Lead-free Dielectric Ceramics Research Articles

EFFECT OF THE CALCINATION TEMPERATURE ON THE DIELECTRIC PROPERTIES OF 0.94NA0.5BI0.5TIO3–0.06BATIO3 CERAMICS

With the miniaturization of electronic products, the portability and the critical need of clean energy for environment have led to the development of lead-free electroceramics. In this work, lead-free dielectric ceramics of 0.94Na[Formula: see text]Bi[Formula: see text]TiO3–0.06BaTiO3 (NBT–0.06BT) are synthesized by wet solid-phase method. The effects of calcination temperature on phase structure, morphology, densification behavior and dielectric properties are investigated. The XRD results indicate that all samples demonstrate typical diffraction peaks of perovskite structure. The SEM and dielectric analytical results show that high-performance dielectric property of NBT–0.06BT ceramic with dense microstructure and appropriate grain size can be achieved when the calcination temperature is appropriate.

Improved dielectric breakdown strength and energy storage properties in Er2O3 modified Sr0.35Bi0.35K0.25TiO3

The development of lead-free dielectric ceramics with excellent energy storage properties has received extensive research attention. Herein, Er2O3 modified Sr0.35Bi0.35K0.25TiO3 (SBKT) composite ceramic is investigated. As 2 wt.% Er2O3 is added, a certain amount of insulating second phase with fewer regions of high local electric field (numerically simulated by COMSOL) is formed, giving rise to the increase in the dielectric breakdown strength (BDS) due to the increased electrical resistivity and band gap, the decreased average grain size and the decreased leakage current density. This optimal composition exhibits many excellent energy storage properties, such as high energy storage density of 2.59 J/cm3, high recoverable energy storage density (Wrec) of 2.17 J/cm3 with high efficiency (η) of 83.9% at 245 kV/cm, superior stability of temperature (<1% variation of Wrec and η in −25 ~ 150 °C), frequency (~1.6% variation of Wrec with ~3.6% variation of η in 10 ~ 500 Hz) and cycling (almost no change of Wrec and η within 105 cycles), and high discharge energy density of 1.51 J/cm3 with high power density of 39.6 MW/cm3 at 200 kV/cm. In this work, we provide a novel strategy and understanding to design the advanced pulse energy storage ceramics.

Realization of temperature insensitive high energy storage performance via introducing NaNbO3 into NBT-KBT system

The development of lead-free dielectric ceramics with temperature insensitive high discharge energy density (Wdis) and high energy efficiency (η) are highly demanded for the practical applications in energy storage capacitors. In this work, we have designed and fabricated the NaNbO3 modified Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT-KBT-xNN) relaxor ferroelectrics. The addition of metastable antiferroelectric NN into the NBT-KBT matrix leads to enhanced relaxor behavior and improved breakdown strength. As a result, the x = 0.4NN specimen not only showed optimal integrated energy storage properties with a large Wdis of 1.7 J/cm3 and η of 90% under a moderate electric field of 150 kV/cm, but also exhibited superior temperature stability with the variation of Wdis within ±15% and η more than 80% from −50 °C to 150 °C. All these properties indicate that NN modified NBT-KBT ceramic was a promising candidate for the practical application of energy storage capacitors.

Effective Strategy to Achieve Excellent Energy Storage Properties in Lead-Free BaTiO3-Based Bulk Ceramics.

Although extensive studies have been done on lead-free dielectric ceramics to achieve excellent dielectric behaviors and good energy storage performance, the major problem of low energy density has not been solved so far. Here, we report on designing the crossover relaxor ferroelectrics (CRFE), a crossover region between the normal ferroelectrics and relaxor ferroelectrics, as a solution to overcome the low energy density. CRFE exhibits smaller free energy and lower defect density in the modified Landau theory, which helps to obtain ultrahigh energy density and efficiency. The (1-x)Ba0.65Sr0.35TiO3-xBi(Mg2/3Nb1/3)O3 ((1-x)BST-xBMN) (x = 0, 0.08, 0.1, 0.18, 0.2) ceramic was synthesized by a solid-state reaction method. The solid solutions exhibit dielectric frequency dispersion, which suggests typical relaxor characteristics with the increasing BMN content. The crossover ferroelectrics of 0.9BST-0.1BMN ceramic possesses a high energy storage efficiency (η) of 85.71%, a high energy storage density (W) of 3.90 J/cm3, and an ultrahigh recoverable energy storage density (Wrec) of 3.34 J/cm3 under a dielectric breakdown strength of 400 kV/cm and is superior to other lead-free BaTiO3 (BT)-based energy storage ceramics. It also exhibits strong thermal stability in the temperature range from 25 to 150 °C under an electric field of 300 kV/cm, with the fluctuations below 3% and with the energy storage density and energy efficiency at about 2.8 J/cm3 and 82.93%, respectively. The enhanced recoverable energy density and breakdown strength of BT-based materials with significantly high energy efficiency make it a promising candidate to meet the wide requirements for high power applications.

Relaxor/antiferroelectric composites: a solution to achieve high energy storage performance in lead-free dielectric ceramics

Compared with the relaxor with pinched P–E loops, the relaxor/antiferroelectric (RE/AFE) composites have narrower and oblique curves, proving the design of RE/AFE is an effective method to improve the energy storage properties of dielectric ceramics.

Dielectric, ferroelectric and high energy storage behavior of (1–&lt;i&gt;x&lt;/i&gt;)K&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;–&lt;i&gt;x&lt;/i&gt;Bi(Mg&lt;sub&gt;0.5&lt;/sub&gt;Ti&lt;sub&gt;0.5&lt;/sub&gt;)O&lt;sub&gt;3&lt;/sub&gt; lead free relaxor ferroelectric ceramics

Lead-free dielectric ceramics with high energy-storage density and efficiency are ideal energy materials for sustainable development of the enery resource. In this paper, (1–&lt;i&gt;x&lt;/i&gt;)K&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;–&lt;i&gt;x&lt;/i&gt;Bi(Mg&lt;sub&gt;0.5&lt;/sub&gt;Ti&lt;sub&gt;0.5&lt;/sub&gt;)O&lt;sub&gt;3&lt;/sub&gt; ((1–&lt;i&gt;x&lt;/i&gt;)KNN-&lt;i&gt;x&lt;/i&gt;BMT, &lt;i&gt;x&lt;/i&gt; = 0.05, 0.10, 0.15, 0.20) lead-free relaxor ferroelectric ceramics are prepared by the traditional solid-state method. The effects of BMT on the phase structure, microstructure, dielectric properties and energy storage behavior of KNN based ceramics are studied. With the increase of BMT content, the crystal structures of (1–&lt;i&gt;x&lt;/i&gt;)KNN-&lt;i&gt;x&lt;/i&gt;BMT ceramics gradually change from orthorhombic to pseudo-cubic phase, and transform into cubic phase finally. The addition of BMT can suppress grain growth of the ceramics, resulting in the average grain size decreasing from 850 to 195 nm when &lt;i&gt;x&lt;/i&gt; increases from 0.05 to 0.20. Dielectric properties exhibit that the Curie temperature decreases with BMT content increasing, and dielectric peak at Curie temperature is broadened due to the addition of BMT. In addition, ferroelectric properties demonstrate that the addition of BMT reduces the remnant polarization (&lt;i&gt;P&lt;/i&gt;&lt;sub&gt;r&lt;/sub&gt;) and coercive field (&lt;i&gt;E&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;) of the ceramics. The results indicate that (1–&lt;i&gt;x&lt;/i&gt;)KNN-&lt;i&gt;x&lt;/i&gt;BMT ceramics transform from ferroelectric to relaxor ferroelectric phase. Based on the calculation of hysteresis loop, the best energy storage performance is obtained at &lt;i&gt;x&lt;/i&gt; = 0.15, of which the recoverable energy storage density (&lt;i&gt;W&lt;/i&gt;&lt;sub&gt;rec&lt;/sub&gt;) and the energy storage efficiency (&lt;i&gt;η&lt;/i&gt;) are 2.25 J·cm&lt;sup&gt;–3&lt;/sup&gt; and 84% at its dielectric breakdown strength of 275 kV·cm&lt;sup&gt;–1&lt;/sup&gt;. Meanwhile, the ceramic with &lt;i&gt;x&lt;/i&gt; = 0.15 exhibits good stability in a frequency range of 1–50 Hz, with an energy density variation of less than 5%, and temperature stability in a range of 25–125 ℃ with change of less than 8%. Moreover, based on direct measurement, the energy storage density (&lt;i&gt;W&lt;/i&gt;&lt;sub&gt;dis&lt;/sub&gt;) of the ceramic with &lt;i&gt;x&lt;/i&gt; = 0.15 is 1.54 J·cm&lt;sup&gt;–3&lt;/sup&gt;, and the discharge time is only 88 ns. The research shows that (1–&lt;i&gt;x&lt;/i&gt;)KNN-&lt;i&gt;x&lt;/i&gt;BMT ceramics have a wide application prospect in the field of environmentally friendly capacitors with high energy storage density.

Achieve ultrahigh energy storage performance in BaTiO3–Bi(Mg1/2Ti1/2)O3 relaxor ferroelectric ceramics via nano-scale polarization mismatch and reconstruction

Development of lead-free dielectric ceramics with large recoverable energy storage density (Wrec), high energy storage efficiency (η) and wide usage temperature range is of great significance to improve the overall performance of power electronic devices. Despite the numerous research efforts, performance of existing lead-free dielectric ceramics is barely satisfactory. Herein, an effective strategy to achieve ultrahigh energy storage performance via nano-scale polarization mismatch and reconstruction is proposed. By developing solid solutions of A-site coupling and B-site coupling ferroelectrics, polarization mismatch and ultrahigh energy storage performance can be realized in intermediated compositions. It is demonstrated that ultrahigh energy storage performance with a η of 93% and a Wrec of 4.49 J/cm3 is achieved in the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 (0.6BT-0.4BMT) ceramic, which is a record high energy storage property in lead-free relaxor ferroelectric bulk ceramics. Excellent temperature stability with a variation of Wrec and η less than 5% is also realized in a wide temperature range from 30 °C to 170 °C. Such an ultrahigh energy storage performance not only verifies our strategy, but also makes the 0.6BT-0.4BMT ceramic a promising candidate material for energy storage. Moreover, of particular significance is that this work provides an effective method to design novel high performance dielectric ceramics for future energy storage devices.

A new family of sodium niobate-based dielectrics for electrical energy storage applications

Although tremendous achievements have been made in enhancing recoverable energy storage density (Wrec) of lead-free dielectric ceramics for electrical energy storage applications in recent years, these ceramics with high Wrec still have two disadvantages: complex chemical composition and difficult preparation process. In this work, we selected NaNbO3 (NN)-based ceramics as base materials and used Bi2O3 as a sintering aid to reduce porosity and enhance dielectric breakdown strengths. Encouragingly, high Wrec, simple chemical composition and facile preparation process were simultaneously realized in 0.77NaNbO3-0.23BaTiO3 (0.77NN-0.23BT) ceramics. A large Wrec of 1.5 J cm−3 at 175 kV cm−1 and excellent thermal stability (variation of Wrec < 15% over the temperature range of 20˜140 °C) were simultaneously achieved in 0.77NN-0.23BT ceramics. More importantly, this work could bring out the development of a series of NN-based ceramics for electrical energy storage in the future such as NN-ABO3 (A = Ca and Sr; B = Ti and Zr).

Grain size engineered lead-free ceramics with both large energy storage density and ultrahigh mechanical properties

Lead-free dielectric ceramics with both a high recoverable energy storage density (Wrec) and excellent mechanical performance are highly desirable for practical applications in next-generation advanced pulsed power capacitors (APPCs). However, lead-free dielectric ceramics exhibit low Wrec owing to small breakdown strength (Eb) and poor mechanical properties because of their large pore size and low relative density, which restrict devices miniaturization and operation in severe environments. Here, we propose a new strategy, namely, grain size engineering, to develop K0.5Na0.5NbO3 (KNN)-based ceramics with both an extremely high Wrec and large mechanical properties. Interestingly, a large Wrec of 2 J cm−3 was achieved in 0.9K0.5Na0.5NbO3-0.1BiFeO3 (0.9KNN-0.1BF) ceramics at 206 kV cm−1, which is superior to other lead-free dielectric ceramics under moderate electric fields (<220 kV cm−1). Encouragingly, the hardness (H) of 0.9KNN-0.1BF ceramics reached 2.45 GPa, which is approximately 5 times higher than that of pure KNN ceramics (0.45 GPa). Moreover, the bending strength (σf), elastic modulus (E) and compression strength (σc) of 0.9KNN-0.1BF ceramics are also enhanced by ~200% over those of pure KNN ceramics. Compared with other lead-free dielectric ceramics, grain size engineered 0.9KNN-0.1BF is the first high-performance ceramic material with both an exceptionally large Wrec and ultrahigh mechanical properties, which can accelerate the practical use of APPCs. Most importantly, the findings in this work will not only provide a guideline for developing other lead-free dielectric ceramics with both extremely high energy storage properties and superior mechanical performance but also open a window to the mechanical properties of dielectric ceramics for APPCs.

Constructing layered structures to enhance the breakdown strength and energy density of Na0.5Bi0.5TiO3-based lead-free dielectric ceramics

The improvement of breakdown strength for NBT-based ceramics is currently the main challenge in applications of lead-free dielectric energy-storage materials.

Stable dielectric properties of Na1+xBiTi6O14+0.5x (x = −0.02, − 0.01, 0.01, 0.02) ceramics with low loss and high operating temperature

New lead-free dielectric ceramics, Na1+xBiTi6O14+0.5x (x = −0.02, − 0.01, 0.01, 0.02), were prepared by the conventional solid-state method. Micro-structural and electrical properties of Na1+xBiTi6O14+0.5x were studied. XRD showed all the samples exhibited a single structured phase. Grains decreased at the beginning, then grew with the increasing x content in SEM. Impedance spectra (IS) analysis evidenced the phenomena that the dielectric permittivity increased firstly, then decreased, while the loss had the opposite trend. Z* plots showed that Na1+xBiTi6O14+0.5x ceramics were a kind of dielectrics. The activation energy (Ea) could be calculated in the range of 1.53–1.65 eV, which indicated they were dielectric ceramics. Na1+xBiTi6O14+0.5x ceramics (x = 0.01) sintered at 1040 °C showed prominent dielectric properties with a dielectric constant of 25.76, loss of 0.07%, Ea of 1.65 eV, density of 3.463 g/cm3, impedance of 0.532 MΩ cm, -Z′′max of 0.1958 MΩ cm, capacitance of 5.56 pF/cm (600 ℃), which were enhanced much compared with other samples. The existence of dielectric properties with high dielectric constant, low dielectric loss and wide operating temperature range makes it possible to develop the ceramics into high-temperature capacitors.

Silver Niobate Lead-Free Antiferroelectric Ceramics: Enhancing Energy Storage Density by B-Site Doping.

Lead-free dielectric ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric ceramics with double ferroelectric hysteresis loops have been proved to be potential candidates for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3 J/cm3 and high thermal stability with minimal energy density variation (<10%) over a temperature range of 20-120 °C have been achieved in W-modified AgNbO3 ceramics. It is revealed that the W6+ cations substitute the B-site Nb5+ and reduce the polarizability of B-site cations, leading to the enhanced antiferroelectricity, which is confirmed by the polarization hysteresis and dielectric tunability. It is believed that the polarizability of B-site cations plays a dominant role in stabilizing the antiferroelectricity in AgNbO3 system, in addition to the tolerance factor, which opens up a new design approach to achieve stable antiferroelectric materials.

Enhanced Energy-Storage Density and High Efficiency of Lead-Free CaTiO3-BiScO3 Linear Dielectric Ceramics.

A novel lead-free (1 - x)CaTiO3-xBiScO3 linear dielectric ceramic with enhanced energy-storage density was fabricated. With the composition of BiScO3 increasing, the dielectric constant of (1 - x)CaTiO3-xBiScO3 ceramics first increased and then decreased after the composition x > 0.1, while the dielectric loss decreased first and increased. For the composition x = 0.1, the polarization was increased into 12.36 μC/cm2, 4.6 times higher than that of the pure CaTiO3. The energy density of 0.9CaTiO3-0.1BiScO3 ceramic was 1.55 J/cm3 with the energy-storage efficiency of 90.4% at the breakdown strength of 270 kV/cm, and the power density was 1.79 MW/cm3. Comparison with other lead-free dielectric ceramics confirmed the superior potential of CaTiO3-BiScO3 ceramics for the design of ceramics capacitors for energy-storage applications. First-principles calculations revealed that Sc subsitution of Ti-site induced the atomic displacement of Ti ions in the whole crystal lattice, and lattice expansion was caused by variation of the bond angles and lenghths. Strong hybridization between O 2p and Ti 3d was observed in both valence band and conduction band; the hybridization between O 2p and Sc 3d at high conduction band was found to enlarge the band gap, and the static dielectric tensors were increased, which was the essential for the enhancement of polarization and dielectric properties.

Good thermal stability and improved piezoelectric properties of (K0.5Na0.5)NbO3–Bi(Mg0.75W0.25)O3 solid solutions

In this paper, (1 − x)(K0.5Na0.5)NbO3–xBi(Mg0.75W0.25)O3 (x = 0–0.015) lead-free dielectric ceramics were investigated. XRD analysis certified that the Bi(Mg0.75W0.25)O3 has diffused into (K0.5Na0.5)NbO3 to fabricate a new solid solution. The addition of Bi(Mg0.75W0.25)O3 depressed the orthorhombic–tetragonal phase transition temperature from 210 to 176 °C and tetragonal–pseudocubic phase transition temperature (Curie point) from 419 to 400 °C. As x = 0.005, the ceramics exhibited high relative permittivity (e ~ 1325), low dielectric loss (tan δ < 2.9%) tan δ stability (Δe/e168°C ≤ ±15%) in the temperature range of 168 ~ 369 °C. Especially, the ceramics also showed optimized piezoelectric constant (d 33 = 122 pC N−1) and remnant polarization (Pr = 32.57 μC cm–2). These results indicated that the BMW added ceramics have potential applications in ferroelectric and thermal stability devices.

Diffuse phase transition, piezoelectric and optical study of Bi0·5Na0·5TiO3 ceramic

Bismuth sodium titanate, Bi0·5Na0·5TiO3 (BNT) is considered to be an excellent candidate for a key material of lead-free dielectric ceramics. In this study, we propose the dielectric and optical study of single phase BNT powder prepared by solid-state reaction route. The phase formation and structural study were done by X-ray diffraction (XRD) which shows well developed crystallite with a pure perovskite phase. The ceramic was sintered at different temperatures from 1050°C to 1175°C to study the effect of sintering temperature on the morphology and density. It was found that the sample sintered at 1150°C shows the highest density. The microstructure of the ceramic was investigated by scanning electron microscopic (SEM) technique. The temperature-dependent dielectric study of the sample sintered at 1150°C was done in the frequency range of 50 kHz–1 MHz which shows a diffuse phase transition. The piezoelectric constant (d 33) was found to be 41 pCN − 1. The P–E hysteresis loop confirms the ferroelectric behaviour in the ceramic. The UV–Vis spectrum indicated that the Bi0·5Na0·5TiO3 ceramic has an optical band gap of 2·94 eV.

Ferroelectric and Dielectric Properties of (1−x)K0.5Na0.5NbO3 –(x/5)Na0.2K2.8Li2Nb5O15 Composite Ceramics

Alkaline niobates ANbO3 (A = K, Li and Na) display multiple phases coexisting, i.e., perovskite (Pe), LiNbO3, completely filled tetragonal tungsten-bronze (cf-TTB) structures. The composite ceramics of K0.5Na0.5NbO3 (KNN) and Na0.2K2.8Li2Nb5O15 (NKLN) were explored as a candidate for the lead-free dielectric and piezoelectric composite ceramics with only the Pe and the cf-TTB structure coexisting. The Pe and the cf-TTB structure showed the ferroelectric distortions along the c-axis with pseudo-tetragonal symmetry. The (1-x)KNN-(x/5)NKLN (x = 0–0.1) composite ceramics displayed the ferroelectric hysteresis at room temperature. We studied the two phases mixing mechanism by comparing the structural and ferroelectric properties.

Diffusion phase transition and dielectric characteristics of Bi 0.5Na 0.5TiO 3–Ba(Hf,Ti)O 3 lead-free ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi 0.5Na 0.5TiO 3, BNT)-barium hafnate titanate (Ba(Hf 0.05,Ti 0.95)O 3, BHT5) were prepared by a two-step sintering process. The BNT–BHT5 ceramics sintered at 1180 ∘C for 2 h in air showed a pure perovskite structure. The results show that the phase transition temperature ( T m ) is suppressed dramatically with a small amount of BHT5 content and then decreased gradually with more BHT5 in the compounds. The diffusion of the phase transition is more distinct for the samples around the morphotropic phase boundary (MPB) of BNT–BHT5 system. In the (1− x)BNT– xBHT5 system, high piezoelectric constants were obtained at x = 0.08 , which is a tetragonal phase near the MPB region. The BNT–BHT5 system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric ceramics.