Pb-free Ceramics Research Articles

Strong Local Polarization Fluctuations Enabled High Electrostatic Energy Storage in Pb-Free Relaxors.

Electrostatic energy-storage ceramic capacitors are essential components of modern electrified power systems. However, improving their energy-storage density while maintaining high efficiency to facilitate cutting-edge miniaturized and integrated applications remains an ongoing challenge. Herein, we report a record-high energy-storage density of 20.3 J cm-3 together with a high efficiency of 89.3% achieved by constructing a relaxor ferroelectric state with strongly enhanced local polarization fluctuations. This is realized by incorporating highly polarizable, heterovalent, and large-sized Zn and Nb ions into a Bi0.5Na0.5TiO3-BaTiO3 ferroelectric matrix with very strong tetragonal distortion. Element-specific local structure analysis revealed that the foreign ions strengthen the magnitude of the unit-cell polarization vectors while simultaneously reducing their orientation anisotropy and forming strong fluctuations in both magnitude and orientation within 1-3 nm polar clusters. This leads to a particularly high polarization variation (ΔP) of 72 μC cm-2, low hysteresis, and a high effective polarization coefficient at a high breakdown strength of 80 kV mm-1. This work has surpassed the current energy density limit of 20 J cm-3 in bulk Pb-free ceramics and has demonstrated that controlling the local structure via the chemical composition design can open up new possibilities for exploring relaxors with high energy-storage performance.

High-Entropy Strategy for Improved Mechanical and Energy Storage Properties in BaTiO3-BiFeO3-Based Ceramics.

Dielectric capacitors are employed extensively due to their exceptional performance, including a rapid charge-discharge speed and superior power density. However, their practical implementation is hindered by constraints in energy-storage density (ESD), efficiency (ESE), and thermal stability. To achieve domain engineering and improved relaxor behavior in 0.67BiFeO3-0.33BaTiO3-based Pb-free ceramics, the concerns have been addressed here by employing a synergistic high-entropy strategy involving the design of the composition of Sr(Mg1/6Zn1/6Ta1/3Nb1/3)O3 with B-site multielement coexistence and high configuration entropy. Remarkably, in (0.67-x)BiFeO3-0.33BaTiO3-xSr(Mg1/6Zn1/6Ta1/3Nb1/3)O3 ceramics with x = 0.08, a good ESE (η) of 75% and a recoverable ESD (Wrec) of 2.4 J/cm3 at 190 kV/cm were attained together with an ultrahigh hardness of ∼7.2 GPa. The high-entropy strategy, which is tailored by an increase in configuration entropy, can be attributed to the superior mechanical and ES properties. It also explains the enhanced random field and relaxation behavior, the structural coexistence of ferroelectric rhombohedral (R3c) and nonpolar pseudocubic (Pm-3m) symmetries, the decreased domain size, and evenly distributed polar nanoregions (PNRs). Moreover, improved thermal stability and outstanding frequency stability are also obtained. By boosting the configuration entropy, BiFeO3-BaTiO3 materials dramatically improved their complete energy storage performance. This suggests that designing high-performance dielectrics with high entropy can be a convenient yet effective technique, leading to the development of advanced capacitors.

The enhancement of energy storage performance of BaTiO3–Bi(Mg0·5Ti0.5)O3 Pb-free ceramics via an optimized viscous polymer process route

In this study, the viscous polymer processing (VPP) technique is implemented to optimize the characteristics of bulk (1-x)BaTiO3-xBi(Mg0·5Ti0.5)O3 (BT-xBMT) lead-free relaxor ferroelectric ceramics, with a focus on enhancing the recoverable energy storage density (Wrec), improving breakdown strength resistance (Eb), and increasing storage efficiency (η). The influence of polyvinyl alcohol (PVA) inclusion in the VPP process on the resulting dielectric ceramics is thoroughly investigated, covering rheological, dielectric, and ferroelectric properties. The results reveal that a gradual increase in PVA quantity during the VPP process effectively improves the density of ceramic blanks. However, an excess of PVA leads to void formation in the ceramic blanks post-debinding, hindering the achievement of a dense structure in the final ceramics and causing performance degradation. The resulting BT-0.405BMT-40 wt% PVA ceramic showed excellent storage performance, with Wrec, η, and Eb of 6.55 J/cm3 81.45 %, and 480 kV/cm, respectively. In comparison to bulk BT-0.405BMT ceramics, there is a notable 2.47-fold increase in Wrec and a 1.92-fold increase in Eb, accompanied by a substantial improvement in η. Moreover, the BT-BMT-40 wt% PVA ceramic exhibits favorable temperature stability (30–150 °C), frequency stability (1–50 Hz), and commendable charge/discharge performance.

Enhancement of mechanical and energy storage properties of Ba(Ti0.8Co0.2)O3 Pb-free ceramics by addition of Nd3+ ions

Preparation of composites of (Ba1−xNdx)(Ti0.8Co0.2)O3 (abbreviated as BNTC) (x:0.1, 0.2 and 0.3 mol%) Pb-free ceramics through a conventional solid-state reaction method.

Giant electric field-induced strain and structure evolution of NaTaO3-modified 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 Pb-free ceramics

To acquire giant electric field-induced strain in non-Pb materials is attracting a great deal of attention in the past decade. In the current investigation, the crystal and domain structures as well as the electrical performances of (1-x) (0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xNaTaO3 (BNBT-xNT) specimens were systematically studied to achieve enhanced strain. The introduction of NT makes the phase structure transit from rhombohedral-tetragonal to pseudo-cubic structure. The original domain structure of BNBT is destroyed, and the disorder degree of the local structure increases. Simultaneously, the remnant polarization, coercive field, and piezoelectric coefficients were significantly decreased. The transition from ferroelectric to ergodic relaxation can be effectively modified, thus lowering the transition zone to room temperature. Finally, the BNBT-3NT ceramics achieve marked strain coefficients at room temperature, with a maximum strain of 0.394% under 65 kV/cm and a d33* of 606 pm/V.

Excellent dielectric energy storage properties of barium titanate based Pb-free ceramics through composition modification and processing improvement

To acquire electric capacitors with enhanced energy storing performance, a composition embellishment and process improvement strategy were adopted. A serial of lead-free (Ba0.875Bi0.125) (Li0.0625Nb0.0625Ti0.875)O3(BBLNT) ceramics were prepared via both conventional solid-state method and viscous polymer processing technology (VPP). The BBLNT-VPP ceramics achieved an ultrahigh energy storing density of 5.34 J/cm3 and a reasonable efficiency of 88% at 470 kV/cm. In addition, the ceramics have particularly extraordinary temperature stability of Wrec2.8 J/cm3, △η2.5% over 30–150 °C, as well as excellent frequency stability with Wrec3.46 J/cm3, η88%, △Wrec±2.7% and △η±4% in the range of 5–300 Hz. Meanwhile, the power density of the ceramic remained above 84.04 MW/cm3 when the temperature was increased from room temperature to about 150 °C, indicating the ceramics possess great promise. Therefore, the BBLNT-VPP ceramics with excellent properties obtained in this work can be potentially applied in dielectric capacitors.

Enhanced dielectric energy storage performance of A-site Ca2+-doped Na0.5Bi0.5TiO3–BaTiO3–BiFeO3 Pb-free ceramics

(1-x) (0.98Na0.5Bi0.5TiO3–0.01BaTiO3–0.01BiFeO3)–xCaTiO3 (NBB-xCT) ceramics were produced using traditional solid-state synthesis methods. The surface morphology, domain structure, and electrical properties of the ceramic samples were systematically studied. In addition, the temperature and frequency stabilities of the NBB-15CT sample at 200 kV/cm were tested. Generally, NBB-xCT ceramics exhibit a typical single perovskite phase structure. The results indicate that the NBB-15CT ceramics showed a high energy density of 3.14 J/cm3 at 250 kV/cm. The piezoresponse force microscopy (PFM) results showed that the addition of CT broke the macrodomains of the 0.98Na0.5Bi0.5TiO3-0.01BaTiO3-0.01BiFeO3 ceramic and helped to form nanodomains, leading to an improved energy storage performance. The above performance indicates that the specimens possess very good temperature-and frequency-dependent energy storage performances at 30–150 °C and 1–100 Hz. Moreover, the electric energy storage and release in the NBB-15CT ceramic indicated that the power density could reach 55.30 MV/cm3 at 180 kV/cm. Therefore, the NBB-15CT ceramic is a promising material for electrical capacitors.

Achieving Excellent Electrocaloric Properties Near Room Temperature in Ba0.75sr0.25tio3 Based Pb-Free Ceramics by Phase Modification

Achieving Excellent Electrocaloric Properties Near Room Temperature in Ba0.75sr0.25tio3 Based Pb-Free Ceramics by Phase Modification

Microstructure and Piezoelectric Properties of 0.97(Na, K, Li)(Nb, Sb, Ta)O₃-0.03(Bi, Na, Sr)ZrO₃ Ceramics Doped with Boron Oxide for Piezoelectric Actuator.

In this study, with the motivation of developing low temperature sintered Pb-free ceramics for use in piezoelectric actuators, 0.97(Na0.52K0.443Li0.037)(Nb0.923Sb0.04Ta0.037)O₃ - 0.03 (Bi0.5Na0.5)0.9 (Sr)0.1ZrO₃ ceramics were manufactured and their piezoelectric properties analyzed. All specimens doped with boron oxide showed a typical pure perovskite structure. The ceramics with x = 0.1 composition showed a co-existence of R-T phases. When boron oxide is doped at 0.1 wt%, excellent physical properties of d33 = 270 pC/N εr = 1386, kp = 0.416, and Qm = 130 were obtained making the ceramic ideal for use in piezoelectric actuators.

Dielectric and piezoelectric properties of 0.965(Na0.5K0.5)0.97Li 0.03(Nb0.96Sb0.04)O3-0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics with CuO addition

Recently, piezoelectric speakers have been widely researched for smartphone application. Accrordingly, in this study, in order to develop the low temperature sintering Pb-free ceramics, the 0.965(Na0.5K0.5)0.97Li0.03(Nb0.96Sb0.04)O3-0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics for these devices were manufactured as a function of CuO addition and the their physical properties were investigated. At the manufactured ceramics, the coexistence phases of rhombohedral and tetragonal(R-T) phase were appeared. An average grain size of the specimen increased according to the increase of CuO addition until 1.5 mol% due to the formation of a liquid phase. The composition ceramics added with 2 mol% CuO showed the excellent physical properties of density = 4.496g/cm3, kp = 0.391, Qm = 88, εr = 1705, and d33 = 241pC/N. These results show that the ceramics added with 2 mol% CuO is an attractive candidate for lead-free piezoelectric actuator application.

Dielectric and Piezoelectric Properties of (Na,K,Li)(Nb,Sb)O3–(Bi,Na)ZrO3 Ceramics with the Addition of BiFeO for Piezoelectric Speaker

In this study, in order to develop Pb-free ceramics capable of being sintered at low temperature, the 0.965((Na0.5K0.5)0.97Li0.03)(Nb0.93Sb0.07)O3–0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics were manufactured according to BiFeO addition and the their dielectric and piezoelectric properties were investigated. According to the increase of BiFeO addition, the dielectric constant was increased and Curie temperature was maintained constantly. The composition ceramics with x = 0.05 showed the excellent physical properties: density = 4.50 g/cm3, kp = 0.429, Qm = 59, er = 2737, and d33 = 316 pC/N. It is considered that the ceramics with x = 0.05 is an attractive candidate for piezoelectric speaker.

Piezoelectricity in perovskite-type pseudo-cubic ferroelectrics by partial ordering of off-centered cations

A large piezoelectric response in ferroelectric ceramics is typically associated with extrinsic contributions from ferroelectric domain structures. However, such domain structures cannot be expected in systems with pseudo-cubic symmetry. In this study, we determine the mechanism of significant piezoelectricity and ferroelectricity in 0.3BaTiO3–0.1Bi(Mg1/2Ti1/2)O3–0.6BiFeO3 ceramic with a perovskite-type pseudo-cubic symmetry. Synchrotron radiation X-ray diffraction reveals that the Bi ions in this ceramic essentially prefer to be off-centered at six sites by approximately 0.4 Å, in the cubic <100> directions. A phase transition occurs at TC ~725 K. However, the crystal seems to present a cubic symmetry even at room temperature. The large piezoelectric response is caused by the combinational partial ordering of the off-centered Bi ions, adapted to any direction of the applied electric field to the ceramic grains. The proposed mechanism for the emergence of a high polarization in the above system will enable designing novel Pb-free ceramics by controlling the fluctuated and off-centered ions under an applied electric field.

Energy storage performance in Dy doped Na0.425Bi0.425Ca0.15TiO3 Pb-free ceramics

High capacity for the dielectric capacitors are necessary for practical applications. Additionally, dielectric capacitors should have some degree of temperature and frequency stability to allow them to adapt to environmental changes. To fulfil these requirements, Na0.425Bi0.425Ca0.15TiO3-xDy (x = 0, 2, 5, and 10 at‰) (NBCT-xDy) energy storage ceramics were produced using a traditional solid-state synthesis method. NBCT-5Dy achieved an excellent energy storage density of 2.35 J/cm3 and a good efficiency of 78.32% at 210 kV/cm. In addition, the sample was tested at 150 kV/cm under variable temperature and frequency conditions, showed a stable energy storage density of ~1.3 J/cm3 and maintains excellent efficiency at 30–150 °C and 0.2–200 Hz. Furthermore, the dielectric constant of the sample was measured at 0–40 kV/cm, and exhibited less than 2% change over this range. These results confirmed that the sample had excellent energy storage density and good stability. In the pulse discharge performance test, a high power density (46.31 MW/cm3 at 150 kV/cm) was obtained, indicating that this material has great application prospects in the pulse capacitor field in the future.

Investigation of electrical and electric energy storage properties of La -doped Na0.3 Sr0.4Bi0.3TiO3 based Pb-free ceramics

Na0.3Sr0.4Bi0.3TiO3 with various concentrations in La modified ceramic specimens were fabricated using a traditional die-press process. All the obtained NBT-ST-xLa ceramics exhibited a typical perovskite structure with a single phase, and the grain sizes were found to be uniform and fine. The electric breakdown strength of the sample after La doping increased significantly. In particular, the ceramic electric breakdown strength of x = 0.02 component reached 190 kV/cm, the stored energy density reached 1.67 J/cm3, and the efficiency was stable and greater than 80%. In addition, the ceramic with x = 0.02 La also exhibited an excellent temperature, frequency stability, and good fatigue resistance. More specific and detailed analysis were conducted in this study.

Enhanced electrical properties and energy storage performances of NBT-ST Pb-free ceramics through glass modification

Abstract In the current study, a strategy incorporating with glass addition has been employed to enhance the energy storage performance of 0.5(Na0.5Bi0.5TiO3)-0.5SrTiO3 Pb-free bulk ceramics through a traditional electroceramic processing route. The strategy is to introduce liquid sintering to dielectric ceramics, and hence lower the sintering temperature, finally resulting in refined grains and enhanced electrical properties. The detailed impacts of different additive contents on the phases, microstructure, electrical properties and energy storage and release of NBT-ST specimens were deeply and systemically studied. The results indicate as the glass content increases, the grains of NBT-ST-xBBZ ceramics are remarkably refined, and the dielectric constant and loss decrease. After glass addition, the breakdown strength of ceramics is nearly doubled. When the doping content of the glass is 1 wt%, the energy density reaches 1.67 J/cm3 under an electric field strength of 200 kV/cm. After further testing of NBT-ST-0.01BBZ ceramic, it exhibits good temperature (from 30 to 150 °C), frequency (0.2–100 Hz) and cycle (104) stability.

Structure evolution, ferroelectric properties, and energy storage performance of CaSnO3 modified BaTiO3-based Pb-free ceramics

Pb-free bulk (1-x)BaTiO3-xCaSnO3, (x = 0.05, 0.10, 0.15, 0.20 mol) ceramics were fabricated with traditional electroceramic processing technology, and the influences of CaSnO3 on the microstructure, morphology, and electrical performance were systemically investigated. All doped ceramics exhibit a single perovskite structure according to the X-ray diffraction (XRD) and Raman spectra. Moreover, the modification mechanism of co-doping with Ca and Sn was investigated. CaSnO3 effects the grain refinement significantly, shifts the phase transition peak to lower temperatures, and enhances the relaxor behaviour. According to the impedance spectra, its effect on the insulation performance transforms from grain boundary contribution to grain contribution as the substitution content increases. When the substitution content is 0.15 mol, the maximum dielectric breakdown strength (BDS) and the maximum energy storage density reach 230 kV/cm, and 1.57 J/cm3, respectively. Furthermore, the BT-0.15CS ceramic shows very good temperature, frequency, fatigue resistance, and charge-discharge performances, which makes it suitable for energy storage applications.

Coexistence of excellent piezoelectric performance and thermal stability in KNN-based lead-free piezoelectric ceramics

With close attention being paid to environmental issues and more legislation coming into force to limit the application of Pb-based materials, accelerating research on lead-free piezoelectric ceramics has become increasingly requisite and urgent. Herein, we have devised and synthesized (1-x)(K0.5Na0.5)0.98Ag0.02(Nb0.96Sb0.04)O3-x(Bi0.5Na0.5)ZrO3 [abbreviated as (1-x)KNANS-xBNZ, x = 0.01, 0.02, 0.03, 0.035, 0.04, 0.045, 0.05, 0.06] Pb-free ceramics. Phase transition, microstructure, electrical properties, and temperature stability of the ceramics have been comprehensively investigated. The findings illustrate that optimizing BNZ content can give rise to a rhombohedral-tetragonal (R-T) phase boundary when x = 0.04, 0.045, 0.05. The specimens with x = 0.04 show improved piezoelectric properties (d33 ~ 440 pC/N, kp ~ 53%, TC ~ 250 °C, d33* ~ 553 pm/V) and good temperature stability. The overall performance is excellent and indicates that (1-x)KNANS-xBNZ ceramics have great potential for replacing their lead-based counterparts.

Study of the structure, electrical properties, and energy storage performance of ZnO-modified Ba0.65Sr0.245Bi0.07TiO3 Pb-free ceramics

Barium titanate ceramic is frequently used as a ferroelectric material and can be applied in the pulse power field in energy storage devices. Its properties, including dielectric, ferroelectric, and energy storage properties, can be significantly improved through doping. In this work, we prepared a series of (1-x)Ba0.65Sr0.245Bi0.07TiO3-xZnO (x = 0.005, 0.01, 0.02, 0.03) lead-free bulk relaxor ferroelectric ceramics by a traditional die-pressing processing route. The uniformity of the grain sizes for these ceramics was improved, and the grains were refined when a certain amount of ZnO was introduced into BaTiO3-based ceramics. In addition, the breakdown strength was improved in the case where the relaxor behavior was not significantly improved. It should be noted that the sample doped with 0.02 mol Zn showed the maximum room-temperature storage density (1.51 J/cm3) at the largest electric field strength (210 kV/cm). At the same time, this ceramic exhibited good stability to temperature (60–150 °C) and frequency (10–100 Hz) variations, as well as fantastic fatigue resistance (10,000 charge-discharge cycles). This paper presents in-depth studies of the structure, morphology, electrical properties, and energy storage performance of ZnO-modified BaTiO3-based ceramics.

Effects of sintering temperature and KBT content on microstructure and electrical properties of (Bi.5Na.5)TiO3-BaTiO3-(Bi.5K.5)TiO3 Pb-free ceramics

A route exploring the morphotropic phase boundaries (MPB) region in (Bi.5Na.5)TiO3-BaTiO3-(Bi.5K.5)TiO3 ternary system has been designed based on the phase diagram. X-ray diffraction (XRD) has been performed to determine the phases of the prepared samples. The dielectric, ferroelectric, and piezoelectric properties of [(1-x) 0.9363(Bi.5Na.5)TiO3–0.0637BaTiO3]-x(Bi.5K.5)TiO3 (BNKBT100x) ternary lead-free piezoelectric ceramics are investigated as the functions of x and sintering temperature. When x was varied from 0 to 0.11, the BNKBT100x ceramics show single perovskite structure sintered at 1130–1210 °C. These ceramics show large dielectric permittivity, small dielectric loss, and diffused phase transition behavior. Well-defined ferroelectric polarization-electric field (P-E) hysteresis loop and relative large piezoelectric and electromechanical coefficients are also found in these ceramics. When increasing x, the electrical performances first increase, then decrease. The same rule is found when varying the sintering temperature. The optimized composition and sintering temperature are finally obtained.

Combined effect of oxygen annealing and La-doping in broadening the phase transition of Ba(Zr0.2Ti0.8)O3 ceramics

The present study focuses on a novel approach to broaden the phase transition in Ba(Zr0.2Ti0.8)O3 by the combined effect of oxygen annealing and La-doping. The (Ba1-xLax)(Ti0.8Zr0.2)O3, Pb-free ceramics, with nominal compositions (x = 0.00, 0.01, 0.02 and 0.03) are synthesized in oxygen annealing atmosphere at 1673 K for 11 h using solid-state reaction method. While the X-ray diffraction confirmed the single phase formation, the secondary electron images revealed inhibited grain growth at a low concentration of La-doping but intermediate 2-dimensional grain growth at higher La-doping. The Raman peak appearing at 836 cm−1 indicates La-substitution at Ba-site and vacancies at Ti-sites. The temperature dependent dielectric permittivity exhibits a broad diffuse phase transition at Tm = 230 K with a full width at half maxima (FWHM) of 289 K for 3 atomic % La-doped sample. The combined effect of oxygen annealing and La-doping results in an extremely broad diffuse phase transition. Such an extremely broad phase transition close to room temperature due to La-doping and oxygen annealing is useful for capacitor applications.