Search

Vat photopolymerized 3D printing technology can be used to fabricate ceramics with complex shapes. However, the extensive use of photosensitive resins as binders is not conducive to achieving crack-free ceramic green parts, especially the Si 3 N 4 ceramics with the weak interlayer bonding. In this work, the influence of different debinding atmosphere on the pyrolysis process of organics in vat photopolymerization 3D printed Si 3 N 4 green parts was investigated. The results showed that the use of 95 vol% N 2 +5 vol% H 2 atmosphere can effectively inhibit the cracking during the debinding process, especially the wall thickness of the 3D printed defect-free Si 3 N 4 green body was successfully increased to 5 mm, and the obtained sintered Si 3 N 4 ceramics exhibited higher true densities and better mechanical properties. The debinding atmospheres proposed in the current work provided additional options of debinding atmosphere for achieving high-performance 3D printed Si 3 N 4 ceramics and are expected to be expanded to other photosensitive slurry systems, with the potential to enable the production of ceramic components with the larger wall thicknesses. [ABSTRACT FROM AUTHOR]

Inspired by the double-helix structure of biological DNA, low-volume fraction and high-strength Al 2 O 3 twisted honeycomb structures with characteristics similar to those of helical structures in the z -axis were prepared by digital light processing 3D printing technology. As the twist angle increased, the compressive strength of the fabricated Al 2 O 3 structure decreased, and the deformation mechanism of the Al 2 O 3 structures gradually changed from stretching-dominated to bending-dominated, which can be predicted by the Gibson–Ashby model. The relationship between the effective elastic modulus and the volume fraction that can be modified by varying the wall thickness was described by the Pabst–Gregorova exponential relationship. The compressive strength of the Al 2 O 3 structure with a twist angle of 0° can reach 62.4 MPa at a volume fraction of 13.3%, providing guidance to optimize lightweight structures of ceramics. [ABSTRACT FROM AUTHOR]

Digital light processing 3D printing can be applied to fabricate complex silicon nitride (Si 3 N 4) components. However, because of the surface hydroxyl groups and large refractive index, it is still a foremost challenge to realize a stable photosensitive Si 3 N 4 slurry with combined benefits of low viscosity and large curing depth. In this study, we propose a new formulation strategy to prepare Si 3 N 4 slurry. Starting from the optimization of monomer ratio, we have systematically optimized powder particle size, dispersant and photoinitiator on the rheological properties and curing properties of Si 3 N 4 slurry. Specifically, we have fabricated a stable photosensitive Si 3 N 4 slurry (48 vol%) with a viscosity of 2.09 Pa s (30 s−1), a critical curing energy of 126.09 mJ/cm2 and a maximum curing depth of 80 µm. Finally, based on this optimized slurry, we have successfully obtained complex Si 3 N 4 green body with no defect, which demonstrates great potential to fabricate arbitrary complex ceramic components for various applications. [ABSTRACT FROM AUTHOR]

Nano-SiO 2 porous thermal insulating material (TIM) has drawn tremendous research interests due to its advantages of low density, high porosity and low thermal conductivity. However, its long-term stability in humid environment can be severely deteriorated by the high hydrophilicity resulting from tetrahedral coordination of oxygen and capillary effect of porous structure. It is still a great challenge to cost-effectively fabricate bulk TIM with superior hydrophobicity and consequent remarkable self-cleaning capability. Herein, via an oil-in-water microemulsion treatment, we have proposed a new strategy to construct 3D superior hydrophobic nano-SiO 2 porous TIM. The polymethylhydrosiloxane-modified TIM exhibits a large water contact angle of 166°, and corresponding excellent self-cleaning characteristic while maintaining low thermal conductivity of 0.031 W/m·K. Moreover, our high hydrophobicity of TIM exhibits excellent durability under high temperature up to 400 °C, high humidity of 100%, and chemical erosions. Detailed knowledge of the physical chemistry basis of the superior hydrophobic nano-SiO 2 porous TIM can provide great opportunity to fabricate advanced self-cleaning and heat insulating devices especially targeted for harsh environments. [ABSTRACT FROM AUTHOR]

Regarding advanced 5G mobile communication, microwave dielectric ceramics are considered as the most potential materials to develop new-generation base station resonators. Herein, ZnNb 2 O 6 ceramics with ε r of approximately 24 have been prepared using the solid-state reaction method, with tailored extra ZnO of x mol% (x = 1, 2 and 3). We have for the first time applied the P-V-L chemical bond theory to investigate ZnNb 2 O 6 ceramics with ZnO doping, by exploring the relationship of dielectric properties and chemical bond characteristics. Particularly, the Raman spectra demonstrates that the full width at half maximum of υ 1 (A g) vibration mode can exhibit significant correlation with the quality factor (Q × f). To further support the experimental study, we have also conducted the first-principle calculation of electron density difference via CASTEP package, which further confirms the change of temperature coefficient of resonance frequency (τ f). Our newly designed ZnNb 2 O 6 ceramics doped with 1 mol% ZnO exhibit excellent dielectric properties, i.e., ε r = 23.74, Q × f = 102,824 GHz and τ f = −55.38 ppm/°C, which demonstrates great potential to construct miniaturized 5G base station with advanced ceramic dielectrics. [ABSTRACT FROM AUTHOR]

Due to its superior reliability and performance, thick film technology is extensively employed in various applications, including automotive electronics, consumer electronics, communication engineering, and aerospace. However, a challenge arises from the mutual diffusion during the electronic paste production process, which leads to a decline in insulation performance and hinders the production of three-dimensional equipment. Inspired by the principles of low-temperature co-fired ceramic technology, a multi-layered ceramic structure has been successfully bonded using thick film technology by introducing a borosilicate glass-ceramics layer. To further enhance the properties of this multi-layered ceramic structure, approximately 8 wt% SiO 2 was incorporated into the borosilicate glass-ceramics. This addition effectively inhibits silver diffusion and reduces the diffusion depth within the glass-ceramic film. The key mechanisms behind this improvement are the increased activation energy for crystallization, resulting in a slower crystallization rate due to the addition of SiO 2. Moreover, the multi-layered ceramic with a sandwich structure exhibits remarkable properties. Notably, the dielectric strength of this system has been significantly enhanced to 13.9 kV/mm, accompanied by a high adhesion strength of 790 N. These enhanced properties of the optimized system indicate promising characteristics for multi-layer circuit applications. [ABSTRACT FROM AUTHOR]

We have optimized a CuO-doped silver paste to significantly improve the adhesion strength of silver thick film on AlN ceramic substrate, which can be widely applied in power electronic packaging applications. Via a combination of scanning electron microscope and X-ray diffraction, we have systematically studied the silver layer morphology on top of AlN ceramic substrate, and the interphases between the silver thick film and AlN substrate. Due to the CuAl 2 O 4 intermediate formed at the silver layer/AlN interface, the adhesion strength of silver thick film can be greatly improved. Particularly, the silver paste with 3 wt% nano-CuO sintered on AlN ceramic substrate exhibits high adhesion strength of 15.3 MPa with good electrical conductivity of 0.9 mΩ/□. [ABSTRACT FROM AUTHOR]

Ceramics joining has been widely applied in MEMS sensors, microwave and imaging devices as well as other ceramic packaging applications to fabricate multifunctional ceramic components. In this study, a glass frit with gradient thermal expansion coefficient (TEC) has been applied as the bonding material to join the ceramic of Al 2 O 3 and AlN. This glass frit consists of two types of glasses with different TEC. The Al 2 O 3 and AlN ceramics have been successfully joined with this glass frit in muffle furnace at 850 °C for 1 h. The bonding strength of Al 2 O 3 /AlN ceramic joined via this glass frit exceeds 40 MPa without any cracks in the joining interface, which is much superior compared with that of conventional glass frit bonding. Our work demonstrates that the gradient-TEC glass frit bonding is an effective method to join different types of ceramics. [ABSTRACT FROM AUTHOR]

PbO–ZnO–B 2 O 3 (PZB) glass with low-melting temperature has been widely applied in microelectromechanical systems (MEMS) packaging. However, the high thermal expansion coefficient (TEC) of PZB glass usually leads to strict packaging requirements. Here, in order to achieve ideal TEC, we have introduced β -eucryptite into PZB/ β -eucryptite composite glass and optimized the composite fabrication process. Firstly, PbO:ZnO:B 2 O 3 in mol ratio of 65:15:20 was selected as glass matrix owing to its low-melting temperature and good wettability. Then, β -eucryptite ceramics with ultra-low TEC were synthesized via a facile solid-state reaction method to optimize subsequent composite TEC value. The combination of corresponding material and device characterizations suggest that the pure phase and regular columnar grains of β -eucryptite ceramic can be obtained by sintering at 1450 °C for three hours, which can result in the lowest negative TEC of α 30-300°C = −10.74 × 10−6 K−1. Furthermore, regarding the PZB/ β -eucryptite composite glasses, systematic experiments demonstrated that the β -eucryptite introduction can greatly impact the TEC of matrix glass with only negligible effect on the softening point (T s). Importantly, composite glasses with TEC of α 30-300°C = 3.26 × 10−6 K−1, T s = 380 °C and wetting angle < 30° are ideal for MEMS packaging. This work implements optimized fabrication process to obtain low-melting PZB/ β -eucryptite composite glasses with ideal TEC values, which can be envisaged to be applied in advanced MEMS packaging applications. [ABSTRACT FROM AUTHOR]

The influence of BaO content (up to 15 mol%) on the crystallization behaviour, structure, thermal properties and microwave dielectric properties of the BaO-CaO-B 2 O 3 -SiO 2 glasses and glass-ceramics system was investigated. The glasses were produced by melting at 1400 °C and quenching into water, and the glass-ceramics were produced via heat treatment at temperatures between 750 and 800 °C. The results of X-ray diffraction analysis showed that increasing the BaO content raised the resistance of the glass against crystallization and favoured the transformation of β-CaSiO 3 and α-CaSiO 3 phases, which crystallized in the Ba-free and in low BaO content compositions, into SiO 2 and Ba 4 Si 6 O 16 , which crystallized in compositions with higher concentrations of BaO. The BaO content had little influence on the glass transition temperature ( T g ) and the linear coefficient of thermal expansion (CTE), but strongly reduced the softening point ( T s ). Even the addition of BaO as minor additives resulted in a dramatic reduction of the T s ; for example, the T s decreased from 902 °C for the Ba-free composition to 682 °C for the BaO-containing one (5%). Low values of the dielectric constant (5.9 ≤  ε r ≤ 6.63) and dielectric loss (1.12 × 10 −3 ≤ tan δ  ≤ 3.15 × 10 −3 ) were measured. [ABSTRACT FROM AUTHOR]

A novel method for preparing aluminum/aluminum nitride ceramics (Al/AlN) substrates is proposed in this paper. The method included two processes: (1) the surface of AlN was coated with a CuO thick film and sintered; (2) Al foil was put on the pretreated (in process 1) AlN surface and bonded to AlN through pre-heating at 400 °C and final heating at 660 °C in N 2 -H 2 reduction atmosphere. The experimental results obtained by optical and scanning electron microscope (SEM) observations as well as by X-ray diffraction analysis at the cross-sections of the joints and the fracture surfaces, suggest that the reaction mechanism starts with the reaction of CuO with AlN to form CuAlO 2 , when the AlN coated with CuO is heat-treated at high temperature. A Cu layer is produced by the reduction of CuO and Cu diffuses in the Al foil, forming strong Al/AlN joints. Elongated crystals of Al 2 Cu are developed in the reaction zone at the interface between Al and AlN. The results of mechanical tests showed that the peeling-off strength of the Al foil from the surface of the AlN substrate reached a value of 15.4 MPa for the Al/AlN couples produced after 30 min of heat treatment at 660 °C. [ABSTRACT FROM AUTHOR]

Perovskite ceramics with a formula of Ca 0.7 Ti 0.7 La 0.3 Al 0.3 O 3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La 3+ -doping methods using powders of La 2 O 3 , or La 2 O 3 /Al 2 O 3 powder mixture, or LaAlO 3 . La 3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La 2 O 3 and La 2 O 3 /Al 2 O 3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO 3 , which caused a coarsening of the microstructure and lowered the La 3+ doping effects on the dielectric properties. The experimental results suggest that La 3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al 3+ ions in small amounts. However, further increase of Al 3+ ions content jeopardizes them. [ABSTRACT FROM AUTHOR]

Ca 0.66 Ti 0.66 Sm 0.34 Al 0.34 O 3 (CTSA) ceramics were produced using a solid-state reaction method, and their sintering behavior, microwave dielectric properties, and microstructure were investigated. Sintering temperature affected the unit cell volume and the lattice parameters of the CTSA ceramics as well as the grain size distribution, the Gibbs free energy, the thermal expansion coefficient (CTE), and the dielectric properties (ε r , Q×f, τ f ). The samples sintered at 1500 °C displayed the best dielectric constant and Q×f, as 42.49 and 46069.86 GHz, respectively. [ABSTRACT FROM AUTHOR]

BaO-Sm 2 O 3 -5TiO 2 (BST5) ceramics with NdAlO 3 additions of up to 15 wt% were produced with a solid state reaction method, and their structural and microwave dielectric properties were determined. Experimental results showed that NdAlO 3 neither merged nor altered the orthorhombic tungsten bronze structure of the main phase of the produced ceramics (except for a shrinkage in the crystal lattice), but it was segregated in distinct grains in the microstructure of the produced ceramics. However, the amount of NdAlO 3 strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (ε r ) and the temperature coefficient of resonant frequency (τ f ) of the produced BLT5 ceramics can be tuned with the amount of NdAlO 3 additions and the sintering process parameters. The best dielectric properties were achieved for BaO-Sm 2 O 3 -5TiO 2 ceramics with 7.5% NdAlO 3 (ε r =73.22, Q×f =10,300 GHz, and τ f =−1.05 ppm/°C). [ABSTRACT FROM AUTHOR]

Surface metallization of aluminum nitride is performed by a reactively thick film method. A layer of copper film is deposited on the surface of AlN ceramics. The morphology and composition of the metalized copper layer on ceramic substrate were investigated via scanning electron microscope (SEM) and X-ray diffraction (XRD). The interface layer between copper film and AlN substrate was examined through SEM, XRD and EDS. Reaction phases, Cu 2 O and intermediate phases (CuAlO 2 and CuAl 2 O 4 ), were detected at the interface layer. Subsequently, the formation process of these phases at the interface layer was discussed. And consequently, the relation within reaction phases and bonding strength was observed. Reaction phases play a key role in increasing bonding strength. The effect of these phases such as Cu 2 O and intermediate phases (CuAlO 2 and CuAl 2 O 4 ) on the mechanical property was discussed. Results show that the presence of Cu 2 O particles are detrimental to bonding strength. However, spinel CuAl 2 O 4 and isolated CuAlO 2 laminates at the interface layer can increase the bonding strength. The experimental results suggest that this thick film method is a useful technology for various metal-ceramics bonding. [ABSTRACT FROM AUTHOR]

Abstract: The production of composites of epoxy molding compounds (EMCs), which can feature a good balance between thermal conductivity and flame-retardant behavior in terms of flammability and burning behavior, was achieved by incorporating high thermal conductivity Si3N4 and flame retardant Al(OH)3 (ATH) fillers in the epoxy matrix. The experimental results were obtained from thermal conductivity measurements and limiting oxygen index (LOI) and UL-94 tests. These results showed that the Si3N4 filler has a great influence on thermal conductivity, which markedly increased for Si3N4 volume fractions >40%, whereas the ATH filler greatly improved the flame resistance of EMCs. The simultaneous presence of both Si3N4 and ATH fillers in the EMCs positively influenced both properties. The aim of this study was to produce composites suitable for electronic packaging applications: an optimum combination of the two fillers was determined for a total volume fraction of fillers in EMC of 60vol.% and a volume ratio of Si3N4:ATH at 3:2; this composite had a thermal conductivity of 2.15W/mK, an LOI of 53.5, and a UL-94 vertical burning test ranking of V-0. [Copyright &y& Elsevier]

Abstract: Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603nm, a full width at half maximum of 110nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31Å. [Copyright &y& Elsevier]

Abstract: CaSi2O2N2 phosphors co-doped with Ce3+ and Eu2+ was synthesized via solid-state reaction method. The experiments aimed at optimizing the composition of those phosphors for achieving the highest luminescence intensity as well as at shedding light in the mechanism that governs their luminescence behavior. The overlap of the blue emission spectrum due to Ce3+ with the yellow excitation spectrum due to Eu2+ suggests resonance-type energy transfer mechanism from Ce3+ to Eu2+ taking place in the CaSi2O2N2 host lattice, where electric dipole–dipole interactions dominate. The properties of the produced phosphors qualify them for further consideration in the technology of white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: Ce3+/Eu2+ co-doped Li2SrSiO4 phosphor yields two emission bands consisted of blue and yellow components, which shows great potential as single host white phosphor for white LEDs. Effective energy transfer occurs in Ce3+/Eu2+ co-doped Li2SrSiO4 due to large spectral overlap between the emission of Ce3+ and excitation of Eu2+. Co-doping of Ce3+ enhances the emission intensity of Eu2+ greatly by transferring its excitation energy to Eu2+. The Ce3+ →Eu2+ energy transfer, thoroughly investigated by their absorption, excitation and photoluminescence decay behaviors, is demonstrated to be in the mechanism of electric dipole–dipole interaction. [Copyright &y& Elsevier]

Abstract: Eu2+ and Mn2+ co-doped SrSi2O2N2 green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500nm and a broad emission band centered at ca. 530nm, attributed to 4f–5d transitions of Eu2+. The emission intensity of Eu2+ ions was greatly enhanced by introducing Mn2+ ions into SrSi2O2N2:Eu2+ due to the energy transfer from Mn2+ to Eu2+. The energy transfer probability from Mn2+ to Eu2+ depends strongly on the Mn2+ concentration, which is maximized at a Mn2+ concentration of 3mol%. It drastically decreases for higher concentrations. The results indicated that SrSi2O2N2:Eu2+, Mn2+ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips. [Copyright &y& Elsevier]

Abstract: Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473nm originated from the 5d–4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: A kind of polymer composite was fabricated using polystyrene as the matrix and Si3N4 powder as filler employing the method of heat press molding. Microstructure, thermal conductivity and dielectric constant of the Si3N4 filled composite were evaluated. The effect of the volume fraction of Si3N4, the particle size of the polystyrene matrix and the silane treatment of Si3N4 filler on the thermal conductivity of the composite was investigated; dielectric constant of the composite was evaluated. The main factors that affect the thermal conductivity of the composite were confirmed through theoretical analyzing of the experimental data and the thermal conductivity model. Experimental results show that with the filler content increasing, a thermally conductive network is formed in the composites, thus the thermal conductivity of the composite increases rapidly. The composites experience a highest thermal conductivity of 3.0W/mK when the volume fraction of the filler reaches 40%. The increasing of thermal conductivity is dominated by the ease of forming a thermal conductive network. A larger polystyrene particle size, a higher Si3N4 filler content and the silane treatment of the filler have a beneficial effect on improving the thermal conductivity. The dielectric constant increases with the content of Si3N4 filler, however, it remains at a relatively low lever (<4, at 1MHz). [Copyright &y& Elsevier]

Abstract: Porous sialon ceramics have been cost-effectively prepared by pressureless sintering from a mixture of elongated SHS β-sialon powders with an α-sialon precursor composition composed of α-Si3N4, AlN, Y2O3 and Al2O3. The obtained porous sialon ceramics exhibited low shrinkage and homogeneous pore size distribution. The results of X-ray diffraction and scanning electron microscopy showed that a uniform microstructure with elongated and intermingled β-SiAlON grains, which were strongly connected by α-SiAlON phase, has been obtained. [Copyright &y& Elsevier]

Abstract: Aluminium nitride (AlN) powders were prepared by self-propagating high-temperature synthesis (SHS). Aluminium and AlN powder mixtures with weight ratios of about 60:40, in the absence and in the presence of 3-wt.% NH4F and 3-wt.% NH4F+3-wt.% carbon powders as additives were ignited in a nitrogen atmosphere of 8 MPa. Highly crystalline AlN particles with regular hexagonal morphology were obtained in the presence of 3-wt.% NH4F+3-wt.% carbon. The microstructure development during the reaction and the influence of these additives were determined by SEM/EDS and XRD analysis of the resulting products. A mechanism for the formation of AlN with a regular hexagonal morphology has been suggested. [Copyright &y& Elsevier]

Reaction sialon suspensions were prepared using 3-wt.% KD1 (a polyester/polyamine condensation copolymer) as dispersant in organic media of 60-vol.% methyletheylketone and 40-vol.% ethanol. Different homogenizing procedures were used and compared, such as: high energetic planetary milling, low energetic ball milling and ultrasonic disaggregation. The effect of different homogenizing routes and solids loading on the rheology of suspensions and on the properties of slip casting green bodies has been studied. The differences observed among the various mixing procedures could be attributed to the different degrees of disaggregation and therefore to different fractions of surface coverage of the reaction sialon powders by the dispersant. [Copyright &y& Elsevier]

For new-generation miniaturized and high-frequency electronics, it is of vital importance to develop advanced electronic packaging materials, which combine high electromagnetic interference (EMI) shielding effectiveness (SE) and efficient thermal management capabilities, including heat absorption, thermal conductivity (TC) and heat dissipation. However, high EMI SE and efficient thermal management usually cannot complement each other for the same packaging material, because EMI shielding devices convert electromagnetic radiation directly into heat consumption, leading to consequent severe challenge to dispose heat dissipation. Herein, we have newly developed a high-performance phase change composites, in which MXene is confined in shape-stabilized phase change material (PCM) for simultaneous achievement of high EMI SE and efficient thermal management. Regarding high EMI, MXene can effectively shield electromagnetic radiation by converting the radiation into heat consumption. As for thermal management, PCM enables efficient heat absorption via the phase change process, and MXene enhances the thermal conductivity (TC) of MXene/PCM composite to facilitate heat dissipation. As a result, our developed MXene/PCM composite can achieve a high EMI SE of 64.7 dB in X-band, with an improved TC of 0.74 W/m·K. Furthermore, the interlayer capillary effect of MXene inhibits the leakage of liquid PCM during the solid-liquid phase transition, which can maintain the PCM shape stability. Our newly-designed shape-stabilized MXene/PCM composites with high EMI SE and large TC shed new light on designing EMI shielding materials with prolonged exposure to electromagnetic radiation, which can be envisioned to exhibit vast implications for advanced new-generation miniaturized and high-frequency electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

• B-site precursor method can effectively inhibit the appearance of second phase. • B-site precursor method can obtain high reactivity Mg 4 Nb 2 O 9 powders. • B-site precursor method can promote integrality of the crystal structure. Mg 4 Nb 2 O 9 ceramics have been prepared by B-site precursor method in this work. Experimental results demonstrate that the uniform particles-size distribution of Mg 4 Nb 2 O 9 powders can be obtained, which exhibit high reactivity to promote the grain growth of Mg 4 Nb 2 O 9 ceramics. Moreover, the Mg 4 Nb 2 O 9 ceramics via B-site precursor method can be sintered at a wide range of sintering temperature from 1275 to 1375 °C with single phase Mg 4 Nb 2 O 9 composition and high crystallinity. Compared to the conventional solid-state method, the Mg 4 Nb 2 O 9 ceramics prepared by B-site precursor method exhibit excellent Q × f value by above 168,756 GHz. [ABSTRACT FROM AUTHOR]

Abstract: Tb-doped SrSi2O2N2 phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400–470nm and 480–650nm, which are attributed to 5D3→7F j (j=5, 4, 3) and 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+, respectively. The green emission from 5D4→7F5 at 543nm showed the highest intensity under the optimized concentration of 0.1mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb3+ was explained by the cross-relaxation of its excited state. [Copyright &y& Elsevier]

Abstract: The oxygen content is usually difficult to control in direct bonding copper process. In this study a new method for preparation of direct bonding copper on alumina ceramic substrates was realized. 96% Al2O3 ceramic substrates were first oxidized by pasting a thin layer of Cu2O and firing at 1150 °C in air. Then copper foil was bonded to the substrate by heating to 1070 °C in pure N2 atmosphere. Microstructure and composition of the interface between the copper and Al2O3 ceramic were analyzed. The XRD and EDS results show that an interphase of CuAlO2 was formed and a eutectic transformation between oxygen and copper took place at the interface of the copper and the ceramic substrate. The interface was much thicker than the traditionally bonded substrates, which resulted in a better bonding strength. The directly bonded copper alumina substrate samples showed no evidence of de-bonding after 50 thermal cycles comprising quenching from 220 °C to room temperature. [Copyright &y& Elsevier]