Ceramic Capacitors Research Articles

Designing a Cost‐Effective and Sustainable Process for the Efficient Production of Planar Anode‐Supported Solid Oxide Fuel Cells

A sustainable process is designed to produce anode‐supported solid oxide fuel cells (SOFCs). Environmentally friendly solvents and additives are selected to prepare sequentially cast slurries to obtain a flexible multilayer tape whose cohesion is ensured by a 3D network of binder. This tape includes the components of the oxide precursor of the half cell with the functional and structural part of the anode. The optimization of debinding and sintering processes allows converting green tape into sintered multilayer ceramic using a single heat treatment. The use of optimized loads maintains planarity of samples with adjusted shape (circular to square) and size (from 0.8 up to 8 cm2) of anodic half cell. The cell's oxide precursor is supplemented by screen printing the cathode and converted to anode‐support SOFC when the cell is first used. The whole process maintains mechanical integrity, microstructure of structured components, and insures interfaces enabling charge transfer high enough to achieve standard performances such as power of 411 mW cm−2. The selection of cheap and harmless solvents and additives and the optimization of heat treatment lead to an ecocompatible low‐cost process for manufacturing SOFCs, easily transferable to the industrial scale and suitable for the manufacture of all systems based on ceramic multilayers.

High energy storage performance under low electric fields and remarkable dielectric temperature stability in (Na0.5Bi0.5)TiO3-based lead-free ceramics

Lead-free ceramic capacitors with superior energy storage properties and dielectric temperature stability are urgent needs for pulsed power devices. However, the risk of high voltage suppresses the improvement of comprehensive performance. Thus, a novel (1-x)(0.55Na0.5Bi0.5TiO3-0.45Ba0.85Ca0.15Zr0.1Ti0.9O3)-xBi(Mg2/3Ta1/3)O3 (NBBCZT-xBMT) ceramics were successfully synthesized to address the above concerns. The addition of BMT is beneficial to maintaining high polarization strength, improving the breakdown strength and optimizing relaxor behavior. As a result, the optimum component exhibits excellent energy storage capability (Wrec = 3.05 J/cm3, η = 94.3 %) at 190 kV/cm and dielectric temperature stability (TCC ≤ ±10 % from 33 to 348 °C, tanδ ≤ 0.01 from 50 to 389 °C). Moreover, the corresponding sample maintains a variation of Wrec less than 6.7 % and η less than 1.6 % at 20–140 °C and 1–100 Hz. These results provide a novel candidate for high-performance ceramic capacitors under low electric fields.

Application of Johnson's approximation in finite element modeling for electric field‐dependent materials

AbstractJohnson's approximation is implemented in a finite element code to simulate the electric field dependence of a core–shell microstructure material. We show how the microstructure, based here on a 50:50 volume fraction, influences the measured effective permittivity as a function of applied voltage. Using a Johnson's parameter of β = 1.0 × 1010 Vm5/C3, verified from commercial BaTiO3‐based multilayer ceramic capacitors (MLCC), we show how the microstructure and the difference in core and shell conductivities alter the local fields generated and how this influences the voltage dependence of the effective permittivity. Systems that comprise a conductive core‐like material surrounded by a resistive shell experience little or modest voltage dependence due to the shell material providing shielding to large electric fields within the cores. Conversely, if the core material is more resistive than the shell material, substantial voltage dependence occurs with simulations showing over a 50% decrease in the effective permittivity. These simulations give improved understanding of voltage dependence and provide a method to help guide the design of future materials for MLCCs with improved performance.

Enhanced Temperature Stability of Pyroelectric Sensing in Multilayer Potassium Sodium Niobate-Based Ceramics with Graded Polarization Rotation.

Pyroelectric effect which refers to electrical responses induced by time temperature-dependent fluctuations has received extensive attention, showing promising application prospects for infrared (IR) technology. Although enhanced pyroelectric performances are obtained in potassium sodium niobate-based ceramics at room temperature via multi-symmetries coexistence design, the poor pyroelectric temperature stability is still an urging desire that needs to be resolved. Herin, by constructing multilayer composite ceramics and adjusting the proportion of stacked layers, improved pyroelectric coefficient, and figures of merit (FOMs), as well as enhanced temperature stabilities can be achieved. With a remained high pyroelectric coefficient of 5.45×10-4C m-2°C-1 at room temperature, the pyroelectric parameters almost keep unchanged in the temperature range of 30-100°C, showing great properties advantages compared with previous reports. The excellent properties can be attributed to the graded polarization rotation states among each lamination induced by successive phase transitions. The novel strategy for achieving stable pyroelectric sensing can further promote the application in the IR sensors field.

High-entropy relaxor ferroelectric ceramics for ultrahigh energy storage

Dielectric ceramic capacitors with ultrahigh power densities are fundamental to modern electrical devices. Nonetheless, the poor energy density confined to the low breakdown strength is a long-standing bottleneck in developing desirable dielectric materials for practical applications. In this instance, we present a high-entropy tungsten bronze-type relaxor ferroelectric achieved through an equimolar-ratio element design, which realizes a giant recoverable energy density of 11.0 J·cm−3 and a high efficiency of 81.9%. Moreover, the atomic-scale microstructural study confirms that the excellent comprehensive energy storage performance is attributed to the increased atomic-scale compositional heterogeneity from high configuration entropy, which modulates the relaxor features as well as induces lattice distortion, resulting in reduced polarization hysteresis and enhanced breakdown endurance. This study provides evidence that developing high-entropy relaxor ferroelectric material via equimolar-ratio element design is an effective strategy for achieving ultrahigh energy storage characteristics. Our results also uncover the immense potential of tetragonal tungsten bronze-type materials for advanced energy storage applications.

High dielectric breakdown strength of antipolar CaTiGeO5 ceramics sintered at optimized temperature

Titanite CaTiSiO5 (CTS) is considered to be a promising dielectric material for preparing high-voltage multilayer ceramic capacitors because it exhibits a positive bias dependence of the dielectric permittivity due to its antipolar crystal structure. In this study, we investigated the dielectric response and breakdown strength of CaTiGeO5 (CTG), a structural analog of CTS, inspired by its higher low-field dielectric permittivity. Particular attention was paid to the sintering temperature to reveal the effect of the microstructure and loss of volatile Ge on the electrical properties of CTG. Dense CTG ceramics with relative densities above 97 % and grain sizes between 1.3 and 3.4 μm were obtained through a conventional solid-state reaction route at sintering temperatures between 1150 and 1250 °C. A secondary phase of CaTiO3 was formed in the ceramics sintered at 1200 and 1250 °C due to Ge loss, but this phase was easily removed by surface polishing alone. The sintering temperature largely affected the dielectric breakdown strength through microstructural development, resulting in the highest breakdown strength of 1190 kV cm−1 for a sample sintered at 1200 °C, while it did not change the low-field dielectric properties of the samples. Furthermore, the sample retained high breakdown strength of >900 kV cm−1 at elevated temperatures up to 150 °C and exhibited a nonlinear polarization response, resulting in the positive electric field dependence of the dielectric permittivity.

Study and manufacturing of strontium calcium titanate lead-free ceramic capacitors for high-frequency applications

Study and manufacturing of strontium calcium titanate lead-free ceramic capacitors for high-frequency applications

Vacancy engineering for high tetragonal BaTiO3 synthesized by solid-state approaches

Conventionally, tetragonality in BaTiO3 powder is attributed to grain size, disregarding the role of Ba/Ti ratio. However, our study reveals a significant impact of Ba/Ti ratio on tetragonality in BaTiO3. With an increase in Ba/Ti ratio from 0.990 to 1.010, particle size remains around 200 nm. Tetragonality initially rises from 1.006 to a maximum of 1.0092 at Ba/Ti = 1.000, then decreases to 1.005. Lower tetragonality is associated with Ba or Ti vacancies, using density functional theory (DFT), we analyzed the electron density and lattice distinction in BaTiO3 powders. Both Ba and Ti vacancies affect lattice distortion, the Ti vacancies leading to more significant lattice expansion and lower tetragonality than Ba vacancies. Using this powder, we fabricated high-density BaTiO3 ceramics and multi-layer ceramics capacitors (MLCCs) with X7R temperature stability (−55 to 125 °C, ±15% coefficient) and excellent reliability. This strategy has broad implications for tetragonal BaTiO3 nanopowders and MLCCs development.

Boost DC‐DC Converter with Non‐dissipative Snubber

To provide a hold‐up time function in DC‐DC supplies for cell site stations or data centers, using a boost converter with a bulk output capacitor as a front‐end converter stage is a simple and highly cost‐effective solution. However, conventional boost converters with a hard‐switching operation result in low conversion efficiency and increased electromagnetic interference emissions. In this paper, a boost converter with a new non‐dissipative snubber is proposed that only requires two additional diodes, an inductor, and a multilayer ceramic capacitor. The main feature of the proposed snubber is that the components are not located on the main power processing path. This means they only require low ratings, improving cost‐effectiveness. A prototype converter is analyzed, realized, and applied to a 300 W redundant DC‐DC power supply module for a 5G cell base station. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Structurally Regulated Design Strategy of Bi0.5Na0.5TiO3-Based Ceramics for High Energy-Storage Performance at a Low Electric Field.

Dielectric ceramic capacitors are prospective energy-storage devices for pulsed-power systems owing to their ultrafast charge-discharge speed. However, low energy-storage density makes them difficult to commercialize for high-pulse-power technology applications. Herein, we presented a structurally regulated design strategy to disrupt a long-range ferroelectric order, refined grains, and eventually achieve excellent comprehensive energy-storage performance in (1 - x) (0.7Bi0.5Na0.5TiO3-0.3SrTiO3)-x Sm(Zn2/3Nb1/3)O3 eco-friendly ceramics. A large Wrec of ∼7.43 ± 0.05 J/cm3 and a high η of ∼85 ± 0.5% of 0.96 (0.7Bi0.5Na0.5TiO3-0.3SrTiO3)-0.04 Sm(Zn2/3Nb1/3)O3 were obtained at a low electric field of 290 kV cm-1 with good energy-storage temperature (25-120 °C), frequency (1-100 Hz) stability, and charge-discharge properties (PD ∼ 74 ± 1 MW/cm3 and τ0.9 ∼ 159 ± 2 ns). This strategy inspires rational structurally regulated designs and aims to promote the development of eco-friendly 0.7Bi0.5Na0.5TiO3-based ceramics with excellent energy-storage characteristics.

Multiphase LLC DC-Link Converter with Current Equalization Based on CM Voltage-Controlled Capacitor

In this study, a current-equalization technology utilizing a variable-capacitance technique for a multiphase inductor–inductor–capacitor (LLC) converter is studied. Accordingly, the proposed method involves adjusting the resonant capacitance of the LLC resonant converter to balance the currents between phases. This is achieved primarily by biasing ferroelectric multilayer ceramic capacitors (MLCCs) through a step-down circuit and a common-mode bias structure. These ferroelectric MLCCs serve as the resonant elements, allowing for variable capacitance by leveraging capacitance sensitivity to their trans voltages. This approach provides additional control flexibility to the resonant circuit. Furthermore, since each phase operates independently, the circuit can be scaled to accommodate any number of phases. Moreover, all switches in the circuit have zero-voltage switching (ZVS) turn-on, minimizing switching losses. This study initially analyzes and evaluates the proposed common-mode bias variable capacitance technique and the corresponding operational principles. Subsequently, a two-phase LLC experimental circuit based on a field-programmable gate array (FPGA) digital controller is utilized to assess current equalization and efficiency. That is to say, this experimentation aims to validate the effectiveness of the current-equalization variable-capacitance technique in an LLC resonant converter.

Gamma‐Ray‐Induced Photoelectric Field Exacerbating Irradiation Damage in Ceramic Capacitors

Ceramic capacitors are widely used in radioactive environments and are known to take irradiation damages, but most of previous studies of its reliability focus on thermal or electrical issues, and much less is known about the microscopic mechanism of its irradiation damaging process. Herein, it is shown that the capacitance of ceramic capacitors can change significantly under continuous gamma‐ray irradiation. Moreover, it is noticed that ex situ measurements will underestimate the effect comparing with the in situ one. Herein, it is discovered that this difference is due to the gamma‐ray‐induced photoelectric field, which dissipate rapidly in ex situ measurements. While the impact of the photoelectric field on the capacitance can be seen in situ, due to the recombination of photogenerated carriers and annealing of defects after irradiation, ex situ measurements only account for a part of the irradiation damage. This discovery indicates that ex situ measurements, which are prevailing in irradiation damage studies, can miss critical information, and in situ measurements are necessary for revealing the mechanism of the process.

Simulation of Mechanical Stresses in BaTiO3 Multilayer Ceramic Capacitors during Desoldering in the Rework of Electronic Assemblies Using a Framework of Computational Fluid Dynamics and Thermomechanical Models.

Multilayer ceramic capacitors (MLCCs) are critical components when thermal processes such as reflow desoldering are used during rework of electronic assemblies. The capacitor's ferroelectric BaTiO3 body is very brittle. Therefore, thermomechanical stresses can cause crack formation and create conductive paths that may short the capacitor. In order to assess the thermally induced mechanical stresses onto an MLCC during reflow desoldering, simulations were carried out, which make use of a framework of computational fluid dynamics and thermomechanical models within the ANSYS software package. In the first step, CFD simulations were conducted to calculate the transient temperature field in the surrounding of the MLCC component, which was then used as an input for FEM simulations to compute the arising mechanical stresses inside the MLCC. The results of the simulations show that the major contribution to mechanical stresses within the MLCC component comes from the mismatch in thermal expansion between the printed circuit board and the MLCC. The temperature gradients along the MLCC component are rather small and account only for moderate internal stresses within the brittle BaTiO3 body.

Investigation of coherent interface on relaxation behavior and reliability of Mg-doped BaTiO3 dielectric ceramics: Experiments and first-principle calculations

The addition of Mg generally enhances the high-temperature stability and reliability of BaTiO3-based multilayer ceramic capacitors (MLCCs). Herein, a series of Mg-doped BaTiO3-based ceramics and ultra-thin MLCCs were successfully fabricated, and the coherent and semi-coherent interface has been observed in samples. Based on the density functional theory (DFT) calculations, the improvement in temperature stability is due to changes in the coherent interface and electronic structure that promote the formation of polar nano-regions (PNRs) and induce relaxation behavior. Based on the atomic displacement, it is found that the excess substitution released the coherent stresses in the form of defects and formed semi-coherent interfaces. The reliability degradation of MLCCs is mainly due to the evolution of the semi-coherent interfaces. This work points out an avenue to obtain high-temperature stability and high reliability in BaTiO3-based MLCCs.

Accelerating densification of the terminal electrode with improved adhesion by sodium ions doping for MLCC copper paste

Glass frits effectively facilitate the sintering densification to produce high-density terminal electrodes, crucial for achieving high reliability of MLCC (Multilayer Ceramic Capacitors) devices. However, manufacturing terminal electrodes with high density and strong adhesion under low-temperature sintering condition still has enormous challenges. Herein, Na2O–BaO–ZnO–B2O3–SiO2 glass has been fabricated for low temperature sintering copper paste. We demonstrate that the densification degree and adhesion strength of the terminal electrode can be notably optimized by adjusting the Na2O content in the glass frit. The doping of Na+ in glass effectively improves the wettability of the melt on the copper substrate and the surface tension of the glass melt, enhancing the capillary force in the liquid phase sintering process. The rate of electrode densification is accelerated by the increase in capillary force, thus reducing the sheet resistance of copper film from 4.52 to 4.30 mΩ/□. Furthermore, with the increase in the Na+ content, the work of adhesion between glass and ceramic gradually increases, which effectively enhances the shear strength of the electrode from 19.66 MPa to 29.55 MPa. Our work provides novel insights for the design of glass compositions in the field of terminal paste.

Antiferroelectric Ceramics for Energy-Efficient Capacitors by Theory-Guided Discovery.

Antiferroelectric ceramics, via the electric-field-induced antiferroelectric (AFE)-ferroelectric (FE) phase transitions, show great promise for high-energy-density capacitors. Yet, currently, only 70-80% energy release is found during a charge-discharge cycle. Here, for PbZrO3-based oxides, geometric nonlinear theory of martensitic phase transitions is applied (first used to guide supercompatible shape-memory alloys) to predict the reversibility of the AFE-FE transition by using density-functional theory to assess AFE/FE interfacial lattice-mismatch strain that assures ultralow electric hysteresis and extended fatigue lifetime. A good correlation of mismatch strain with electric hysteresis, hence, with energy efficiency of AFE capacitors is observed. Guided by theory, high-throughput material search is conducted and AFE compositions with a near-perfect charge-discharge energy efficiency (98.2%), i.e., near-zero hysteresis are discovered. And the fatigue life of the capacitor reaches 79.5 million charge-discharge cycles, a factor of 80 enhancement over AFE ceramics with large electric hysteresis.

Erratum: “Improved prediction for failure time of multilayer ceramic capacitors (MLCCs): A physics-based machine learning approach” [APL Mach. Learn. 1, 036107 (2023)

Erratum: “Improved prediction for failure time of multilayer ceramic capacitors (MLCCs): A physics-based machine learning approach” [APL Mach. Learn. 1, 036107 (2023)

Excellent energy storage properties in ZrO2 toughened Ba0.55Sr0.45TiO3-based relaxor ferroelectric ceramics via multi-scale synergic regulation

Lead-free ceramic capacitors offer ultrahigh power density and ultrafast discharging rates, making them critical energy storage components for advanced pulsed power systems. However, the greatest obstacle to broader applications remains the relatively low energy storage density. In this study, a relaxor ferroelectric ceramic based on (0.6-x)Ba0.55Sr0.45TiO3-0.4Bi0.5Na0.5TiO3-xSrZrO3 ((0.6-x)BST-0.4BNT-xSZ) is prepared using the tape casting method, resulting in an excellent energy density (Wrec ≈ 10.0 J cm−3) and high energy storage efficiency (η ≈ 91 %). The solid solution of linear dielectrics SrZrO3 synergistically regulates both relaxor properties and breakdown strength. The variation of relaxor property was explored utilizing New Glass model and the multi-polarization model, with confirmation provided by piezoresponse force microscopy. Furthermore, the breakdown strength could be attributed to improvements in electric insulation and the widening of the bandgap. As SrZrO3 content increases, the in-situ emergence of the second phase ZrO2, accompanied by a martensitic transformation, not only improves the fracture toughness of ceramics but also serves to elongate the breakdown path. Encouragingly, x = 0.20 ceramics also achieve excellent temperature stability (−95–125 ℃), frequency stability (1–1000 Hz), cycling reliability (1–106 cycles), and great charging-discharging properties. This multiscale synergic regulation strategy plays a guiding role in the screening of high-performance energy storage dielectric materials.

Lead‐Free High Permittivity Quasi‐Linear Dielectrics for Giant Energy Storage Multilayer Ceramic Capacitors with Broad Temperature Stability

AbstractElectrostatic energy storage capacitors are essential passive components for power electronics and prioritize dielectric ceramics over polymer counterparts due to their potential to operate more reliably at > 100 ˚C. Most work has focused on non‐linear dielectrics compositions in which polarization (P)/electric displacement (D) and maximum field (Emax) are optimized to give values of energy density, 6≤U≤21 J cm−3. In each case however, either saturation (dP/dE = 0, AFE) or “partial” saturation (dP/dE → 0, RFE) of P limits the value of U which can be achieved before breakdown. It is proposed that U can be further improved with respect to relaxors (RFEs) and anti‐ferroelectrics (AFEs) by designing high permittivity quasi‐linear dielectric (QLD) behaviour in which dP/dE remains constant up to ultrahigh Emax. QLD multilayer capacitor prototypes with dielectric layers composed of 0.88NaNb0.9Ta0.1O3‐0.10SrTiO3‐0.02La(Mg1/2Ti1/2)O3 deliver room temperature U ≈ 43.5 J cm−3, supporting an extremely‐large Emax ≈ 280 MV m−1, both of which exceed current state‐of‐art by a factor of two for devices based on powder, tape‐cast technology. Importantly QLD capacitors exhibit scant variation in U (≈15 J cm−3) up to > 200 ˚C and robust resistance to cyclic degradation, offering a promising new approach for the development of sustainable technology.

Wide Temperature Stability of BaTiO3-NaNbO3-Gd2O3 Dielectric Ceramics with Grain Core–Shell Structure

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 εr = 4266 and dielectric loss tan δ = 0.95% conforms to the X8R standard (from −55 °C to 150 °C, TCC < ±15%); volume resistivity ρv = 10,200 GΩ·cm and breakdown strength Eb = 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.