Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 from co-precipitation method

High dielectric Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were firstly prepared by co-precipitation method at low temperature. X-ray diffraction results revealed that pure phase of NBCTO was achieved by calcination at 950 °C for 2 h. Thermo-gravimetric analysis on a dried NBCTO precursor was carried out to study the thermal decomposition process. The microstructure and dielectric properties of NBCTO ceramics sintered at different temperatures were investigated. The results indicate that the sintering temperature has a sensitive influence on the microstructure and dielectric properties. Higher sintering temperature gave rise to increased dielectric constant and dielectric loss of NBCTO samples, and the sample sintered at 975 °C for 8 h exhibits high dielectric constant of 8.3?×?10³ and low dielectric loss of 0.069 at 10 kHz. The dielectric properties were further discussed by the impedance spectroscopy.     

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.     

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.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

The effect of Bi4Ti3O12 particles addition in lead-free Bi0.5(Na0.75K0.25)0.5TiO3 ceramics

We studied the effect of Bi₄Ti₃O₁₂ (BiT) platelet addition in Bi_0.5(Na_0.75K_0.25)_0.5TiO₃ (BNKT) ceramics by preparing two kinds of BNKT ceramics. One type of BNKT ceramic was fabricated by a conventional solid state reaction method (normal sample), while the other by addition of 15 wt% BiT platelets to BNKT powders (BiT-added sample). In the case of BiT-added BNKT ceramics, plate like grains were formed by the reaction of BiT platelets with Na₂CO₃, K₂CO₃, and TiO₂ during the sintering process. The grain size of BiT-added BNKT ceramics was 10 times larger than that of normal BNKT ceramic. The piezoelectric strain and d₃₃ values of BiT-added BNKT ceramics were 0.135% and 225 pm/V, respectively. These values were 35% higher than those of normal BNKT ceramics. The piezoelectric properties of BiT-added BNKT ceramics were enhanced by the higher domain activity due to a decrease in domain density at larger grain sizes.     

Phase transition,microstructure and properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>1-x</Subscript>Ba<Subscript>x</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

In this article, (Na_0.5Bi_0.5)_1-xBa_xTiO₃ lead-free piezoelectric ceramics were prepared by solid-state reaction. The influence of Ba contents on phase structures, compositional distribution and electrical properties of (Na_0.5Bi_0.5)_1-xBa_xTiO₃ ceramics were systematically investigated to further understand the nature of phase transition. It was found that the phase structure of (Na_0.5Bi_0.5)_1-xBa_xTiO₃ transforms from rhombohedral to tetragonal symmetry at x = 0.06 ~ 0.07 and Ba²⁺ segregation forms the coexistence of Ba-rich tetragonal and Ba-deficient rhombohedral phases close to MPB. The electrical properties of prepared samples regularly changed with Ba content, which is closely related to the distribution of rhombohedral and tetragonal phases. The prepared sample near MPB exhibited the largest dielectric constant and the excellent piezoelectric properties (the maximal measuring field reached 78 kV/cm and the piezoelectric constant d ₃₃ = 151pC/N).     

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.     

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.     

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.     

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.     

Preparation and modification of high Curie point BaTiO<Subscript>3</Subscript>-based X9R ceramics

BaTiO₃ (BT) based X9R ceramics with high permittivity about 1700 were prepared by doping and pre-sintering technique. Pure Bi_0.5Na_0.5TiO₃ (BNT) dopant was synthesized by the conventional solid state reaction first. Using this new approach, high performance BTBNT (BT doped with BNT) materials, owning high Curie temperature (139 °C), flat ferroelectric transition region and large permittivity at room temperature, were obtained. The effects of several dopants on dielectric properties of BTBNT ceramics were measured by the LCR meter. The suppression effect for the peaks in the dielectric constant at Curie temperature of these dopants have been ranked as follows: BiNbO₄ > CaZrO₃ > Nb₂O₅ > BNT.     

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.     

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT

Lead-free piezoelectric ceramics (K_0.5Na_0.5)(Nb_1-xSb_x)O₃+0.5 mol.%MnO₂, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO₂ functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm³ for undoped (K_0.5Na_0.5)NbO₃ to 4.40 g/cm³ for Mn/Sb⁵⁺ co-doped ceramics. The co-effects of MnO₂ doping and Sb⁵⁺ substitution lead to significant improvement in dielectric and piezoelectric properties: ε at the T_c increased from 6000 (KNN) to 12400 (x = 0.04), d₃₃ = 92 ÷ 192 pC/N, k_p = 0.32 ÷ 0.46, k_t = 0.34 ÷ 0.48.     

PREPARATION AND PROPERTIES OF LITHIUM-DOPED K0.5Na0.5NbO3 THIN FILMS BY CHEMICAL SOLUTION DEPOSITION

ABSTRACT

Lithium-doped K_0.5Na_0.5NbO₃ (KLNN) films were fabricated by chemical solution deposition on Pt/TiO₂/SiO₂/Si substrates. Homogeneous and stable precursor solutions were prepared by controlling the reaction of starting metal alkoxides. Perovskite KLNN single-phase thin films were successfully synthesized on Pt/TiO _x /SiO₂/Si substrates. The 0.75-μ m-thick KLNN film annealed at 650°C exhibited ferroelectric polarization hysteresis loops at ?250°C. The loop at room temperature was round, indicating the film contained leakage components. The dielectric constant under zero bias was 490 at room temperature. A typical upside-down butterfly DC bias-capacitance curve was obtained in the KLNN film capacitors at room temperature, indicating that polarization reversal occurred in the obtained KLNN films.     

Effect of sintering temperature on piezoelectric and dielectric properties of 0.98(Na0.5K0.5)NbO3-0.02Li(Sb0.17Ta0.83)O3+0.01wt%ZnO ceramics

We studied sintering temperature to enhance the piezoelectric and dielectric properties of 0.98(Na_0.5?K_0.5)NbO₃-0.02Li(Sb_0.17Ta_0.83)O₃?+?0.01wt%ZnO (hereafter NKN-LST+ZnO) lead free piezoelectric ceramics. The synthesis and sintering method were the conventional ceramic technique and sintering was executed at 1080?～?1120°C. We found that optimal sintering temperature and NKN-LST+ZnO ceramics showed the highest piezoelectric properties and dielectric properties at the optimal sintering temperature. The NKN-LST+ZnO ceramics sintered at 1090°C show a superior performance with piezoelectric constant d ₃₃?=?185 pC/N, k _p?=?0.36, ε ₃₃ ^T /ε₀?=?491 respectively. These results reveal that NKN-LST+ZnO ceramics are promising candidate materials for lead-free piezoelectric application.     

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%.     

Fabrication and operation limit of lead-free PTCR ceramics using BaTiO3–(Bi1/2Na1/2)TiO3 system

The electric properties of BaTiO₃–(Bi_1/2Na_1/2)TiO₃ (BT–BNT) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130°C. For determining the maximum switching temperature T _s, the phase diagram of BT–BNT binary system was clarified. Two semiconductorization processes and their electric properties are described. The lanthanum(La)-doped BBNT ceramics sintered in air still showed dielectric behaviors, but the niobium(Nb)-doped ones had a low resistivity at room temperature, ρ _RT, on the order of 10³ Ωcm and showed a PTC behavior. Sintering under a low O₂ atmosphere produces BT–BNT ceramics with less than 10² Ωcm compared to those prepared in air. Our current research produced the BBNT ceramics with T _s values around 210°C by increasing the (Bi_1/2Na_1/2) content in the ceramics.     

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.     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Grain growth kinetics of textured 0.92Na0.5Bi0.5TiO3—0.08BaTiO3 ceramics by tape casting with Bi2.5Na3.5Nb5O18 templates

Plate-like Bi_2.5Na_3.5Nb₅O₁₈ particles were used as templates to fabricate grain-oriented Na_0.5Bi_0.5TiO₃—BaTiO₃ (NBTBT) ceramics by reactive-templated grain growth. The effects of sintering conditions on the grain orientation and microstructure of the textured NBTBT ceramics were investigated, and the kinetic mechanism of grain growth is discussed. The results show that textured ceramics were successfully obtained with orientation factor more than 0.6. NBTBT specimens are composed of strip-like grains and equiaxed shaped grains. The textured ceramics have a microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit an {h00} preferred orientation. The degree of grain orientation increases initially, then decreases with increasing sintering temperature and soaking time. The maximum texture fraction is 0.69 when sintered at 1185 °C for 6 h. The kinetic exponent n and activation energy Q of the two types of grain in textured NBTBT ceramics were calculated. The results show that the grain growth mechanism of oriented grains is controlled not only by grain lattice diffusion, but also by grain boundary diffusion. The grain growth mechanism of matrix grains is mainly controlled by the grain boundary curvature.