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Among the various ceramic substrate materials, Si3N4 ceramics have demonstrated high thermal conductivity, good thermal shock resistance, and excellent corrosion resistance. As a result, they are well-suited for semiconductor substrates in high-power and harsh conditions encountered in automobiles, high-speed rail, aerospace, and wind power. In this work, Si3N4 ceramics with various ratios of α-Si3N4 and β-Si3N4 in raw powder form were prepared by spark plasma sintering (SPS) at 1650 °C for 30 min under 30 MPa. When the content of β-Si3N4 was lower than 20%, with the increase in β-Si3N4 content, the ceramic grain size changed gradually from 1.5 μm to 1 μm and finally resulted in 2 μm mixed grains. However, As the content of β-Si3N4 seed crystal increased from 20% to 50%, with the increase in β-Si3N4 content, the ceramic grain size changed gradually from 1 μm and 2 μm to 1.5 μm. Therefore, when the content of β-Si3N4 in the raw powder is 20%, the sintered ceramics exhibited a double-peak structure distribution and the best overall performance with a density of 97.5%, fracture toughness of 12.1 MPa·m1/2, and a Vickers hardness of 14.5 GPa. The results of this study are expected to provide a new way of studying the fracture toughness of silicon nitride ceramic substrates. [ABSTRACT FROM AUTHOR]

In this study, a type of micro-nano Si3N4 matrix ceramic cutting tool material was successfully prepared by controlling the addition amount of TiC0.7N0.3 and the hot-pressing sintering temperature. The effects of different volume fractions of TiC0.7N0.3 on the microstructure, mechanical properties, particle size distribution, and relative density of Si3N4 ceramic tools at the same temperature were investigated. The results show that the addition of TiC0.7N0.3 makes the β-Si3N4 grains with different diameters and aspect ratios interlaced and tightly bonded, thus achieving the strengthening and toughening effects. In addition, the effects of different hot-press sintering temperatures on the properties of Si3N4 ceramic tool materials were studied. It was concluded that the density of the material increased with the increase of the hot-pressing temperature. The relative density, flexural strength, and fracture toughness of the samples with 1 vol% TiC0.7N0.3 added at 1750 °C and 30 MPa pressure reached 99.22%, 993 MPa, and 9.81 MPa·m1/2, respectively. [ABSTRACT FROM AUTHOR]

An easy approach is described for the preparation of ZrO2-coated Y2O3 nanopowder from a solution of zirconium nitrate with commercial Y2O3 nanopowder. The evolution process of the ZrO2 coating layer upon calcination, such as the phase and microstructure of the particles' surface, was studied. Calcination of the powder at 700 °C resulted in ZrO2-coated Y2O3 nanopowder. The rheological properties of the suspensions of ZrO2-coated Y2O3 powders were studied. A well-dispersed suspension with a solid loading of 35.0 vol% using ZrO2-coated Y2O3 nanopowder was obtained. The consolidated green body obtained by the centrifugal casting method showed improved homogeneity with a relative density of 50.2%. Transparent ceramic with high transparency and an average grain size of 1.7 µm was obtained by presintering at 1500 °C for 16 h in air, followed by post-HIP at 1550 °C for 2 h under 200 MPa pressure. The in-line transmittance at the wavelength of 1100 nm (1.0 mm thick) reached 81.4%, close to the theoretical transmittance of Y2O3 crystal. [ABSTRACT FROM AUTHOR]

In this work, CeO2 sintering additive reinforced B4C ceramic composites were prepared by hot‐pressing reaction sintering under different processes of low temperature–long holding time (1980°C, 30 MPa, 3 h, 4 wt% CeO2) and high temperature–short holding time (2050°C, 30 MPa,.5 h, 4 wt% and 6 wt% CeO2). The effect of sintering process and CeO2 content on the microstructure and mechanical properties of B4C‐CeB6 composites were investigated. The existed impurities in the obtained composites were also analyzed. Results show that CeO2 is an active sintering additive. CeB6 is formed by the reaction between CeO2, B4C and C in sintering process. The densification of B4C ceramics is enhanced, and the grains can be refined by the formed CeB6, which promotes the strength. The thermal expansion coefficient mismatch, crack deflection, and fracture mode change caused by the in situ formed CeB6 improve the toughness. The process of low temperature–long holding time is more suitable for playing the role of CeO2 additive in sintering of B4C, under which condition the relative density, flexural strength, fracture toughness, and hardness reach 99%, 417 MPa, 5.32 MPa·m1/2, and 30.66 GPa, respectively. The impurities in the composites are the kinds of Ti‐contained, C‐O‐Mg‐Ca‐contained, C‐O‐Ca‐S‐contained, and Si‐contained impurities. [ABSTRACT FROM AUTHOR]

The rapid development of current multifunctional and flexible electronics has posed increased demand for low-temperature solder materials. The joining of Ag-plated PZT ceramics at a low soldering temperature of 100 °C using Bi–Pb–Sn–Cd solder paste was demonstrated. The Bi–Pb–Sn–Cd solder particles with good solderability were synthesized by shearing liquid into complex particles (SLICE) method. The joining of Ag-plated PZT ceramic has been achieved by the formation of an intermetallic compound (IMC) layer consisting of Ag–Cd compounds at a relatively low soldering temperature of 100 °C. For the joints soldered at 100 °C for 8 h, the shear strength is 31 MPa. The re-melting point of the joint increases from 72 to 93 °C. The low soldering temperature of Bi–Pb–Sn–Cd solder pastes allows us to join PZT ceramics on flexible PET substrate at a quite low reflowing temperature of 100 °C. The samples are bendable and the Bi–Pb–Sn–Cd solder are thus usable for flexible applications. [ABSTRACT FROM AUTHOR]

Macro-porous alumina ceramics were prepared by the gel-casting method using sacrificial polystyrene spheres as the template. The resulted porous alumina ceramics have regularly arranged pores and high cell wall densities, which confer high mechanical strength to the porous ceramics. The highest compressive strength for a porous alumina ceramic, with a relative density of 30%, in this work is 28 MPa, which is at least 74% higher than that of previously reported porous alumina ceramics with the same porosity. The results show that the cell wall density, window size and cell size can be adjusted by controlling the sintering temperature, solid loading percentage of the alumina slurry and the size of the polystyrene spheres. With the increase in cell wall density and decrease in cell size and window size, the compressive strength of the porous alumina increases. Thus, a novel porous structure with high porosity and high strength can be made by this flexible method which is also suitable for making complicated shapes and large sizes. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication of Gd2O3‐MgO nanocomposite optical ceramics via hot‐pressing using sol‐gel derived cubic‐Gd2O3 and MgO nanopowders was investigated. The precursor powder calcined at 600°C had an average particle size of 12 nm. The effects of hot‐pressing temperature on constituent phases, microstructure, mid‐infrared transmittance, and microhardness were studied. The crystallographic modifications of Gd2O3 phase varied with the increase in sintering temperature from 1250 to 1350°C. The monoclinic‐Gd2O3 phase was retained for the composite sintered at 1350°C and the sample had an average grain size of 90 nm, excellent transmission (80.4%‐84.8%) over 3‐6 μm wavelength range, and enhanced hardness value of 14.1 GPa. [ABSTRACT FROM AUTHOR]

The effects of CaO-LaO additives on sintering temperature and microwave dielectric properties of (ZrSn)TiO (ZST) ceramics prepared by solid-state reaction method were investigated. Structural characterization and microstructure of materials were studied via X-ray diffraction and scanning electron microscopy. crystalline and single phase exhibiting orthorhombic symmetry were identified. Small quantities of CaO and LaO promoted the densification of the ceramics improving dielectric properties, otherwise, an excessive CaO and LaO amount gave an abnormal grain growth which deteriorated dielectrical parameters. Dense ZST ceramics doped with 0.5% CaO and 1 wt% LaO were attained after sintering at 1335 °C during 4h, in air atmosphere. Microwave dielectric parameters of ε = 39.56, Q × f = 44100 GHz (at 5.6 GHz), τ = −1.66 ppm/°C were derived. [ABSTRACT FROM AUTHOR]

In this paper, YAG:Ce microspheres were fabricated by a laser heating method. The microspheres are polycrystalline. The melting of the YAG:Ce powder due to the extremely high temperature provided by the laser heating may account for the fast synthesis of the transparent YAG:Ce microspheres. Due to the temperature gradient during cooling, equiaxed and columnar grains were found inside the microspheres. The equiaxed grains are always located at the outer part of the spheres where large under-cooling was created. However, columnar grains are always found at the inner part of powder where a steep temperature gradient presented during cooling. The average size of the equiaxied crystallites observed from the SEM images is about 5~\mu\m. The columnar crystallites are about 5~\mu\m wide and 20~\mu\m long. In the luminescence investigation, the optimum concentration of Ce^3+ was found to be 2 at%. Furthermore, transparent spheres of other chemical compositions are also possible to be fabricated by this method, indicating its wide range of potential applications. [ABSTRACT FROM PUBLISHER]

Monoclinic Gd2O3 transparent ceramics with spherical shape were successfully fabricated by a laser heating method. A simple model was used to describe the heating depth and cooling rate during the laser scanning process. The XRD analysis shows that these microspheres exhibit monoclinic structure which is room temperature thermodynamically unstable but kinetically possible due to the fast cooling rate. The SEM images show that these micro-spheres are polycrystalline and composed of randomly oriented Gd2O3 grains about 10 \mum in particle diameter. No cracks, pores or secondary phase were observed at the grain boundary or inside the grains. A close-packed Gd2O3 spheres single layer was designed and prepared, and the in-line transmittance of this layer is about 44% in the visible light range. Pore-free monoclinic Gd2O3 can be transparent due to the slight difference between its ordinary and extraordinary refractive index (ne and no). Another reason for its transparency is the small amount of grain boundaries though which light pass. Medical radiograph needs scintillators with small volume size (to increase the image lateral resolution and minimize optical cross-talking) and good transparency (to avoid severe light scattering and increase signal intensity). Transparent ceramic spheres may provide the possibility to meet those criterions. [ABSTRACT FROM PUBLISHER]

This article presents a detailed study on the nanoscaled interface between microelongated gold particles ( GP) and biphase leucite/feldspar glass-ceramic matrix. The glass-ceramic composite with a nonuniform GP distribution was processed through hot-pressing under vacuum using a commercial dental ceramic furnace for glass-ceramic dental crown manufacturing. Heat treatments at 900°C, 1100°C, and 1300°C were conducted, and microstructural features along the interface were used to verify the chemical reactions between GP and glass-ceramic matrix. It was observed that the amorphous glass-ceramic matrix had nanoscaled biphase structures, and the distributed nanoscaled amorphous leucite phase was attracted to GP during hot-pressing, and was more reactive with GP than the feldspar phase. The thickness of the interfacial phase formed through chemical reactions between GP and glass-ceramic matrix is around 30 nm. The chemically bonded interface has contributed significantly toward the substantial improvements in both strength and toughness of the GP-reinforced glass-ceramic matrix composite. Characterization techniques, including X-ray diffraction and field-emission scanning electron Microscopy, incorporating X-ray microanalysis using energy dispersive spectrometry, have been employed in this study. [ABSTRACT FROM AUTHOR]

Monodispersed yttrium aluminum garnet ( YAG) powders have been synthesized via homogeneous precipitation method from the mixed solutions of yttrium nitrate, aluminum nitrate, and ammonium aluminum sulfate using urea as the precipitant. The molar ratio of aluminum nitrate to ammonium aluminum sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical precursor particles can be obtained when the ratio is 1:1. During the homogeneous precipitation process, aluminum ions precipitate first and form monodispered spherical powders, and then yttrium ions precipitate onto the surface of the existing spheres. Monodispersed spherical YAG particles with 500 nm in diameter were obtained by calcining the precursor powder at 1100°C for 5 h. The so-prepared monodispersed spherical Nd: YAG powders have good sinterability, and can be sintered into transparent ceramics by vacuum sintering at 1650°C for 3.5 h. [ABSTRACT FROM AUTHOR]

Synthesis of nanocrystalline yttria powder from Y(NO3)3 solution and ammonia water was investigated. It was found that the precursor precipitate is Y2(OH)5(NO3).H2O. The addition of small amount of ammonia sulfate in yttrium nitrate solution can reduce the agglomeration and particle size of the produced yttria powders. Nanocrystalline yttria powder (60 nm in average size) was obtained by calcining the precursor at 1100 °C for 4 h. Using this yttria powder and a commercial ultrafine Al2O3 powder, fully transparent YAG ceramics was fabricated by vacuum sintering at 1700 °C for 4 h through a solid-state reaction method. It was found that the addition of 0.5 wt.% tetraethyl orthosilicate (TEOS) is suitable for the fabrication of transparent YAG ceramics. If the amount of TEOS is less than 0.05 wt.%, abnormal grain growth occurs, and pores are entrapped in the grains. If the amount of TEOS is more than 3 wt.%, large amount of liquid phase is yielded, leaving some residual inclusions at grain boundaries. These are detrimental for the transparency of YAG ceramics. [Copyright &y& Elsevier]

Yttria nanopowders were synthesized using a chemical precipitation method. pH value at the end of the precipitation process has a significant effect on the size and morphology of the precursor and the yttria powders. Under the same calcination condition, the yttria powders made from the precursor obtained at a pH of 8 are smaller in mean particle size and narrower in size distribution than those made from the precursor obtained at a pH of 10. It was found that the optimum calcination temperature is 1000 °C, and the yttria powder obtained is fine (30 nm) and well dispersed. Using the yttria powder, transparent yttria ceramics was produced by vacuum sintering at 1700 °C for 4 h without any additives. [Copyright &y& Elsevier]

This study aimed to compare the effects of two surface-coating methods on the shear bond strength (SBS) of veneering ceramics (VC) to zirconia. Eighty pre-sintered zirconia cubes were randomly assigned into four study groups: E60S, E60P, N60S, and N60P. The zirconia surface was coated with a mixture of two types of glaze and alumina (<60 μm) by airbrush spraying and fine- brush painting. Surface roughness (Ra), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and SBS measurements (both initial and artificial aged conditions, including one month of water storage) were performed. The Ra results revealed significant differences among all groups (p < 0.001). The N60P group exhibited higher values of Ra (5.717 ± 0.20 µm) and SBS before and after water storage with values of 37.22 ± 4.954 MPa and 34.42 ± 3.977 MPa, respectively. The fine-brush coatings showed significantly higher SBS than that of airbrush coatings, in both initial and artificial conditions. Both coating methods and various coating materials (p < 0.001) produced a significant influence on VC-zirconia SBS. A significant correlation between Ra and SBS (Spearman's rho = 0.808; p < 0.001) was found. The novel coating by fine-brush painting is a promising surface treatment and an easy technique for obtaining a rougher surface, which subsequently improves the bond strength to VC. [ABSTRACT FROM AUTHOR]

The application of high-power laser-driven lighting is limited by the insufficient heat dissipation of phosphor converters and the poor color quality of white light. In this study, the Al 2 O 3 (Gd,Ce) 3 (Al,Ga) 5 O 12 (Al 2 O 3 GAGG:Ce) composite ceramics were designed to improve thermal performance of phosphors, while maintaining excellent color rendering under high-power laser excitation. Dense composite ceramics were fabricated by pre-sintering at 1600 °C in air followed by HIP at 1700 °C through the investigation of the phase evolution and sintering process. The emission spectrum of GAGG:Ce shows a red shift of 31 nm and a high full width at half maximum (FWHM) of 128 nm. Meanwhile, the thermal conductivity was increased to 13.2 W·m−1K−1 by addition of Al 2 O 3 , which is 72% higher than that of single-phase GAGG:Ce ceramic. Therefore, warm white light with high color rendering index (CRI) of 71.4 and low correlated color temperature (CCT) of 4352 K was attained under excitation of high-power LDs. [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]

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]

By pre-treating and component design of the ceramic powders, cubic (Lu,Gd) 2 O 3 :Eu solid-solution ceramics with high optical quality were achieved by the solid-state reaction method combined with vacuum sintering. The effects of Gd3+ doping (x = 0.05–0.6) on powder characteristics, phase compositions, microstructures and optical performances of the (Lu 0.95- x Gd x Eu 0.05) 2 O 3 ceramics were systematically investigated to obtain the optimum Gd3+ content. The results indicated that the incorporation of moderate amounts of Gd3+ (5–50 mol%) effectively promoted mass diffusion and grain growth during sintering. The 50 mol% Gd3+-doped Lu 2 O 3 :Eu transparent ceramic (using the powder calcined at 1200 °C) sintered at 1750 °C for 5 h exhibited the optimum transmittance of 77.0 % in the visible spectral region (∼1 mm in thickness), which was significantly higher than the reported transmittance of vacuum sintered (Lu,Gd) 2 O 3 :Eu ceramics (less than 65.0 %). Owing to the lower electronegativity of Gd3+ relative to Lu3+, the bandgap energies of the final ceramics decreased gradually with increasing Gd3+ substitution, and the redshift of the CTB centre was observed with more Gd3+ addition. Under CTB excitation, the incorporation of Gd3+ enhanced the red emission intensity and shortened the fluorescence lifetime. • Highly transparent (Lu,Gd) 2 O 3 :Eu ceramics were achieved by pre-treating and component design of ceramic powders. • Gd3+ doping promotes mass diffusion and grain growth during sintering. • The (Lu 0.45 Gd 0.5 Eu 0.05) 2 O 3 ceramic exhibits the transmittance of 77.0 % in the visible range. • Incorporation of Gd3+ results in enhanced luminescence intensity and shortened lifetime. [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]

(Nb 0.5 Ga 0.5) x Ti 1−x O 2 (x = 0.05%,0.2%,0.5%,1%,5%) single crystals were prepared by Verneuil method. Even if the doping amount is 0.05%, the dielectric permittivity (ε′) is obviously higher than that of pure rutile TiO 2 (260), reaching more than 104. As the doping amount x increase, the ε′ increases, and reaches the maximum value when x = 5%, but the dielectric loss increases correspondingly. The best dielectric performance (ε′=1.0 ×105, tanδ=0.034 under 1 kHz) is obtained when the doping amount is 0.5%. Even at 106 Hz, the dielectric loss is only 0.019, much lower than the reported ceramic samples. This may be due to the fact crystalline materials can effectively reduce defects such as grain boundary, second phase, porosity and segregation. The dielectric spectra, impedance analysis, XPS and DC bias results show that the colossal permittivity (CP) properties could be attributed to EPDD polarization. With the increase of doping concentration (>1%), the hopping polarization occurs, resulting in a slight increase in dielectric loss. These results indicate that TiO 2 crystal materials with lower dielectric loss are good candidates for dielectric materials. Taking TiO 2 crystal as the research object, we can have a clearer understanding of the origin of TiO 2 dielectric properties and the influence of doping ion content, which is of great significance to the development of TiO 2 -based dielectric materials. • (Nb 0.5 Ga 0.5) x Ti 1-x O 2 single crystals were prepared and their dielectric properties were studied for the first time. • The dielectric properties of doped crystal are improved and the best performance is obtained when the doping amount is 0.5%. • The dielectric loss is 0.019 at 106Hz , lower than the reported ceramics. And less than 0.1 from room temperature to 255℃. • Single crystal can eliminate the effects of defects and better understand the origin of dielectric properties. [ABSTRACT FROM AUTHOR]