NbO3 Piezoelectric Ceramics Research Articles

Water-mediated production of K0.5Na0.5NbO3 piezoelectric ceramics with cold-sintering assisted route: Enhanced dielectric properties

Cold sintering is an attractive method to densify ceramics, providing the opportunity to produce ferroelectrics efficiently. This is particularly important for cases where ceramics like perovskites are prone to high A-site element volatilization at high temperatures. The resulting uncontrolled creation of defects is often detrimental to the ferroelectric properties. In this work, cold-sintering assisted production of KNN ceramics with water (no corrosive transient liquid) leads to a homogenous, high-density pure KNN with high dielectric permittivity and lower dielectric losses as compared to high-temperature sintering techniques. Our work could, therefore, open a new venue for further modification of defect chemistry in lead-free piezoelectrics.

Visualizing sintering process and electrical properties of SnO2 doped K0.48Na0.52NbO3 piezoelectric ceramics

In this study, the conventional solid-state sintering of lead-free (1−x)K0.48Na0.52NbO3-xSnO2 piezoelectric green bodies was analysed using thermal imaging and longitudinal/transverse shrinking. The phase structure, fracture morphology, densification, permittivity, ferroelectricity, piezoelectricity, and domain-switching activation energy were investigated with increasing SnO2 content (x). Sn4+ first occupied the A site in the ABO3 structure and then substituted the B site with increasing x. This resulted in various contents of defect dipoles and oxygen vacancies, which were mainly responsible for the different ferroelectricity and piezoelectricity values. The permittivity and domain-switching activation energy were significantly affected by the local compositional disorder or fluctuation. Moreover, the influences of phase, densification, fine grain size, and domain wall on the electrical properties are also discussed. The optimum electrical properties, with Pr = 34.7 μC/cm2, d33 = 294 pC/N, and TC = 337 °C were determined for x = 0.30 mol%. This study provides a specific explanation and reference for the various electrical properties of lead-free piezoelectric ceramics.

The effect of (Bi0.5Li0.5)0.9Sr0.1ZrO3 substitution on the construction of polymorphic phase boundary and high curie temperature of K0.45Na0.55NbO3 piezoelectric ceramics

The effect of (Bi0.5Li0.5)0.9Sr0.1ZrO3 substitution on the construction of polymorphic phase boundary and high curie temperature of K0.45Na0.55NbO3 piezoelectric ceramics

Preparation and physicochemical properties of K0.5Na0.5NbO3 ceramics obtained using a modified wet chemistry method

A modified wet chemical method involving different chelating acids was applied to prepare a series of lead-free K0.5Na0.5NbO3 (KNN) piezoelectric ceramics. The microstructural, dielectric, spectral and ferroelectric properties of the obtained ceramics were investigated as part of a comparative study. Thermal characteristics specific to a phase transition were detected via high-temperature HT-XRD, FT-IR and EIS. The obtained sinters were dense and consisted of micro-sized grains. Sinters obtained from powders prepared from oxalic acid with the addition of tartaric acid exhibited lower dielectric constants and lower coercive field values than those synthesized using oxalic acid only (332 vs 399 and 10 vs 9.5 kV⋅cm−1, respectively) measured at room temperature. The KNN ceramics exhibited high conductivity (>10−3 S/cm at 600 °C), dielectric loss (∼200 at 1 kHz) and high remnant polarization (∼310−3 μC/cm2).

Ferroelectric domain formation and photocatalytic activity on porous alkali niobate piezoelectric ceramics

Present study showed synthesis of novel type of porous alkali niobate piezoelectric ceramics, and the formation of domains and photocatalytic activity for the porous piezoelectric ceramics were investigated while comparing with dense ceramics to confirm enhancement of domain orientation and photocatalytic activity around pores. Porous Li0.06Na0.47K0.47NbO3 piezoelectric ceramics were synthesized by a template method using polymethylmethacrylate as a pore former agent. Uniform pores with 6 µm in diameter were dispersed in the porous ceramics. Porous ceramics synthesized with 10 vol % of the pore former agent showed piezoelectric voltage coefficient, 29 mVm/N, which is same as that of the dense ceramics. Smaller striped domains formed at an edge of pores on the porous ceramics, indicating that orientation of domains was promoted by electric field concentration around the pores. Through photoreduction reaction of Ag+ ion, local precipitation of Ag was shown around the pores on the poled porous ceramics, whereas Ag was located over an entire surface of unpoled porous ceramics. Highest photocatalytic activity was shown for the poled porous ceramics in photodecomposition test of methylene blue. These results clearly indicated photocatalytic activity was enhanced on ferroelectric domains around pores of porous piezoelectric ceramics.

A study of lead-free (K0.5N0.5)NbO3 piezoelectric ceramics processed by additive manufacturing

Lead-free (K[Formula: see text]N[Formula: see text]NbO3 piezoelectric ceramics have drawn wide attention due to its environment-friendly and excellent piezoelectric performance. Since the difficulty of post-processing of ceramics limit its further development and practical application, three-dimensional (3D) printing technology has been developed in this work. A homogeneous piezoelectric ceramic suspension with 40 vol% modified (K[Formula: see text]N[Formula: see text]NbO3 nanoparticles can be 3D printed well based on a stereolithography process. In addition, by the post heat treatment under different sintering temperature, a density value of 4.31[Formula: see text]g[Formula: see text]cm[Formula: see text] with the relative density of about 96% was obtained in the sample sintered at 1120[Formula: see text]C, which results in the larger dielectric constant and lower dielectric loss in this sample. These printed ceramics exhibit two successive phase transitions and reduce with increase of sintering temperature at measured temperature range.

High performance lead-free Na0.5K0.5NbO3 piezoelectric ceramics obtained via oscillatory hot-pressing

Lead-free Na0.5K0.5NbO3 (KNN) piezoelectric ceramics is regarded as a potential candidate for PZT material, while high performance is difficult to be obtained due to its poor sinterability and non-stoichiometric component. In this work, oscillatory pressure-assisted hot pressing (OPAHP) is utilized to fabricate KNN ceramics with high density. The KNN ceramics sintered at 860 °C exhibits superior performance with piezoelectric parameter (d33) of 142 pC/N, electromechanical coupling factors (kp) of 0.41, and relative permittivity (εT33/ε0) of 472–620. Additionally, hardness and flexural strength are measured as 3.55 GPa and 99.13 MPa, respectively. This work indicates that OPAHP technique is effective for fabricating KNN piezoelectric ceramics with high performance.

Fabrication of Three-Dimensional Piezoelectric Ceramics Using the Dispenser System

Abstract We fabricated lead-free (K,Na,Li)NbO3 (KNLN) and BaTiO3 (BT) piezoelectric ceramics using a dispenser system. After dissolving polyvinyl butyral in ethanol, a paste for extrusion was fabricated by mixing KNLN or BT ceramic powders. After several times of paste extrusion with a dispenser system, degreasing was performed at 650°C. The KNLN moldings were sintered, at 1,100–1,170°C, and sintering of BT moldings were performed by two-step sintering at 1,320°C and 1,150°C. From the x-ray diffraction pattern, the fabricated KNLN ceramics had a perovskite structure. The density of the KNLN and BT moldings fabricated by the dispenser system was 3.94 and 5.42 g/cm3, respectively. In addition, the BT moldings had the dielectric constant εr = 1.95 × 103. The Curie temperature of the BT moldings was confirmed at about 125°C, as with the BT piezoelectric ceramics fabricated by uniaxial pressure molding. The BT moldings had the piezoelectric constant d33 = 60 pC/N. The fabrication methods studied in this work provided the potential to fabricate simple three-dimensional piezoelectric ceramic devices for applications in acoustic wave sensors.

Phase Structure, Microstructure and Electrical Properties of KxNa(1-x)NbO3 Piezoelectric Ceramics with Different K/Na Ratio

The KxNa(1-x)NbO3 (x = 0.45, 0.46, 0.47, 0.48, 0.49, 0.50) lead-free piezoelectric ceramics was fabricated by conventional solid-state sintering method. It was found that the ratio of alkaline metal would affect the microstructure, bulk density, and optimum sintering temperatures of ceramics. Meanwhile, the electrical properties were also influenced by modulating the K/Na ratio, exhibiting corresponding composition-dependent properties. The optimum electrical properties of KxNa(1-x)NbO3 such as piezoelectric constant d33 = 115 pC/N, mechanical quality factor Qm = 20, Curie temperature Tc = 365 °C, eT33/e0= 588.1, dielectric loss tan δ = 0.024, bulk density (ρ) = 3.08 g/cm3, remnant polarization (Pr) = 8.87 μC/cm2 and coercive field (Ec) = 13.79 kV/cm were obtained at x = 0.46.

Composition, microstructure and electrical properties of K0.5Na0.5NbO3 ceramics fabricated by cold sintering assisted sintering

In this paper, cold sintering was served as a forming method to assist the conventional sintering, which is so-called cold sintering assisted sintering (CSAS) method. Lead-free K0.5Na0.5NbO3 piezoelectric ceramics were prepared by the CSAS method, and the effects of the different procedures on the sintering behaviors and electrical properties of KNN ceramics were studied. Compared with conventional sintering (CS), cold sintering process can induce potassium-rich phase on the KNN particle surface, and remarkably increase both the green and sintering density of KNN ceramics. Meanwhile, the potassium-rich phase would transform to K4Nb6O17 second phase on the grain surface, and subsequently suppress the volatilization of potassium element. The sinterability and electrical properties were greatly improved, and KNN piezoelectric ceramics with high performance can be manufactured in a wide sintering temperature range (1055 °C–1145 °C), which proves that CSAS has the potential to be an excellent sintering technique for producing KNN based ceramics.

Improved Li and Sb doped lead-free (Na,K)NbO3 piezoelectric ceramics for energy harvesting applications

Piezoelectric energy harvesting is the most widely investigated technology for renewable energy applications. In this work, (1-x)(Na0.5K0.5)NbO3-xLiSbO3 piezoelectric ceramics were prepared through conventional mixed oxide fabrication methods with different sintering temperatures. Although the (Na0.5K0.5)NbO3 piezoelectric material is representative among the lead-free ceramics, it is difficult to densify by typical sintering techniques owing to its easy evaporation properties of potassium (K+) and sodium ion (Na+). Hence, lithium (Li+) and antimony ion (Sb5+) were used for the partial substitution of (Na0.5K0.5)NbO3. With the optimized sintering temperature, Li+ and Sb5+ are expected to be crucial in increasing the density and enhance the piezoelectric and ferroelectric properties. In this study, the phase, microstructure, and dielectric and electrical properties of (1-x)(Na0.5K0.5)NbO3-xLiSbO3 ceramics depending on the sintering temperature is examined by employing X-ray diffraction, field emission scanning electron microscopy, impedance analyzer, and mechanical force system for energy harvesting.

Effects of LiNbO3-doping on properties of (Na0.535K0.48)NbO3 piezoelectric ceramics with high electromechanical coupling coefficient for application in surface acoustic wave devices

Abstract In this study, lead-free LiNbO3-doped (Na0.535K0.48)NbO3 (NKN) ceramics (NKLxN, x = 0–0.09) were prepared using a conventional mixed oxide method to investigate the effects of LiNbO3 additives on the microstructure and electrical properties. The addition of LiNbO3 reduced the optimal sintering temperature from 1100 to 950 ℃ and increased the bulk relative density to 99.61% (g/cm3) at x = 0.05 through the formation of a homogeneous microstructure. The electrical properties remained highly stable, even when the ambient temperature was increased from room temperature to 140 ℃. NKLxN ceramics sintered at 950 ℃ with x = 0.05 exhibited the following excellent piezoelectric properties: kp：50% (34%); kt：53% (40%); Qm：168 (112); d33：150 pC/N (80 pC/N); and tan δ ：4% (8%). These values far exceed those of pure NKN ceramics sintered at 1100 ℃. Surface acoustic wave (SAW) devices fabricated using the proposed NKLxN (x = 0.05) ceramics presented high phase velocity of 3210 m/s, k2 of 6.7%, and TCF of approximately −282 ppm/℃. Our results clearly demonstrate the effectiveness of adding LiNbO3 to prevent deliquescence and thereby enhance resistance to the effects of humidity. The resulting devices are highly sensitive to changes in temperature, making them ideally suited to electromechanical transducers as well as SAW temperature sensors.

Characterization of domain structure and domain wall kinetics in lead-free Sr2+ doped K0.5Na0.5NbO3 piezoelectric ceramics by piezoresponse force microscopy

ABSTRACTThe domain structure and local polarization reversal were studied in lead-free ceramics (K0.5Na0.5)1-2xSrxNbO3 by various modes of scanning probe microscopy. It was shown that the increase in Sr concentration led to a decrease in both grain and domain sizes. The local polarization reversal study provided important information on the domain wall dynamics in this complicated system. The defect distribution in doped ceramics was proposed as a major factor limiting domain wall mobility and internal bias field decrease together with the increase of the activation field for domain wall motion.

Ferroelectric Domain Structure and Local Piezoelectric Properties of Lead-Free (Ka0.5Na0.5)NbO₃ and BiFeO₃-Based Piezoelectric Ceramics.

Recent advances in the development of novel methods for the local characterization of ferroelectric domains open up new opportunities not only to image, but also to control and to create desired domain configurations (domain engineering). The morphotropic and polymorphic phase boundaries that are frequently used to increase the electromechanical and dielectric performance of ferroelectric ceramics have a tremendous effect on the domain structure, which can serve as a signature of complex polarization states and link local and macroscopic piezoelectric and dielectric responses. This is especially important for the study of lead-free ferroelectric ceramics, which is currently replacing traditional lead-containing materials, and great efforts are devoted to increasing their performance to match that of lead zirconate titanate (PZT). In this work, we provide a short overview of the recent progress in the imaging of domain structure in two major families of ceramic lead-free systems based on BiFeO3 (BFO) and (Ka0.5Na0.5)NbO3 (KNN). This can be used as a guideline for the understanding of domain processes in lead-free piezoelectric ceramics and provide further insight into the mechanisms of structure–property relationship in these technologically important material families.

Field-induced large strain in lead-free 0.99[(1−x) Bi0.5(Na0.80K0.20)0.5TiO3–xBiFeO3]–0.01(K0.5Na0.5)NbO3 piezoelectric ceramics

Lead-free 0.99[(1−x) Bi0.5(Na0.80K0.20)0.5TiO3–xBiFeO3]–0.01(K0.5Na0.5)NbO3 (BNKT20–100xBF–1KNN) piezoelectric ceramics were fabricated through conventional techniques. Results showed that changes in BF content of BNKT20–100xBF–1KNN induced transition from the ferroelectric phase to the ergodic relaxor phase. These changes also significantly disrupted long-range ferroelectric order, thereby correspondingly adjusting the ferroelectric-relaxor transition point TF-R to room temperature. A large strain of 0.39% at the electric-field of 80kV/cm (corresponding to a large signal d33* of 488pm/V) was obtained at x=0.06, which originated from the composition proximity to the ferroelectric-relaxor phase boundary. Moreover, the high-strain material exhibited exceptional fatigue resistance (up to 106 cycles) as a result of the reversible field-induced phase transition. The proposed material exhibits potential for novel ultra-large stroke and nonlinear actuators that require enhanced cycling reliability.

Effects of NaNbO<sub>3 </sub>Crystals on Electrical Properties of K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Ceramics

Lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics were studied and synthesized by the seed-induced method. NaNbO3 crystal was used as seed and prepared by molten salt synthesis (MSS). The average particles size of NaNbO3 seed crystal was about 1-3 mm. Then, the NaNbO3 seed was mixed with KNN powder and ball milled for 24 h. The mixed powder was calcined at 700-900 °C and sintered at 1100 °C. The phase structure and morphology of the ceramics were investigated by X-ray diffraction and scanning electron microscope and the electrical properties were studied. The results indicated that all samples showed a pure perovskite phase. The highest density of the ceramic was 93% compared to the theoretical density. The results showed that NaNbO3seed crystal improved piezoelectric properties of KNN ceramics.

Effects of GeO2 Addition on Sintering and Properties of (K0.5Na0.5)NbO3 Ceramics

Lead‐free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics doped with different amounts of GeO2 were prepared and characterized. GeO2 was found to effectively improve the sinterability and piezoelectric properties of the material. The improvement in the sinterability is ascribed to the formation of a liquid phase, which decreased the sintering temperature from 1080°C to 1010°C. The improvement in the properties is attributed to the replacement of Nb5+ with Ge4+ to form acceptor dopants. The following optimized properties were obtained from the KNN ceramic with 0.75 wt% GeO2: piezoelectric constant (d33) = 126 pC/N, planar electromechanical coupling coefficient (kp) = 42.8%, mechanical quality factor (Qm) = 140, and dielectric loss (tanδ) = 3.8%.

Good Quality Factor in GdMnO3-Doped (K0.5Na0.5)NbO3 Piezoelectric Ceramics

(1 − x)(K0.5Na0.5)NbO3 − xGdMnO3 (KNN–xGM) ferroelectric ceramics (0 ≤ x ≤ 5 mol.%) were obtained through a solid state technique. For all the studied compositions, orthorhombic perovskite crystalline structures were obtained at room temperature. GdMnO3 suppresses the grain growth and gives rather homogenous microstructures as the concentration increases. The doped ceramics exhibita good dielectric response, a “hard” ferroelectric behavior and good piezoelectric properties. An improved mechanical quality factor of 1180 and a high Curie temperature T C = 400°C, coupled with k p = 0.426, makes the composition x = 1 mol.% GdMnO3 suitable for lead-free piezoelectric materials for high-power and high-temperature applications.

Structure and asymmetric ferroelectric loops of (K0.48Na0.52)NbO3–1mol%CuO–xmol%Co2O3 ceramics with low-temperature sintering

Lead-free piezoelectric ceramics, (K0.48Na0.52)NbO3–1 mol%CuO–x mol%Co2O3 [KNN–Cu–xCo hereafter], were prepared by a conventional solid-state sintering method, and the low-temperature sintering behavior and ferroelectric property of Co2O3 doped (K0.48Na0.52)NbO3 piezoelectric ceramics were investigated. It was found that CuO and Co2O3 additions are very effective to improve the density and sintering behavior of KNN ceramics. KNN–Cu–0.1Co ceramics with the highest density (ρ ∼ 4.38 g/cm3) could be prepared at such a low sintering temperature of 930 °C. Hard ferroelectrics KNN–Cu–xCo show an asymmetric P–E hysteresis loop, attributing to an internal bias field Ei. The improvement measures of Ei was discussed through the analysis on its affected factors, including doped level, sintering temperature, and measuring frequency. The results also suggested that mechanical quality factor Qm has similar variation trend with Ei as the variation sintering temperature or composition. KNN–Cu–0.5Co ceramics sintered at 980 °C obtain the excellent properties: Qm ∼ 577, kp ∼ 30% and d33 ∼ 83 pC/N.

Microstructure and Electrical Properties of Cerium-Doped Bismuth-Layer 0.9Bi4Ti3O12-0.1K0.5Na0.5NbO3 Piezoelectric Ceramics

The cerium doped 0.9Bi4Ti3O12-0.1K0.5Na0.5NbO3 (BTO-KNN) piezoelectric ceramics were synthesized using conventional solid state processing. The effects of CeO2 doping on the microstructure and the electrical properties of BTO-KNN ceramics were investigated. It is found that the ceramics possess a pure phase of bismuth oxide layer-type structure. The piezoelectric properties of BTO-KNN-based ceramics are significantly improved after cerium doping. The piezoelectric constant d33, dielectric loss tan δ, mechanical quality factor Qm and remanent polarization Pr for the BTO-KNN ceramics with 0.75 wt% CeO2 dopant are found to be 28 pC/N, 0.29%, 2897, 11.83 µC/cm2, respectively, and with high Curie temperature TC (∼615 °C) and stable piezoelectric properties, demonstrating that the cerium doped BTO-KNN piezoelectric ceramics are the promising candidates for high-temperature applications.