferroelectric behavior. However, a transformation from a ferroelectric to a relaxor-like behavior is noted with increasing x concentration. Impedance Spectroscopy (IS) analysis indicates that the presence of excellent dielectric constants is due to the heterogeneous conduction in the ceramics after adding SFN, which can be explained in terms of the Maxwell-Wagner polarization mechanism.     

Synthesis of (Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>)(Ti<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> ceramics and effect of Sr content on room temperature dielectric properties

The compositions in the system (Ba_1−x Sr _x )(Ti_0.5Zr_0.5)O₃ with different Sr (x) content, were synthesized through solid oxide reaction route. The phase formation behaviors in the system were investigated by XRD. The room temperature dielectric properties of the compositions were investigated in the frequency range 10 Hz to 13 MHz. The solid solution system Ba_1−x Sr _x Ti_0.5Zr_0.5O₃ remains as cubic perovskite up to x < 0.6 and transforms into the tetragonal structure above x > 0.6. Composition with x = 0.6 contains a mixture of cubic and tetragonal phases with broadened diffraction pattern. It is observed that the increasing of Sr substitution results in the decreasing of bulk density, average grain size and dielectric constants etc. in the composition system. The AC dielectric conductivity of the ceramics also decreases with the increase in Sr-substitution due to decrease in loss as well as grain size with that substitution.     

Thermal Expansion Behavior of (Bi0.5Na0.5)Zr1-x Ti x O3 Ceramics

(Bi_0.5Na_0.5)Zr_1-xTi_xO₃ with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 ceramics were fabricated by a conventional sintering technique at 850–950°C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0 ≤ x ≤ 0.2), mixed-phase region (0.3 ≤ x ≤ 0.4), and rhombohedral phase region (0.5 ≤ x ≤ 0.6). The thermal expansion coefficient data indicated the phase transition in the temperature range from 100°C–150°C of the ceramics. The thermal strain curve of all compositions suggested a decrease of local polarization with temperature increment up to the Burns temperature.     

Pyroelectric, dielectric, and piezoelectric properties of MnO2-doped (Na0.82 K0.18)0.5Bi0.5TiO3 lead-free ceramics

MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ lead-free piezoelectric ceramics were prepared by conventional solid-state reaction process and the effect of MnO₂ addition on the pyroelectric, piezoelectric and dielectric properties were studied. The experiment results showed that the pyroelectric, piezoelectric, and dielectric properties strongly depended on MnO₂ addition in the (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramics. Excellent electrical properties were obtained in (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ with 0.8?mol% MnO₂. The large dielectric loss of pure BNT ceramics was significantly reduced, the piezoelectric constant was improved, and it also showed excellent pyroelectric properties when compared with other lead free ceramics, with pyroelectric coefficient p?=?17?×?10^?4?C/m²K and figure of merit F _d ?=?6.56?×?10^?5?Pa^?0.5. With these outstanding pyroelectric properties, the 0.8?mol% MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramic can be a promising material for pyroelectric sensor applications in future.