Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Piezoelectric and dielectric properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Ba0.77Ca0.23TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5(Na_0.84K_0.16)_0.5TiO₃–xBa_0.77Ca_0.23TiO₃ (BNKT–xBCT, x = 0–0.04) were synthesized by conventional solid-state reaction method. The piezoelectric, dielectric, and ferroelectric characteristics of the ceramics are investigated and discussed. The XRD results show that Ba_0.77Ca_0.23TiO₃ (BCT) has diffused into Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ (BNKT) lattices to form a new solid solution. It is shown that moderate additive of BCT (x ≤ 0.025) in BNKT–xBCT ceramics can enhance their piezoelectric and ferroelectric properties. Three dielectric anomalies are observed in BNKT–xBCT (x ≤ 0.03) ceramics. The piezoelectric measurements and P–E hysteresis loops reveal that BNKT–0.025BCT ceramic has the highest piezoelectric performance and strongest ferroelectricity in all the samples. Piezoelectric constants d ₃₃, k _p, and k _t of 175 pC/N, 29.1, and 54% are, respectively, achieved. Remnant polarization P _r and coercive field E _c reach 28.3 μC/cm² and 24.2 kV/cm, respectively.     

Structure and electrical properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Bi0.5(Na0.82K0.18)0.5TiO3–BiAlO3 lead free piezoelectric ceramics

0.09(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–(0.01 − x) Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–x BiAlO₃ (BNBKT–xBA) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction processes. Structure, ferroelectric and piezoelectric properties of BNBKT–xBA ceramics were investigated. X-ray diffraction data shows that BNBKT–xBA ceramics form the pure perovskite phases and the ceramics have the morphotropic phase boundary when x ≤ 0.030. At room temperature, the BNBKT–xBA ceramics at x = 0.030 have better electrical properties, the piezoelectric constant d₃₃ and planar coupling factor k_p of BNBKT–xBA ceramics reaches peak values at x = 0.030: d₃₃ = 217 pC N⁻¹, k_p = 0.308. The remnant polarization P_r, mechanical quality factor Q_m and relative dielectric constant ?_r of BNBKT–xBA ceramics at x = 0.030 attains 33.8 μC cm⁻², 133 and 928 (100 KHz), respectively. As BA content increase, the depolarization temperature T_d shift toward lower temperature, and T_d of BNBKT–xBA ceramics with x = 0.030 decreased to 55 °C.     

Phase diagram and electric properties of the (Mn, K)-modified Bi0.5Na0.5TiO3–BaTiO3 lead-free ceramics

In this study, the phase diagram and electric properties were demonstrated for a (Mn, K)-modified Bi_0.5Na_0.5TiO₃ (BNT)-based solid solution. (0.935−x) Bi_0.5Na_0.5TiO₃−xBi_0.5K_0.5TiO₃−0.065BaTiO₃ with 0.5% mol Mn doping was prepared by a conventional solid-state reaction method. A morphotropic phase boundary (MPB) formed between the ferroelectric rhombohedral and tetragonal phases around x of 0.04 with the MPB tolerance factor t of 0.984–0.986. The temperature and composition dependence of the dielectric, piezoelectric, ferroelectric properties along with the strain characteristics were investigated in detail and a phase diagram was presented. Around the MPB region, the maximum values of piezoelectric constant d₃₃^* d_{33}^{*} of 290 pC/N, d ₃₃ of 155 pC/N, dielectric constant e₃₃^T /e₀ \varepsilon_{33}^{T} /\varepsilon_{0} of 1059 and low dielectric loss tangent tan δ of 0.017 were obtained. In addition, the authors also suggest that the solid solution with composition x of 0.24, exhibiting both high-depolarization temperature T _d of 182 °C, d₃₃^* d_{33}^{*} of 156 pC/N, d ₃₃ of 130 pC/N, will be favorable for high-temperature actuator and sensor applications.     

Ferroelectric and piezoelectric properties of [(Bi0.98La0.02Na1?xLix)0.5]0.94Ba0.06TiO3 lead-free ceramics

Lead-free ceramics [(Bi_0.98La_0.02Na_1−x Li _x )_0.5]_0.94Ba_0.06TiO₃ have been prepared by an ordinary sintering technique and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Li⁺, Ba²⁺, and La³⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure. The partial substitution of Li⁺ lowers the coercive field E _c and improves the remanent polarization P _r. Because of the larger P _r and lower E _c, the ceramic with x = 0.10 exhibits optimum piezoelectric properties: d ₃₃ = 212 pC/N and k _P = 36.1%. The partial substitution of Li⁺ for Na⁺ shifts the depolarization temperature T _d toward low temperature. The ceramics exhibit relaxor characteristic, which is probably resulted from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics contain both the polar and non-polar regions near/above T _d, which cause the polarization hysteresis loop become deformed and the ceramics become depolarized.     

Effects of ball milling on microstructure and electrical properties of sol–gel derived (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

A citrate sol–gel method was investigated for synthesizing lead-free piezoelectric compositions of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNT) and the effect of ball milling on the sintering, microstructure and electrical properties of BNT ceramics was emphasized. The thermal analysis and X-ray diffraction results show that crystalline powders with a single perovskite structure can be obtained when calcined at 600 °C for 3 h. The average particle size of as-calcined powder and electrical properties of sintered samples were obviously dependent on an additional ball milling. Because of well-dispersed superfine powders (∼100 nm), the BNT ceramics can be well densified at temperature 50 °C lower than that by mixed-oxide method and conventional sol–gel method and as a result exhibit enhanced electrical properties of a piezoelectric constant d₃₃ ∼ 180 pC/N and a planar electromechanical coupling factor k_p ∼ 0.29.     

Electrical properties of (K0.5Na0.5)1? x Ag x NbO3 lead-free piezoelectric ceramics

(K_0.5Na_0.5)_1−x Ag _x NbO₃ lead-free piezoelectric ceramics have been fabricated by an ordinary ceramic technique. The results of XRD reveal that Ag⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with an orthorhombic perovskite structure and the solubility of Ag⁺ into A-sites of K_0.5Na_0.5NbO₃ is about 0.20. The ceramics can be well-sintered at 1,100–1,110 °C. The partial substitution of Ag⁺ for A-site ion (K_0.5Na_0.5)⁺ decreases slightly both paraelectric cubic-ferroelectric tetragonal (T _C) and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures (T _O−T). The ferroelectricity of the ceramics becomes weak at high Ag⁺ concentration. The ceramic with x = 0.10 possesses optimum electrical properties: d ₃₃ = 135 pC/N, k _P = 0.43, k _t = 0.46, ε _r = 470, tanδ = 3.39%, and T _C = 394 °C.     

Densification behavior, microstructure, and electrical properties of sol–gel-derived niobium-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

Superfine powders (~100 nm) with compositions of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + xNb⁵⁺ (BNTBT6 + xNb) with x from 0 to 0.02 were synthesized by an improved citrate sol–gel method using Nb₂O₅ as Nb⁵⁺ source. The sintering behavior, microstructure, and various electrical properties of BNTBT6 + xNb ceramics were investigated. The results indicated that the addition of a small amount of Nb⁵⁺ has no remarkable effect on the crystal structure and grain morphology, but the electrical properties of the ceramics are obviously influenced. The BNTBT6 + 0.005Nb compositions exhibit enhanced densification behavior and improved electrical properties of a piezoelectric constant d ₃₃ ~ 205 pC/N and a planar electromechanical coupling factor k _p ~ 33%.     

Structure and piezoelectric properties of K0.5Na0.5NbO3–Bi0.5Li0.5TiO3 lead-free ceramics

Lead-free (1−x) K_0.5Na_0.5NbO₃–xBi_0.5Li_0.5TiO₃ + 1 mol% MnO₂ piezoelectric ceramics have been prepared by a conventional ceramic technique and their structure and piezoelectric properties have been studied. Our results reveal that Bi_0.5Li_0.5TiO₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. The addition of Bi_0.5Li_0.5TiO₃ to the K_0.5Na_0.5NbO₃ solid solution decreases the paraelectric cubic-ferroelectric tetragonal phase transition temperature (T _C) slightly, but shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (T _O−T) significantly to low temperatures. As a result, coexistence of the orthorhombic and tetragonal phases is formed at 0.01 < x < 0.03 near room temperature, leading to a significant improvement in the piezoelectric properties of the ceramics. The ceramic with x = 0.025 exhibits a relatively high T _C (392 °C) and optimum piezoelectric properties: d ₃₃ = 191 pC/N, k _p = 51.5% and k _t = 45.5%. The ceramic also exhibit a good thermal stability of piezoelectric properties.     

Microstructure and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3–0.05(Bi0.5K0.5)Zr1−x Ti x O3 ceramics

0.95(Na_0.5K_0.5)NbO₃–0.05(Bi_0.5K_0.5)Zr_1?x Ti _x O₃ (abbreviated as KNN–BKZT _x ) ceramics were prepared by the conventional solid state method, and the effect of the Ti content on the surface morphology, crystalline structure, and electrical properties of KNN–BKZT _x ceramics were mainly investigated. With the increase of Ti content, the temperature of the orthorhombic–tetragonal (O–T) phases transitions shifted to lower temperatures, and the O–T phase boundary of KNN–BKZT _x ceramics was identified in the composition with 0 ≤ x ≤ 0.3 at room temperature. It was considered that the piezoelectric properties of the ceramics were enhanced significantly owing to the more possible polarization states resulting from the coexistence of two phases. The ceramic with x = 0.2 exhibited optimum properties: d ₃₃ = 260 pC/N, k _p = 0.38, and T _C = 323 °C.     

Structure,ferroelectric and piezoelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics

A new lead-free solid solution of (0.75 ? x)BiFeO₃–0.25BaTiO₃–xBi_0.5(Na_0.8K_0.2)_0.5TiO₃ + 1 mol% MnO₂ has been prepared by a conventional ceramic technique and the effects of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ and sintering temperature on the structure, ferroelectric and piezoelectric properties of the material have been studied. The ceramics sintered at 960 °C for 2 h possess a pure perovskite structure and no second phases can be detected. After the addition of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃, a morphotropic phase boundary of rhombohedral and orthorhombic phases is formed at x = 0.01. The addition of a small amount of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ can promote the grain growth, while excess Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ causes an inhibition of grain growth. Sintering temperature has an important influence on the structure and electrical properties of the ceramics. The sintering temperature of 960 °C is a critical temperature to obtain the ceramics with good piezoelectric properties. For the ceramic with x = 0.01 sintered at/above 960 °C located at the morphotropic phase boundary, large grains, good densification, high resistivity and enhanced electrical properties are obtained.     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

Structure and electrical properties of K0.5Na0.5NbO3–SrTiO3 lead-free piezoelectric ceramics with LiSbO3 doping

Lead-free piezoelectric ceramics (1 ? x)K_0.5Na_0.5NbO₃–xSrTiO₃ with 6 mol% LiSbO₃ doping have been prepared by conventional solid state sintering technique at 1,125 °C for 3 h in air. The effects of the SrTiO₃ and LiSbO₃ on the phase structure and electrical properties of the ceramics were systematically investigated. All ceramic samples show a single phase perovskite structure with tetragonal symmetry when LiSbO₃ content was 6 mol% and SrTiO₃ content was 2–10 mol% by X-ray diffraction analysis and highly dense structure by SEM patterns. The ceramic with x = 0.04 exhibits optimum electrical properties at room temperature (d ₃₃ = 267 pC/N, k _p = 46 %, ε _r = 1,168, tanδ = 0.021, P _r = 30.3 μC/cm², E _C = 1.98 kV/mm), which suggests that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Sr、Nb掺杂(Bi0.5Na0.5)0.94Ba0.06TiO3陶瓷的介电性能研究

采用固相反应法制备Sr、Nb掺杂BNBT无铅压电陶瓷,利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和介电谱仪表征了样品的晶体结构,表面形貌及介电性能,研究了陶瓷的相结构,微观形貌和介电响应。结果表明,BNBT陶瓷为单一的钙钛矿结构,而BNBT-3SN、BNBT-3SN-3Sr和BNBT-3SN-1Nb陶瓷除了主相钙钛矿结构,存在少量第二相。形貌结构显示出样品相对比较致密,晶粒尺寸分布均匀。SrNb₂O₆的引入使介电峰T_s向低温方向移动,增强弛豫相变程度从而提高了陶瓷基体的介电温度稳定性,BNBT-3SN陶瓷在40～406℃内表现出良好的温度稳定性。通过阻抗图谱分析可知,所有样品主要为晶界传导机制。而且研究表明Sr、Nb掺杂可通过对BNBT-3SN陶瓷氧空位浓度的作用,实现对电导率的调控。随着Sr²⁺的增加,样品的氧空位浓度增加,电导率增大;而Nb⁵⁺的增加,填充了氧空位导致氧空位浓度减小促使电导率降低。     

Bi0.5Na0.5TiO3和Bi0.5K0.5TiO3含量对三元固溶体系无铅PTC热敏陶瓷性能的影响

PTC热敏陶瓷的无铅化是绿色智能加热及电路智能保护元件研制的重要前提。为了获得可在空气气氛下烧结且兼具高居里温度和高升阻比的无铅化PTC热敏陶瓷,本工作采用固相法制备了(1-x)BaTiO₃-0.5xBi_0.5Na_0.5TiO₃-0.5xBi_0.5K_0.5TiO₃和0.98BaTiO₃-0.02yBi0_.5Na_0.5TiO₃-0.02(1-y)Bi_0.5K_0.5TiO₃三元固溶体系无铅PTC热敏陶瓷材料,研究了不同含量的Na和K元素对无铅PTC热敏陶瓷材料的烧结特性和电学性能的影响。结果表明,BNT和BKT均与BaTiO₃形成固溶体,随着BNT含量的增加,PTC陶瓷平均晶粒尺寸减小;当BNT和BKT含量相同时,PTC陶瓷可以在较宽的烧结温度范围内实现半导化,且在...     

Preparation and properties of ceramics based on (Na0.5Bi0.5)1 ? xAxTiO3 (A = Sr, Cd) solid solutions

This paper describes the preparation and properties of (Na_0.5Bi_0.5)_{1 − x} A _x TiO₃ (A = Sr, Cd) lead-free ferroelectric ceramics. The (0.63–0.66)Na_0.5Bi_0.5TiO₃ · (0.37–0.34)Sr_0.7Bi_0.2TiO₃ ceramics are shown to have the best dielectric and piezoelectric properties: tanδ = 0.013–0.009, ɛ_RT = 1200–1500, d ₃₁ = (370–400) × 10⁻¹² C/N, and k _ρ = 0.4–0.58. The cadmium-containing ceramics offer low dielectric losses and high dielectric permittivity at room temperature.     

Structures and electrical properties of (Na0.5K0.5)NbO3–Li(Ta0.5Nb0.5)O3 lead-free piezoelectric ceramics

Solid solutions of (Na_0.5K_0.5)NbO₃ (NKN) and Li(Ta_0.5Nb_0.5)O₃ (LTN) were investigated as a potential candidate of lead-free piezoelectric ceramics. It was found that the Curie temperature of solid solutions increases slightly with increasing the LTN content and simultaneously the polymorphic phase transition temperature linearly decrease till below room temperature. An orthorhombic to tetragonal phase transformation at room temperature, or a morphotropic phase boundary, in NKN is induced by ~7 at% LTN addition, where the best dielectric, piezoelectric and electromechanical properties are achieved. The 0.94NKN–0.07LTN ceramics possess a dielectric constant of 765, a loss tangent of 0.04 at 1 kHz, a piezoelectric constant d₃₃ of 253 pC/N and an electromechanical coupling factor k_p of 48%.     

Effects of Co doping on microstructure and properties of (K0.5Na0.5)NbO3–LiSbO3–BiFe(1−x)Co x O3 lead-free piezoelectric ceramics

0.998 [(0.95(K_0.5Na_0.5)NbO₃–0.05LiSbO₃]–0.002BiFe_(1?x)Co _x O₃ (KNN–LS–BF_(1?x)C _x ) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The influences of Co content on the phase structure, microstructure, density and related electrical properties were investigated. The results reveal that the substitution of Co significantly improves the sinterability and the electrical properties of KNN–LS–BF_(1?x)C _x ceramics, sintered at a lower temperature of 1,030 °C, compared with that of KNN–LS–BF ceramics. With increasing x from 0 to 0.8, all samples show a pure perovskite structure, but the grain size increases continuously,and the porosity level reaches it’s lowest value at x = 0.2. The density ρ, piezoelectric constant d ₃₃, coupling factor k _p and dielectric constant ε _r increase with x up to 0.2, and then decrease with further increase in x value, but the variation of dielectric loss tan δ is opposite. The density and electrical properties achieve optimal value of ρ = 4.287 g/cm³, d ₃₃ = 276 pC/N, k _p  = 48 %, ε _r  = 1,284 and tan δ = 1.95 %, when x = 0.2. And Tc ≈ 340 °C at all the variation range of Co content.