Investigation of enhanced performance in BF-xPT-0.05BZ ternary ceramics for high temperature applications

(0.95-x)BiFeO₃-xPbTiO₃-0.05BaZrO₃ (BF-xPT-0.05BZ) ternary ceramics were synthesized by the solid-state reaction method, which present a perovskite structure without detectable second phase. BF-0.32PT-0.05BZ ceramics display the dominant rhombohedral structure with a small amount of tetragonal phase, revealing the characteristics of morphotropic phase boundary (MPB). The well-densified ceramics possess the average grain size of 8–15 μm with different PT contents. The ferroelectric-paraelectric phase transition of BF-xPT-0.05BZ ceramics shows the characteristic of the first-order transition, which occurs at around 550 °C. It is noticeable that BF-0.32PT-0.05BZ ceramics exhibit the giant remnant polarization of 60 μC/cm² under the field of 175 kV/cm. Moreover, BF-0.32PT-0.05BZ ceramics show the highest piezoelectric constant d₃₃ of 105 pC/N and Q_m of 501. The depolarization temperatures of BF-xPT-0.05BZ ceramics are much close to their Curie temperature T_C, proving the extensive prospect for high temperature piezoelectric applications.     

High-temperature BiFeO3–PbTiO3-Ba(Zr,Ti)O3 ternary ceramics with excellent piezoelectricity

Ternary ceramics of (0.87−x)BiFeO₃–xPbTiO₃–0.13Ba(Zr_0.5Ti_0.5)O₃ (BF–xPT–0.13BZT, 0.27 ≤ x ≤ 0.37) were prepared by the traditional solid state reaction methods. X-ray diffraction results display that BF-xPT-0.13BZT ternary ceramics of x ≥ 0.29 exhibit the perovskite structure with dominant tetragonal (T) phases mixed with a small amount of rhombohedral (R) phases. Scanning electron microscopy (SEM) images reveal that the average grain size of BF-xPT-0.13BZT ternary ceramics is in a range of 10–11 μm, increasing first and then decreasing with the increase of PbTiO₃ (PT) content. The low tanδ of about 0.015 and high Curie temperature T_c of above 450°C were obtained for BF-xPT-0.13BZT ternary ceramics. Moreover, the fluctuation of piezoelectric coefficient d₃₃ is less than ±10% over a broad temperature range of 30°C–400°C. BF-xPT-0.13BZT ternary ceramics for x = 0.33 possess the maximum T_c and d₃₃ of 470°C and 320 pC/N respectively, with the room temperature resistivity of about 10¹¹ Ω·cm. These results indicate that BF-xPT-0.13BZT ternary ceramics for x = 0.33 with both excellent piezoelectric properties and high Curie temperature have promising applications in high-temperature piezoelectric devices.     

Enhanced piezoelectric properties in BF-BT based lead-free ferroelectric ceramics for high-temperature devices

Due to the high Curie temperature (T_C), BiFeO₃–BaTiO₃ (BF-BT) ceramics have been broadly investigated in high-temperature piezoelectric devices. The piezoelectric constant is one of the most significant factors in determining the sensitivity and reliability of piezoelectric functional components. However, the poor piezoelectric constant (d₃₃) of BF-BT ceramic has prevented the practical application of the material. In this work, we innovatively introduce the 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (0.93NBT-0.07BT) component to 0.7BF-0.3BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d₃₃. The XRD analysis shows that the (0.7BF-0.3BT)-x(0.93NBT-0.07BT) ceramics are still in the MPB region with R–PC phases coexistence, and exhibits a homogeneous solid solution. Moreover, the introduction of 0.93NBT-0.07BT ceramic suppresses the generation of defects and facilitates grain growth, thus enhancing piezoelectric property. In consequence, an optimum piezoelectricity d₃₃ = 213 pC/N along with T_c～450 °C was obtained in (0.7BF-0.3BT)-0.01(0.93NBT-0.07BT). This research provides a new idea for the application of BF-BT ceramics in high-temperature piezoelectric devices.     

Enhanced piezoelectric strain of BiFeO3–Ba(Zr0.02Ti0.98)O3 lead-free ceramics near the phase boundary

The xBiFeO₃-(1-x)Ba(Zr_0.02Ti_0.98)O₃ + 1.0 mol% MnO₂ (xBF-BZT) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The structure, dielectric, and piezoelectric properties were studied. X-ray diffraction (XRD) analysis showed that xBF-BZT ceramics exhibited pure perovskite structure with the coexistence of tetragonal and rhombohedral phases (0.66 ≤ x ≤ 0.74). The Curie temperature T_c, the dielectric constant ε_r (1 kHz), dielectric loss tanδ (1 kHz), piezoelectric constant d₃₃, coercive field E_c (80 kV/cm), and remnant polarization P_r (80 kV/cm) of 0.7BF-0.3BZT-Mn ceramics were 491°C, 633, 0.044, 165 pC/N, 35.6 kV/cm, and 22.6 μC/cm², respectively. The unipolar strain of 0.7BF-0.3BZT reached up to 0.20% under the electric field of 60 kV/cm, which is larger than that (0.15%) of BiFeO₃–BaTiO₃ ceramics. These results indicated that the xBF-BZT ceramics were promising candidates for high-temperature piezoelectric materials.     

Large piezoelectricity and high Curie temperature in novel bismuth ferrite-based ferroelectric ceramics

The requirement for ferroelectric ceramics with a high Curie temperature and a high piezoelectric coefficient remains an important research task for high-temperature sensors and actuators applications. (0.76-x)BiFeO_3-0.24PbTiO_3-xBa(Sn_0.2Ti_0.8)O₃ (BF-PT-BST) piezoelectric ceramics were fabricated using the solid-state reaction method. XRD analysis indicated that the incorporation of large ionic radius Ba²⁺ at A-site and nonferroelectric-active Sn⁴⁺ at B-site generated a decrease in the tetragonality degree c/a. A wide multiphase coexistence region was formed with the content of BST ranging from 0.13 to 0.28. The enhanced piezoelectric coefficient (d₃₃ ~ 200pC/N) was achieved while maintaining a high Curie temperature (T_C ~ 500°C) and a high depolarization temperature (T_d ~ 450°C) for the composition of 0.6BF-24PT-0.16BST. TEM patterns provided clear evidence for the presence of nanodomains (~2nm) would be the predominant source for the enhanced piezoelectricity for the composition x = 0.20. The designed BF-PT-BST ternary system provides great potential for high-temperature piezoelectric applications.     

Structural and electrical properties of BZT-added BNLT ceramics

Lead free piezoelectric ceramics (1−x)BNLT−xBZT with x=0.00, 0.06, 0.09 and 0.12 were prepared using a two-step mixed oxide method. Dielectric, ferroelectric and piezoelectric properties of the ceramics were improved by the addition of the BZT. XRD results show tetragonal symmetry structure of the BNLT–BZT ceramics. It was found that the tetragonality increases with increasing BZT content. The optimum composition is x=0.09, where the maximum values of the piezoelectric constant d₃₃ (~126 pC/N) and dielectric constant (~2400) were obtained at room temperature. This BNLT–BZT system can be a promising candidate for lead-free piezoelectric ceramics.     

High and temperature-insensitive piezoelectric performance in the lead-free Sm-doped BiFeO3–BaTiO3 ceramics with high Curie temperature

Large sensor piezoelectric constant (d₃₃ = 334 pC/N) and superior actuator piezoelectric constant (d₃₃* = 552 pm/V) as well as a high Curie temperature (T_C = 454 °C) were obtained simultaneously in the lead-free 0.67Bi_1.03FeO₃-0.33Ba_1-xSm_xTiO₃ ceramics. Such an excellent and temperature-insensitive piezoelectric performance with only 10% temperature variation of piezoelectric strain at the range of 25–125 °C is highly desirable for real applications. The structural origin of the enhanced piezoelectric performance is mainly attributed to the morphotropic phase boundary and the highest known tetragonality (c_T/a_T = 1.02) in such materials. Transmission electron microscopy and electro-mechanical phenomenological theory demonstrate that the superior d₃₃ and d₃₃* are associated with the hybrids nanodomains (60–90 nm) and flattened thermodynamic energy profile owing to the local structure heterogeneity. These results are superior as the piezoelectric properties are temperature-independent and the material has large d₃₃*, and high T_C compared to other lead-free piezoelectric ceramics.     

The evolution of structure and electrical properties for BiFeO3–PbTiO3–Ba(Zr0.3Ti0.7)O3 high-temperature piezoceramics near the morphotropic phase boundary

The development of piezoceramics with high Curie temperature and high piezoelectrical performance has always been a long-cherished goal for many researchers. In this work, we have fabricated 0.55BiFeO₃-(0.45-x)PbTiO₃-xBa(Zr_0.3Ti_0.7)O₃ ternary ceramics near the morphotropic phase boundary (MPB) by conventional solid-state method. XRD patterns indicate that there is an evolution from the tetragonal (T) to pseudo-cubic (PC) phase with BZT content increasing from 0.125 to 0.225. Also, the slim P-E loop transforms into a saturated shape with the decrease of coercive field E_c. Piezoresponse force microscope (PFM) analysis reveals that when x (BZT content) increases, domain density increases. The optimum piezoelectric coefficient d₃₃ (~220 pC/N) is obtained at x = 0.175, while Curie temperature T_C and dielectric loss tanδ are 434 °C and 0.019, respectively. These results show that BF-PT-based piezoceramics are competitive candidates in future high-temperature applications of piezoelectric ceramics.     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.     

Improved ferroelectric properties of BiFeO3-based piezoelectric ceramics through morphotropic phase boundary construction

The ceramic (1-x)BiFe_0.985Sc_0.015O₃-xBaZr_0.2Ti_0.8O₃ + 1mol% MnO₂ (x = 0.20, 0.25, 0.30, 0.35) (BFS-xBZT) was synthesized using the traditional ceramic sintering method. The components of the ceramic were determined by constructing a morphotropic phase boundary (MPB) which consists of rhombohedral (R) and tetragonal (T) phases (0.24≤ x ≤ 0.26). With the accumulation of BZT content, relax behaviors were observed by dielectric properties measurements. At the MPB, the crystal structures of the R phase and T phase change abruptly. The distortion degree of the R phase increases, and the differences between a and c of the T phase decrease. An enhanced ferroelectricity Pr of ~27.8 μC/cm² and apex piezoelectric coefficient d₃₃ of 131 ± 4 pC/N are obtained near the MPB (x = 0.25), due to the R-T phase coexistence near room temperature. The results show that BFS-xBZT ceramics could be a candidate for lead-free piezoelectric ceramics at high operating temperatures.     

Bi(Zn1/2Ti1/2)O3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics with high temperature stability

Lead-free high-temperature ceramics with compositions of 0.71BiFe_1−x(Zn_1/2Ti_1/2)_xO₃–0.29BaTiO₃ (BFZTx–BT, x=0–0.05 mol fraction) were fabricated by a conventional solid state reaction method. The effect of Bi(Zn_1/2Ti_1/2)O₃ (BZT) addition on the microstructure, electrical properties, relaxor behavior, and temperature stability has been studied. XRD patterns revealed that all compositions formed a single perovskite phase of pseudo-cubic crystal structure. The grain size was slightly affected by BZT addition. The diffuse phase transition and strong frequency dispersion of dielectric permittivity are observed for BZT modified ceramics. The addition of BZT into BFZTx–BT was also found to affect the piezoelectric properties and temperature stability of the ceramics with maximum values observed for x=0.5% and 1% BFZTx–BT compositions, respectively. The optimum piezoelectric properties with d₃₃=163 pC/N, together with high-temperature stability with a depolarization temperature T_d∼380 °C, reveal the BFZTx–BT ceramics to be promising high-temperature Pb-free piezoelectric materials.     

Piezoelectric properties of Ca-modified Pb0.6Bi0.4(Ti0.75Zn0.15Fe0.10)O3 ceramics

Perovskite-structured Pb_0.6Bi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃ ceramics was reported with high Curie temperature T_C of 705 °C and tetragonality of c/a = 1.10, promising for high temperature applications with large piezoelectric anisotropy. In this paper, it was experimentally demonstrated to ease poling processing and enhance piezoelectricity through substituting lead with calcium of Pb_0.6?xCa_xBi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃. For the x = 0.18 sample, electromechanical coupling factor ratio of k_t/k_p → ∞, dielectric constant of 380, piezoelectric coefficient d₃₃ of 80 pC/N, mechanical quality factor Q_m of 50 and Curie point T_C of 237 °C were obtained, which exhibits better piezoelectric performance than the (Pb_0.76Ca_0.24)(Ti_0.96(Co_0.5W_0.5)_0.04)O₃. The enhanced piezoelectric response was analyzed with relation to the reduction of tetragonality and Curie temperature.     

Effects of CuO addition on the sinterability and electric properties in PbNb2O6-based ceramics

PbNb₂O₆ (PN)-based ceramics with tungsten bronze structure are promising piezoelectric materials in high-temperature devices such as piezoelectric vibration transducers. However, the PN-based ceramics usually exhibit a low bulk density, which greatly limits their practical applications. In this work, CuO was used as the sintering aid to form a liquid-phase bridge, leading to an obvious increase of the bulk density of PN-based ceramics by 11% (from 5.25 to 5.85 g cm⁻³) and the improvement of the piezoelectric constant (d₃₃) (from 168 to 190 pC/N) and the Curie temperature (T_C) from 367 to 395 °C. The positive influence of CuO on densification has been proved by SEM and fracture toughness. The XRD patterns confirmed that there was no secondary phase introduced by CuO addition. The Raman spectra revealed that part of Cu²⁺ ions has probably diffused into host lattice of the PN and preferred to occupy on A-sites. These results not only demonstrate the high potential of the CuO added PN-based ceramics for high-temperature piezoelectric applications, but also reveal the corresponding structure-properties relationship as well as provide a way to improve the sinterability, d₃₃, and T_C simultaneously.     

Lead-free high performance Bi(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 piezoceramics

In this article, structure, dielectric, ferroelectric and piezoelectric properties of Bi rich Bi_1.05(Zn_0.5Ti_0.5)O₃-modified BiFeO₃-BaTiO₃ (BF-BT-xBZT) ceramics were investigated experimentally. Crystal structure, phase purity and microstructure were examined through X-ray diffractometry and scanning electron microscopy, respectively. The crystallographic results show the formation of single-phase solid solutions for all compositions except x?=?10?mol%. The BF-BT modification through BZT instigates variation in grain size, enhancement in Curie temperature (T_C) and field induced polarization and strain response. Large field induced strain of ～0.24% at low driving field along with a small hysteresis of ～38% was observed for 2?mol% BZT modified BF-BT ceramics. These investigated results signpost the potentiality of BF-BT-xBZT ceramics in high temperature piezoelectric device applications.     

Achieving large piezoelectric response and ultrahigh electrostriction in [001] textured BiScO3-PbTiO3 high-temperature piezoelectric ceramics

[001] textured 0.40BiScO₃-0.60PbTiO₃-0.125 mol%Nb⁵⁺ (BS-60PT-0.125Nb) high-temperature piezoelectric ceramics were synthesized using templated grain growth process. A high texture degree F₀₀₁ of 99% was obtained using 2 vol% BaTiO₃ (BT) templates. The piezoelectric charge constant d₃₃ and the unipolar strain under 40 kV cm⁻¹ at room temperature for the textured ceramics are 646 pC N⁻¹ and 0.36%, respectively, which is over two times as those for untextured ceramics (∼243 pC N⁻¹ and 0.17%). The electrostriction Q₃₃ value of the textured sample remarkably increased from 0.034 m⁴ C⁻² to 0.068 m⁴ C⁻² under 30 kV cm⁻¹, showing a twice higher than untextured. Compared with random ceramics, the improvement piezoelectric response of the textured ceramics is primarily attributed to the increase of the dielectric constant ε_r and electrostriction coefficient Q₃₃ along [001] orientation, which is originating from the anisotropy of piezoelectricity. The BS-60PT-0.125Nb textured ceramics have large piezoelectric response and ultrahigh electrostriction with high temperature stability (high depolarization temperature T_d of ∼360°C and high Curie temperature T_c of 421°C), showing great potential for the piezoelectric applications at high temperatures.     

Electromechanical properties of Ba(Zr0.2Ti0.8)O3 ceramics prepared by spark plasma sintering

Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared by spark plasma sintering (SPS) and conventional sintering. The dynamic field-induced displacement and small-signal remnant piezoelectric constant measured by a resonant–antiresonant frequency method were evaluated. By normal sintering, the density, grain size, and dielectric constant of the ceramics increased with sintering temperature. The BZT20 ceramics prepared by SPS were characterized by linear field-induced strain. In response to the application of post-annealing at 1300 °C, BZT20 ceramics exhibited linear strain loop and high field-induced strain corresponding to dynamic strain/field d₃₃ at 20 kV/cm of 290 pm/V. The remnant piezoelectric properties of the BZT20 ceramics were found to largely depend on the preparation conditions, including the sintering temperature and annealing temperature. The BZT20 ceramics prepared by SPS and post-annealed at 1300 °C showed Q_m and k_p values of 325 and 25.1 (%), respectively.     

Enhanced electrical properties of lead-free BNLT–BZT ceramics by thermal treatment technique

Electrical properties of lead-free solid solution ceramics from the Bi_0.4871Na_0.4871La_0.0172TiO₃ (BNLT) and BaZr_0.05Ti_0.95O₃ (BZT) system have been improved by a thermal treatment technique. A modified two step mixed-oxide method was employed for the preparation of the (1?x)BNLT–xBZT ceramics, where x=0.06, 0.09, 0.12 and 0.20. After sintering at 1125 °C for 4 h, the BNLT–BZT ceramics were annealed at 825, 925 and 1025 °C. The annealing treatment caused an increase in dielectric constant of BNLT–BZT ceramics with x≤0.09 mol% and with x higher than 0.09 mol% the dielectric value dropped considerably. The ferroelectric properties of all annealed ceramic samples tend to decrease with increasing annealing temperature as confirmed by the slimmer P–E loops. The piezoelectric coefficient (d₃₃) increased with annealing temperatures and a maximum value of ～170 pC/N was obtained from the ceramic samples annealed at 1025 °C with x=0.02.     

Processing and enhanced electrical properties of Sr1-x(K0.5Bi0.5)xBi2Nb2O9 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, Sr_1−x(K_0.5Bi_0.5)_xBi₂Nb₂O₉ (SKBN-x, x=0, 0.2, 0.5, 1.0), were synthesized by a conventional solid-state reaction. Structural and electrical properties of SKBN-x ceramics were investigated. X-ray diffraction analysis suggested that the substitution led to the formation of a layered perovskite structure. Plate-like morphologies for the grains were clearly observed in all the samples, which are characteristic for layer-structure Aurivillius compounds. The Curie temperature (T_c) is found to shift to higher temperature from 445 °C to 509 °C with increasing (K, Bi) content. Excellent remanent polarization (2P_r∼15 μC/cm²) were obtained for SKBN-0.2 ceramic. High piezoelectric coefficient of d₃₃∼21  pC/N were obtained for the samples at x=0.5. Additionally, thermal annealing studies indicated that the piezoelectric coefficient (d₃₃) of SKBN-0.5 was unchanged even if annealing temperature increased to be 450 °C, demonstrating the ceramics are the promising candidates for high-temperature applications.     

The high nano-domain improves the piezoelectric properties of KNN lead-free piezo-ceramics

Due to their high Curie temperature and large dielectric constant, potassium sodium niobate-based lead-free piezo-ceramics (KNN) are regarded as one of the most hopeful piezo-ceramics candidate materials. Herein, (1-x) (K_0.5Na_0.5)(Nb_0.96Sb_0.04)O₃ - x (Ba_0.5Sr_0.25)ZrO₃ [abbreviated as (1-x) KNNS - x BSZ, x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05] lead-free piezo-ceramics are prepared through chemical doping using the traditional solid phase method. The phase structure, domain structure, and microstructure of KNN ceramics have been thoroughly examined. Doping of BZS causes the formation of R-O-T phase boundaries and increases the proportion of polar nano-domains within the crystals, thus increasing the rate of motion of the domain walls and making the domains more easily deflected. The piezoelectric and dielectric properties of the material are improved simultaneously. When x = 0.04, the piezoelectric properties of ceramics reach the optimal value (d₃₃ = 351 pC/N, T_C = 305 °C, K_p = 43% and ε_r = 41267). This work offers a fresh concept for enhancing the overall performance of lead-free piezo-ceramics and aids in understanding the nature of doping modification of lead-free piezo-ceramics.