Search Results (31)

Relaxor ferroelectrics based on sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) have attracted more interest recently as potential ecologically acceptable materials for pulse power technology because of their excellent full-energy storage capabilities. This paper formed (1 − x){0.97[0.98(BNT-ST)-0.02CN]-0.03AlN}-xNN ceramics through a traditional solid-state reaction process. It was noted that the incorporation of NaNbO₃ enhances the property of energy storage by elevating the breakdown strength and causing the creation of an ergodic relaxation state. The effective energy storage density (W_rec) and the energy storage efficiency (η) are 1.09 J/cm³ and 85%, respectively. The breakdown field strength E_b reached 155 kV/cm at x = 40%. These ceramics have excellent temperatures and frequency stabilities from 0.5 to 50 Hz and 20 to 60 °C. Full article

Crystallographic texture engineering through templated grain growth (TGG) has gained prominence as a highly effective strategy for optimizing the electromechanical performance of lead-free piezoelectric ceramics, offering a pathway toward sustainable alternatives to lead-based systems like lead zirconate titanate (PZT). By achieving high degrees of texture, with Lotgering factors (LFs) often exceeding 90%, these systems have demonstrated piezoelectric properties that rival or even surpass their lead-based counterparts. Despite these advancements, the field lacks a comprehensive understanding of how specific template parameters influence the texture quality and functional properties across different material systems. This review provides an in-depth analysis of the influence of the template morphology, composition, and crystallographic orientation on the texturing of key lead-free systems, including BaTiO₃ (BT), (K_0.5Na_0.5)NbO₃ (KNN), and Bi_0.5Na_0.5TiO₃ (BNT). Furthermore, it explores how the template selection affects the induced crystallographic direction, and how this impacts the material’s phase structure and domain configurations, ultimately influencing the piezoelectric and dielectric properties. By consolidating the existing knowledge and identifying current challenges, this work highlights key strategies for optimizing the texture and electromechanical performance in lead-free ceramics, providing essential insights for future research aimed at advancing high-performance, environmentally friendly piezoelectric materials for applications such as sensors, actuators, and energy-harvesting devices. Full article

In order to obtain large room-temperature electrocaloric effect (ECE) and wide operation temperature range simultaneously in lead-free ceramics, we proposed designing a relaxor ferroelectric with a T_m (the temperature at which the maximum dielectric permittivity is achieved) near-room temperature and glass addition. Based on this strategy, we designed and fabricated lead-free 0.76NaNbO₃–0.24BaTiO₃ (NN-24BT) ceramics with 1wt.% BaO–B₂O₃–SiO₂ glass addition, which showed distinct relaxor ferroelectric characteristics with strongly diffused phase transition and a T_m near-room temperature. Based on a direct measurement method, a large ΔT (adiabatic temperature change) of 1.3 K was obtained at room temperature under a high field of 11.0 kV mm⁻¹. Additionally, large ECE can be maintained (>0.6 K@6.1 kV mm⁻¹) over a broad temperature range from 23 °C to 69 °C. Moreover, the ECE displayed excellent cyclic stability with a variation in ΔT below ±7% within 100 test cycles. The comprehensive ECE performance is significantly better than other lead-free ceramics. Our work provides a general and effective approach to designing lead-free, high-performance ECE ceramics, and the approach possesses the potential to be utilized to improve the ECE performance of other lead-free ferroelectric ceramic systems. Full article

In this study, an Integrated Electronics Piezoelectric (IEPE)-type accelerometer based on an environmentally friendly lead-free piezoceramic was fabricated, and its field applicability was verified using a cooling pump owned by the Korea Atomic Energy Research Institute (KAERI). As an environmentally friendly piezoelectric material, 0.96(K,Na)NbO₃-0.03(Bi,Na,K,Li)ZrO₃-0.01BiScO₃ (0.96KNN-0.03BNKLZ-0.01BS) piezoceramic with an optimized piezoelectric charge constant (d₃₃) was introduced. It was manufactured in a ring shape using a solid-state reaction method for application to a compression mode accelerometer. The fabricated ceramic ring has a high piezoelectric constant d₃₃ of ~373 pC/N and a Curie temperature T_C of ~330 °C. It was found that the electrical and physical characteristics of the 0.96KNN-0.03BNKLZ-0.01BS piezoceramic were comparable to those of a Pb(Zr,Ti)O₃ (PZT) ring ceramic. As a result of a vibration test of the IEPE accelerometer fabricated using the lead-free piezoelectric ceramic, the resonant frequency f_r = 20.0 kHz and voltage sensitivity S_v = 101.1 mV/g were confirmed. The fabricated IEPE accelerometer sensor showed an excellent performance equivalent to or superior to that of a commercial IEPE accelerometer sensor based on PZT for general industrial use. A field test was carried out to verify the applicability of the fabricated sensor in an actual industrial environment. The test was conducted by simultaneously installing the developed sensor and a commercial PZT-based sensor in the ball bearing housing location of a centrifugal pump. The centrifugal pump was operated at 1180 RPM, and the generated vibration signals were collected and analyzed. The test results confirmed that the developed eco-friendly lead-free sensor has comparable vibration measurement capability to that of commercial PZT-based sensors. Full article

Electrostrictive materials based on (Na_0.5Bi_0.5)TiO₃ are promising lead-free candidates for high-precision actuation applications, yet their properties require further improvement. This study aims to enhance the electromechanical properties of a predominantly electrostrictive composition, 0.685(Na_0.5Bi_0.5)TiO₃-0.065BaTiO₃-0.25SrTiO₃, by using templated grain growth. Textured ceramics were prepared with 1~9 wt% NaNbO₃ templates. A high Lotgering factor of 95% was achieved with 3 wt% templates and sintering at 1200 °C for 12 h. Polarization and strain hysteresis loops confirmed the ergodic nature of the system at room temperature, with unipolar strain significantly improving from 0.09% for untextured ceramics to 0.23% post-texturing. A maximum normalized strain, S_max/E_max (d₃₃*), of 581 pm/V was achieved at an electric field of 4 kV/mm for textured ceramics. Textured ceramics also showed enhanced performance over untextured ceramics at lower electric fields. The electrostrictive coefficient Q₃₃ increased from 0.017 m⁴C⁻² for untextured ceramics to 0.043 m⁴C⁻² for textured ceramics, accompanied by reduced strain hysteresis, making the textured 0.685(Na_0.5Bi_0.5)TiO₃-0.065BaTiO₃-0.25SrTiO₃ composition suitable for high-precision actuation applications. Dielectric properties measured between −193 °C and 550 °C distinguished the depolarization, Curie–Weiss and Burns temperatures, and activation energies for polar nanoregion transitions and dc conduction. Dispersive dielectric constants were found to observe the “two” law exhibiting a temperature dependence double the value of the Curie–Weiss constant, with shifts of about 10 °C per frequency decade where the non-dispersive THz limit was identified. Full article

As consumer electronics and industrial control systems continue to evolve, the operating temperature range of capacitors is gradually increasing. Barium titanate-based ceramic capacitors are widely used in the field of high dielectrics, so temperature-stable barium titanate-based dielectric materials have been a hot research topic in the field of dielectric ceramics. The construction of a core–shell structure by unequal doping is an effective way to obtain temperature-stable dielectric materials. At the same time, this structure retains part of the highly dielectric tetragonal phase, and materials with overall high dielectric constants can be obtained. In this work, we prepared BaTiO₃-xNaNbO₃-0.002Gd₂O₃ (x = 1.0–6.0 mol%) as well as BaTiO₃-0.05NaNbO₃-yGd₂O₃ (y = 0–0.30 mol%) dielectric ceramics. On the basis of high-electronic-bandgap NaNbO₃-modified BaTiO₃ dielectric ceramics, a core–shell structure with a larger proportion of core phase was obtained by further doping the amphiphilic rare-earth oxide Gd₂O₃. By designing this core–shell structure, the temperature stability range of capacitors can be expanded. At a doping level of 5.0 mol% NaNbO₃ and 0.20 mol% Gd₂O₃, the room temperature dielectric constant ε_r = 4266 and dielectric loss tan δ = 0.95% conforms to the X8R standard (from −55 °C to 150 °C, TCC < ±15%); volume resistivity ρ_v = 10,200 GΩ·cm and breakdown strength E_b = 13.5 kV/mm is attained in BaTiO₃-based ceramics. The system has excellent dielectric and insulating properties; it provides a new solution for temperature-stable dielectric ceramics. Full article

(K_0.5Na_0.5)NbO₃ (KNN)-based ceramics have been extensively investigated as replacements for Pb(Zr, Ti)O₃-based ceramics. KNN-based ceramics exhibit an orthorhombic structure at room temperature and a rhombohedral–orthorhombic (R–O) phase transition temperature (T_R–O), orthorhombic–tetragonal (O–T) phase transition temperature (T_O–T), and Curie temperature of −110, 190, and 420 °C, respectively. Forming KNN-based ceramics with a multistructure that can assist in domain rotation is one technique for enhancing their piezoelectric properties. This review investigates and introduces KNN-based ceramics with various multistructures. A reactive-templated grain growth method that aligns the grains of piezoceramics in a specific orientation is another approach for improving the piezoelectric properties of KNN-modified ceramics. The piezoelectric properties of the [001]-textured KNN-based ceramics are improved because their microstructures are similar to those of the [001]-oriented single crystals. The improvement in the piezoelectric properties after [001] texturing is largely influenced by the crystal structure of the textured ceramics. In this review, [001]-textured KNN-based ceramics with different crystal structures are investigated and systematically summarized. Full article

Environmentally friendly lead-free K_1-xNa_xNbO₃ (KNN) ceramics possess electromechanical properties comparable to lead-based ferroelectric materials but cannot meet the needs of device miniaturization, and the corresponding thin films lack theoretical and experimental studies. To this end, we developed the nonlinear phenomenological theory for ferroelectric materials to study the effects of non-equiaxed misfit strain on the phase structure, electromechanical properties, and electrical response of K_0.5Na_0.5NbO₃ epitaxial films. We constructed in-plane misfit strain ($u_1-u_2$) phase diagrams. The results show that K_0.5Na_0.5NbO₃ epitaxial film under non-equiaxed in-plane strain can exhibit abundant phase structures, including orthorhombic $a_{1}c$, $a_{2}c$, and $a_1{a}_2$ phases, tetragonal $a_1$, $a_2$, and $c$ phases, and monoclinic $r_{12}$ phases. Moreover, in the vicinity of $a_{2}c-r_{12}$, $a_{1}c-c$, and $a_1{a}_2-a_2$ phase boundaries, K_0.5Na_0.5NbO₃ epitaxial films exhibit excellent dielectric constant ${\epsilon }_{11}$, while at $a_{2}c-r_{12}$ and $a_{1}c-c$ phase boundaries, a significant piezoelectric coefficient $d_{15}$ is observed. It was also found that high permittivity ${\epsilon }_{33}$ and piezoelectric coefficients $d_{33}$ exist near the $a_{2}c-a_2$, $a_1{a}_2-r_{12}$, and $a_{1}c-a_1$ phase boundaries due to the existence of polymorphic phase boundary (PPB) in the KNN system, which makes it easy to polarize near the phase boundaries, and the polarizability changes suddenly, leading to electromechanical enhancement. In addition, the results show that the K_0.5Na_0.5NbO₃ thin films possess a large electrocaloric response at the phase boundary at the $a_1{a}_2-r_{12}$ and $a_{1}c-a_1$ phase boundaries. The maximum adiabatic temperature change $\mathsf{\Delta }T$ is about 3.62 K when the electric field change is 30 MV/m at room temperature, which is significantly enhanced compared with equiaxed strain. This study provides theoretical guidance for obtaining K_1−xNa_xNbO₃ epitaxial thin films with excellent properties. Full article

(K_0.5Na_0.5)NbO₃-based piezoelectric ceramics are of interest as a lead-free replacement for Pb(Zr,Ti)O₃. In recent years, single crystals of (K_0.5Na_0.5)NbO₃ with improved properties have been grown by the seed-free solid-state crystal growth method, in which the base composition is doped with a specific amount of donor dopant, inducing a few grains to grow abnormally large and form single crystals. Our laboratory experienced difficulty obtaining repeatable single crystal growth using this method. To try and overcome this problem, single crystals of 0.985(K_0.5Na_0.5)NbO₃-0.015Ba_1.05Nb_0.77O₃ and 0.985(K_0.5Na_0.5)NbO₃-0.015Ba(Cu_0.13Nb_0.66)O₃ were grown both by seed-free solid-state crystal growth and by seeded solid-state crystal growth using [001] and [110]-oriented KTaO₃ seed crystals. X-ray diffraction was carried out on the bulk samples to confirm that single-crystal growth had taken place. Scanning electron microscopy was used to study sample microstructure. Chemical analysis was carried out using electron-probe microanalysis. The single crystal growth behaviour is explained using the mixed control mechanism of grain growth. Single crystals of (K_0.5Na_0.5)NbO₃ could be grown by both seed-free and seeded solid-state crystal growth. Use of Ba(Cu_0.13Nb_0.66)O₃ allowed a significant reduction in porosity in the single crystals. For both compositions, single crystal growth on [001]-oriented KTaO₃ seed crystals was more extensive than previously reported in the literature. Large (~8 mm) and relatively dense (<8% porosity) single crystals of 0.985(K_0.5Na_0.5)NbO₃-0.015Ba(Cu_0.13Nb_0.66)O₃ can be grown using a [001]-oriented KTaO₃ seed crystal. However, the problem of repeatable single crystal growth remains. Full article

Na_0.5Bi_0.5TiO₃ (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO₃ (BT) was introduced to the 0.94Na_0.5Bi_0.5TiO₃-0.06Bi(Mg_2/3Nb_1/3)O₃ system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na_0.5Bi_0.51TiO₃-xBaTiO₃]-0.06Bi(Mg_2/3Nb_1/3)O₃ (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum P_max (38.29 μC/cm²) and E_b (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of W_rec ~ 1.02 J/cm³ and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications. Full article

Lead-based electro-ceramic compositions are excellent energy storage materials used for high-energy storage density applications in dielectric ceramic capacitors. However, these materials have lead contents in their compositions, making them toxic, with a negative impact on human health and the environment. For this reason, we synthesized a lead-free bismuth-based electro-ceramic perovskite, 0.80(0.92Bi_1/5Na_1/5TiO₃-0.08BaTiO₃)-0.20(Na_0.73Bi_0.09NbO₃₋xTa₂O₅), abbreviated (BNT-BT-NBN_1−xT_x), from mixed oxides with doping of tantalum (Ta) at different concentrations, using a conventional solid-state reaction method. The effects of Ta doping on the phase evolution, microstructure development, and energy storage applications were investigated. Detailed powder X-ray diffraction analysis revealed a pure perovskite phase with Ta doping at ≤0.05. Furthermore, it was observed that excessive addition of Ta has been resulted in secondary phase generation. Scanning electron microscopy validated the development of dense microstructures with a reduced grain size for the Ta concentration of ≤0.01. Electrochemical analysis revealed a maximum polarization (P_m) of ~22 µC/cm² and a recoverable energy density of 1.57 J/cm³ with 80% efficiency for Ta doping at 0.05 with an applied field of 175 kV/cm. These results demonstrate the development of enhanced ferroelectric characteristics in an as-synthesized electro-ceramic perovskite for high-energy storage density applications in electro-ceramic capacitors. Full article

Piezoelectric accelerometers using a lead-free (K,Na)NbO₃ (KNN) piezoceramic modified by a mixture of two Bi-based perovskites, Bi(Na,K,Li)ZrO₃ (BNKLZ) and BiScO₃ (BS), were designed, fabricated and characterized. Ring-shaped ceramics were prepared using a conventional solid-state reaction method for integration into a compression-mode accelerometer. A beneficial rhombohedral–tetragonal (R–T) phase boundary structure, especially enriched with T phase, was produced by modifying intrinsic phase transition temperatures, yielding a large piezoelectric charge coefficient d₃₃ (310 pC/N) and a high Curie temperature T_c (331 °C). Using finite element analyses with metamodeling techniques, four optimum accelerometer designs were obtained with high magnitudes of charge sensitivity S_q and resonant frequency f_r, as evidenced by two key performance indicators having a trade-off relation. Finally, accelerometer sensor prototypes based on the proposed designs were fabricated using the KNN-BNKLZ-BS ceramic rings, which exhibited high levels of S_q (55.1 to 223.8 pC/g) and mounted f_r (14.1 to 28.4 kHz). Perfect charge-to-acceleration linearity as well as broad flat frequency ranges were achieved with excellent reliability. These outstanding sensing performances confirm the potential application of the modified-KNN ceramic in piezoelectric sensors. Full article

Here, (K_0.44Na_0.52Li_0.04)(Nb_0.9−xTa_0.1Sb_x)O₃ [KNL−(N_0.9−xTS_x)] lead-free ceramics with potential technological applications are made through B-position substitution on the perovskite structure by Sb ions. This strategy generates crystal structure changes and stabilizes a tetragonal symmetry, T, giving place to an orthorhombic (O–T) phase boundary close to room temperature. Specifically, our results establish that an increase in relative volume fractions of the T on the O–T phase boundary produces an increase in functional properties. More relevantly, this improvement in properties is accompanied by controlling the grain size. Therefore, an increase in grain size promotes the increased domain size, favoring more domain wall motion and domain switching. Both effects result in an increase in the d₃₃ coefficient. Finally, we believe this work helps to understand the factors that determine the improvement in the functional properties of the KNN–based piezoelectric ceramics. Full article

Lead-free ceramics are promising candidates for replacing lead-based piezoelectric materials such as lead-zirconate-titanate (PZT) if they can compete in dielectric and ferroelectric characteristics. In this work, for lead-free piezoelectric ceramic, 0.74(Bi_0.5Na_0.5TiO₃)-0.26(SrTiO₃) (BNT-ST26) and niobium-substituted (Nb-BNT–ST26) ceramics were synthesized by solid-state reactions. The evolution of niobium substitution to the perovskite phase structure of BNT-ST26 ceramics was confirmed by X-ray diffraction (XRD) analysis and Raman spectra. Electromechanical properties of Nb-BNT-ST26 ceramics initially increased with the addition of niobium up to 0.5% and decreased with a further increase in Nb content. Temperature-dependent dielectric curves showed that the depolarization temperature (T_d) decreased below room temperature because of Nb substitution. The composition with 0.5% Nb yielded a maximum bipolar strain (S_max) of 0.265% and normalized strain of d₃₃* ~ 576 pm/V under an electric field of 4.6 kV/mm at room temperature. At this critical concentration of 0.5% Nb, maximum saturation polarization of 26 μC/cm² was achieved. The dielectric constant with temperature peaks became more diffused and the depolarization temperature decreased with the increasing Nb content. The study concludes that Nb-doped BNT-ST26 is an excellent material for high-temperature, stable, frequency-dependent, lead-free piezoelectric devices. Full article

Lead-free piezoelectric 0.92(K_0.445Na_0.5Li_0.05)NbO₃-0.08BaZrO₃ (KNLN-BZ) ceramics were prepared via conventional sintering. Single-step, 2-step and 3-step temperature-controlled conditions were designed. The structure and electrical properties of ceramics obtained using different temperature-controlled procedures were systematically studied. It was found that ceramic prepared using the 3-step method with a holding time of 20 h showed the highest electrical properties. The Curie temperature was approximately 286 °C, and the dielectric constant and dielectric loss at room temperature were 1350 and 4.5% at the frequency of 1 kHz, respectively. The highest remanent polarization, piezoelectric strain and piezoelectric coefficient, d₃₃*, were obtained 60 °C, indicating a phase transition between ferroelectric phases. Although the ceramics did not show excellent piezoelectric properties, the 3-step sintering method can be considered an effective method to optimize the electrical performances of KNN-based ceramics. Combined with an appropriate composition, ceramics with excellent electrical properties could be obtained. This study provides a path to enhance the density and electrical properties for KNN-based ceramics with simple composition and potential for industry application. Full article