Effect of CuO on the sintering temperature and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3-0.05CaTiO3 ceramics

The addition of a small amount of CuO to the 0.95(Na_0.5K_0.5)NbO₃-0.05CaTiO₃ (0.95NKN-0.05CT) ceramics sintered at 960 °C for 10 h produced a dense microstructure with large grains due to the liquid phase sintering. Due to the negligible Na₂O evaporation, poling was easy for all specimens sintered at 960 °C. The piezoelectric properties of the specimens were considerably influenced by the relative density, grain size and liquid phase amount. The high piezoelectric properties of d₃₃ = 200 pC/N, k_p = 0.37, and Q_m = 350 were obtained for the 0.95NKN-0.05CT ceramics containing 2.0 mol% CuO sintered at 960 °C for 10 h. Therefore, the 0.95NKN-0.05CT ceramics containing a small amount of CuO are a good candidate material for lead-free piezoelectric ceramics.     

Lead-free ceramics based on alkaline niobate tantalate antimonate with excellent dielectric and piezoelectric properties

This paper reports lead-free (Na_0.52K_0.48−x)(Nb_0.94−xSb_0.06)O₃-xLiTaO₃ compositions with significantly enhanced piezoelectric properties. The 6% Sb substituted Na_0.52K_0.48NbO₃ was modified by a small amount of LiTaO₃, leading to the formation of a morphotropic phase boundary between orthorhombic and tetragonal phases in the range of x = 0.035-0.04 where the materials show a strong compositional dependence of various electrical properties. Excellent properties of d₃₃ = 335 pC/N, k_p = 53%, , Q_m = 41 and T_c = 291 °C were obtained in the composition with x = 0.04, indicating that the ceramics studied are promising as a lead-free piezoelectric candidate.     

Influence of sintering temperature on piezoelectric properties of (K0.5Na0.5)NbO3-LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(K_0.5Na_0.5)NbO₃-xLiNbO₃ have been synthesized by traditional ceramics process without cold-isostatic pressing. The effect of the content of LiNbO₃ and the sintering temperature on the phase structure, the microstructure and piezoelectric properties of (1 − x)(K_0.5Na_0.5)NbO₃-xLiNbO₃ ceramics were investigated. The result shows that the phase structure transforms from the orthorhombic phase to tetragonal phase with the increase of the content of LiNbO₃, and the orthorhombic and tetragonal phase co-exist in (K_0.5Na_0.5)NbO₃-LiNbO₃ ceramics when the content of LiNbO₃ is about 0.06 mol. The sintering temperature of (1 − x)(K_0.5Na_0.5)NbO₃-xLiNbO₃ decreases with the increase of the content of LiNbO₃. The optimum composition for (1 − x)(K_0.5Na_0.5)NbO₃-xLiNbO₃ ceramics is 0.94(K_0.5Na_0.5)NbO₃-0.06LiNbO₃. The optimum sintering temperature of 0.94(K_0.5Na_0.5)NbO₃-0.06LiNbO₃ ceramics is 1080 °C. Piezoelectric properties of 0.94 (K_0.5Na_0.5)NbO₃-0.06LiNbO₃ ceramics under the optimum sintering temperature are piezoelectric constant d₃₃ of 215 pC/N, planar electromechanical coupling factor k_p of 0.41, thickness electromechanical coupling factor k_t of 0.48, the mechanical quality factor Q_m of 80, the dielectric constant of 530 and the Curie temperature T_c = 450 °C, respectively. The results indicate that 0.94(K_0.5Na_0.5)NbO₃-0.06LiNbO₃ piezoelectric ceramics is a promising candidate for lead-free piezoelectric ceramics.     

Effects of CuO doping on the electrical properties of 0.98K0.5Na0.5NbO3-0.02BiScO3 lead-free piezoelectric ceramics

CuO-doped 0.98K_0.5Na_0.5NbO₃-0.02BiScO₃ (0.98KNN-0.02BS-xCu) lead-free piezoelectric ceramics have been fabricated by ordinary sintering technique. The effects of CuO doping on the dielectric, piezoelectric, and ferroelectric properties of the ceramics were mainly investigated. X-ray diffraction reveals that the samples at doping levels of x ≤ 0.01 possess a pure tetragonal perovskite structure. The specimen doped with 1 mol% CuO exhibits enhanced electrical properties (d₃₃ ~ 207 pC/N, k_p ~ 0.421, and k_t = 0.424) and relatively high mechanical quality factor (Q_m = 288). These results indicate that the 0.98KNN-0.02BS-0.01Cu ceramic is a promising candidate for lead-free piezoelectric ceramics for applications such as piezoelectric actuators, harmonic oscillator and so on.     

Highly enhanced mechanical quality factor in lead-free (K0.5Na0.5)NbO3 piezoelectric ceramics by co-doping with K5.4Cu1.3Ta10O29 and CuO

Effects of Cu doping on the ferroelectric and piezoelectric properties of 0.0038 mol K_5.4Cu_1.3Ta₁₀O₂₉ modified (K_0.5Na_0.5)NbO₃ ceramics have been investigated. On the basis of analyses on crystal structure and polarization hysteresis, it is suggested that Cu ions reveal amphoteric doping behavior in KNN ceramics. At doping levels up to 1 mol%, the Cu ions substitute pentavalent B-site cations, acting as acceptors that generate O-vacancies to resultantly harden the ceramics. At doping levels above 1.5 mol%, however, Cu ions play a role as donors by replacing monovalent A-site cations. A specimen doped with 0.5 mol% CuO shows an extremely high mechanical quality factor of 3053, which is higher than those of any other reports on KNN-based ceramics.     

Effect of CuO and MnO2 on sintering temperature, microstructure, and piezoelectric properties of 0.95(K0.5Na0.5)NbO3-0.05BaTiO3 ceramics

In this letter we report the effect of CuO and MnO₂ additives on the sintering behavior of 0.95(Na_0.5K_0.5)NbO₃-0.05BaTiO₃ ceramics. It was found that the composition corresponding to 0.95(Na_0.5K_0.5)NbO₃-0.05BaTiO₃ + 2.0 mol% CuO + 0.5 mol% MnO₂, sintered at 950 °C for 10 h, exhibited excellent piezoelectric properties corresponding to: k_p = 0.41, d₃₃ = 248 pC/N, Q_m = 305, ε₃^T/ε₀ = 1258, and T_c = 280 °C. These results indicate the prominence of this composition in lead-free systems.     

Characterization of (K0.5Na0.5)NbO3 powders and ceramics prepared by a novel hybrid method of sol–gel and ultrasonic atomization

(K_0.5Na_0.5)NbO₃ powders and ceramics were prepared by a novel hybrid method of sol–gel and ultrasonic atomization, in which Nb₂O₅ was used as the niobium source to replace those expensive soluble niobium salts. X-ray diffraction and thermal analysis were performed to investigate the synthesis process and phase transformation behavior of (K_0.5Na_0.5)NbO₃ powders. The results showed that (K_0.5Na_0.5)NbO₃ powders with a reasonably fine particle size and single-phase perovskite structure were formed at a temperature as low as 650 °C. Dense (K_0.5Na_0.5)NbO₃ ceramics with a relative density of 93% were obtained using the refined powders. The (K_0.5Na_0.5)NbO₃ ceramics prepared by the novel hybrid method exhibited relatively good properties (d₃₃ = 90 pC/N, k_p = 0.32, P_r = 20.6 μC/cm², T_c = 405 °C, ε_r = 712), suggesting that this novel hybrid method might be a promising method for the powders and ceramics preparation.     

Fabrication of (K, Na)NbO3 glass-ceramics and crystal line patterning on glass surface

Crystallization behavior of (30−x)K₂O-xNa₂O-25Nb₂O₅-45SiO₂ (KNNS; x = 0, 5, 10, 20 and 30) (mol%) glasses was clarified and perovskite-type nonlinear optical (K, Na)NbO₃ (KNN) crystals were synthesized by using a conventional glass-ceramics method. It was found that Na₂O amounts over around x = 10 mol% were necessary to form perovskite-type KNN crystals showing second-harmonic generations. The substitution of K⁺ and Na⁺ ions was confirmed from X-ray diffraction (XRD) analysis. A continues-wave of Yb:YVO₄ fiber laser (wavelength: 1080 nm) was irradiated onto CuO doped KNNS; x = 10 (Cu-KNNS) surface. The absorption coefficient of this Cu-KNNS glass was determined to be α = 5.0 cm⁻¹. Perovskite-type KNN crystals were patterned in the condition of the laser power of >1.20 W and the laser scanning speed of S = 7 μm/s, and their structure was determined by Raman scattering spectra and XRD analysis.     

Influence of Bi2O3 and CuO addition on low-temperature sintering and dielectric properties of Ba0.6Sr0.4TiO3 ceramics

In this study, we tried to lower the sintering temperature of Ba_0.6Sr_0.4TiO₃ (BST) ceramics by several kinds of adding methods of Bi₂O₃, CuO and CuBi₂O₄ additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi₂O₄ was the most effective way for lowering the sintering temperature of BST. When CuBi₂O₄ of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.     

Effect of Pb(Fe1/2Nb1/2)O3 modification on dielectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbZr0.52Ti0.48O3 ceramics

10 mol% Pb(Fe_1/2Nb_1/2)O₃ (PFN) modified Pb(Mg_1/3Nb_2/3)O₃-PbZr_0.52Ti_0.48O₃ (PMN-PZT) relaxor ferroelectric ceramics with compositions of (0.9 − x)PMN-0.1PFN-xPZT (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared. X-ray diffraction investigations indicated that as-prepared ceramics were of pure perovskite phase and the sample with composition of x = 0.8 was close to morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase. Dielectric properties of the as-prepared ceramics were measured, and the Curie temperature (T_c) increased sharply with increasing PZT content and could be higher than 300 °C around morphotropic phase boundary (MPB) area. At 1 kHz, the sample with composition of x = 0.1 had the largest room temperature dielectric constant ?_r = 3519 and maximum dielectric constant ?_m = 20,475 at T_m, while the sample with composition of x = 0.3 possessed the maximum dielectric relaxor factor of γ = 1.94. The largest d₃₃ = 318 pC/N could be obtained from as-prepared ceramics at x = 0.9. The maximum remnant polarization (P_r = 28.3 μC/cm²) was obtained from as-prepared ceramics at x = 0.4.     

Effect of BiFeO3 additions on the dielectric and piezoelectric properties of (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 ceramics

(1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary between the orthorhombic and tetragonal phases was identified in the composition range of 0.004 < x < 0.006. The ceramics near the morphotropic phase boundary exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 0.6 mol.% BiFeO₃ exhibit good electrical properties (d₃₃ ∼ 246 pC/N, k_p ∼ 43%, T_c ∼ 285 °C, ?_r ∼ 1871, and tan δ ∼ 1.96%). These results show that the (1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ ceramic is a promising lead-free piezoelectric material for applications in different devices.     

Effects of Cr2O3 doping on the electrical properties and the temperature stabilities of PNW-PMN-PZT ceramics

The ceramics with 0.90Pb(Zr_0.50Ti_0.50)O₃-0.07Pb(Mn_1/3Nb_2/3)O₃-0.03Pb(Ni_1/2W_1/2)O₃ were prepared by adding Cr₂O₃. The effects of Cr₂O₃ doping on the phase structure, the microstructure and the electrical properties of ceramics were investigated. Meanwhile, the temperature stabilities of the resonant frequency (f_r) and the electromechanical coupling factor (K_p) were studied. The results showed that the better temperature stability could be obtained at x = 0.2 wt.% when the calcining temperature was 800 °C and the sintering temperature was 1150 °C. The parameters were Δf_r/f_r25 °C = −0.17% and ΔK_p/K_p25 °C = −1.39%. Moreover, the optimized electrical properties were also achieved, which were K_P = 0.54, Q_m = 1730, d₃₃ = 330 pC/N, ?_r = 2078 and tan δ = 0.0052. The optimized properties make the ceramics with this composition to be a good candidate for high power piezoelectric transformers applications.     

Co2O3 doped (Na0.65K0.35)NbO3 piezoceramics

Lead-free (Na_0.65K_0.35)NbO₃ + x wt.% Co₂O₃ (KNN-xCo) piezoceramics were synthesized by conventional ceramic processing and the effects of low Co₂O₃ concentration on the microstructure and electrical properties were investigated. The experimental results show that the orthorhombic-tetragonal phase transition temperature (T_O-T) decreases slightly whereas the tetragonal-cubic phase transition temperature (T_C) and crystal structure keep unchanged with the increasing of Co₂O₃ content. The doping of Co₂O₃ facilitates the grain growth and improves the density and piezoelectric properties of the ceramics. The sample of x = 0.2 exhibits good piezoelectric properties of piezoelectric coefficient d₃₃ = 127pC/N and electromechanical coupling coefficient k_p = 35.1% with density of ρ = 4.31/cm³. These results strongly suggest that the composition of (Na_0.65K_0.35)NbO₃ is another promising lead-free candidate for investigation besides (Na_0.5K_0.5)NbO₃ system.     

Effects of K4CuNb8O23 on the structure and electrical properties of lead-free 0.94(Na0.5K0.5)NbO3–0.06LiNbO3 ceramics

Dense K₄CuNb₈O₂₃-modified (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics were prepared by normal sintering. The effects of K₄CuNb₈O₂₃ on the phase structure, microstructure and electrical properties of the ceramics were studied. Results showed that K₄CuNb₈O₂₃ induced a perovskite structure transition from coexistence of orthorhombic and tetragonal phases to orthorhombic symmetry. The addition of K₄CuNb₈O₂₃ promoted the sintering of (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics and simultaneously caused the grain growth. Moreover, K₄CuNb₈O₂₃-doping changed the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ to “hard” ceramics and significantly enhanced the mechanical quality factor Q_m. It was found that the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics doped with 0.60 mol% K₄CuNb₈O₂₃ exhibited a high mechanical quality factor (Q_m  983) as well as relatively large d₃₃ (136 pC/N) and k_p (35.9%), suggesting that this material is a promising candidate for lead-free piezoelectric ceramics for high-frequency applications.     

Synthesis, low-temperature sintering and the dielectric properties of the ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2)

ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V₂O₅ and B₂O₃ with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn₂(Ti_1−xSn_x)O₄ solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO₂-0.12SnO₂ ceramics sintered at 900 °C exhibit a good dielectric property: ?_r = 29 and tan δ = 9.86 × 10⁻⁵. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor.     

Fabrication and characterization of potassium-sodium niobate piezoelectric ceramics by spark-plasma-sintering method

High density (Na_1−xK_x)NbO₃ (x = 0.5, 0.6, and 0.7) ceramics were successfully prepared by spark-plasma-sintering (SPS) method. The dielectric and piezoelectric properties of the SPS samples were investigated and compared to that of hot-pressed samples. It is found that, the SPS-sintered (Na_1−xK_x)NbO₃ samples show higher room temperature dielectric constant, higher coercive fields, lower remnant polarizations and lower electromechanical coefficients than that of the hot-pressed (Na_1−xK_x)NbO₃ samples. The dielectric and piezoelectric property differences between the SPS-sintered and hot-pressed samples have been attributed to grain size effects.     

Dielectric and piezoelectric properties of Y2O3 doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free piezoelectric ceramics

Y₂O₃ doped lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (0-0.7 wt%) were synthesized by the conventional solid state reaction method, and the effect of Y₂O₃ addition on the structure and electrical properties was investigated. X-ray diffraction shows that Y₂O₃ diffuses into the lattice of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ to form a solid solution with a pure perovskite structure. The temperature dependence of dielectric constant of Y₂O₃ doped samples under various frequencies indicates obvious relaxor characteristics different from typical relaxor ferroelectric and the mechanism of the relaxor behavior was discussed. The optimum piezoelectric properties of piezoelectric constant d₃₃ = 137 pC/N and the electromechanical coupling factor k_p = 0.30 are obtained at 0.5% and 0.1% Y₂O₃ addition, respectively.     

(5 − x)BaO-xMgO-2Nb2O5 ceramics prepared using a reaction-sintering process

(5 − x)BaO-xMgO-2Nb₂O₅ (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO₃, MgO, and Nb₂O₅ was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)₅Nb₄O₁₅ was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg_1/3Nb_2/3)O₃ was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?_r = 36.69, Qf = 20,097 GHz, and τ_f = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?_r = 39.2, Qf = 43,878 GHz, and τ_f = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb₂O₅ ceramics for applications in microwave dielectric resonators.     

Enhanced dielectric,ferroelectric and optical properties of lead free (K0.17Na0.83)NbO3 ceramic with WO3 addition

Polycrystalline lead-free ceramics (K_0.17Na_0.83)NbO₃ + x wt.% WO₃; (x = 0, 1, 3 and 5) have been synthesized via solid state reaction method. X-ray diffraction pattern at room temperature indicates the formation of pure perovskite phase with monoclinic structure for all samples. Dielectric constant versus temperature measurements shows an increase in dielectric constant with a shift in Curie temperature (T_C) toward higher temperature side. Remnant polarization (P_r) is found to be enhanced and reached upto 24 μC/cm² for x = 5 wt.% WO₃ from 12.5 μC/cm² for pure (K_0.17Na_0.83)NbO₃ ceramic. The value of coercive field (E_c) decreases with increasing wt.% of WO₃. From optical band gap study, we found blue shift in the band gap of (K_0.17Na_0.83)NbO₃ with increasing concentration of WO₃.     

Electrical and microstructural properties of CaTiO3-doped K1/2Na1/2NbO3-lead free ceramics

Microstructure, electrical properties and dielectric behaviour of K_1/2Na_1/2NbO₃ (KNN) and CaTiO₃-modified K_1/2Na_1/2NbO₃ (CTO-KNN) systems, were investigated. Discs doped with 0 to 0·55% mol of CaTiO₃ (CTO) were sintered at 1125°C for 2 h. Although minority phases were found in doped samples, CaTiO₃ was not detected. It was also observed that CTO changed the microstructure and grain size of KNN drastically. Also, the Curie temperature and permittivity values decreased. Addition of CTO between 0·15 and 0·45 mol% decreases the density and dielectric values. Samples prepared with higher content of CTO than 0·45 mol% showed better electrical properties.