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A homogeneous co-precipitation method was developed to synthesize well dispersed yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) powders. This method ensures the co-precipitation of Y 3+ and Al 3+ , solving the problem of differential precipitation of Y 3+ and Al 3+ in the conventional homogeneous precipitation method. Furthermore, the pH value can be controlled to be a plateau (around 5.2) during the titration process due to the continuous decomposition of the heated urea which can compensate for the pH reduction when adding the mother salts, which is beneficial to the narrow size distribution of the precipitates. Pure YAG nanopowders can be obtained at 900 °C without the formation of impurity phases such as YAM (Y 4 Al 2 O 9 ) or YAP (YAlO 3 ). The resultant YAG powders are well dispersed and have excellent sinterability that can be sintered into transparent ceramics at 1700 °C by vacuum sintering. [ABSTRACT FROM AUTHOR]

Superhydrophobic surfaces are used in fields such as self-cleaning, anti-corrosion and anti-rust, and electromagnetic shielding because they are not wetted by water droplets. We manipulated the scanning spacing and scanning times of the femtosecond laser to control the surface morphology of alumina ceramics, resulting in the creation of two microstructures: micropillars and microhills. Subsequent heat treatment in an oven at 100 °C for 12 h formed a superhydrophobic surface without additional chemical modification, with a contact angle as high as 171.706°. Experimental results show that the superhydrophobicity of the alumina ceramic surface is due to the micro-nano structure of the ceramic surface under specific laser parameters and the hydroxylation of the alumina ceramic itself combined with organic compounds in the air. In addition, the ceramic still has excellent superhydrophobic properties up to 155° after being left in the air for 35 days and abraded by 800-grit sandpaper for 1 m under a pressure of 2.2kpa. Our work uses a new environmentally friendly method to make alumina ceramic surfaces both wear-resistant and superhydrophobic. [ABSTRACT FROM AUTHOR]

Copper matrix composites can be used to address the issue of heat dissipation in electronic devices. Nevertheless, the thermal conductivity (TC) of carbon fiber (CF)/copper (Cu) composites falls significantly below expectations. This is primarily attributed to the challenge of achieving a well-ordered arrangement of CF within the matrix, coupled with the issue of low interfacial bonding strength. A highly effective and uncomplicated approach to fabricate copper matrix composites featuring a "sandwich structure" of Cu-CF-Cu is introduced in this paper. This configuration, achieved through structural design facilitated by hot-press sintering and vacuum suction filtration, exhibited a three-dimensional graphene-like networks (3D-GLNs) and meticulously ordered CF layers over long distances. More importantly, in comparison to pure copper (350 W m−1 K−1), the laminated composite with 40 vol% CF of the CF layer had an in-plane TC of 510 W m−1 K−1, which was approximately 1.5 times greater than that of pure copper. Additionally, the coefficient of thermal expansion (CTE) of the laminated composite with 45 vol% was 9.98 ppm/K. The in-plane TC of the composite was comparable to that of the graphene/Cu composites with the same content. This underscores the advantages of the structural design, even in cases where the TC of the reinforced phase differs by a factor of two. The aforementioned findings demonstrate that this methodology for developing a unique "sandwich" structure can effectively enhance in-plane TC in CF/metal composites, presenting potential for utilization in electronic packaging requiring efficient directional heat transfer. [ABSTRACT FROM AUTHOR]

Y 2 O 3 and CaO are ideal ceramic materials for precision casting of TiAl alloy, overcoming challenges associated with intricate component removal, such as turbine blades, leveraging the stability of Y 2 O 3 and the water solubility of CaO. To address these challenges, we employed Isobam104 in a novel gel casting method, serving as both a dispersant and a gelling agent. This method enabled us to create a stable Y 2 O 3 –CaCO 3 slurry with high solid content (up to 55 vol%) and low viscosity (101.51 mPa·s at a shear rate of 10 s−1). Following sintering at 1500 °C for 2 h, Y 2 O 3 –CaO composite ceramics were produced. Surprisingly, two distinct characteristics of CaO were noted. One showed a rod-shaped morphology with high chemical reactivity crucial for water solubility, while the other displayed a flat-like feature, forming a well-maintained interface due to its coherent or semi-coherent matching relationship with Y 2 O 3 , thereby providing excellent hydration resistance. Ultimately, we acquired composite ceramics showcasing a 30-day "shelf life" alongside exceptional water solubility. This establishes the theoretical groundwork for storing and employing soluble ceramic cores in the precision casting of TiAl alloy. [ABSTRACT FROM AUTHOR]

A series of RE(OH)SO 4 layered compounds (RE = La–Tb lanthanides) were successfully synthesized via hydrothermal reaction under near-neutral solution pH and the mild temperature of 180 °C for 24 h, and the temperature/pH/time courses of phase/morphology evolution were clarified with RE = Tb for example. The compounds were characterized in detail for crystallite morphology, crystal structure, thermal behavior and vibrational property, and the intrinsic influence of lanthanide contraction was unveiled. Tb(OH)SO 4 was analyzed to be isostructural with its La–Gd analogues (CN = 9 for Tb), instead of the reportedly Dy–Yb ones (CN = 8), and have parameters of a = 4.3806 Å, b = 12.1729 Å, c = 6.7674 Å and β = 106.3967° for its monoclinic unit cell (P 2 1 / n space group). The Eu and Tb compounds exhibited red (λ ex = 395 nm, λ em = 616 nm) and green (λ ex = 369 nm, λ em = 545 nm) emissions, and have fluorescence lifetimes of ∼0.84 and 1.07 ms and chromaticity coordinates of around (0.632, 0.365) and (0.295, 0.481), respectively. [ABSTRACT FROM AUTHOR]

In the arena of advanced anti-counterfeit research, developing a multi-level, anti-counterfeit material with tunable luminescence is a hot topic. However, current research has mainly focused on the visible light signal, despite the fact that near-infrared is also suitable for optical anti-counterfeit applications. The importance of the near-infrared signal is because it is more difficult to observe than the visible light signal. Here, a new, persistent, luminescent, near-infrared material composed of Zn 2+ x Ga 4-2 x Sn x O 8 :0.5%Cr3+ (x = 0-0.4) has been synthesized using the sol-gel method. A new anti-site-like defect [ Zn Ga ′ - Sn Ga. ] appeared after incorporating both Zn2+ and Sn4+, along with an intrinsic, anti-site defect [ Zn Ga ′ - Ga Zn. ]. Specifically, the former and latter defects contributed to the deep and shallow traps, respectively. Introducing Zn2+ and Sn4+ resulted in a significant, two-fold enhancement of the NIR emission intensity. This led to an obvious improvement in its persistent luminescence. In the absence of light irradiation, the NIR emitted light lasted for several hours. If heated, the disappeared NIR signal reappeared and lasted for 10 min. Primarily due to both the shallow and deep traps, the prepared samples exhibited dynamic NIR luminescence behavior. This behavior then contributed to the dynamic display information. Collectively, these results indicate that persistent phosphors have great potential for use in advanced, optical anti-counterfeit materials, owing to their ability to afford higher security. [ABSTRACT FROM AUTHOR]

Various defects have a profound impact on the dielectric properties and polarization mechanisms of (Nb,Ga) codoped TiO 2 crystals. However, the research conducted in this area remains limited. To address this, we grew (Nb,Ga) codoped TiO 2 crystals via the Verneuil method and investigated their dielectric properties under various atmospheric annealing conditions. Annealing in oxygen reduces the number of defects. In this case, the point defects associated with oxygen vacancies is unable to fully form the ideal complex defect clusters which can form effective pegging of free electrons. On the other hand, the defects are mainly in the form of simple defect clusters that causes hopping polarization. Annealing under mixed gas (Ar:H 2 = 95%:5%) increases the number of defects and contains more free carriers, which migrate to the interface between the sample and the electrode, leading to interfacial polarization. Both hopping polarization and interfacial polarization are slow polarization, resulting in an increase in dielectric loss and a decrease in frequency stability. Annealing in air or nitrogen atmospheres forms ideal defect dipole clusters, where the electron-pinned defect dipoles (EPDD) are predominantly polarized, resulting in superior dielectric properties. It has been clarified that EPDD as the main polarization form can yield better dielectric properties. By focusing on single crystals as the research subject, we effectively eliminate the influence of grain boundaries, enabling a more accurate assessment of the effects of various crystal defects on dielectric properties. This study holds substantial implications for the advancement of TiO 2 -based dielectric materials, offering valuable insights into their performance optimization. [ABSTRACT FROM AUTHOR]

Large quantities of red mud tailings cause serious negative impacts to both the environmental sustainability and public health. Eco-friendly utilization of tailings can address this issue and achieve its commercial value. We reported an approach to preparing transparent basic glass and opaque glass-ceramics utilizing red mud tailings as the starting material. Crystallization kinetics, phase transition, microstructure evolution, and performances of glass-ceramics were studied. The crystallization activation energy was calculated to be only 125.5 kJ/mol, which made the transformation from red mud tailings to glass-ceramics much easier. The Avrami coefficient of crystallization was calculated to be around 2, revealing that one-dimensional bulk crystallization occurred in glass-ceramics. Fluorapatite crystals having a one-dimensional morphology were found to generate in glass-ceramics, which endowed the glass-ceramics with superior performances, such as the density of 2.7 g/cm3, the crack resistance of 2.43 MPa m1/2, and the Vickers hardness of 643.67 HV. These results and findings demonstrate that hazardous red mud tailings could become eco-friendly glass and glass-ceramics for construction applications. [Display omitted] [ABSTRACT FROM AUTHOR]

We show the effects of the Zr4+-doping on the microstructural, optical, and luminescent properties of (Lu, Gd) 2 O 3 : Eu transparent ceramics in its as-sintered state and annealed state. Zr4+-dopant greatly enhanced the transparency of (Lu, Gd) 2 O 3 : Eu ceramic, giving Lu 0.42 Gd 0.5 Zr 0.03 Eu 0.05 O 1.5+δ ceramic with a transmittance of up to 80% at 600 nm. It is found that Zr4+-dopant dominates the luminescent properties of Eu ions in both as-sintered and annealed ceramics. Energy transfer from Eu2+ to Eu3+ was found by photoluminescence spectra, and the ratio of Eu2+/(Eu2++Eu3+) was affected by Zr4+ content in as-sintered ceramics. Moreover, the oxygen vacancy concentration increased with increasing Zr4+ content in as-sintered ceramics. The annealing process enhanced the intensity of all the excitation bands of 4f→4f transitions and the intensity of charge transfer band (CTB) decreased as the Zr4+ content increased in the annealed ceramics. This work highlights that Zr4+ doping is a potential way to improve the transmittance and red emission intensity of 4f→4f transition of Eu3+ in the (Lu, Gd) 2 O 3 : Eu ceramic for extended applications. [ABSTRACT FROM AUTHOR]

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al 2 O 3 –YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al 2 O 3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting. [ABSTRACT FROM AUTHOR]

Infrared transparent Ho: Y 2 O 3 -MgO nanocomposite ceramics with a volume ratio of 50:50 (RE 2 O 3 : MgO) were prepared by combining sol-gel powder synthesis and hot-pressing sintering techniques. In order to obtain Ho: Y 2 O 3 -MgO nanocomposite ceramics with fine grain size, dense microstructure and homogeneous phase domains, the effect of sintering temperature and Ho3+ doping concentration were studied. Transmittance and SEM measurement revealed that the grain size of 3 at.% Ho: Y 2 O 3 -MgO ceramic sintered at 1250 °C is 141 nm, and the transmission is up to 85.2% at 5 μm. The detailed spectroscopic investigation of x at.% Ho: Y 2 O 3 -MgO (x = 1, 3, 5, 7, 9, 15) ceramics was performed. The nanocomposites exhibited photoluminescence properties similar to that of Ho: Y 2 O 3 crystals and ceramics. In addition, the thermal conductivity of 3 at.% Ho: Y 2 O 3 -MgO ceramic is 13.04 W/m·K, which is superior to that of Ho:Y 2 O 3 ceramics. The high transmission, excellent thermal conductivity, and outstanding optical characteristics indicated that Ho: Y 2 O 3 -MgO ceramics is a promising material for efficient infrared solid-state laser. [ABSTRACT FROM AUTHOR]

Long persistent luminescence materials developed to commercial standards are primarily concentrated in the blue and green regions, with only a few in the red region. Red, as one of the three basic colors, can be mixed in various proportions with blue and green to yield various colors. The development of red persistent phosphors has a broader application potential but remains a challenge. A solid-state reaction method was used to synthesize new red persistent luminescent materials of Ba 1- x Sr x Ga 2 O 4 :Sm3+ (x = 0–0.09). In BaGa 2 O 4 , both Sr2+ and Sm3+ preferentially occupy the Ba2+ site rather than the Ga3+ site. When exposed to UV light at 254 nm, the phosphors emit the characteristic red emission of Sm3+ at wavelengths ranging from 500 nm to 750 nm. After removing the UV light source, an intense red afterglow that lasted more than 1400 s was observed. The red afterglow signal reappears after a heating process. Doping Sr2+ reduces the trap depth and improves the red persistent luminescence significantly. Because the escaped electrons from traps compensate for the emission loss of Sm3+ during the heating process, the red phosphors have unimaginably luminescent thermal stability. Thus, the emission intensity at 200 °C is 1.6 times that at room temperature. The prepared red persistent phosphors show multimode luminescence, with the output signal being time and temperature sensitive, indicating that they are potential luminescent materials for anti-counterfeiting applications. Finally, a building-block strategy for advanced anti-counterfeiting applications of dynamic display information is proposed, with red persistent phosphors serving as an important component combined with upconversion phosphors of NaYF 4 :Yb3+, Tm3+, and green persistent phosphors of SrAl 2 O 4 :Eu2+, Dy3+. [ABSTRACT FROM AUTHOR]

Large (30 mm in diameter) TiO 2 (rutile) single crystals with low dislocation density were grown by the Verneuil method using a single crystal furnace designed and improved by the authors. The structure of the burner was optimized by numerical simulation analysis so that the crystal could be grown at a low gas flow rate. The investigation of the growth process parameters (i.e., growth rate, outer flow rate of O 2 , inner flow rate of O 2 , and the increment of H 2 flow rate) shows that the inner flow rate of O 2 and the increment of H 2 flow rate have the strongest influence on the crystal growth process. On this basis, other growth parameters (growth rate, outer flow rate of O 2) were also optimized. Compared with the conventional Verneuil method, the crystal can be grown at a considerably low gas flow rate (40–50% lower) with the method in this work, which reduces the melt turbulence impacted by gas flow, enabling a steady and clear solid-liquid interface and improving the crystal quality. The optimum growth conditions are for the growth rate of 6 mm/h, O 2 outer flow rate of 3.5 L/min, O 2 inner flow rate of 5.5 L/min, and increment of H 2 flow rate of 0.1 L/4 min. The etch pit density of the rutile crystals is 3.29 × 104 cm−2, an order of magnitude lower than that of the crystals grown by the conventional Verneuil method. The optical properties of the crystal are comparable to those grown by the floating zone method. Especially, it is easier to obtain a larger crystal size with lower production costs. Our results provide a possible route for industrializing the Verneuil production of large, high-quality and low-cost rutile single crystals. [ABSTRACT FROM AUTHOR]

Uniform phosphor mono-spheres have received continuously increasing attention owing to their excellent luminescence properties. Submicron/near micron-sized Lu 2 O 3 :Eu mono-spheres were successfully prepared by a facile and modified homogeneous precipitation technique from corresponding single-source precursor of Lu(OH)CO 3 :Eu⋅ n H 2 O, without the assistance of any dispersants. The sizes of the precursor spheres can be tuned in the range of 56–790 nm via controlling the primary particle nucleation and particle growth in the homogeneous precipitation. After calcination at 1000 °C, the synthesized precursor spheres (165–790 nm) were converted to Lu 2 O 3 :Eu (110–630 nm) without changing their original spherical shape and excellent dispersion. The particle size-dependent photoluminescence properties of Lu 2 O 3 :Eu mono-spheres were investigated in detail. Enhanced photoluminescence intensity, shorter lifetime, higher external quantum efficiency and almost the same CIE chromaticity coordinates were observed for a particle size of 480 nm. Moreover, temperature-dependent photoluminescence spectra indicated the obtained phosphor mono-spheres have good thermal stability. [ABSTRACT FROM AUTHOR]

SrTiO 3 is a promising thermoelectric material for applications in harsh environments, owing to its excellent thermoelectric (TE) properties and high-temperature stability. The effect of annealing in carbon powders on the TE properties of SrTiO 3−δ in the [111] direction was experimentally investigated and analysed using first-principles calculation. The electrical conductivity of the SrTiO 3−δ single crystals in the [111] direction increases with an increase in annealing temperature in the range of 1573–1673 K, which is opposite to that in the [510] direction as shown in a previous experiment. This is attributed to the different variation trend of carrier concentration. First-principle calculation results show that the carrier concentration in the [111] direction increases with increasing oxygen vacancy concentration, but it is the opposite in the [510] direction. Strong anisotropy of carrier concentration should be caused by the difference in atomic arrangement, making difference in the amount of free electrons that maybe constrained at high oxygen vacancy in different directions. Although the SrTiO 3−δ single crystal annealed at 1573 K shows a lower electrical conductivity, it obtains higher power factor with the maximum value of 2.24 mW m−1 K−2 at 323 K, which is predominantly due to its higher effective mass. It also yields the highest ZT value of 0.18 at 873 K owing to the lower thermal conductivity. The results of this study are imperative for the design and development of perovskite TE materials. [ABSTRACT FROM AUTHOR]

Spherical silicate phosphor has widespread application in display or lighting industry. By using spherical silica particles as the core, we successfully prepared shell-thickness-controllable core/shell spherical particles, which can then be controllably converted to spherical X 1 -Y 2 SiO 5 :Eu (YSO:Eu) and α-Y 2 Si 2 O 7 :Eu (YPS:Eu) particles upon annealing. Even after 1000–1200 °C annealing, both X 1 -YSO:Eu and α-YPS:Eu particles still had the spherical shape and narrow size distribution. The shell thickness and annealing temperature synergistically controlled the phase evolution upon annealing. Thinner shell of around 30 nm, having extremely high chemical reaction activity, promoted the formation of spherical X 1 -YSO:Eu particles at 1000 °C and α-YPS:Eu particles at 1100 °C. Shell of around 85 nm produced spherical X 1 -YSO:Eu particles at 1100 °C and α-YPS:Eu particles at 1200 °C. Thicker shell also promoted the formation of spherical particles, but these particles usually had the mixed silicate phases. The phase-dependent photoluminescence properties were investigated in detail. Both spherical X 1 -YSO:Eu and α-YPS:Eu phosphors emitted reddish-orange color, with nearly 100% color purity and dominant wavelength of around 601 nm, which would absorb great attention for the application in display or lighting devices. Spherical red-emitting X 1 -Y 2 SiO 5 :Eu and α-Y 2 Si 2 O 7 :Eu phosphors having the nearly 100% color purity were obtained, and the phase transformation sequence was clearly clarified. [Display omitted] [ABSTRACT FROM AUTHOR]

SnO 2 powders with four distinct morphologies of prismoids, hollow rhomboidal tubes, solid rhomboidal rods, and needles have been prepared through morphology-conserved transformation from SnC 2 O 4 precursors. The SnC 2 O 4 precursors were synthesized by a facile oxalate precipitation method. A controllable periodic bond chain (PBC) growth was found to be critical for the formation of these SnC 2 O 4 samples. In the case of forward titration, SnC 2 O 4 prismoids were generated because the formed Sn 3 O(OH) 2 SO 4 was attached on { 1 - 01} polar facets and inhibited the PBC growth along the c axis. By contrast, in the case of reverse titration, SnC 2 O 4 samples preferably formed one-dimensional shapes. Dissolution and ripening were observed during the formation of hollow tubes in the case of low molar ratio of Sn2+ to C 2 O 4 2−. Further, the formation of SnC 2 O 4 needles was ascribed to the selective coordination of polyvinylpyrrolidone (PVP) on the side surface. The as-prepared SnO 2 powders were used as reinforcement of Ag–SnO 2 electrical contact materials, and a good adhesion was observed at the Ag (111)/SnO 2 (200) interface. Further, the characterization results revealed that the sample reinforced by SnO 2 tubes (with one-dimensional shape and hollow structure) had the lowest degradation rate under cathode arc erosion, which might be attributed to its good resistance to the dual action (heat and force) of cathode arc. [ABSTRACT FROM AUTHOR]

Zirconia-coated Cr 2 O 3 aggregates synthesized by mixing ZrO 2 powders and Cr 2 O 3 aggregates with a phenolic resin binder followed by thermosetting treatment were employed as modified Cr 2 O 3 aggregates to obtain Cr 2 O 3 –Al 2 O 3 –ZrO 2 bricks (high-chromia bricks). The elastic modulus (E) and cold modulus of rupture (CMOR) of these high-chromia bricks before and after thermal shock cycles were systematically investigated, and the residual ratios of CMOR and E were calculated. The thermal shock resistance of the high-chromia bricks was significantly improved by the factor of modification of Cr 2 O 3 aggregates. The mechanism of the improved thermal shock resistance of these high-chromia bricks was studied via microstructure analysis, and the crack propagation behavior was analyzed by scanning electron microscopy (SEM). The fracture work (γ WOF), thermal shock damage factor (R′′′′), and thermal stress crack stability parameter (R st) were measured and calculated using the wedge splitting test (WST). The results indicate that the porous ZrO 2 coating layer wrapped the Cr 2 O 3 aggregates, forming modified Cr 2 O 3 aggregates that can increase crack deflection, free path of crack propagation, and fracture work, thus improving the thermal shock resistance of high-chromia bricks. The thermal shock resistance of the fabricated high-chromia bricks was highly correlated with the thickness of the ZrO 2 coating layer surrounding the Cr 2 O 3 aggregates. The variation trend of R st is well consistent with the experimental results, which is suitable to evaluate the thermal shock resistance of high-chromia bricks. [ABSTRACT FROM AUTHOR]

A series of phosphate glasses composed of (65-x)P 2 O 5 –15BaO–5Al 2 O 3 –5ZnO–10Na 2 O-xB 2 O 3 (x = 0, 2, 4, 6, and 8 mol%) were successfully prepared using the melt-quenching method. The effects of the addition of boron trioxide (B 2 O 3) on the physical, structural, and mechanical properties of the glasses were investigated. As the added content of B 2 O 3 increased from 0 to 6 mol%, the glass exhibited increased density and transition temperature, and decreased molar volume, indicating optimization of the glass stability. Raman spectroscopy revealed that the introduction of B 2 O 3 transformed the glass from a chain structure to a three-dimensional network structure, which enhanced the chemical stability of the glass by the cross-linking of long phosphate chains with boron ions. Regarding the mechanical properties, when the boron content was 6 mol%, the flexural strength of the glass was 41% higher than that of the undoped boron, while the Vickers hardness and Knoop hardness values increased by 20.58% and 7.05%, respectively, and the fracture toughness was slightly decreased. In general, improving the mechanical properties of phosphate glass is of great significance for increasing the applications of this glass. [ABSTRACT FROM AUTHOR]

The miniaturization of high-brightness white light-emitting diodes (WLEDs) is limited by the low thermal performance of phosphors. In this study, the microstructure, optical properties, and thermal performance of Al 2 O 3 –Y 3 Al 5 O 12 :Ce3+ (Al 2 O 3 –YAG:Ce) composite ceramics fabricated by hot pressing were investigated. By promoting the growth of Al 2 O 3 grains while maintaining a high composite density, thermal performance of the composite ceramics was significantly increased. The thermal conductivity of a Al 2 O 3 –40-vol% YAG:Ce ceramic reached 21.8 W/m/K, which is close to the theoretical value. In addition, this composite ceramic exhibited the highest energy efficiency. After packaging with a high-power LED chip with dimensions of 1 mm × 1 mm, a high luminous flux of 639 lm was generated, while the reduction in output power at 250 °C was as low as 6%. This indicated excellent high-temperature stability and potential for applications in solid-state lighting. [ABSTRACT FROM AUTHOR]

Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated by the solid-state method using monodispersed spherical Y 2 O 3 powders as well as commercial Al 2 O 3 and Yb 2 O 3 powders. Pure YAG phase was obtained at low temperature due to homogeneous mixing of powders. Under the same sintering conditions, the Yb:YAG ceramics with different doping contents of Yb3+ had similar morphologies and densification rates. After being sintered at 1700 °C in vacuum, the ceramic samples had high transparencies. The Yb:YAG ceramics doped with 0.5 wt% SiO 2 formed Y–Si–O liquid phase and nonstoichiometric point defects that enhanced sintering. Compared with Nd doping, Yb doping hardly affected the YAG grain growth, sintering densification or optical transmittance, probably because Yb3+ easily entered the YAG lattice and had a high segregation coefficient. [ABSTRACT FROM AUTHOR]

Abstract Silver-matrix composites are the most important electric contact materials. Here, porous Y 2 O 3 fiber-reinforced silver composites were prepared by the hot-press sintering. Y 2 O 3 fibers, composed of nanocrystals with a size of around 50 nm, were obtained by the infiltration and calcination method using cotton as the template. Among these nanocrystals, pores were clearly observed. This hierarchical structure enabled the deposition of silver on the inner and outer surface of Y 2 O 3 fibers during the subsequent reduction process. Bunched Ag-Y 2 O 3 mixed powders were thus obtained. After the hot-press sintering, the fibrous structures were uniformly distributed in Ag matrix. In each fibrous zone, Ag particles nearly filled the whole fibrous zone, and Y 2 O 3 particles scattered among these Ag particles. This unique structure enabled Ag-Y 2 O 3 composites to have excellent mechanical and electrical properties. Among all samples, Ag-15 vol% Y 2 O 3 composite exhibited the best properties, which had the high density (9.67 g cm−3), high hardness (12.13 ×102 N mm−2), high conductivity (71.42% IACS), high breakdown strength (3.04 ×106 V m−1), and no silver splashing was observed on its surface after 200 times arc ablation. Graphical abstract Porous Y 2 O 3 fiber-reinforced silver composites, exhibiting enhanced mechanical and electrical properties, were successfully prepared by the hot-press sintering. fx1 [ABSTRACT FROM AUTHOR]

A novel Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite was designed and prepared for the first time by hot pressing. The addition of cBN was found to be very effective in simultaneously enhancing the hardness and toughness of the Al 2 O 3 -Ti(C 0.7 N 0.3 ) ceramics. The optimum cBN content of the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite was determined to be 5 vol%. The optimal properties were achieved by sintering at 1400 °C for 20 min under 40 MPa，and the Vickers hardness, bending strength, and fracture toughness were 20 GPa, 548 MPa, and 5.3 MPa m 1/2 , respectively. When turning stellite 3 using the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN insert, the longest cutting length achieved at a cutting speed of 117 m/min was 5122 m, 73% and 45% longer than those of the Al 2 O 3 -Ti(C 0.7 N 0.3 ) and commercial A66N inserts, respectively. This indicates that the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite is a promising tool material for the turning of stellite alloys. [ABSTRACT FROM AUTHOR]

(Tb 0.985 Ce 0.015 ) 3 (Al 1- x Ga x ) 5 O 12 garnet phosphors ( x = 0, 0.1, 0.2, 0.3, and 1.0) were prepared by calcining their coprecipitated precursors in air at 1500 °C, followed by reduction in hydrogen at 1200 °C. Rietveld refinement of the XRD results suggested that the Ga dopant predominantly resides at the octahedral Al site of the garnet lattice. Ga doping led to linearly expanded lattice constant, cell volume and theoretical density of the garnet compound and successively lower intensity and longer average fluorescence lifetime of the ~ 570 nm emission of Ce 3+ . Blue shifted emission and 4f( 2 F 5/2 )→5d 1 (E 2g ) excitation and red shifted 4f( 2 F 5/2 )→5d 2 (E 2g ) excitation were also observed for the Ce 3+ activator at a higher Ga content. The phenomena were interpreted by considering the band structure of the host, distortion of the CeO 8 polyhedron, and centroid shift and field splitting of the Ce 3+ 5d energy levels. [ABSTRACT FROM AUTHOR]

A series of eulytite-type Sr 3 Y 1- x (PO 4 ) 3 : x Eu 3+ ( x = 0–0.13) and Sr 3- y Y(PO 4 ) 3 : y Eu 2+ ( y = 0–0.10) phosphors were successfully synthesized via gel-combustion and subsequent calcination in O 2 and Ar/H 2 atmospheres at 1250 °C, respectively. Detailed crystal structure analysis via Rietveld refinement showed that the phosphors were crystallized in the cubic system (space group I -43 d , No. 220), in which the Eu 3+ and Eu 2+ activators reside at the Y 3+ and Sr 2+ sites, respectively. The trivalent Eu 3+ ions (CN = 6) exhibited typical narrow-band luminescence via intra-4 f 6 transitions, with the red emission at ~ 615 nm being dominant ( 5 D 0 → 7 F 2 transition, FWHM = 15.9 ± 0.2 nm). The divalent Eu 2+ ions (CN = 6 and 9) showed broad-band luminescence ranging from light-blue to blue via 4 f 6 5 d 1 → 4 f 7 transitions (FWHM = 115 ± 2 nm). The optimal Eu 3+ and Eu 2+ concentrations were determined to be 10 at% ( x = 0.10) and 7 at% ( y = 0.07), respectively, and the mechanisms of concentration quenching were discussed. The excitation/emission properties, fluorescence decay kinetics, CIE chromaticity, and particularly the rarely addressed thermal stability of the phosphors were investigated in detail. [ABSTRACT FROM AUTHOR]

Sc 2 O 3 -Y 2 O 3 solid solution (SYSS) ceramics with novel nanocrystalline structures have been successfully fabricated by spark plasma sintering (SPS) method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR and indentation techniques. The SYSS ceramics can possess high hardness by keeping their excellent infrared transmission performance. Especially, the transmittance of as-obtained SYSS ceramics can exceed as high as 80% in the infrared region of 2–6 µm. Moreover, the Vickers hardness is increased to 9.18 GPa by increasing the addition ratio of Sc 2 O 3 to 20 at%. Here, it is very important to point out that the mechanical strength of yttria ceramics can be evidently enhanced without deteriorating their optical transmission performance by the addition of Sc 2 O 3 as well as the application of SPS technique, where the solid solution strengthening and fine grain strengthening are involved during the synthesis process, respectively. [ABSTRACT FROM AUTHOR]

(Tb 1 -x Ce x ) 3 Al 5 O 12 yellow phosphors (0≤x≤0.05) were calcined from their coprecipitated carbonate precursors, and the effects of the temperature and atmosphere (air and H 2 ) of calcination on the sequence of phase evolution and the characteristics of the powders were investigated in detail. The activation energy for the crystallite growth during calcination was estimated to be ~39 kJ/mol. The powder calcined at 1000 °C showed good reactivity and was sintered into a ceramic plate of ~97% dense (average grain size: ~1.3 µm) in a H 2 /Ar gas mixture at the relatively low temperature of 1500 °C. The phosphors simultaneously exhibit the 4f 8 →4f 7 5d 1 , 7 F 6 → 5 D 3 and 7 F 6 → 5 D 4 excitations of Tb 3+ and the 4f 1 →5d 1 excitation of Ce 3+ when monitoring the yellow emission of Ce 3+ at 560 nm, suggesting the presence of efficient Tb 3+ →Ce 3+ energy migration. The optimal Ce 3+ content for luminescence was found to be x =0.015 and 0.01 under the direct excitation of Ce 3+ and through Tb 3+ →Ce 3+ energy transfer, respectively, and concentration quenching of luminescence was analyzed to be resulted from exchange interaction. Luminescence features of the phosphors, including excitation, emission, quantum yield, fluorescence lifetime, color coordinates and color temperature, were thoroughly investigated against the processing temperature and Ce 3+ content, with an in-depth discussion on the process of energy transfer among the optically active Tb 3+ and Ce 3+ ions. The materials may find application in blue-light excited white LEDs. [ABSTRACT FROM AUTHOR]

In the present work, transparent Y 2 O 3 ceramics were prepared via colloidal processing method from nano-sized Y 2 O 3 powders. The effects of triammonium citrate (TAC) on the colloid stability of aqueous suspensions of nano-sized Y 2 O 3 powders were studied. The surface properties of yttria powders were notably affected by the addition of TAC dispersant. The adsorption of TAC on the particle surface shifts the IEP to lower pH values and increases the absolute zeta potential in alkaline region. Rheological characterization of the investigated system revealed an optimal dispersant concentration of 1 wt%, which correlated well with the saturation adsorption of TAC on Y 2 O 3 powder surfaces. The suspensions with solid loadings up to 35 vol% were achieved with further addition of Tetramethylammonium hydroxide (TMAH) into the dispersing system. The consolidated green bodies were treated by cold isostatic pressing to further increase the green density. Transparent Y 2 O 3 ceramics were prepared after vacuum-sintering at 1700 °C for 5 h. The transmittances of the sample were 74.5% at 800 nm and 79.8% at 2000 nm, respectively. [ABSTRACT FROM AUTHOR]

Nanosized anatase TiO 2 particles anchored on nanocarbon substrates have great potential for practical applications in high-performance lithium ion batteries and efficient photocatalysts. The synthesis of this material usually utilizes calcination to crystallize amorphous titania, which normally causes the formation of aggregates and some side effects. In this work, we demonstrated that sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets in aqueous solution at a temperature of 90 °C and atmospheric pressure, without further calcination. The photocatalytic oxidation activity and electrochemical properties of graphene oxide/anatase TiO 2 (GO/A) and reduced graphene oxide/anatase TiO 2 (RGO/A) were comparatively investigated. We found that GO/A showed higher photocatalytic oxidation activity than RGO/A under UV light irradiation. Graphene oxide accepted electrons and suffered reduction, which finally decreased GO/A’s photocatalytic oxidation activity to an extent similar to RGO/A. We also found that, as anode material for Li-ion battery, the specific capacity of RGO/A was nearly three times that of GO/A at the same current rate. This study will inspire better design of metal oxide/nanocarbon nanocomposites for high performance lithium ion battery and photocatalysis applications. [ABSTRACT FROM AUTHOR]

The metastable garnet lattice of Yb/Er co-doped Gd 3 Al 5 O 12 (GdAG:Yb/Er) has been effectively stabilized by doping with significantly smaller Lu 3+ to form (Gd,Lu)AG:Yb/Er solid solutions. The phase-pure (Gd,Lu)AG:Yb/Er garnet particles have been successfully achieved by calcining their respective precursors synthesized via carbonate co-precipitation. Partially replacing Gd 3+ with Lu 3+ up to 50 at% ( x =0.5) not only lowers the temperature of garnet crystallization, but also raises the theoretical density of the material. The resultant [(Gd 1− x Lu x ) 0.948 Yb 0.05 Er 0.002 ]AG ( x =0.1–0.5) powders, with good dispersion and fairly uniform particle morphology, exhibit strong green (~510 to 590 nm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 transitions of Er 3+ ) and red (~635 to 700 nm, 4 F 9/2 → 4 I 15/2 transition of Er 3+ ) emissions under 978 nm laser excitation. The Lu 3+ incorporation effect on the visible emission color and intensity of Er 3+ , as well as the dependence of emission intensity on pumping power were all discussed in detail. The up-conversion phosphor of Yb/Er codoped (Gd,Lu)AG garnet developed in this work may potentially be used as a new type of luminescent material. [ABSTRACT FROM AUTHOR]

Mono-dispersed spherical Lu 2 O 3 :Eu (5 mol%) powders for transparent ceramics fabrication were synthesized by urea-based homogeneous precipitation technique. The effects of the doped-Eu 3+ on the synthesis of Lu 2 O 3 :Eu particles were investigated in detail. The results show that the doping of Eu 3+ ions into Lu system can significantly decrease the particle size of the resultant precursor spheres. Owing to the sequential precipitation in Lu/Eu system, there are compositional gradients within each of the resultant precursor spheres. Well dispersed, homogeneous and spherical/near spherical Lu 2 O 3 :Eu powders were obtained after calcination at 600–1000 °C for 4 h. The powder calcined at 600 °C shows better sintering behavior and can be densified into transparent ceramic after vacuum sintering at 1700 °C for 5 h. The luminescence properties of the obtained Lu 2 O 3 :Eu powder and transparent ceramic were also studied. [ABSTRACT FROM AUTHOR]

Abstract: The properties of YAG precursors aged at various pH levels for different aging times were examined to explore the influence of pH on the evolution of the chemical composition and the morphology of the precipitate, on the variation of phase composition during the calcination process. Precursors obtained at pH lower than 8.0 can be transformed into mono-phase YAG by calcination at low temperature, while those obtained at higher pH exhibit a variety of crystalline structures. Aging at high pH increased the impurity content of the calcined powder. Based on monitoring the pH during the precursor aging process, and the measurement of the Y/Al ratio in the precipitates, the mechanism of the chemical variation is discussed and the influence of pH and aging time on the synthesis of YAG precursor is discussed. [Copyright &y& Elsevier]