Robust and Tunable Ferroelectricity in Ba/Co Codoped (K_(0.5)Na_(0.5))NbO_(3) Ceramics

The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.

Preparation and Photostriction Properties of BiFeO_(3)-BaTiO_(3)Ceramics

Under illumination by 405,520 and 655 nm monochromatic visible light(light intensity of 30 kW/m^(2)),large photostriction(ΔL/L)of 0.19%,0.13%and 0.26%for 67BiFeO_(3)-33BaTiO_(3)(67BF-33BT)lead-free ferroelectric ceramics are obtained,respectively.By studying the ferroelectric and photoelectric properties in conjunction with in situ Raman spectroscopy,it is found that the photostrictive effect of 67BF-33BT is not caused by the electrical strain induced by abnormal photovoltaic voltage,but related to the optical induced oxygen octahedral distortion.The 67BF-33BT lead-free ferroelectric material with excellent photostrictive response in the visible light region is expected to play an important role in the field of optical drive electromechanical devices.

Microstructure Characteristics and Possible Phase Evolution of the Coal Gangue-Steel Slag Ceramics Prepared by the Solid-State Reaction Methods

Industrial wastes such as steel slag and coal gangue etc.were chosen as raw materials for preparing ceramic via the conventional solid-state reaction method.With steel slag and coal gangue mixed in various mass ratios,from 100%steel slag to 100%coal gangue at 10%intervals,microstructure and possible phase evolution of the coal gangue-steel slag ceramics were investigated using X-ray powder diffraction,scanning electron microscopy,mercury intrusion porosimetry and Archimedes boiling method.The experimental results suggest that the phase compositions of the as-prepared ceramics could be altered with the increased amount of coal gangue in the ceramics.The anorthite-diopside eutectic can be formed in the ceramics with the mass ratios of steel slag to coal gangue arranged from 8:2 to 2:8,which was responsible for the melting of the steel slag-coal gangue ceramics at relatively high temperature.Further investigations on the microstructure suggested that the addition of the proper amount of steel slag in ceramic compositions was conducive to the pore formation and further contributed to an increment in porosity.

Rational Design of Ruddlesden-Popper Perovskite Ferrites as Air Electrode for Highly Active and Durable Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells(RePCCs)hold promise for efficient energy storage,but their practicality is hindered by a lack of high-performance air electrode materials.Ruddlesden-Popper perovskite Sr_(3)Fe_(2)O_(7−δ)(SF)exhibits superior proton uptake and rapid ionic conduction,boosting activity.However,excessive proton uptake during RePCC operation degrades SF’s crystal structure,impacting durability.This study introduces a novel A/B-sites co-substitution strategy for modifying air electrodes,incorporating Sr-deficiency and Nb-substitution to create Sr_(2.8)Fe_(1.8)Nb_(0.2)O_(7−δ)(D-SFN).Nb stabilizes SF’s crystal,curbing excessive phase formation,and Sr-deficiency boosts oxygen vacancy concentration,optimizing oxygen transport.The D-SFN electrode demonstrates outstanding activity and durability,achieving a peak power density of 596 mW cm^(−2)in fuel cell mode and a current density of−1.19 A cm^(−2)in electrolysis mode at 1.3 V,650℃,with excellent cycling durability.This approach holds the potential for advancing robust and efficient air electrodes in RePCCs for renewable energy storage.

Microstructure and Oxidation Behavior of ZrB_(2)-SiC Ceramics Fabricated by Tape Casting and Reactive Melt Infiltration

ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.

Low-firing and temperature stability regulation of tri-rutile MgTa_(2)O_(6)microwave dielectric ceramics

A glass frit containing Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)component was used to explore the low-temperature sintering behaviors and microwave dielectric characteristics of tri-rutile MgTa_(2)O_(6)ceramics in this study.The good low-firing effects are presented due to the high matching relevance between Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass and MgTa_(2)O_(6)ceramics.The pure tri-rutile MgTa_(2)O_(6)structure remains unchanged,and high sintering compactness can also be achieved at 1150℃.We found that the Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass not only greatly improves the low-temperature sintering characteristics of MgTa_(2)O_(6)ceramics but also maintains a high(quality factor(Q)×resonance frequency(f))value while still improving the temperature stability.Typically,great microwave dielectric characteristics when added with 2wt%Li_(2)O-MgO-ZnO-B_(2)O_(3)-SiO_(2)glass can be achieved at 1150℃:dielectric constant,ε_(r)=26.1;Q×f=34267 GHz;temperature coefficient of resonance frequency,τ_(f)=-8.7×10^(-6)/℃.

Clay Materials for Ceramics Application from N’Djamena in the Chad Republic: Mineralogical, Physicochemical and Microstructural Characterization

Herein, we report some characteristics of the clayey materials (CMs) collected from Kaliwa (C1), Kabé (C2) and Malo (C3) district in N’Djamena (Chad). Three samples were characterized applying XRF, XRD, FTIR, SEM. In addition, TGA/DSC were performed to control decomposition/mass loss and show phase transitions respectively of CMs. Geochemical analysis by XRF reveals the following minerals composition: SiO2 (~57% - 66%), Al2O3 (~13% - 15%), Fe2O3 (~6% - 10%), TiO2 (~1% - 2%) were the predominant oxides with a reduced proportion in C1, and (~7%) of fluxing agents (K2O, CaO, Na2O). Negligible and trace of MgO (~1%) and P2O5 was noted. The mineralogical composition by XRD shows that, C1, C2 and C3 display close mineralogy with: Quartz (~50%), feldspar (~20%) as non-clay minerals, whereas clays minerals were mostly kaolinite (~15%), illite (~5%) and smectite (~10%). FTIR analysis exhibits almost seemingly similar absorption bands characteristic of hydroxyls elongation, OH valence vibration of Kaolinite and stretching vibration of some Metal-Oxygen bond. SEM micrographs of the samples exhibit microstructureformed by inter-aggregates particles with porous cavities. TGA/DSCconfirm the existence of quartz (570˚C to 870˚C), carbonates (600˚C - 760˚C), kaolinite (569˚C - 988˚C), illite (566˚C - 966˚C), MgO (410˚C - 720˚C) and smectite (650˚C - 900˚C). The overall characterization indicates that, these clayey soils exhibit good properties for ceramic application.

Study on Acoustic Emission Characteristics of Deformation Damage Process of Zirconia Ceramics

Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.

The B-site ordering in RFe_(0.5)Cr_(0.5)O_(3)ceramics and its effect on magnetic properties

To insight into the B-site ordering in RFe_(0.5)Cr_(0.5)O_(3)ceramics,a series of RFe_(0.5)Cr_(0.5)O_(3)ceramics(R=La,Y,Lu)were synthesized by the sol-gel method,and the structural and magnetic properties were systemically investigated.By using the Rietveld refinement of all samples,it is found that the structural distortion is increased as the R ionic radius decreases,leading to the weakened interactions between Fe/Cr ions.Moreover,the Fe and Cr are arranged in disorder in LaFe_(0.5)Cr_(0.5)O_(3),but partially ordered in YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3),showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius.Through fitting the temperature-dependent magnetizations,it is identified that the magnetization reversal(MR)in disorder LaFe_(0.5)Cr_(0.5)O_(3)is resulted from the competition between the moments of Cr and Fe sublattices.In the partially ordered YFe_(0.5)Cr_(0.5)O_(3)and LuFe_(0.5)Cr_(0.5)O_(3)ceramics,because of the presence of Fe-O-Cr networks in the ordered domains whose moment is antiparallel to that of Fe-O-Fe and Cr-O-Cr in the disordered domains,the compensation temperature T_(comp)of MR is increased by nearly 50 K.These results suggest that the changing of R-site ions could be used very effectively to modify the Fe-O-Cr ordering,apart from the structural distortion,which has a direct effect on the magnetic exchange interactions in RFe_(0.5)Cr_(0.5)O_(3)ceramics.Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion,one can expect a higher transition temperature Tcomp,providing a different view for adjustment of the magnetic properties of RFe_(0.5)Cr_(0.5)O_(3)ceramics for practical applications.

Physics-embedded machine learning search for Sm-doped PMN-PT piezoelectric ceramics with high performance

Pb(Mg_(1/3)Nb_(2/3))O_(3)–PbTiO_(3)(PMN-PT)piezoelectric ceramics have excellent piezoelectric properties and are used in a wide range of applications.Adjusting the solid solution ratios of PMN/PT and different concentrations of elemental doping are the main methods to modulate their piezoelectric coefficients.The combination of these controllable conditions leads to an exponential increase of possible compositions in ceramics,which makes it not easy to extend the sample data by additional experimental or theoretical calculations.In this paper,a physics-embedded machine learning method is proposed to overcome the difficulties in obtaining piezoelectric coefficients and Curie temperatures of Sm-doped PMN-PT ceramics with different components.In contrast to all-data-driven model,physics-embedded machine learning is able to learn nonlinear variation rules based on small datasets through potential correlation between ferroelectric properties.Based on the model outputs,the positions of morphotropic phase boundary(MPB)with different Sm doping amounts are explored.We also find the components with the best piezoelectric property and comprehensive performance.Moreover,we set up a database according to the obtained results,through which we can quickly find the optimal components of Sm-doped PMN-PT ceramics according to our specific needs.

Porous high-entropy rare-earth phosphate(REPO_(4),RE=La,Sm,Eu,Ce,Pr and Gd)ceramics with excellent thermal insulation performance via pore structure tailoring

Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures.In this study,a new porous high-entropy(La_(1/6)Ce_(1/6)Pr_(1/6)Sm_(1/6)Eu_(1/6)Gd_(1/6))PO_(4)(HE(6RE_(1/6))PO_(4))ceramics was prepared by combining the high-entropy method with the pore-forming agent method and the effect of different starch contents(0–60vol%)on this ceramic properties was systematically investigated.The results show that the porous HE(6RE_(1/6))PO_(4)ceramics with 60vol%starch exhibit the lowest thermal conductivity of 0.061 W·m^(-1)·K^(-1)at room temperature and good pore structure stability with a linear shrinkage of approximately1.67%.Moreover,the effect of large regular spherical pores(>10μm)on its thermal insulation performance was discussed,and an optimal thermal conductivity prediction model was screened.The superior properties of the prepared porous HE(6RE_(1/6))PO_(4)ceramics allow them to be promising insulation materials in the future.

IMPROVING MATERIAL REMOVAL RATE OF BRITTLE CERAMICS THROUGH HONING INCIDENTAL TENSILE STRESSES

The stress intensity factors and stress conditions of machining cracks are analyzed by fracture mechanics on the basis of honing characteristics and of brittle ceramic mechanical behavior.Because the honing incidental tensile stresses effectively decrease the critical grinding stresses and increase the stress intensity factors of machining cracks,the honing process can be carried out easily.The results show that honing can be an efficient machining method for brittle materials.

Effects of ZnO,FeO and Fe_(2)O_(3)on the spinel formation,microstructure and physicochemical properties of augite-based glass ceramics

Augite-based glass ceramics were synthesised using ZnO,FeO,and Fe_(2)O_(3)as additives,and the spinel formation,matrix structure,crystallisation thermodynamics,and physicochemical properties were investigated.The results showed that oxides resulted in numerous preliminary spinels in the glass matrix.FeO,ZnO,and Fe_(2)O_(3)influenced the formation of spinel,while FeO simplified the glass network.FeO and ZnO promoted bulk crystallisation of the parent glass.After adding oxides,the grains of augite phase were refined,and the relative quantities of augite crystal planes were also influenced.All samples displayed good mechanical properties and chemical stability.The 2wt%ZnO-doping sample displayed the maximum flexural strength(170.3 MPa).Chromium leaching amount values of all the samples were less than the national standard(1.5 mg/L),confirming the safety of the materials.In conclusion,an appropriate amount of zinc-containing raw material is beneficial for the preparation of augite-based glass ceramics.

Improved microwave dielectric properties of MgAl_(2)O_(4)spinel ceramics through(Li_(1/3)Ti_(2/3))^(3+)doping

A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.

Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Minimizing Carbon Content with Three-in-One Functionalized Nano Conductive Ceramics:Toward More Practical and Safer S Cathodes of Li-S Cells

Using porous carbon hosts in cathodes of Li-S cells can disperse S actives and offset their poor electrical conductivity.However,such reservoirs would in turn absorb excess electrolyte solvents to S-unfilled regions,causing the electrolyte overconsumption,specific energy decline,and even safety hazards for battery devices.To build better cathodes,we propose to substitute carbons by In-doped SnO_(2)(ITO)nano ceramics that own three-in-one functionalities:1)using conductive ITO enables minimizing the total carbon content to an extremely low mass ratio(~3%)in cathodes,elevating the electrode tap density and averting the electrolyte overuse;2)polar ITO nanoclusters can serve as robust anchors toward Li polysulfide(LiPS)by electrostatic adsorption or chemical bond interactions;3)they offer catalysis centers for liquid–solid phase conversions of S-based actives.Also,such ceramics are intrinsically nonflammable,preventing S cathodes away from thermal runaway or explosion.These merits entail our configured cathodes with high tap density(1.54 g cm^(−3)),less electrolyte usage,good security for flame retardance,and decent Li-storage behaviors.With lean and LiNO_(3)-free electrolyte,packed full cells exhibit excellent redox kinetics,suppressed LiPS shuttling,and excellent cyclability.This may trigger great research enthusiasm in rational design of low-carbon and safer S cathodes.

COMBINED DAMAGE FRACTURE CRITERIA FOR PIEZOELECTRIC CERAMICS

Mechanical and electrical damages are introduced to study the fracture mechanics of piezoelectric ceramics in this paper. Two kinds of piezoelectric fracture criteria are established using the method of least squares combined with a damage analysis of the well-known piezoelectric fracture experiments of Park and Sun’s. One is based on a linear combination of the mechanical and electrical damages and the other on their nonlinear combination. When the combined damage D is up to its critical value Dc, piezoelectric fracture occurs. It is found from the qualitative comparison of the numerical results with the experimental data that the nonlinearly combined damage fracture criterion can give a better prediction of piezoelectric fracture. And it is concluded from the nonlinearly combined damage fracture criterion that a negative electric feld impedes fracture whereas the efect of a positive electric feld on fracture depends on its magnitude.

Preparation of Cordierite-mullite Ceramics for Solar Thermal Storage

We developed cordierite-mullite composite ceramic materials to package and encapsulate PCM, and presented a preparation process from raw materials of kaolin, talc and alumina. The properties and microstructre of cordierite-mullite composite ceramic were studied. Due to the strengthening effects of mullite, the sample C2(80 wt% of cordierite and 20 wt % of mullite) sintered at 1 420 ℃ possessed excellent physical properties. Determined by X-ray diffraction(XRD), scanning electron microscope(SEM) and energy dispersive spectroscopy(EDS) analysis, cuboid-shaped cordierite crystals and needle-like or long quadrilateral-prism mullite crystals with staggered patterns were found, which endowed the composites preferable mechanical strength. After 30 cycles of thermal shock(room temperature to about 1 100 ℃, air-cooled), the sample presented superior thermal shock resistance, which is suitable to be applied as solar thermal storage materials.

Microwave dielectric properties and compatibility with silver of low-fired Li_2MgTi_3O_8 ceramics with Li_2O-MgO-B_2O_3 frit

The effects of Li2O-MgO-B2O3 （LMB） glass additive on the sintering characteristics, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 ceramics were investigated. The experimental results demonstrate that the addition of LMB glass effectively lowers the sintering temperature of Li2MgTi3O8 ceramic from 1025 ℃ to 875 ℃ and induces no obvious degradation of the microwave dielectric properties. Typically, the 1.5%LMB glass-added Li2MgTi3O8 ceramic sintered at 875 ℃ for 4 h shows excellent microwave dielectric properties of Q×f=45403 GHz, εr=25.9 and τf≈0 ℃-1. The dielectric ceramic exhibits stability against the reaction with the Ag electrode, which indicates that the ceramics could be applied in multilayer microwave devices requiring low firing temperatures.

Physic, Chemical and Mineralogical Characterizations of Clays Used in the Making of Traditional Ceramics in the City of Katiola, C ôte d’Ivoire

In C ?te d’Ivoire, traditional ceramics are widely used in the form of pottery. The latter is used to store food, water and cereals. Analyzes (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductive plasma optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM) and analysis thermal gravimetric (ATG)) were carried out to determine the morphology, the chemical, physical and pedological constituents of these raw materials. It appears from this study that the clays used in the Mangoro pottery of Katiola contain silica SiO2, alumina Al2O3 and iron oxide Fe2O3 as well as kaolinite, muscovite, smectite and quartz.