非化学计量比对(K0.465Na0.465Li0.07)(Nb0.95Sb0.05)O3无铅压电陶瓷结构及性能的影响

通过传统固相合成工艺制备了(K0.465+xNa0.465+yLi0.07)(Nb0.95-zSb0.05)O3(x,y,z=-0.01～0.02)无铅压电陶瓷,研究了非化学计量比对陶瓷结构及压电性能的影响。结果表明符合化学计量比的陶瓷具有四方钙钛矿结构;在实验范围内,K和Nb的过量或少量均不会改变体系的相结构,而Na过量将会导致体系正交-四方相变温度升高到室温以上,并且正交-四方相变温度随y的增加而升高;过量添加约0.5%(摩尔分数)的K或Na便能补偿在高温烧结时的碱金属元素的挥发损失,进而提高陶瓷的压电性能;该体系陶瓷的组分在较大范围内变化时(如当y=z=0时,x=0～0.02;当x=z=0时,y=0～0.01;以及当x=y=0时,z=-0.01～0.005),仍然能保持d33>200pC/N和kP>40%这样较好的性能。上述结果不仅有利于在研究中材料制备工艺的重复,而且有利于当材料在器件应用时所面临的规模化生产。     

BiCoO3-doped (K0.475Na0.475Li0.05)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics

(1--x)(K_0.475Na_0.475Li_0.05)(Nb_0.8Ta_0.2)O₃--xBiCoO₃ (KNLNT--BC) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. Effects of the BC content on the phase structure, microstructure and electrical properties of KNLNT--BC ceramics were investigated. XRD patterns reveal that all the ceramic samples are in the pure perovskite-type structure, and the phase structure changes from the tetragonal to pseudo-cubic phase with the increase of the BC content. After the substitution of BC, the grain size is significantly reduced and relaxer behaviors are induced. By adding a small amount of BC to KNLNT ceramics, piezoelectric properties are improved, while further addition of BC makes the piezoelectric properties deteriorate markedly. The optimized electrical properties at x = 0.005 are as follows: d₃₃ = 194 pC/N, k_p = 0.44.     

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.     

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.     

Modified (K0.5Na0.5)(Nb0.9Ta0.1)O3 ceramics with high Qm

Lead-free ceramics (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) + x mol% K₄CuNb₈O₂₃ (KCN) + y mol% MnO₂ have been prepared using the conventional solid-state reaction technique. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The low dielectric loss tanδ and relatively high piezoelectric properties were obtained when KCN and MnO₂ were added into KNNT ceramics. The ceramics with x = 1.0, y = 0.50 exhibited excellent piezoelectric properties: high mechanical quality factor Q_m = 1563, piezoelectric coefficient d₃₃ = 96pC/N, electromechanical coupling coefficient k_p = 42.2%, k_t = 44.5%, k₃₃ = 58.4%, relative dielectric constant ε′ = 308, tanδ = 0.4%. This material is a promising candidate for the lead-free piezoelectric transformer applications.     

Enhanced temperature stability of modified (K0.5Na0.5)0.94Li0.06NbO3 lead-free piezoelectric ceramics

To improve both the temperature stability and the mechanical quality factor of (K_0.5Na_0.5)_0.94Li_0.06NbO₃ (KNLN6) ceramics, dense (K₄CuNb₈O₂₃, Bi₂O₃)-modified KNLN6 lead-free ceramics were prepared. Results showed that the (K₄CuNb₈O₂₃, Bi₂O₃)-modified ceramics exhibited a flat, temperature-stable behavior over the range of 20–120 °C. K₄CuNb₈O₂₃ (KCN) and Bi₂O₃-codoping changed the KNLN6 to “hard” ceramics with a significant improvement of mechanical quality factor, Q _m, from 82 to 756. Meanwhile, the piezoelectric constant, d ₃₃, and the planar electromechanical coefficient, k _p, still maintained relatively high levels (d ₃₃ ~118 pC/N, k _p ~35.6%). These results indicate that the modified KNLN6 ceramics are promising lead-free piezoelectric candidates for practical applications.     

SmAlO3-modified (K0.5Na0.5)0.95Li0.05Sb0.05Nb0.95O3 lead-free ceramics with a wide sintering temperature range

Lead-free ceramics (1 − x)(K_0.5Na_0.5)_0.95Li_0.05Sb_0.05Nb_0.95O₃-xSmAlO₃ (KNLNS-xSA) were prepared by conventional sintering technique. The phase structure, dielectric and piezoelectric properties of the ceramics were investigated. All compositions show a main perovskite structure, exhibiting room-temperature symmetries of tetragonal at x ≤ 0.0075, of pseudo-cubic at x = 0.0100. The Curie temperature of KNLNS-xSA ceramics decreases with increasing SmAlO₃ content. Moreover, the addition of SmAlO₃ can effectively broaden the sintering temperature range of the ceramics. The KNLNS-xSA ceramic with x = 0.0050 has an excellent electrical behavior of piezoelectric coefficient d₃₃ = 226 pC/N, planar mode electromechanical coupling coefficient k_p = 38%, dielectric loss tan δ = 3.0%, mechanical quality factor Q_m = 60, and Curie temperature T_C = 327 °C, suggesting that this material could be a promising lead-free piezoelectric candidate for piezoelectric applications.     

Ca2+ doping effects in (K,Na, Li)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics

Lead-free (K_0.5−x/2Na_0.5−x/2Li_x)(Nb_0.8Ta_0.2)O₃ (KNLNT) and (K_0.49−x/2Na_0.49−x/2- Li_xCa_0.01)(Nb_0.8Ta_0.2)O₃ (KNLNT-Ca) ceramics were prepared by a conventional ceramic processing. Structural analysis shows that the Ca²⁺ doping takes the A site of ABO₃ perovskite and decreases the phase transition temperature. Property measurements reveal that as a donor dopant, the Ca²⁺ doping results in higher room-temperature dielectric constant, lower dielectric loss, and lower mechanical quality factor. In addition, the Ca²⁺ doping does not change the positive piezoelectric coefficient d₃₃, but increases the converse piezoelectric coefficient d₃₃^* significantly. This is likely due to the increase in the relaxation, as well as the appearance of (Ca_Na/K^•--V_Na/K′) defect dipoles.     

Tantalum influence on physical properties of (K0.5Na0.5)(Nb1−xTax)O3 ceramics

Lead-free (K_0.5Na_0.5)(Nb_1−xTa_x)O₃ ceramics with x = 0.00-0.30 were prepared by the solid-state reaction technique. The effects of Ta on microstructure, crystallographic structure, phase transition and piezoelectric properties have been investigated. It has been shown that the substitution of Ta decreases Curie temperature T_C and orthorhombic-tetragonal phase transition temperature T_O-T, while increasing the rhombohedral-orthorhombic phase transition temperature T_R-O. In addition, piezoelectric activity is enhanced with the increase of Ta content. The ceramics with x = 0.30 have the high value of piezoelectric coefficient d₃₃ = 205 pC/N. Moreover, k_p shows little temperature dependence between −75° C and 75 °C, and d₃₃ exhibits very good thermal stability over the range from −196 °C to 75 °C in the aging test.     

High piezoelectric d33 coefficient of lead-free (Ba0.93Ca0.07)(Ti0.95Zr0.05)O3 ceramics sintered at optimal temperature

Lead-free (Ba_0.93Ca_0.07)(Ti_0.95Zr_0.05)O₃ (BCZT) ceramics were prepared using a solid-state reaction technique. The structure and electrical properties were investigated with a special emphasis on the influence of sintering temperature. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The BCZT ceramics sintered at 1450 °C show the highest densification and exhibit excellent piezoelectric properties of high piezoelectric coefficient d₃₃ = 387 pC/N, planar mode electromechanical coupling coefficient k_p = 44.2%, mechanical quality factor Q_m = 140 and Curie temperature T_c = 108 °C.     

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.     

Dielectric and piezoelectric properties of alkaline-earth titanate doped (K0.5Na0.5)NbO3 ceramics

(K_0.5Na_0.5)NbO₃ (KNN) and 0.995(K_0.5Na_0.5)NbO₃-0.005AETiO₃ (AE = Mg, Ca, Sr, Ba) were successfully prepared by conventional ceramic processing and without the cold-isostatic-pressing (CIP) process. The effects of low AETiO₃ (AET) concentration on crystal structure, density, dielectric and piezoelectric properties of the KNN based ceramics were evaluated. The results show that adding MgTiO₃(MT) and BaTiO₃(BT) to KNN can lead to the appearance of a trace amount of second phase(s), reduced density and deteriorated electrical properties. Adding CaTiO₃(CT) and SrTiO₃(ST) to KNN can promote densification and optimize electrical properties. Two phase transitions at T_t-o ( the temperature at which the phase transition from orthorhombic to tetragonal occurs) and T_c (the Curie temperature) were observed in KNN and all KNN-AET ceramics, by using differential scanning calorimetry (DSC) analysis and dielectric characterization. Adding AET to KNN caused the variations of T_t-o and T_c.     

Frequency and temperature dependence of dielectric and electrical properties of radio-frequency sputtered lead-free K0.48Na0.52NbO3 thin films

Lead-free K_0.48Na_0.52NbO₃ (KNN) ferroelectric thin films were prepared using the radio-frequency magnetron sputtering method. The crystallized KNN phase was confirmed using X-ray diffraction. The KNN thin film exhibited a well-saturated ferroelectric polarization-electric field hysteresis loop with high remanent polarization. The dielectric and electrical properties of the KNN thin film were investigated over a wide range of frequencies from 10 Hz to 1 MHz, and over a wide range of temperatures from 25 °C to 500 °C. The complex impedance relaxations are shown in an impedance Cole-Cole plot. With increasing temperature, the AC conductivity increased, which obeys the power law, σ(ω) = σ₀ + Aω^s. The activation energy for the conduction process is calculated to be 0.57 eV from the slope of the AC conductivity at the low frequency.     

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.     

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.     

The effect of Sb2O5 additions on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

The sintering behavior and dielectric properties for perovskite Ag(Nb_0.8Ta_0.2)O₃ ceramic with Sb₂O₅ doping was explored. A small amount of Sb₂O₅ (2.5 wt.%) led to high densification at temperatures < 1060 °C. The dielectric constant increased and the temperature coefficient decreased with increasing concentration of Sb₂O₅, and the dielectric constant reached 673, combined with a low temperature coefficient of 147 ppm/°C, and dielectric loss of 0.0044 (at 1 MHz) for the sample with 3.5 wt.% Sb₂O₅ sintered at 1080 °C.     

Dielectric and piezoelectric properties of LiSbO3 doped 0.995 K0.5Na0.5NbO3-0.005BiFeO3 piezoelectric ceramics

LiSbO₃ doped and undoped 0.995 K_0.5Na_0.5NbO₃-0.005BiFeO₃ piezoelectric ceramics with high properties have been fabricated in air by the conventional ceramic processing. By adding LiSbO₃ to K_0.5Na_0.5NbO₃-BiFeO₃ ceramics, the dielectric and piezoelectric properties evidently increase. The doped ceramics exhibit good electrical properties. The enhanced piezoelectric properties of the ceramics should be attributed to optimum LiSbO₃ substitution and better microstructure with high density. Results show that LiSbO₃ doped K_0.5Na_0.5NbO₃-BiFeO₃ lead-free piezoelectric ceramics are a promising lead-free piezoelectric material for applications in different devices.     

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.     

Dielectric properties and electrical conductivity of Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 ferroelectric solid solutions

The dielectric properties and electrical conductivity of the ferroelectric perovskite solid solutions Li_0.07Na_0.93Ta_0.1Nb_0.9O₃ and Li_0.07Na_0.93Ta_0.111Nb_0.889O₃ have been studied at temperatures from 290 to 700 K and frequencies from 25 Hz to 1 MHz. In this temperature range, the solid solutions undergo a first-order ferroelectric phase transition. Li_0.07Na_0.93Ta_0.111Nb_0.889O₃ (prepared from coprecipitated Ta_2y Nb_{2(1 − y)}O₅ pentoxides) has a markedly lower Curie temperature (by ∼75 K) and higher ionic conductivity and high-frequency dielectric permittivity in comparison with Li_0.07Na_0.93Ta_0.1Nb_0.9O₃ (prepared from a mechanical mixture of Ta₂O₅ and Nb₂O₅).     

Crystallographic and dielectric properties of barium-substituted Pb(Mg1/3Ta2/3)O3 ceramics

Ceramic powders of (Ba,Pb)Pb(Mg_1/3Ta_2/3)O₃ were prepared via a B-site precursor route. Crystal symmetries and lattice parameters were determined. Monophasic perovskite was developed after the two-step reaction process, in which the lattice parameters showed linear changes in the entire composition range. Dielectric responses of the ceramics with compositional and frequency changes were investigated. The results were also compared with the (Ba,Pb)(Zn_1/3Ta_2/3)O₃ data.