Showing papers on "Ceramic published in 2020"

Grain-orientation-engineered multilayer ceramic capacitors for energy storage applications.

Abstract: Dielectric ceramics are highly desired for electronic systems owing to their fast discharge speed and excellent fatigue resistance. However, the low energy density resulting from the low breakdown electric field leads to inferior volumetric efficiency, which is the main challenge for practical applications of dielectric ceramics. Here, we propose a strategy to increase the breakdown electric field and thus enhance the energy storage density of polycrystalline ceramics by controlling grain orientation. We fabricated high-quality -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 (NBT-SBT) ceramics, in which the strain induced by the electric field is substantially lowered, leading to a reduced failure probability and improved Weibull breakdown strength, on the order of 103 MV m−1, an ~65% enhancement compared to their randomly oriented counterparts. The recoverable energy density of -textured NBT-SBT multilayer ceramics is up to 21.5 J cm−3, outperforming state-of-the-art dielectric ceramics. The present research offers a route for designing dielectric ceramics with enhanced breakdown strength, which is expected to benefit a wide range of applications of dielectric ceramics for which high breakdown strength is required, such as high-voltage capacitors and electrocaloric solid-state cooling devices. The energy density of dielectric ceramic capacitors is limited by low breakdown fields. Here, by considering the anisotropy of electrostriction in perovskites, it is shown that -textured Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 ceramics can sustain higher electrical fields and achieve an energy density of 21.5 J cm−3.

Lithium Dendrite in All-Solid-State Batteries: Growth Mechanisms, Suppression Strategies, and Characterizations

Abstract: Summary Li metal has been attracting increasing attention as an anode in all-solid-state batteries because of its lowest electrochemical potential and high capacity, although the problems caused by dendritic growth impedes its further application. For a long time, all-solid-state Li metal batteries (ASLBs) are regarded to revive Li metal due to high mechanical strength. However, numerous works revealed that the dendrite issue widely exists in ASLBs, and the mechanism is complex. This review provides a systematic and in-depth understanding of the thermodynamic, kinetic, electrochemical, chemomechnical, structural stability, and characterizations of Li dendrite in ASLBs. First, the mechanisms for dendrite formation and propagation in polymer, ceramic and glass electrolyte were discussed. Subsequently, based on these mechanisms of dendrite growth, we reviewed various strategies for dendrite suppression. Furthermore, advanced characterization techniques were reviewed for better understanding of dendrite in solid-state batteries.

YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting

Abstract: Y3 Al5 O12 :Ce3+ (YAG:Ce3+ ) transparent ceramic phosphors (TCPs) are regarded as the most promising luminescent converter for laser-driven (LD) lighting. High-quality YAG:Ce3+ TCPs are still urgent for high efficiency LD lighting devices. YAG:Ce3+ TCPs in a vacuum ambience by using nano-sized raw materials are prepared. Controlling defects by adding nano-sized MgO and SiO2 simultaneously enables a high transmittance nearly 80%. After annealing in air furthermore, the luminous efficiency is enhanced greatly from 106 to 223 lm W-1 , which is the best result reported now for LD lighting. These results demonstrate that the optimizing YAG:Ce3+ TCPs in a fitting strategy will brighten once again in the next-generation LD lighting. Based on scanning electron microscopy (SEM) coupled with a cathodoluminescence system, defects and Ce3+ distributions in grains are identified directly for the first time.

A Flexible Ceramic/Polymer Hybrid Solid Electrolyte for Solid-State Lithium Metal Batteries.

Abstract: Ceramic/polymer hybrid solid electrolytes (HSEs) have attracted worldwide attentions because they can overcome defects by combining the advantages of ceramic electrolytes (CEs) and solid polymer electrolytes (SPEs). However, the interface compatibility of CEs and SPEs in HSE limits their full function to a great extent. Herein, a flexible ceramic/polymer HSE is prepared via in situ coupling reaction. Ceramic and polymer are closely combined by strong chemical bonds, thus the problem of interface compatibility is resolved and the ions can transport rapidly by an expressway. The as-prepared membrane demonstrates an ionic conductivity of 9.83 × 10-4 S cm-1 at room temperature and a high Li+ transference numbers of 0.68. This in situ coupling reaction method provides an effective way to resolve the problem of interface compatibility.

A general method to synthesize and sinter bulk ceramics in seconds.

Abstract: Ceramics are an important class of materials with widespread applications because of their high thermal, mechanical, and chemical stability. Computational predictions based on first principles methods can be a valuable tool in accelerating materials discovery to develop improved ceramics. It is essential to experimentally confirm the material properties of such predictions. However, materials screening rates are limited by the long processing times and the poor compositional control from volatile element loss in conventional ceramic sintering techniques. To overcome these limitations, we developed an ultrafast high-temperature sintering (UHS) process for the fabrication of ceramic materials by radiative heating under an inert atmosphere. We provide several examples of the UHS process to demonstrate its potential utility and applications, including advancements in solid-state electrolytes, multicomponent structures, and high-throughput materials screening.

Materials development and potential applications of transparent ceramics: A review

Abstract: Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Tape-Casting Li 0.34 La 0.56 TiO 3 Ceramic Electrolyte Films Permit High Energy Density of Lithium-Metal Batteries

Abstract: Ceramic oxide electrolytes are outstanding due to their excellent thermostability, wide electrochemical stable windows, superior Li-ion conductivity, and high elastic modulus compared to other electrolytes. To achieve high energy density, all-solid-state batteries require thin solid-state electrolytes that are dozens of micrometers thick due to the high density of ceramic electrolytes. Perovskite-type Li0.34 La0.56 TiO3 (LLTO) freestanding ceramic electrolyte film with a thickness of 25 µm is prepared by tape-casting. Compared to a thick electrolyte (>200 µm) obtained by cold-pressing, the total Li ionic conductivity of this LLTO film improves from 9.6 × 10-6 to 2.0 × 10-5 S cm-1 . In addition, the LLTO film with a thickness of 25 µm exhibits a flexural strength of 264 MPa. An all-solid-state Li-metal battery assembled with a 41 µm thick LLTO exhibits an initial discharge capacity of 145 mAh g-1 and a high capacity retention ratio of 86.2% after 50 cycles. Reducing the thickness of oxide ceramic electrolytes is crucial to reduce the resistance of electrolytes and improve the energy density of Li-metal batteries.

Superior energy density through tailored dopant strategies in multilayer ceramic capacitors

Abstract: The Gerson–Marshall (1959) relationship predicts an increase in dielectric breakdown strength (BDS) and therefore, recoverable energy density (Wrec) with decreasing dielectric layer thickness. This relationship only operates however, if the total resistivity of the dielectric is sufficiently high and the electrical microstructure is homogeneous (no short circuit diffusion paths). BiFeO3–SrTiO3 (BF–ST) is a promising base for developing high energy density capacitors but Bi-rich compositions which have the highest polarisability per unit volume are ferroelectric rather than relaxor and are electrically too conductive. Here, we present a systematic strategy to optimise BDS and maximum polarisation via: (i) Nb-doping to increase resistivity by eliminating hole conduction and promoting electrical homogeneity and (ii) alloying with a third perovskite end-member, BiMg2/3Nb1/3O3 (BMN), to reduce long range polar coupling without decreasing the average ionic polarisability. These strategies result in an increase in BDS to give Wrec = 8.2 J cm−3 at 460 kV cm−1 for BF–ST–0.03Nb–0.1BMN ceramics, which when incorporated in a multilayer capacitor with dielectric layers of 8 μm thickness gives BDS > 1000 kV cm−1 and Wrec = 15.8 J cm−3.

(Na 0.5 Bi 0.5 ) 0.7 Sr 0.3 TiO 3 modified by Bi(Mg 2/3 Nb 1/3 )O 3 ceramics with high energy-storage properties and an ultrafast discharge rate

Abstract: The design of ceramic dielectrics with high energy-storage properties and outstanding temperature stability is an important but challenging topic in advanced electronic and electrical power systems. Here, we utilized a strategy to achieve synergistic enhancement of energy density and energy efficiency in the (1 − x)(Na0.5Bi0.5)0.7Sr0.3TiO3–xBi(Mg2/3Nb1/3)O3 systems based on refined grain size and the introduction of Bi3+'s lone pair electron 6s2 configuration, respectively. As a result, a giant discharge energy density of 3.45 J cm−3 and a high energy efficiency of 88.01% were simultaneously achieved in the 0.85NBST–0.15BMN ceramic, which precede those of recently reported lead-free dielectric ceramic materials. Meanwhile, excellent temperature (30–150 °C) and frequency (1–100 Hz) stability were also observed at 200 kV cm−1. Moreover, an outstanding power density (PD) of 38.47 MW cm−3 and an ultrafast discharge rate (t0.9) of 52.8 ns were also achieved in the 0.85NBST–0.15BMN ceramic at 120 kV cm−1. These results may provide a feasible approach to develop more NBST-based lead-free ceramics with vastly improved energy-storage properties.

Lightweight, tough, and sustainable cellulose nanofiber-derived bulk structural materials with low thermal expansion coefficient

Abstract: Sustainable structural materials with light weight, great thermal dimensional stability, and superb mechanical properties are vitally important for engineering application, but the intrinsic conflict among some material properties (e.g., strength and toughness) makes it challenging to realize these performance indexes at the same time under wide service conditions. Here, we report a robust and feasible strategy to process cellulose nanofiber (CNF) into a high-performance sustainable bulk structural material with low density, excellent strength and toughness, and great thermal dimensional stability. The obtained cellulose nanofiber plate (CNFP) has high specific strength [~198 MPa/(Mg m-3)], high specific impact toughness [~67 kJ m-2/(Mg m-3)], and low thermal expansion coefficient (<5 × 10-6 K-1), which shows distinct and superior properties to typical polymers, metals, and ceramics, making it a low-cost, high-performance, and environmental-friendly alternative for engineering requirement, especially for aerospace applications.

High temperature lead-free BNT-based ceramics with stable energy storage and dielectric properties

Abstract: High-temperature dielectric ceramics are in urgent demand due to the rapid development of numerous emerging applications. However, producing dielectric ceramics with favorable temperature, frequency and electric field stability is still a huge challenge. The construction of multi-phase coexistence material systems is an effective way to obtain stable dielectric and energy storage properties. In this work, NaNbO3 (NN) modified 0.95Bi0.5Na0.5TiO3–0.05SrZrO3 (BNTSZ) ceramics ((1 − x)BNTSZ–xNN) are designed to achieve the coexistence of rhombohedral and tetragonal phases. The variation in the dielectric permittivity of the 0.8BNTSZ–0.2NN ceramic is less than ±15% over the temperature range from −55 °C to 545 °C, which is the reported record-high upper operating temperature, with a high room-temperature dielectric permittivity of 1170. The 0.8BNTSZ–0.2NN ceramic exhibits excellent frequency and electric field stability as well. Additionally, a large discharge energy density of 3.14 J cm−3 is obtained in the 0.85BNTSZ–0.15NN ceramic with an energy efficiency of 79% at a high temperature of 120 °C under 230 kV cm−1, with the variation in the discharge energy density being less than ±4% in the temperature range from 25 °C to 180 °C under 120 kV cm−1. All these features demonstrate that the (1 − x)BNTSZ–xNN ceramics are promising candidates for use at extremely high temperature in both dielectric and energy storage capacitor applications.

Temperature stable Li2Ti0.75(Mg1/3Nb2/3)0.25O3-based microwave dielectric ceramics with low sintering temperature and ultra-low dielectric loss for dielectric resonator antenna applications

Abstract: Microwave dielectric ceramics are considered to be one of the key materials of dielectric resonators/filters and have wide application prospects in fifth generation (5G) mobile communication systems. Here we prepared two kinds of low-sintering temperature and high-performance microwave dielectric ceramics with monoclinic rock salt structure by adding a small amount of V2O5 and 0.6CuO–0.4B2O3 sintering aids to Li2Ti0.75(Mg1/3Nb2/3)0.25O3 (LTMN0.25). The sintering temperature of LTMN0.25 ceramics with 2 wt% V2O5 and 1 wt% 0.6CuO–0.4B2O3 additions could be effectively reduced from 1170 °C to below 910 °C due to the liquid phase effects resulting from the additives. Typically, high performance microwave dielectric properties can be obtained in the LTMN0.25 + 2 wt% V2O5 ceramic sintered at 910 °C for 2 h, with a er ∼ 20.7, a Q × f ∼ 60 460 GHz and a TCF ∼ +4.3 ppm °C−1. The best dielectric properties of er ∼ 19.9, a Q × f ∼ 60 950 GHz and a TCF ∼ −6.1 ppm °C−1 were obtained for the samples with 1 wt% 0.6CuO–0.4B2O3 sintered at 870 °C for 2 h. A prototype dielectric resonator antenna (DRA) was fabricated by LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 ceramic. The antenna resonated at 10.02 GHz with a bandwidth ∼175 MHz at −10 dB transmission loss (S11). Moreover, the chemical compatibility with Ag powder suggests that the LTMN0.25 + 2 wt% V2O5 and LTMN0.25 + 1 wt% 0.6CuO–0.4B2O3 ceramics may be suitable candidates for low temperature co-fired ceramic technology applications.

Highly compressible and anisotropic lamellar ceramic sponges with superior thermal insulation and acoustic absorption performances.

Abstract: Advanced ceramic sponge materials with temperature-invariant high compressibility are urgently needed as thermal insulators, energy absorbers, catalyst carriers, and high temperature air filters. However, the application of ceramic sponge materials is severely limited due to their complex preparation process. Here, we present a facile method for large-scale fabrication of highly compressible, temperature resistant SiO2-Al2O3 composite ceramic sponges by blow spinning and subsequent calcination. We successfully produce anisotropic lamellar ceramic sponges with numerous stacked microfiber layers and density as low as 10 mg cm−3. The anisotropic lamellar ceramic sponges exhibit high compression fatigue resistance, strain-independent zero Poisson’s ratio, robust fire resistance, temperature-invariant compression resilience from −196 to 1000 °C, and excellent thermal insulation with a thermal conductivity as low as 0.034 W m−1 K−1. In addition, the lamellar structure also endows the ceramic sponges with excellent sound absorption properties, representing a promising alternative to existing thermal insulation and acoustic absorption materials. Temperature-invariant highly compressible ceramic sponges are attractive for thermal insulators and energy absorbers, but development is limited by complex preparation processes. Here the authors report large-scale fabrication of silica-alumina composite ceramic sponges via blow spinning and calcination.

A review on the development of lead-free ferroelectric energy-storage ceramics and multilayer capacitors

Abstract: Energy storage materials and their applications have attracted attention among both academic and industrial communities. Over the past few decades, extensive efforts have been put on the development of lead-free high-performance dielectric capacitors. In this review, we comprehensively summarize the research progress of lead-free dielectric ceramics for energy storage, including ferroelectric ceramics, composite ceramics, and multilayer capacitors. The results indicate that dielectric capacitors with both high energy density and high efficiency are feasible using the materials providing high breakdown electric field and a slim hysteresis loop. This article also lists the factors affecting the fabrication cost of dielectric capacitors, such as sintering temperature, raw material costs, and types of internal electrodes, to promote the industrial application of ceramic energy storage capacitors.

A powder-metallurgy-based strategy toward three-dimensional graphene-like network for reinforcing copper matrix composites

Abstract: Three-dimensional graphene network is a promising structure for improving both the mechanical properties and functional capabilities of reinforced polymer and ceramic matrix composites. However, direct application in a metal matrix remains difficult due to the reason that wetting is usually unfavorable in the carbon/metal system. Here we report a powder-metallurgy based strategy to construct a three-dimensional continuous graphene network architecture in a copper matrix through thermal-stress-induced welding between graphene-like nanosheets grown on the surface of copper powders. The interpenetrating structural feature of the as-obtained composites not only promotes the interfacial shear stress to a high level and thus results in significantly enhanced load transfer strengthening and crack-bridging toughening simultaneously, but also constructs additional three-dimensional hyperchannels for electrical and thermal conductivity. Our approach offers a general way for manufacturing metal matrix composites with high overall performance. Graphene networks have been used to reinforce polymer and ceramic composites, but connecting graphene into a three dimensional network in a metal matrix is challenging. Here the authors use a powder-metallurgy-based strategy to construct a three-dimensional graphene network reinforced copper matrix composite.

High energy-storage density under low electric fields and improved optical transparency in novel sodium bismuth titanate-based lead-free ceramics

Abstract: A novel (1-x)Na0.5Bi0.5TiO3-xBaHfO3 (abbreviated as (1-x)NBT-xBH) transparent ceramic was fabricated by the solid state reaction method. X-ray diffraction analysis showed that NBT-based transparent ceramics exhibit a cubic-like perovskite structure and the solid solubility of BH in NBT reached to 0.15. The Landau-Devonshire theory and I-E curves revealed that the transition between the antiferroelectric like phase and the ferroelectric phase deeply relies on the variation of composition and free energy. One sample (x = 0.15) was found to show a high dielectric constant (˜2418±10%) over the temperature range 57–400 °C. These ceramics also exhibited a high discharge energy density (Wd) of 2.1 J/cm3 and a high maximum polarization Pm of 34 μC/cm2 under relatively low electric fields which were less than 175 kV/cm. There was also high transparency in the visible spectra (more than 0.5) when the sample thickness was 250 μm.

Anisotropic and hierarchical SiC@SiO2 nanowire aerogel with exceptional stiffness and stability for thermal superinsulation.

Abstract: Ceramic aerogels are promising lightweight and high-efficient thermal insulators for applications in buildings, industry, and aerospace vehicles but are usually limited by their brittleness and structural collapse at high temperatures In recent years, fabricating nanostructure-based ultralight materials has been proved to be an effective way to realize the resilience of ceramic aerogels However, the randomly distributed macroscale pores in these architectures usually lead to low stiffness and reduced thermal insulation performance Here, to overcome these obstacles, a SiC@SiO2 nanowire aerogel with a nanowire-assembled anisotropic and hierarchical microstructure was prepared by using directional freeze casting and subsequent heat treatment The aerogel exhibits an ultralow thermal conductivity of ~14 mW/m·K, an exceptional high stiffness (a specific modulus of ~247 kN·m/kg), and excellent thermal and chemical stabilities even under heating at 1200°C by a butane blow torch, which makes it an ideal thermally superinsulating material for applications under extreme conditions

Size and scaling effects in barium titanate. An overview

Abstract: Ferroelectric perovskites such as BaTiO3 and Pb(Zr,Ti)O3 are well-suited for a variety of applications including piezoelectric transducers and actuators, multilayer ceramic capacitors, thermistors with positive temperature coefficient, ultrasonic and electro-optical devices. Ferroelectricity arises from the long-range ordering of elemental dipoles which determines the appearance of a macroscopic polarization and a spontaneous lattice strain. The confinement of a ferroelectric system in a small volume produces a perturbation of the polar order because of the high fraction of surface atoms and ferroelectricity vanishes when the size of the material is reduced below a critical dimension. This critical size is of a few nanometres in the case of epitaxial thin films and of 10−20 nm for nanoparticles and nanoceramics. The change in properties with decreasing physical dimensions is usually referred to as size effect. Thin films and ceramics are particularly prone to show size effects. A progressive variation of dielectric, elastic and piezoelectric properties of ferroelectric ceramics is already observed when the grain size is reduced below ≈10 μm, i.e. at a length scale much larger than the critical size. In this case it is more appropriate to refer to scaling effects as they are not related to material confinement. The aim of this contribution is to review the current understanding of size and scaling effects in perovskite ferroelectric ceramics and, in particular, in BaTiO3. After a short survey on the intrinsic limits of ferroelectricity and on the impact of particle/grain size on phase transitions, the role of interfaces such as ferroelectric/ferroelastic domain walls and grain boundaries in scaling of dielectric and piezoelectric properties will be discussed in detail. Multiple mechanisms combine to produce the observed scaling effects and the maximization of the dielectric constant and piezoelectric properties exhibited by BaTiO3 ceramics for an intermediate grain size of ≈1 μm. The broad dispersion of experimental data is determined by spurious effects related to synthesis, processing and variation of Ba/Ti ratio. Furthermore, we will consider these size effects, and other properties in relation to the downsizing the modern multilayer BaTiO3 based capacitors.

Large energy storage density in BiFeO3-BaTiO3-AgNbO3 lead-free relaxor ceramics

Abstract: Lead-free (0.70-x)BiFeO3-0.30BaTiO3-xAgNbO3+5‰mol CuO (abbreviated as BF-BT-xAN) ceramics were fabricated using a modified thermal quenching technique. BF-BT-xAN ceramics are of a perovskite structure with morphotropic phase boundary (MPB) and show strong relaxor properties. Remarkably, the high recoverable energy storage density of 2.11 J/cm3 is obtained for BF-BT-xAN with x = 0.14. For the x = 0.14 ceramics, its energy storage efficiency is as high as 84 % at relative low field of 195 kV/cm, together with an outstanding thermal stability in a broad temperature range from 25 °C to 150 °C. In addition, this ceramic maintains superior energy storage performance even after 8 × 104 electrical cycles due to its high densification after doping Ag2O and Nb2O5. The result suggests that lead-free BF-BT-xAN ceramics may be promising candidate for dielectric energy storage application.