Showing papers in "Journal of The European Ceramic Society in 2022"
TL;DR: In this article , 5.5 wt% TiO2 (MAS-T5.5) was used to adjust τf of MAS to −2.8 ppm/℃ whilst retaining low εr (5.24) and good Q×f (33,400 GHz), properties consistent with those obtained by infrared reflectance.
Abstract: 5G and forthcoming 6G communication systems require dielectric ceramics with low relative permittivity (εr) and near-zero temperature coefficient of resonant frequency (τf) for the lower part of the microwave (MW) band and at sub-Terahertz. Mg2Al4Si5O18 (MAS) ceramics are promising candidates due to their low εr (~ 6) and high-quality factor (Q×f > 40,000 GHz) but have a large τf. In this study, 5.5 wt% TiO2 (MAS-T5.5) was used to adjust τf of MAS to −2.8 ppm/℃ whilst retaining low εr (5.24) and good Q×f (33,400 GHz), properties consistent with those obtained by infrared reflectance. A demonstrator microstrip patch antenna with gain 4.92 dBi and 76.3% efficiency was fabricated from MAS-T5.5.
53 citations
TL;DR: In this article , the 3D printing technologies for fabricating porous ceramic parts are introduced, including binder jetting, selective laser sintering, direct ink writing, stereolithography, laminated object manufacturing, and indirect 3D print processes.
Abstract: Three-dimensional (3D) printing of ceramics has gained widespread attentions in recent years. Many excellent reviews have reported the printing of ceramics. However, most of them focus on printing of dense ceramics or general ceramic aspects, there is no systematical review about 3D printing of porous ceramics. In this review paper, the 3D printing technologies for fabricating of porous ceramic parts are introduced, including binder jetting, selective laser sintering, direct ink writing, stereolithography, laminated object manufacturing, and indirect 3D printing processes. The techniques to fabricate hierarchical porous ceramics by integrating 3D printing with one or more conventional porous ceramics fabrication approaches are reviewed. The main properties of porous ceramics such as pore size, porosity, and compressive strength are discussed. The emerging applications of 3D printed porous ceramics are presented with a focus on the booming application in bone tissue engineering. Finally, summary and a perspective on the future research directions for 3D printed porous ceramics are provided.
36 citations
TL;DR: In this article , a low-carbon MgO-C refractories with enhanced thermal shock resistance and slag resistance were designed and successfully prepared by introducing Al 2 O 3 as a reinforcer and La 2 O3 as a modifier, which showed that the refractory samples with additives show better overall performance than those without additives.
Abstract: In order to achieve high-quality and stable production of special steel, the performance of low-carbon MgO-C refractories needs to be further optimized. For this purpose, low-carbon MgO–Al 2 O 3 –La 2 O 3 –C refractories with enhanced thermal shock resistance and slag resistance were designed and successfully prepared by introducing Al 2 O 3 as a reinforcer and La 2 O 3 as a modifier. The results showed that the refractory samples with additives show better overall performance than those without additives. When 10 wt% of Al 2 O 3 and La 2 O 3 were added, the oxidation resistance, thermal shock resistance and slag resistance of the refractory samples coked at 1400 °C are increased by 13.57%, 17.75% and 43.09%, respectively. The analysis found that this can be mainly attributed to the formation of MgAl 2 O 4 , Mg 2 SiO 4 , and 2CaO·4La 2 O 3 ·6SiO 2 and the consequent volume expansion effect and intergranular phase enhancement effect. Therefore, a low-cost and enforceable reinforcement strategy for low-carbon MgO-C refractories is proposed, which is expected to be applied in steelmaking.
34 citations
TL;DR: In this article , the state-of-the-art in additive manufacturing of ceramic materials for various energy applications is reviewed. But the focus of the review is on material selections, processing, and opportunities for additive manufacturing technologies in energy related ceramic materials manufacturing.
Abstract: Among engineering materials, ceramics are indispensable in energy applications such as batteries, capacitors, solar cells, smart glass, fuel cells and electrolyzers, nuclear power plants, thermoelectrics, thermoionics, carbon capture and storage, control of harmful emission from combustion engines, piezoelectrics, turbines and heat exchangers, among others. Advances in additive manufacturing (AM) offer new opportunities to fabricate these devices in geometries unachievable previously and may provide higher efficiencies and performance, all at lower costs. This article reviews the state of the art in ceramic materials for various energy applications. The focus of the review is on material selections, processing, and opportunities for AM technologies in energy related ceramic materials manufacturing. The aim of the article is to provide a roadmap for stakeholders such as industry, academia and funding agencies on research and development in additive manufacturing of ceramic materials toward more efficient, cost-effective, and reliable energy systems.
31 citations
TL;DR: In this paper, a synergistic effect design strategy has been proposed that combined the merits of relaxor ferroelectrics with high polarization/low remanent polarization and enhanced linear materials with relatively high polarization and ultrahigh dielectric breakdown strength.
Abstract: Developing lead-free dielectric ceramics with outstanding energy storage properties has become urgent for dielectric capacitors. Herein, a synergistic effect design strategy has been proposed that combined the merits of relaxor ferroelectrics with high polarization/low remanent polarization and enhanced linear materials with relatively high polarization/ultrahigh dielectric breakdown strength. Hence, a novel lead-free 0.955Bi0.5Na0.5TiO3-0.045Ba(Al0.5Ta0.5)O3-based ceramics are engineered though introducing the enhanced linear dielectrics of 0.9CaTiO3-0.1BiScO3. A large recoverable energy density (Wrec∼3.13 J/cm3) and high efficiency (η∼88.4 %) as well as excellent power density (PD∼95.1 MW/cm3) and discharge speed (t0.9∼36 ns), along with superior stabilities, have been simultaneously realized. The piezoelectric force microscope measurements reveals that incorporating CT-BS generates more highly-dynamic polar nanoregions (PNRs), giving rise to rapid reversibility of PNRs with concurrently tailored energy storage performance. This study demonstrates synergistic effect design is a feasible and paradigmatic way to explore high-efficiency dielectrics for high-power energy storage applications.
31 citations
TL;DR: In this article , high-entropy rare-earth zirconates (La 0.2Nd0.2Sm 0.6.2Gd 0.4.2)2Zr2O7 and (Yb0.1 Nd0 1.2Eu 0.5.2
Abstract: Emerging of high-entropy ceramics has brought new opportunities for designing and optimizing materials with desired properties. In the present work, high-entropy rare-earth zirconates (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 and (Yb0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 are designed and synthesized. Both high-entropy ceramics exhibit a single pyrochlore structure with excellent phase stability at 1600 °C. In addition, the Yb-containing system possesses a high coefficient of thermal expansion (10.52 × 10−6 K-1, RT∼1500 °C) and low thermal conductivity (1.003 W·m-1 K-1, 1500 °C), as well as excellent sintering resistance. Particularly, the Yb-containing system has significantly improved fracture toughness (1.80 MPa·mm1/2) when compared to that of lanthanum zirconate (1.38 MPa·mm1/2), making it a promising material for thermal barrier coatings (TBCs) applications. The present work indicates that the high-entropy design can be applied for further optimization of the comprehensive properties of the TBCs materials.
30 citations
TL;DR: In this article, a high-purity CsPbBr3 PQDs embedded glass with 71.5 % PLQY was successfully prepared and the thermal stability, and photo-aging properties were also improved.
Abstract: Embedding all-inorganic cesium lead halide CsPbX3 (X=Cl, Br, I) perovskite quantum dots (PQDs) PQDs into glass is one of the most effective strategies to improve their optical, thermal and chemical stabilities. Herein, by using PbO instead of PbBr2 as the lead source, it is effective to lower the melting temperature and reduce the volatilization pollution from lead halide raw materials. Thus, a high-purity CsPbBr3 PQDs embedded glass with 71.5 % PLQY was successfully prepared. The thermal stability, and photo-aging properties were also improved. By simply changing the halogen element, the red and blue CsPbX3 PQDs embedded glasses were successfully prepared. The white LED fabricated by coating obtained green/red CsPbX3 PQDs embedded glass on a blue chip displays high color gamut of 121.9 % NTSC standard and >91.1 % Rec. 2020 standard, which embodies the great potential of PQDs embedded glass in lighting and display fields.
28 citations
TL;DR: In this article, the authors examined ten current ceramic radome materials under research and development and provided a comprehensive overview of available high temperature and high frequency data from literature, and their preliminary experimental results of a high-temperature metamaterial design are presented.
Abstract: This review paper examines ten current ceramic radome materials under research and development and provides a comprehensive overview of available high temperature and high frequency data from literature. An examination of metamaterials for radio-frequency transparent radomes is given and our preliminary experimental results of a high-temperature metamaterial design are presented. The next-generation hypersonic vehicles’ radome temperatures will exceed 1000℃ and speeds will exceed Mach 5. An ideal radome material will have a high flexural strength, low dielectric constant and loss tangent, and high resistance to thermal shock and corrosion. The microstructural effect on the dielectric and mechanical properties and the effects of environmental factors such as rain are discussed. The impact of metamaterial structure on key radome factors such as boresight error, gain, and polarization is examined. After examining the associated benefits with the use of metamaterials, our preliminary results for a potential high-temperature metamaterial design are presented.
25 citations
TL;DR: In this paper , the authors examined ten current ceramic radome materials under research and development and provided a comprehensive overview of available high temperature and high frequency data from literature, and their preliminary experimental results of a high-temperature metamaterial design are presented.
Abstract: This review paper examines ten current ceramic radome materials under research and development and provides a comprehensive overview of available high temperature and high frequency data from literature. An examination of metamaterials for radio-frequency transparent radomes is given and our preliminary experimental results of a high-temperature metamaterial design are presented. The next-generation hypersonic vehicles’ radome temperatures will exceed 1000℃ and speeds will exceed Mach 5. An ideal radome material will have a high flexural strength, low dielectric constant and loss tangent, and high resistance to thermal shock and corrosion. The microstructural effect on the dielectric and mechanical properties and the effects of environmental factors such as rain are discussed. The impact of metamaterial structure on key radome factors such as boresight error, gain, and polarization is examined. After examining the associated benefits with the use of metamaterials, our preliminary results for a potential high-temperature metamaterial design are presented.
25 citations
TL;DR: In this article , the effects of divalent ions on the phase structure, microstructure, and microwave dielectric properties of Mg1.8R0.2Al4Si5O18 (R = Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, Zn) cordierite ceramics were investigated.
Abstract: In this work, the effects of divalent ions on the phase structure, microstructure, and microwave dielectric properties of Mg1.8R0.2Al4Si5O18 (R = Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, Zn) cordierite ceramics were investigated. Complex chemical bond theory, Raman spectrum and infrared reflectance spectrum were employed to understand the relationship among structural characteristics, vibration modes and microwave dielectric properties for alkaline earth and transitional metal divalent elements doped cordierite ceramics. The optimal microwave dielectric properties were obtained for Mg1.8Ni0.2Al4Si5O18 with εr of 4.53, Q×f of 61,880 GHz and τf of -32 ppm/℃. Finally, a 5G-Sub 6GHz patch antennas with a central frequency of 4.91 GHz was successfully designed and fabricated using a Mg1.8Ni0.2Al4Si5O18 substrate. The antenna exhibited excellent performance with a gain of 5.83 dBi and an efficiency of 76 %, showing promise to be employed in 5 G/6G millimeter-wave communication technology.
24 citations
TL;DR: In this paper , four different gradient transition Al 2 O 3 -ZrO 2 FGC samples were prepared by laser directed energy deposition (LDED) method, and the results showed that there is an obvious interface in direct transition sample.
Abstract: Functionally graded ceramics (FGC), which combine properties of different ceramics in one part, usually have better comprehensive function and structural efficiency. In this study, four different gradient transition Al 2 O 3 -ZrO 2 FGC samples were prepared by laser directed energy deposition (LDED) method. The results show that there is an obvious interface in direct transition sample. The transition section bears tensile stress caused by difference of thermophysical properties of materials, resulting in significant longitudinal cracks. Element transition in interface region shows a step sharp transition. The direct transition sample shows intergranular fracture and the bonding strength is very low. Gradient transition mode can effectively suppress cracks, and avoid the step transition of microstructure and elements. Elements, microhardness of 25, 20 wt% FGC samples realized a nearly linear smooth transition. The interface fracture of FGC samples changed to transgranular fracture, bonding strength was significantly improved, and the maximum flexural strength reached 160.19 MPa.
TL;DR: In this article, a reverse manipulation of donor point defects, i.e., suppressing mobile zinc interstitial but increasing stable oxygen vacancy, was achieved to improve the long-term stability of NiO-doped ZnO varistor ceramics, with a degradation rate of 0.064 μA cm−2 h−0.5.
Abstract: Excellent electrical properties and the improved long-term stability of ZnO varistor ceramics were simultaneously achieved by doping NiO. The microstructural features were investigated using X-ray diffractometer, scanning electron microscopy, and energy dispersive spectroscopy, while the intrinsic point defects were characterized using frequency domain dielectric spectroscopy and verified by photoluminescence and Raman spectra. The results indicated that in the ZnO varistor ceramics, a reverse manipulation of donor point defects, i.e., suppressing mobile zinc interstitial but increasing stable oxygen vacancy, was achieved. The long-term stability of NiO-doped ZnO ceramics was improved via a decrease in zinc interstitial density, with a degradation rate of 0.064 μA cm−2 h−0.5. Meanwhile, due to an increase in oxygen vacancy density, the excellent nonlinear current–voltage performance, i.e., a high nonlinear coefficient (72.9), low leakage current density (0.08 μA cm−2), and low grain resistivity (13.43 × 10−3 Ω m), was maintained. The findings of this study provide a possible method for developing high-performance ZnO varistor ceramics by manipulating point defects.
TL;DR: In this paper , the effect of temperature on the phase composition, crystal structure, textural characteristics, particle size and morphology, as well as sorption properties to Cs + ions was studied.
Abstract: Hydrothermal synthesis of NaY-type zeolite was carried out and the effect of temperature on the phase composition, crystal structure, textural characteristics, particle size and morphology, as well as sorption properties to Cs + ions was studied. Solid-state matrices based on NaY zeolite the Faujasite structure containing 26.1 wt% cesium were obtained by spark plasma sintering (SPS) with high values of compressive strength (to 132.9 MPa) and Vickers microhardness to HV~ 698, Fracture toughness (K 1c ) ~ 1.26 MPa m 1/2 . The kinetics of ceramic matrices consolidation, phase composition and morphology using dilatometric studies, XRD, and SEM were studied. The thermogravimetric analysis shown the high thermal stability of the obtained samples up to 1300 °C. The high hydrolytic stability of CsAlSiO 4 ceramic was proven (leaching rate of 2.33 ×10 −8 g·cm − 2 ·day −1 and cesium diffusion coefficient De 1.41 ×10 −13 ), which exceeds the requirements of GOST R 50926–96 and ISO 6961:1982 for solid-state matrices.
TL;DR: In this paper , an alternate coating consisting of four sublayers with 10 and 70 vol.% SiC was prepared on SiC-coated carbon/carbon (C/C) composites through plasma spraying technique.
Abstract: Based on the investigation of ablation behavior and thermal stress of the monolayered ZrC-SiC coatings with different SiC amounts, an alternate coating consisting of 4 sublayers with 10 and 70 vol.% SiC was prepared on SiC-coated carbon/carbon (C/C) composites through plasma spraying technique. Ablation tests were carried out under oxyacetylene torch with a heat flux of 2.38 MW/m2. The alternate coating could offer 90 s ablation shield for C/C composites, providing superior ablation properties than all monolayered coatings. The improved ablation resistance is mostly induced by the fact that the outmost scale with abundant ZrO2 particles was able to better endure the mechanical denudation from the torch. Moreover, due to the indirect contact with torch, the innermost sublayers were placed into relatively mild environment, thereby most of Si-based oxides could be retained and further hinder oxygen transport inward during ablation.
TL;DR: A comprehensive review of the current advances on titanate glass-ceramic composite materials as waste forms for actinide immobilization is given in this paper , where some technical analysis and perspectives are provided pointing to the potential future studies.
Abstract: A comprehensive review of the current advances on titanate glass-ceramic composite materials as waste forms for actinide immobilization is given. Apart from providing a comprehensive summary of earlier works in the field, some technical analysis and perspectives are provided pointing to the potential future studies. • A comprehensive review on titanate glass-ceramic waste forms for actinide immobilization is provided. • Current advances on the titanate glass-ceramic composite materials are summarised. As the emerging versatile waste forms for immobilizing actinide-rich radioactive wastes, glass-ceramic composite materials based on some durable ceramic phases are being developed. They have apparent advantages over the conventional borosilicate glasses and multi- or single- phase ceramics as they essentially combine the chemical and processing flexibilities of glasses to accommodate processing impurities and excellent chemical durability of ceramic phases to host actinides. More recently, some new advances have been made on scientific and technological aspects including new glass-ceramic systems; improved understanding of ceramic phase evolution in glass; actinide validation studies and simplified processing techniques. This review is intended to cover the current advances on the development of glass-ceramic composite waste forms focusing on titanate ceramic phases (zirconolite, pyrochlore and brannerite) for immobilizing various actinide-rich radioactive wastes arising from the nuclear fuel cycle.
TL;DR: In this paper , a systematic overview of the design, fabrication, properties, and application of lightweight wear linings refractories is presented, and the scope for future work on this topic is presented.
Abstract: The design of lightweight wear linings is crucial in terms of the energy and resource efficiency of industrial furnaces and quality of final products. This review aims to present a systematic overview of the design, fabrication, properties, and application of lightweight wear lining refractories. The crucial properties and process routes of lightweight aggregates are summarised. Then, the structural design and factors that affect the refractories are described, and the application efficiency of the refractories is evaluated. Further, the scope for future work on this topic is presented.
TL;DR: In this article , the structural stability and mechanical properties of 56 quinary high-entropy metal carbides composed of carbon and groups IVB, VB, and VIB refractory transition metals, Ti, Zr, Hf, V, Nb, Ta, Mo, and W, were investigated.
Abstract: We have employed thermodynamics and first-principles density-functional calculations to investigate the structural stability and mechanical properties of fifty-six quinary high-entropy metal carbides composed of carbon and Groups IVB, VB, and VIB refractory transition metals, Ti, Zr, Hf, V, Nb, Ta, Mo, and W, thirty-eight of which have not yet been synthesized. To determine the stability of the quinary high-entropy metal carbides, we have constructed a three-dimensional phase diagram in terms of the average melting point, mixing enthalpy, mixing entropy, and lattice size difference, from which we predict that it is feasible to synthesize 38 new high-entropy metal carbides. We have further found that all the 56 metal carbides would have unique mechanical properties of high hardness and high fracture toughness. In addition, our study suggests that the brittleness of high-entropy metal carbides steadily decreases with the increase of the valence electron concentration.
TL;DR: In this article , a high-entropy n-type thermoelectric material with pure perovskite phase was prepared using a conventional solid state processing route, and the results of TEM and XPS showed various types of crystal defects and lattice distortions, such as oxygen vacancies, edge dislocations, in-phase rotations of octahedron and antiparallel cation displacements coexist in this highentropy ceramic, showed both a low thermal conductivity (1.89 W/m/K) and a high Seebeck coefficient (393 μV/K).
Abstract: In this work, a novel high-entropy n -type thermoelectric material Sr 0.9 La 0.1 (Zr 0.25 Sn 0.25 Ti 0.25 Hf 0.25 )O 3 with pure perovskite phase was prepared using a conventional solid state processing route. The results of TEM and XPS show that various types of crystal defects and lattice distortions, such as oxygen vacancies, edge dislocations, in-phase rotations of octahedron and antiparallel cation displacements coexist in this high-entropy ceramic. At 873 K, the high-entropy ceramics showed both a low thermal conductivity (1.89 W/m/K) and a high Seebeck coefficient (393 μV/K). This work highlights a way to obtain high-performance perovskite-type oxide thermoelectric materials through high-entropy composition design.
TL;DR: In this article, flash sintered MgO-doped Al2O3 ceramics were fabricated by flash sintering (FS) and pressureless sinterings (PS), and the results showed that FS-fabricated sample exhibited higher hardness (21.02 GPa) and fracture toughness (3.46 MPa m1/2).
Abstract: MgO-doped-Al2O3 ceramic discs were fabricated by flash sintering (FS) and pressureless sintering (PS). The results showed that MgO-doped Al2O3 exhibited typical characteristics of flash sintering under an electric field in excess 2500 V/cm. Compared with the PS- fabricated specimen, the flash sintered specimens exhibited sub-micron grains (≤760 nm) and homogeneous microstructures. The relative density of the flash sintered MgO-doped Al2O3 ceramics increased with current density, reaching 99.91 % when the current density increased to 7 mA/mm2. The FS-fabricated sample exhibited higher hardness (21.02 GPa) and fracture toughness (3.46 MPa m1/2) than PS-fabricated sample.
TL;DR: In this article , two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory.
Abstract: Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl2O4) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.
TL;DR: In this paper , the authors used a viscous polymer rolling process to synthesize a novel and eco-friendly 0.65Bi 0.5 Na 0.4 K 0.35 [2/3SrTiO 3 -1/3Bi(Mg 2/3 Nb 1/3 )O 3 ] (BNKT-ST-BMN) dielectric material, which possesses a very typical RAFE-like characteristic.
Abstract: Ideal relaxor antiferroelectrics (RAFEs) have high field-induced polarization, low remnant polarization and very slim hysteresis, which can generate high recoverable energy storage W rec and high energy storage efficiency η , thus attracting much attention for energy storage applications. True RAFEs, on the other hand, are extremely rare, and the majority of them contain environmentally hazardous lead. In this work, we use a viscous polymer rolling process to synthesize a novel and eco-friendly 0.65Bi 0.5 Na 0.4 K 0.1 TiO 3 -0.35[2/3SrTiO 3 -1/3Bi(Mg 2/3 Nb 1/3 )O 3 ] (BNKT-ST-BMN) dielectric material, which possesses a very typical RAFE-like characteristic. As a result, this material has a high W rec of 4.43 J/cm 3 and a η of 86% at an electric felid of 290 kV/cm, as well as a high thermal stability of W rec (>3 J/cm 3 ) over a wide range of 30–140 °C at 250 kV/cm. Our findings suggest that the BNKT-ST-BMN material could be a potential candidate for use in energy storage pulse capacitors.
TL;DR: In this paper , Zn-Ni co-modified LiMg 0.9 Zn 0.1-Ni 0.04 PO 4 sintered at 875 ℃ for 2 h.
Abstract: In this work, Zn-Ni co-modified LiMg 0.9 Zn 0.1- x Ni x PO 4 ( x = 0–0.1) microwave dielectric ceramics were fabricated using a solid state synthesis route. Rietveld refinement of the XRD data revealed that all ceramic samples have formed a single phase with olivine structure. SEM images showed that the samples have a dense microstructure, that agrees with the measured relative density of 97.73 %. Based on the complex chemical bond theory, Raman and infrared reflectance spectra, we postulate that ε r is mainly affected by the ionic polarizability, lattice and bond energy, while P-O bond plays a decisive role in Q×f and τ f value. Optimum properties of Q×f ~ 153,500 GHz, ε r ~ 7.13 and τ f ~ −59 ppm/°C were achieved for the composition LiMg 0.9 Zn 0.06 Ni 0.04 PO 4 sintered at 875 ℃ for 2 h. This set of properties makes these ceramics an excellent candidate for LTCC, wave-guide filters and antennas for 5 G/6 G communication applications.
TL;DR: In this article , a reverse manipulation of donor point defects, i.e., suppressing mobile zinc interstitial but increasing stable oxygen vacancy, was achieved to improve the long-term stability of NiO-doped ZnO varistor ceramics, with a degradation rate of 0.064 μA cm−2 h−0.5.
Abstract: Excellent electrical properties and the improved long-term stability of ZnO varistor ceramics were simultaneously achieved by doping NiO. The microstructural features were investigated using X-ray diffractometer, scanning electron microscopy, and energy dispersive spectroscopy, while the intrinsic point defects were characterized using frequency domain dielectric spectroscopy and verified by photoluminescence and Raman spectra. The results indicated that in the ZnO varistor ceramics, a reverse manipulation of donor point defects, i.e., suppressing mobile zinc interstitial but increasing stable oxygen vacancy, was achieved. The long-term stability of NiO-doped ZnO ceramics was improved via a decrease in zinc interstitial density, with a degradation rate of 0.064 μA cm−2 h−0.5. Meanwhile, due to an increase in oxygen vacancy density, the excellent nonlinear current–voltage performance, i.e., a high nonlinear coefficient (72.9), low leakage current density (0.08 μA cm−2), and low grain resistivity (13.43 × 10−3 Ω m), was maintained. The findings of this study provide a possible method for developing high-performance ZnO varistor ceramics by manipulating point defects.
TL;DR: In this article, two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory.
Abstract: Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl2O4) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.
TL;DR: In this paper , six dense multicomponent carbides (containing 5-8 cations) were prepared by a novel ultrafast high-temperature sintering (UHS) technique within a full period of 6 min, and three of them formed a single-phase high-entropy solid solution.
Abstract: Recently, high-entropy carbides have attracted great attention due to their remarkable component complexity and excellent properties. However, the high melting points and low self-diffusion coefficients of carbides lead to the difficulties in forming solid solution and sintering densification. In this work, six dense multicomponent carbides (containing 5–8 cations) were prepared by a novel ultrafast high-temperature sintering (UHS) technique within a full period of 6 min, and three of them formed a single-phase high-entropy solid solution. The solid solubility of the UHSed multicomponent carbides was highly sensitive to the compositional variation. The presence of Cr3C2 liquid had significant contributions to the formation of solid solution and the densification of multicomponent carbides. All UHSed multicomponent carbides exhibited high hardness, which, unexpectedly, did not simply increase with increasing number of the components. The highest nanohardness with a value of 36.6 ± 1.5 GPa was achieved in the (Ti1/5Cr1/5Nb1/5Ta1/5V1/5)Cx high-entropy carbide. This work is expected to expedite the development of high-entropy carbides and broaden the application of UHS in the synthesis and densification of advanced ceramics.
TL;DR: In this article , the authors reported an optimum composition of 0.7Bi(Fe 0.999Mn 0.001)O3-0.3BaTiO3 ceramic with a large piezoelectric constant (d33) of 230 pC/N and a high Curie temperature (TC) of 505 °C, which was attributed to the intentional introducing of the ceramic with MnO and MnO2 mixture.
Abstract: BiFeO3–BaTiO3–based solid solutions are promising candidates for high–temperature piezoelectric devices because of their high Curie temperature (TC) and considerable electrical properties. Here, we reported an optimum composition of 0.7Bi(Fe0.999Mn0.001)O3–0.3BaTiO3 ceramic with a large piezoelectric constant (d33) of 230 pC/N and a high TC of 505 °C, which was attributed to the intentional introducing of the ceramic with MnO and MnO2 mixture. Furthermore, an in situ d33 measurement was carried out, demonstrating excellent thermal stability for the 0.7Bi(Fe0.999Mn0.001)O3–0.3BaTiO3 specimen. The d33 remained above 200 pC/N in the temperature range of 25 °C–400 °C and its fluctuation was less than ± 15 %. It was determined that the high d33 in the 0.7BiFe0.999Mn0.001)O3–0.3BaTiO3 ceramic originated from a synergistic effect of rhombohedral distortion, intrinsic response, and ferroelectric order. The findings establish a solid correlation between electrical properties and phase/domain structure, and provide a novel approach to improve the piezoelectric properties for BiFeO3–BaTiO3–based ceramics.
TL;DR: In this paper , four kinds of sandwich-structured C/C-SiC composites with or without a SiC interphase were designed and fabricated by a joint process of electromagnetic coupling chemical vapor infiltration (ECVI) and precursor infiltration and pyrolysis (PIP).
Abstract: Four kinds of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with or without a SiC interphase deposited by isothermal chemical vapor infiltration (ICVI), were designed and fabricated by a joint process of electromagnetic coupling chemical vapor infiltration (ECVI) and precursor infiltration and pyrolysis (PIP). The fabricated composites are macroscopically nonhomogeneous materials with low density, high strength and low ablation rate. The interphase and matrix constituents had remarkable effects on the mechanical and ablation properties of these composites. The C/C-SiC composites with an ICVI-SiC interphase exhibited the highest flexural strength of 306.5 MPa. While the C/C-SiC-ZrC composites with the interphase showed the best anti-ablation performance with low linear and mass ablation rates of 0.37 μm/s and 0.04 mg/cm2·s, respectively, after the ablation for 500 s under an oxyacetylene flame test at around 2000 °C.
TL;DR: In this paper , the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content, which is conducive to improving hardness and toughness, as well as reducing grain size.
Abstract: High-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics, with different carbon contents (x=0.55−1), were prepared by spark plasma sintering using powders synthesized via a carbothermal reduction approach. Single-phase, high-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics could be obtained when using a carbon content of x=0.70−0.85. Combined ZrO2 and Mo-rich carbide phases, or residual graphite, existed in the ceramics due to either a carbon deficiency or excess at x=0.55 and 1, respectively. With the carbon content increased from x=0.70 to x=0.85, the grain size decreased from 4.36 ± 1.55 μm to 2.00 ± 0.91 μm, while the hardness and toughness increased from 23.72 ± 0.26 GPa and 1.69 ± 0.21 MPa·m1/2 to 25.45 ± 0.59 GPa and 2.37 ± 0.17 MPa·m1/2, respectively. This study showed that the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content. High carbon content is conducive to improving hardness and toughness, as well as reducing grain size.
TL;DR: In this paper, the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content, which is conducive to improving hardness and toughness, as well as reducing grain size.
Abstract: High-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics, with different carbon contents (x=0.55−1), were prepared by spark plasma sintering using powders synthesized via a carbothermal reduction approach. Single-phase, high-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics could be obtained when using a carbon content of x=0.70−0.85. Combined ZrO2 and Mo-rich carbide phases, or residual graphite, existed in the ceramics due to either a carbon deficiency or excess at x=0.55 and 1, respectively. With the carbon content increased from x=0.70 to x=0.85, the grain size decreased from 4.36 ± 1.55 μm to 2.00 ± 0.91 μm, while the hardness and toughness increased from 23.72 ± 0.26 GPa and 1.69 ± 0.21 MPa·m1/2 to 25.45 ± 0.59 GPa and 2.37 ± 0.17 MPa·m1/2, respectively. This study showed that the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content. High carbon content is conducive to improving hardness and toughness, as well as reducing grain size.
TL;DR: In this paper , the existence of the secondary phase significantly increases the τ f value and improves the sintering behavior of Zn 0.85 (Li 0.5 Bi 0.25 ) O 4 secondary phase.
Abstract: Zn 1−x (Li 0.5 Bi 0.5 ) x Mo x W 1−x O 4 (x = 0–0.25) ceramics were prepared using the solid-state reaction process. The results show that the existence of the (Li 0.5 Bi 0.5 )MoO 4 secondary phase significantly increases the τ f value and improves the sintering behavior. When sintered at 755 °C, the sample with x = 0.05 exhibits the highest Q × f value (37,551 GHz), while the ceramics with x = 0.15 and 0.20 display excellent τ f values, − 6.569 and − 3.097 ppm/°C, respectively. Additionally, X-ray diffraction refinement, Raman and infrared spectroscopy, and the complex bond valence theory were used to investigate the relationship between the phase, structure, and vibration characteristics and the microwave dielectric properties. Good microwave dielectric properties were obtained for the Zn 0.85 (Li 0.5 Bi 0.5 ) 0.15 Mo 0.15 W 0.85 O 4 ceramic sintered at 755 ° C: ε r = 18.937, Q × f = 20,022 GHz , and τ f = −6.569 ppm/°C, which provides a promising candidate for low temperature co-fired ceramic technology.