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.     

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.     

Structure and electrical properties of (1 − x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 ceramics near morphotropic phase boundary

The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi_0.5K_0.5TiO₃ content. Electrical properties of ceramics are significantly influenced by the Bi_0.5K_0.5TiO₃ content. Two phase transitions at T_t (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and T_c (the Curie temperature) were observed in all the ceramics. Adding Bi_0.5K_0.5TiO₃ content caused the variations of T_t and T_c. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d₃₃, the electromechanical coupling factor K_p and the dielectric constant ?_r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.     

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 Mn doping on the structure and electrical properties of high-temperature BiScO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 piezoelectric ceramics

The effects of Mn addition on the structure, ferroelectric, and piezoelectric properties of the 0.35BiScO₃-0.60PbTiO₃-0.05Pb(Zn_1/3Nb_2/3)O₃ ceramics were studied. The results demonstrate that the addition of small amounts of Mn did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure and ferro-piezoelctric properties. The addition of Mn can induce combinatory “hard” and “soft” piezoelectric characteristics due to aliovalent substitutions. The optimal electrical properties are obtained in the 0.25 mol% Mn-doped composition with a high Curie temperature, indicating that Mn doping contributes to the electrical properties of the ceramics. It can be expected that the improved piezoelectric material can be a promising candidate for high-temperature piezoelectric applications.     

Processing, dielectric properties and impedance characteristics of Na0.5Bi0.5Cu3Ti4O12 ceramics

Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (R_g) was 12.10 Ω cm and the grain boundary resistance (R_gb) was 2.009 × 10⁵ Ω cm when the ceramics were sintered at 1000 °C for 7.5 h.     

Crystallite structure,microstructure, dielectric,and piezoelectric properties of (Pb1.06−xBax)(Nb0.94Ti0.06)2O6 piezoelectric ceramics prepared using calcined powders with different phases

In an attempt to obtain dense lead metaniobate-based ceramics with improved dielectric and piezoelectric properties, the (Pb_1.06−xBa_x)(Nb_0.94Ti_0.06)₂O₆ (x = 0, 0.04, 0.08, 0.12) piezoelectric ceramics were prepared separately from the two kinds of calcined powders, i.e., the powders with the rhombohedral phase and orthorhombic phase. For obtaining the calcined powders with the different phases, two different calcination temperatures of 900 °C and 1250 °C were chosen. The calcined powders were characterized using X-ray diffraction, scanning electron microscope, laser particle size analyzer and differential scanning calorimetry. Effects of the phase structures of the calcined powders on crystallite structure, microstructure, dielectric and piezoelectric properties of the ceramics were studied in detail. The lattice parameters and grain size of the ceramics are related to the phase structures of the calcined powders. The doping of Ba²⁺ has an influence on the dielectric and piezoelectric properties of the ceramics. The ceramics with x = 0.08 fabricated from the calcined powders with the orthorhombic phase demonstrate the optimum dielectric and piezoelectric properties.     

Dielectric and ferroelectric properties of (1-x)(Na0.5K0.5)NbO3-xBaTiO3 ceramics

(1-x)(Na_0.5K_0.5)NbO₃-xBaTiO₃ ceramics were prepared by a solid state reaction approach, and their dielectric and ferroelectric properties were evaluated together with the crystal structure. Three phase transitions at T_t1, T_t2 and T_t3 were observed by the combination of DTA analysis and dielectric characterization. These phase transitions corresponded to those of (Na_0.5K_0.5)NbO₃, and they were greatly pulled down by forming solid solution with BaTiO₃. The phase transition around T_t1 was incompletely diffusive and the appearance of diffusiveness of non ferro-paraelectric phase transition was an exception. The hysteresis loops changed their shapes from “square” into “thin square” with increasing x.     

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.     

Tunable and microwave dielectric properties of Ba0.5Sr0.5TiO3-BaWO4 composite ceramics doped with Co2O3

Co₂O₃ doped BaWO₄-Ba_0.5Sr_0.5TiO₃ composite ceramics, prepared by solid-state route, were characterized systematically, in terms of their phase compositions, microstructure and microwave dielectric properties. Doping of Co₂O₃ promoted grain growth, reduced Curie temperature and broadened phase-transition temperature range of BaWO₄-Ba_0.5Sr_0.5TiO₃, which were attributed mainly to the substitution of Co³⁺ for Ti⁴⁺ at B site in the perovskite lattice. Dielectric diffusion behaviors of the composite ceramics were discussed. The composite ceramics all had dielectric tunability of higher than 10% at 30 kV/cm and 10 kHz, with promising microwave dielectric properties. Specifically, the sample doped with 0.2 wt.% Co₂O₃ exhibited a tunability of 20%, permittivity of 225 and Q of 292 (at 1.986 GHz), making it a suitable candidate for applications in electrically tunable microwave devices.     

Synthesis and characterization of (Na0.85K0.15)0.5Bi0.5TiO3 ceramics by different methods

The (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (BNKT) powders were synthesized by solid-state method, sol-gel method and stearic acid method. Microstructure, piezoelectric and dielectric properties of the ceramics were investigated. Attempts had been made to understand the reaction processes by using thermo gravimetric (TG) and differential scanning calorimetry (DSC). The BNKT powders have a perovskite structure with average crystallite sizes of 168 nm, 85 nm and 79 nm, corresponding to the solid-state method, the sol-gel method and the stearic acid method, respectively. The ceramics derived from the powder synthesized by sol-gel method presents the most homogeneous microstructure and largest grain size (5-7 μm). The effects of average crystallite size on microstructures and electric properties of the BNKT ceramics were investigated. Both the piezoelectric properties and dielectric properties were enhanced with the increase of grain size.     

Structure and ferroelectric properties in (K0.5Bi0.5)TiO3-BiScO3-PbTiO3 piezoelectric ceramic system

(K_0.5Bi_0.5)TiO₃-BiScO₃-PbTiO₃ ceramics were synthesized by conventional solid-state method. A morphotropic phase boundary (MPB) was confirmed with the aid of structural analysis. Two dielectric anomalous peaks were observed, the one around dielectric maximum temperature (T_m) due to phase transformation from ferroelectric to paraelectric while the second one could be ascribed to space charges. Furthermore, the existence of space charges also resulted in the independence of T_m with frequency at low lead composition. A new high temperature piezoelectric ceramic, 0.30(K_0.5Bi_0.5)TiO₃-0.30BiScO₃-0.40PbTiO₃ close to MPB exhibited excellent electrical properties with T_m of 384 °C, d₃₃ of 247 pC/N, k_p of 38.9%, P_r of 19.41 μC/cm², and E_c of 2.25 kV/mm, indicative of a candidate for high temperature application.     

Study on properties of BaxSmyTi7O20 ceramics with CaO-SiO2-B2O3 glass

The effect of CaO-SiO₂-B₂O₃ (CSB) glass addition on the sintering temperature and dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics has been investigated using X-ray diffraction, scanning electron microscopy and differential thermal analysis. The CSB glass starts to melt at about 970 °C, and a small amount of CSB glass addition to Ba_xSm_yTi₇O₂₀ ceramics can greatly decrease the sintering temperature from about 1350 to about 1260 °C, which is attributed to the formation of liquid phase. It is found that the dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics are dependent on the amount of CSB glass and the microstructures of sintered samples. The product with 5 wt% CSB glass sintered at 1260 °C is optimal in these samples based on the microstructure and the properties of sintering product, when the major phases of this material are BaSm₂Ti₄O₁₂ and BaTi₄O₉. The material possesses excellent dielectric properties: ?_r = 61, tan δ = 1.5 × 10⁻⁴ at 10 GHz, temperature coefficient of dielectric constant is −75 × 10⁻⁶ °C⁻¹.     

Effects of Ca and Zr substitution upon structure and properties of Ba5LaTi3Ta7O30 low-loss dielectric ceramics

Effects of Ca and Zr substitution upon the dielectric properties of Ba₅LaTi₃Ta₇O₃₀ ceramics were investigated together with the structural characterization. All the samples of Ba₅La(Zr_xTi_1−x)₃Ta₇O₃₀ formed a filled tungsten-bronze structures, whereas the solid solution limit was determined as x=0.25 in (Ca_xBa_1−x)₅LaTi₃Ta₇O₃₀. Beyond this limit secondary phase of CaTa₂O₆ was detected and it would become the major phase for the Ca-rich compositions. The temperature coefficient of dielectric constant was improved with increasing Zr content while the dielectric constant decreased and the low dielectric loss varied little (in the order of 10⁻⁴). In the case of (Ca_xBa_1−x)₅LaTi₃Ta₇O₃₀, small temperature coefficient of dielectric constant could be obtained with increasing Ca content while the dielectric constant decreased significantly, and a small amount substitution of Ca for Ba induced decrease in dielectric loss.     

Piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics synthesized by spray drying method

Potassium-sodium niobate was synthesized at 800 °C for 1 h using dried precursors in a powder form obtained by the spray drying method. Different samples were sintered from 1060 to 1120 °C for 2 h reaching a relative density as high as 96% of the theoretical value. Piezoelectric and ferroelectric properties were studied for these samples and some of the most prominent results are: k_p, d₃₁, 2P_r, and 2E_C of 0.36, 39 pC/N, 29 μC/cm² and 16.5 kV/cm, respectively, for the sample sintered at 1080 °C. The methodology presented in this study can be used to synthesize submicrometer powders.     

Effect of CeO2 addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics prepared by citric method

(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics added with 0–0.8 wt.% CeO₂ were prepared by a citrate method, and the influence of the CeO₂ addition on the structure and electrical properties was investigated. The specimens containing various amounts of CeO₂ show the coexistence of rhombohedral and tetragonal phases, with the relative content of the tetragonal phases gradually enhancing with increasing amount of CeO₂. Compared with (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃, the specimen added with a small amount of CeO₂ (≤0.2 wt.%) display a slightly improved electromechanical coupling factor (k_p) and piezoelectric constant (d₃₃) in conjunction with a reduced dielectric loss (tg δ) and an enhanced mechanical quality factor (Q_m), while higher CeO₂ amounts led to a rapid deterioration of the piezoelectric and ferroelectric properties. The variation of the electrical properties with the CeO₂ addition was tentatively interpreted with respect to doping effect, crystal-structural evolution and stability of ferroelectric domains.     

Influences of poling condition and sintering temperature on piezoelectric properties of (Na0.5Bi0.5)1 − xBaxTiO3 ceramics

The structure, ferroelectric characteristics and piezoelectric properties of (Na_0.5Bi_0.5)_1 − xBa_xTiO₃ (x = 0.04, 0.06, 0.10) ceramics prepared by conventional solid state method were investigated. The influences of poling condition and sintering temperature on the piezoelectric properties of the ceramics were examined. The piezoelectric properties of the ceramics highly depend on poling field and temperature, while no remarkable effect of poling time on the piezoelectric properties was found in the range of 5-25 min. Compared with (Na_0.5Bi_0.5)_0.96Ba_0.04TiO₃ and (Na_0.5Bi_0.5)_0.90Ba_0.10TiO₃, the piezoelectric properties of (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ are more sensitive to poling temperature due to the relatively low depolarization temperature. Moderate increase of sintering temperature improved the poling process and piezoelectric properties due to the development of microstructural densification and crystal structure. With respect to sintering behavior and piezoelectric properties, a sintering temperature range of 1130-1160 °C was ascertained for (Na_0.5Bi_0.5)_0.90Ba_0.10TiO₃.     

Abnormal electrocaloric effect of Na0.5Bi0.5TiO3–BaTiO3 lead-free ferroelectric ceramics above room temperature

We demonstrate the electrocaloric effect (ECE) of Na_0.5Bi_0.5TiO₃–BaTiO₃ (NBT–BT) lead-free ferroelectric ceramics, which were fabricated by the solid-state reaction method. Based on a Maxwell relation, the ECE was characterized via P–T curves under different electric fields. The polarization of NBT increases monotonically within the temperature range of 25–145 °C. It indicates that the NBT has an abnormal ECE with a negative temperature change (ΔT₁₄₀ = −0.33 K at E = 50 kV/cm) opposite to that of the normal ferroelectrics. The 0.92NBT–0.08BT composition near the morphotropic phase boundary has a normal ECE under low electric fields and an abnormal ECE under high electric fields. The abnormal ECE character originates from the relaxor characteristic between ferroelectric and antiferroelectric phases, while the common ECE is always related to the normal ferroelectric–paraelectric phase transition.     

Effect of MnO addition on structure and electrical properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics prepared by citrate method

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ ceramics added with 0–0.8 wt.% MnO were prepared by a citrate method, and the influence of the MnO addition on the structure and electrical properties was investigated. The results indicate that the addition of small amounts of MnO did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure. The dielectric constant (_r) and piezoelectric constant (d₃₃) significantly decrease with increasing MnO content, while the electromechanical coupling factor (k_p) presents a slight variation in the range of 0.25–0.28. The dissipation factor (tan δ) and mechanical quality factor (Q_m) attain a minimum value of 1.5% and a maximum value of 304 when adding 0.4 and 0.5 wt.% MnO, respectively. This research demonstrates that doping effect and microstructural evolution contribute cooperatively to the electrical properties of the ceramics.     

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.