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Abstract: The crystal structure, band gap energy and bowing parameter of In-rich In x Al1−x N (0.7< x <1.0) films grown by magnetron sputtering were investigated. Band gap energies of In x Al1−x N films were obtained from absorption spectra. Band gap tailing due to compositional fluctuation in the films was observed. The band gap of the as-grown InN measured by optical absorption method is 1.34eV, which is larger than the reported 0.7eV for pure InN prepared by molecular beam epitaxy (MBE) method. This could be explained by the Burstein–Moss effect under carrier concentration of 1020 cm−3 of our sputtered films. The bowing parameter of 3.68eV is obtained for our In x Al1−x N film which is consistent with the previous experimental reports and theoretical calculations. [Copyright &y& Elsevier]

Abstract: Ba2+-doped Sr2SiO4:Eu2+ phosphors were synthesized with the high-temperature solid-state reaction technique. The experimental results, summarized in the successful production of a single-phase powder with fine microstructure of spherical particles with smooth surface, suggest that Ba2+-doping favors the stabilization of α′-Sr2SiO4. Rietveld refinement of X-ray diffractograms suggests that Ba2+ and Eu2+ ions occupy the sites of Sr2+ in the lattice of α′-Sr2SiO4. The produced phosphors show two intense emission bands at green and yellow regions of spectrum, originated from Eu2+ ions accommodated at two different sites in the host crystal, whose peaks depend on the concentrations of Ba2+ and Eu2+. Intense and broad excitation spectra extend from ultraviolet to the blue region. [Copyright &y& Elsevier]

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF2 and YF3 as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F2 and Ca12Al14O32F2. Liquid CaYAlO4 mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F2 at a relatively low temperature results in homogeneous YF3 distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity. [Copyright &y& Elsevier]

The ability of Hypermer KD1 to disperse high solids loading reaction sialon suspensions for slip casting has been characterised. It has been found to be a very effective dispersant in organic media of 60-vol.% MEK and 40-vol.% Ethanol, yielding fluid and highly homogeneous suspensions. The effects of added amounts of KD1 have been observed through adsorption data, sedimentation tests and rheology measurements. KD1 imparts low viscosity and stability to the suspension. It has been found that 3-wt.% addition of KD1, based on the weight of reaction sialon powders, results in a very stable and high flowable suspension with near Newtonian flow behavior. Less amounts of dispersant lead to unstable suspensions with obvious shear thinning flow behaviors, while adding excessive dispersant leads to high viscosities, especially at high solids loading. Measuring the pore size distribution of green bodies from different suspensions has proved the effects of dispersant amounts on dispersing the slurries and on slip casting performance. [Copyright &y& Elsevier]

The oxidation of AlN powder added by the fluorides at temperatures below 700°C in air was discovered in this study. The obvious onset of oxidation of AlN with cryolite and YF3 additions is below 700°C with the product of α-Al2O3 phase, which usually occurs in single AlN powder above 1100°C. The changes on the weight and the FTIR spectra of the AlN powder fired at temperatures lower than 700°C show that cryolite and YF3 greatly promote the oxidation of AlN powder at these temperatures. Different from the action of cryolite and YF3 powder, CaF2 has no obvious effect on the oxidation of AlN. A possible oxidation process, in part corroborated by FTIR and XRF, was proposed to explain the results in the experiments. The oxidation kinetics of AlN in the presence of cryolite were also discussed at the temperatures ranging from 550 to 700°C from the data of the weight gains in this region. The result shows that the oxidation follows a linear law, which implies a reaction rate-controlled process. The considerably low activation energy of 67 kJ mol−1, which is associated with the quick oxidation and the formation of α-Al2O3 at temperatures below 700°C, was determined from the slope of the line fit. [ABSTRACT FROM AUTHOR]

• Polymer-matrix composites. • 3-Dimensional reinforcement. • Thermal properties. • Syntactic foams. • Hollow glass microspheres. Electronic packaging materials with low dielectric constant (D k) and high thermal conductivity (TC) are of vital importance in mitigating signal delay and enhancing heat dissipation efficiency in modern electronics. However, low D k and high TC are difficult to complement each other, because high TC filler usually possesses a high D k. Herein, we have newly designed a composite material simultaneously with low D k and high TC through hollow glass microspheres (HGMs), boron nitride particles, epoxy resin and reticulated porous ceramic (RPC). The composite material prepared by sintering HGMs and RPC is more effective in improving TC while keeping low D k. Specifically, the D k of the newly designed composite is lower than 3.0 with a large TC of 0.96 W/m·K. This new epoxy-matrix composite with both low D k and high TC can shed new light on designing electronic packaging materials for advanced miniaturized electronics. [ABSTRACT FROM AUTHOR]

As a light-weighting structural material, aluminum alloy is being applied in the automobile and high-speed train, the property of which however is affected by the content of hydrogen, and much importance has been attached to the impact property of aluminum alloy. In this study, hydrogen was determined in ER5183 welding wire and afterwards the effect of hydrogen content on the impact property of Al–Mg MIG weld is investigated to clarify the mechanism of hydrogen action which provided a reasonable control range of hydrogen content in aluminum welding wire. The results show that the impact toughness of the weld is decreased with the increasing hydrogen content. In addition, the decohesion of impurities from the matrix and the formation of porosity are also observed in the weld. The morphology of impact fracture appears facet and porosity due to the "hydrogen-enhanced localized plasticity" effect on plasticity. Considering the good impact property as well as the fine microstructure of the weld, hydrogen content of the ER5183 welding wires should be controlled below 0.18 μg/g. • Introducing hydrogen by using ER5183 welding wires into Al–Mg weld. • Studying the effect of hydrogen embrittlement on impact properties of Al–Mg weld. • Investigating the influence of hydrogen on morphology of impact fracture of Al–Mg weld. • Describing the hydrogen-induced dislocation motion and multiplication phenomenon. • Giving a reasonable range of hydrogen content in ER5183 aluminum welding wire. [ABSTRACT FROM AUTHOR]

A new composite structure (glass fiber assembly-filled honeycomb sandwich panel) is prepared in order to improve the acoustic properties. Effect of glass fiber assembly with different filling shapes (random and fiber ball), fiber diameter, fiber content and air-layer on acoustic properties are explored. Sound absorption coefficient (SAC) and sound transmission loss (STL) are determined by a B&K impedance tube. The experiment results indicate that the first resonance frequency of SAC disappears along with the improvement of the second resonance frequency by reducing the fiber diameter or increasing the fiber content. STL can be improved by the increase of the fiber content. Random glass fiber assembly with the fine fibers has the best STL in the all testing samples. The advantage of glass fiber assembly for improving the STL of honeycomb sandwich panel is particularly clear at frequencies below 4.5 kHz. Especially, the STL difference reaches the maximum at around 20 dB at frequencies below 3.0 kHz. [ABSTRACT FROM AUTHOR]

YAG:Ce3+ yellow phosphor are particularly used luminescent materials to produce white light in phosphor-converted white LED (pc-WLED). Surface coating of YAG phosphor is the main concern for desired optical performance of the phosphors. Many scholars conducted various experimental analysis on the surface coating of phosphors to improve yellow emission, but the theoretical explanation by which phosphor coating could help improving light efficiency has not yet been studied. In this paper, based on Mie theory, the optical constants such as scattering coefficient, absorption coefficient and asymmetry parameter of YAG:Ce3+ phosphor and YAG@SiO 2 (YAG:Ce3+ phosphor surface coated with nano-SiO 2 layer) were calculated. An optical configuration of chip scale packages (CSP) WLED was constructed by coupling YAG:Ce3+ or YAG@SiO 2 phosphors with a LED laser. Based on the optical parameters calculated by Mie theory, the luminescent properties of YAG:Ce3+ and YAG@SiO 2 WLED were simulated by Monte Carlo method. The results showed that a thin SiO 2 coating layer on YAG phosphor result in an overall increase in luminous performances compared with original YAG WLED. The absorption coefficient of phosphor is the main concern affecting the light emission in WLED. Due to the fact that YAG@SiO 2 possess higher 460 nm absorption coefficient (460 μ a b s) , it could absorb more blue light than YAG, thereby it has a 1.2% higher conversion efficiency than YAG, finally the enhanced luminous efficiency of YAG@SiO 2 WLED is obtained. The results obtained in this work provides a potential method in future WLED packaging designing. • We improve the overall light extraction efficiency from the perspective of adjusting the structure of a single phosphor particle. • The optical constants of YAG phosphor and YAG@SiO 2 (YAG surface coated with nano-SiO 2 layer) were calculated based on Mie theory. • The luminescence performances of YAG and YAG@SiO 2 CSP WLED were simulated, the results showed that the absorption coefficient of phosphor is the main concern affecting the light emission in WLED. [ABSTRACT FROM AUTHOR]

• MXene/AgNWs aerogels with interpenetrating double-network structure were fabricated. • The porous structure contributes to higher attenuation of electromagnetic waves. • 3D network provides channel for electron and phonon transmission in epoxy composites. • The composites possess remarkable EMI SE and thermal conductivity. The novel multifunctional materials with anti-electromagnetic interference (EMI) and effective thermal management are ideal for modern electronic industry. Generally, the EMI shielding effectiveness (SE) and thermal conductivity (TC) of materials can be effectively enhanced by compounding with high electrically and thermally conductive fillers. However, it seems that the high-performance cannot be compensated without sacrificing the high fillers loading. Herein, from one-dimensional silver nanowires (AgNWs) and two-dimensional MXene, three-dimensional MXene/AgNWs aerogels were designed as electric and heat transferring skeletons for epoxy nanocomposites by directional-freezing and freeze-drying methods. The resultant MXene/AgNWs/Epoxy nanocomposites with a low MXene/AgNWs content of 8.2 wt% combine a high electrical conductivity of 1532 S/m, and an exceptional EMI SE value of 94.1 dB with 3 mm thickness at the X-band frequency, as well as an improved TC of 2.34 W/m·K. The fabricated MXene/AgNWs/Epoxy nanocomposites possess excellent comprehensive properties enable valuable applications in electronic devices for EMI shielding and thermal management. [ABSTRACT FROM AUTHOR]

Effects of Li2O on the densification and the thermal conductivity of AlN ceramics sintered at a low temperature were studied by using Li2CO3, CaF2 and Y2O3 as additives. DTA and XRD were employed to identify the formation of the liquid and the changes of the phase compositions during the sintering. SEM and TEM were used to observe the microstructures of AlN specimens sintered at 1650 °C. The results show that Li2O is an effective sintering aid, leading to high densification and high thermal conductivity at low sintering temperatures. AlN specimens with full densification and thermal conductivity were achieved with Li2O addition. The high densification comes from the promotion of the liquid containing Li and CaYAlO4. The high thermal conductivity is attributed to the purification of the AlN lattice, the enhancement of the density and the elimination of some grain-boundary phases. [Copyright &y& Elsevier]