Optimization of Ce3+ concentration and Y4MgSi3O13 phase in Mg2+-Si4+ Co-doped Ce: YAG ceramic phosphors

As a promising replacement for nitride red phosphors, Ce: Y₃(Mg_1.8Al_1.4Si_1.8)O₁₂ (Ce: YMASG) ceramic phosphors have attracted significant attention recently for their advantages in inorganic encapsulation and massive red-shifting of Ce³⁺ emission. In this work, Ce: YMASG with different doping concentrations of Ce³⁺ and Al₂O₃, was fabricated by vacuum sintering to investigate its effects on the elimination of the impurity phase and the enhancement of the luminescent properties of white light-emitting diodes (w-LEDs). It was discovered that the emission wavelength redshifts from 592 to 606 nm as the Ce³⁺ concentration increases, while at 450 K, the emission intensity deteriorates from 0.47 to 0.36 of its initial value. The Rietveld analysis revealed the presence of an impurity phase of Y₄MgSi₃O₁₃ with a concentration of 17.021 wt% in Ce: YMASG. With the introduction of Al₂O₃, the impurity phase was eliminated from the matrix completely, the emission peak shifted to a shorter wavelength, and the thermal stability was greatly improved. When the correlated color temperature was controlled at around 3000 K in the packaged w-LEDs, the commission international de l'éclairage (CIE) chromaticity coordinates shifted toward the bottom left corner of the diagram with increasing concentration of Ce³⁺. Conversely, the luminous efficiency (LE) increased from 36 lm/W to 58.6 lm/W as the concentration of Al₂O₃ increased from 0 to 10 wt%, which demonstrated the application prospect of the fabricated phosphor in warm w-LEDs.     

Thermophysical properties of rare earth barium aluminates

The super low thermal conductivity and ultrahigh thermal expansion of Ba₆Ln₂Al₄O₁₅ (Ln = Gd, Dy, Er, and Yb) compounds with one‐sixth of the oxygen vacancy have been synthesized by the solid‐state reaction method. The lowest thermal conductivity of Ba₆Yb₂Al₄O₁₅ was found to be 0.98 W/(m.K) at 1073 K. The large concentration of oxygen vacancies in Ba₆Ln₂Al₄O₁₅ compounds leads to low elastic modulus and loose chemical bonds. The average thermal expansion coefficients of Ba₆Ln₂Al₄O₁₅ compounds was 11.8 × 10^?6 ? 13.6 × 10^?6 · K^?1. The loose chemical bonds with Young's moduli were in the range of 102.8 ? 135.9 GPa.     

Free occupying mechanism of simulated tetravalent waste ions in Gd2Zr2O7 and performance evaluation of the waste forms

To extend the practicability of ceramics in immobilizing nuclear waste with fluctuant composition, structural design should be abandoned. The simulated tetravalent actinide waste An⁴⁺ (Ce⁴⁺) was directly doped into prepared Gd₂Zr₂O₇, and the waste forms were synthesized by high-temperature solid-state reaction. It has been shown that the maximum loading of CeO₂ in Gd₂Zr₂O₇ lies between 20 and 30 wt.%, and Ce elements are uniformly distributed in the matrix. Existing in Ce³⁺ and Ce⁴⁺, cerium ions automatically occupied both the Gd and Zr sites in Gd₂Zr₂O₇ according to valence equilibrium. This occupation causes the change of r(A³⁺)/r(B⁴⁺) and eventually leads to the structure transition from pyrochlore to fluorite. In addition, the normalized leaching rate of the sample with 60 wt.% of dopant was about 2.5 × 10⁻⁷ g m⁻² d⁻¹ on the 35th day. In this study, a free occupation of simulated waste ions in ceramics was proposed.     

Role of Al3+ on tuning optical properties of Ce3+‐activated borosilicate scintillating glasses prepared in air

A colorless Ce³⁺‐activated borosilicate scintillating glass enriched with Gd₂O₃ is successfully synthesized in air atmosphere for the first time. The full replacement of 10 mol% BaO by Al₂O₃, and the partial substitution of 3 mol% SiO₂ by Si₃N₄ in the designed glass composition are crucial for this success. The role of Al³⁺ on tuning the optical properties of Ce³⁺‐activated borosilicate scintillating glass synthesized in air are analyzed by optical transmittance, X‐ray absorption near edge spectroscopy (XANES) spectra, photoluminescence (PL) and radioluminescence (RL) spectra. The results suggest that the stable Ce⁴⁺ ions can be effectively reduced to stable Ce³⁺ ions by the full replacement of BaO by Al₂O₃, and both the PL andRL intensity of the designed borosilicate scintillating glass are enhanced by a factor of 6.7 and 5.2, respectively. The integral RL intensity of the synthesized Ce³⁺‐activated borosilicate scintillating glass is ~17.2%BGO, with a light output of about 1180 ph/MeV. The strategy of substituting BaO by Al₂O₃ will trigger more scientific and technological considerations in designing novel fast scintillating glasses.     

The influence of air annealing on the microstructure and scintillation properties of Ce,Mg:LuAG ceramics

The microstructures and optical properties of Ce,Mg:Lu₃Al₅O₁₂ scintillator ceramics are investigated with particular focus on the effect of postannealing in air from 1000 to 1450°C. The formation of Al₂O₃ clusters after annealing above 1300°C is evidenced by scanning electron microscopy. The presence of this secondary phase is tentatively explained by the occurrence of Ce and Mg evaporation, proved by inductive coupled plasma optical emission spectrometry measurements, followed by defect diffusion and clustering during high temperature annealing. Meanwhile, optical investigations including absorption, X-ray induced luminescence, light yield, scintillation decay, and thermoluminescence prove the positive role of post-annealing that leads to a brighter and faster scintillation emission. This behavior is associated to the removal of oxygen vacancies occurring during such treatments. In parallel, the partial conversion of Ce³⁺ ions into Ce⁴⁺ is also observed as a consequence of annealings and the role of Ce⁴⁺ ions in the scintillation process is discussed.     

Nanostructured co-precipitated Ce0.9Ln0.1O2 (Ln = La,Pr, Sm,Nd, Gd,Tb, Dy,or Er) for thermochemical conversion of CO2

The influence of lanthanide metal cations doped into the CeO₂ crystal structure (to form Ce_0.9Ln_0.1O₂; Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, or Er) on thermochemical reduction and the CO₂ splitting ability of Ce_0.9Ln_0.1O₂ is scrutinized using thermogravimetric analysis. Ce_0.9Ln_0.1O₂ redox materials are effectively synthesized by co-precipitation of hydroxides. As-synthesized Ce_0.9Ln_0.1O₂ redox materials are further characterized based on their phase composition, crystallite size, surface area, and morphology using powder X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, and scanning electron microscopy. The thermal reduction and CO₂ splitting aptitude of Ce_0.9Ln_0.1O₂ redox materials are examined by performing 10 consecutive thermochemical cycles. The results imply that insertion of Sm³⁺, Er³⁺, Tb³⁺, Dy³⁺, and La⁺³ in place of Ce⁴⁺ in the fluorite crystal structure of CeO₂ (forming Ce_0.9Ln_0.1O₂) enhances the O₂ liberation by 22.5, 14.6, 12.6, 5.85, and 2.96 μmol O₂/g·cycle, respectively. Besides, CeLa is observed to be more active towards the CO₂ splitting reaction than CeO₂ and the other Ce_0.9Ln_0.1O₂ redox materials investigated in this study.     

K2CaSi4O10: A novel phase in the ternary system K2O–CaO–SiO2 and member of the litidionite group of crystal structures

The main goal of this work was to verify whether a phase with composition K₂CaSi₄O₁₀ exists in the ternary system K₂O‐CaO‐SiO₂. Therefore, a series of solid‐state reactions of stoichiometric mixtures of K₂CO₃, CaCO₃ and SiO₂ was performed at 800 and 900?C which, indeed, resulted in the formation of this previously unknown potassium calcium silicate. More detailed characterizations of this compound were based on single‐crystal X‐ray diffraction experiments. Basic crystallographic data are as follows: triclinic symmetry, space group P‐1, a = 7.0915(7) Å, b = 8.4211(9) Å, c = 10.2779(12) Å, α = 104.491(10)°, β = 100.570(9)°, γ = 113.738(9)°, V = 515.26(10) ų, Z = 2. Structure solution was performed by direct methods. Subsequent refinement calculations using anisotropic displacement parameters for all atoms converged to a residual of R(|F|) = 0.0355 for 1889 independent reflections with I > 2σ(I). From a structural point of view K₂CaSi₄O₁₀ belongs to the so‐called litidionite family of A′AMSi₄O₁₀ compounds for which several natural and synthetic representatives have been described in the literature. Actually, it is the first member where the A′‐ and A‐positions are exclusively occupied by K‐ions. Following the nomenclature for oxosilicates K₂CaSi₄O₁₀ can be allocated to the group of the tubular chain silicates. Fundamental building units are loop‐branched dreier double chains (running parallel to [100]) which can be described using the following structural formula: {lB,}[³Si₈O₂₀]. Ca‐ions are coordinated by 5 nearest oxygen neighbors in form of distorted trigonal bipyramids. By sharing a common edge two adjacent bipyramids are linked into [Ca₂O₈]‐dimers providing linkage between consecutive tubes in the direction of the c‐axis. Charge compensation is achieved by the incorporation of the larger potassium ions into cavities of the heteropolyhedral network. Powder X‐ray diffraction patterns of the bulk material of the synthesis products revealed that, additionally to K₂CaSi₄O₁₀, the 800°C ‐sample contained K₈CaSi₁₀O₂₅ and at least one further, yet unknown crystalline phase. This unidentified so‐called 22‐Å compound was also present in the 900 °C‐specimen together with K₂CaSi₄O₁₀ and K₂Ca₄Si₈O₂₁. Our proof of existence of K₂CaSi₄O₁₀ is a further step towards a better understanding of the ternary system K₂O‐CaO‐SiO₂ and provides a basis for identification and quantification of this compound in phase analysis. It corrects earlier phase‐analytical studies on this system which is of relevance for applied and technical mineralogy including different types of residual materials such as slags or ashes from biomass combustion. The results of our investigation show that even comparatively simple ternary oxide systems are not as well understood as expected.     

Al2O3–Ce:YAG composite phosphor ceramics for white laser lighting: Novel preparation and regulatable properties

In this work, a series of Al₂O₃–Ce:YAG phosphor powders were synthesized by regulating the excess Al³⁺ of (Y,Ce)₃Al₅O₁₂ via coprecipitation method for the first time, where Al³⁺, Ce³⁺, and Y³⁺ elements were uniformly distributed. With the increase of Al³⁺ content, the morphology of the powders changed from wormlike shapes to flaky shapes, and Y₃Al₅O₁₂ phases had a tendency to convert to YAlO₃ phases. The x wt.% Al₂O₃–(Y_0.999Ce_0.001)₃Al₅O₁₂ (x = 20, 30, 40, 50, 60, and 70) composite phosphor ceramics (CPCs) were obtained by vacuum sintering (1775°C × 10 h), where Al₂O₃ and Ce:YAG phases were also well-distributed. When the Al₂O₃ content was 30–40 wt.%, the average grain size of Al₂O₃ was close to that of Ce:YAG. A solid-state laser lighting device was constructed by a 450 nm laser source and CPCs in a reflection mode. By adjusting the laser power, the correlated color temperature (CCT) values of white laser diodes (LDs) were achieved close to the standard white light of 6500 K. Impressively, the white LDs equipped with the 40 wt.% Al₂O₃-containing CPCs showed the optimum CCT of 6498 K (color coordinates: 0.31 and 0.38), as well as a high luminous flux of 1169 lm and efficiency of 166 lm/W at the LD power of 7.05 W. This work has provided a potential idea to optimize the composition uniformity of Al₂O₃–Ce:YAG CPCs as also to explore their excellent performance in the application of white laser lighting.     

Optimized phase compositions and microwave dielectric properties of low loss Ca2Sn2Al2O9-based ceramics by M4+ substitution

The traditional solid-state reaction method was used to prepare Ca₂Sn_2−xM_xAl₂O₉ (M = Ti, Zr, and Hf) ceramics. Then, the impact of an M⁴⁺ substitution of Sn⁴⁺ on the phase transition, crystal structural parameter, and microwave dielectric properties of Ca₂Sn_2−xM_xAl₂O₉ (0 ≤ x ≤ 0.4) ceramics were investigated. Ti⁴⁺ could not replace the Sn⁴⁺ of Ca₂Sn₂Al₂O₉ due to its small ionic radius, and the Al-based second phases of Ca₂Sn_2−xTi_xAl₂O₉ ceramics were confirmed by the X-ray diffractometer and EDS map scanning results. With the Zr⁴⁺ and Hf⁴⁺ substitutions of Sn⁴⁺, the SnO₂ and CaSnO₃ second phases of Ca₂Sn₂Al₂O₉ ceramic were inhibited, and the Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) single-phase ceramics with orthorhombic structure (Pbcn space group) were obtained. New MO₂ (M = Zr and Hf) and CaAl₂O₄ second phases appeared in the Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.3 ≤ x ≤ 0.4) ceramics, and their contents increased gradually with the increase in x. The Ca₂Sn_2−xM_xAl₂O₉ (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) ceramics exhibited high Q × f because of their pure phase compositions, and the Q × f of Ca₂Sn₂Al₂O₉ ceramic was improved to 77 800 GHz (12.6 GHz) in the Ca₂Sn_1.9Zr_0.1Al₂O₉ ceramic. The Q × f values of Ca₂Sn_2−xM_xAl₂O₉ single-phase ceramics were mainly controlled by r_c (Sn/M–O) and r_c (Al–O). The τ_f values of single-phase Ca₂Sn_2−xM_xAl₂O₉ ceramics were related to octahedral distortions. The Zr⁴⁺ and Hf⁴⁺ substitution of Sn⁴⁺ optimized the phase compositions and microwave dielectric properties of the Ca₂Sn_2−xM_xAl₂O₉ ceramics, and the Ca₂Sn_1.9Zr_0.1Al₂O₉ ceramic sintered at optimal temperature exhibited excellent microwave dielectric properties (ε_r = 8.67, Q × f = 77 800 GHz at 12.6 GHz and τ_f = −69.8 ppm/°C).     

Crystal Structure and Optical Performance of Al3+ and Ce3+ Codoped Ca3Sc2Si3O12 Green Phosphors for White LEDs

Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce) green phosphors used for white light‐emitting diodes (LEDs) are synthesized and codoped with Al³⁺ via a solid‐state reaction method. The crystal structure and vibrational modes are analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman scattering spectroscopy. The energy transfer behavior and optical performance are characterized by photoluminescence and excitation spectra, quantum efficiency, and time‐resolved photoluminescence. The incorporation of Al³⁺ into CSS:Ce can inhibit the formation of the impurity phases Sc₂O₃ and CeO₂, improve crystallinity, and enhance the photoluminescence intensity as well as quantum efficiency. The substitution of Sc³⁺ with Al³⁺ increased the crystal field splitting of Ce³⁺ and resulted in the red shift of photoluminescence. The results show that Ca₃Sc_2?xAl_xSi₃O₁₂:Ce³⁺ has high quantum efficiency, making it a promising green phosphor that can be collocated with a commercial 450 nm blue LED and a red phosphor for solid‐state lighting applications.     

Solid state reactions in highly dispersed Ce1−xYbxO2−y-Al2O3 system

This paper reports the results of studies on the interaction of Ce_1−xYb_xO_2−y mixed oxide nanocrystals (x=0.3 and 0.5) with gamma Al₂O₃. Nano-sized (3–4 nm) crystalline Ce-Yb mixed oxides, prepared by a water-in-oil (W/O) microemulsion technique, or simple co-impregnation by aqueous solutions of lanthanide ions, were supported on high surface area gamma alumina. Solid state reactions occurring in these systems upon heat treatment in air or hydrogen at 900–1100 °C were studied by TEM, SAED and XRD techniques. As a result of solid state reactions between pure or mixed lanthanide oxides and high surface area Al₂O₃, various aluminates were formed, depending on the heating temperature and atmosphere. Lattice parameters measured for the Yb₄Al₂O₉ (monoclinic) and CeAlO₃ (tetragonal) aluminates formed in Ce_0.5Yb_0.5O_1.75-Al₂O₃ and CeO₂+Yb₂O₃-Al₂O₃ systems suggest that they may contain other Ln-ions in the structure, and thus should be described as Ce_1−aYb_aAlO₃ and (Yb_1−bCe_b)₄Al₂O₉. Similar products were formed from solid state reactions in Ce-rich (CeO₂-Al₂O₃ and Ce_0.7Yb_0.3O_1.85-Al₂O₃) or Yb-rich (Yb₂O₃-Al₂O₃ and Ce_0.5Yb_0.5O_1.75-Al₂O₃) systems. The author postulates that, different solid state reaction routes were taken, depending on the Yb-ions concentration in the oxide structure, which was connected with the microstructure of lanthanide oxides (F or F# for Ce-rich systems and C or C# for Yb-rich systems).     

Broadband emission of single-phase Ca3Sc2Si3O12:Cr3+/Ln3+ (Ln = Nd,Yb, Ce) phosphors for novel solid-state light sources with visible to near-infrared light output

Novel single-component phosphors Ca₃Sc₂Si₃O₁₂:Cr³⁺/Ln³⁺ (CSS:Cr³⁺/Ln³⁺, Ln = Nd, Yb, Ce) with broadband near-infrared (NIR) emissions are synthesized. Their phase structure, photoluminescence properties and energy transfer between Cr³⁺ and Ln³⁺ ions are investigated. In the CSS host, Cr³⁺ ions occupy Sc³⁺ sites with low-field octahedral coordination, and thus show a broadband emission in 700–900 nm under the blue light excitation. Nd³⁺, Yb³⁺ and Ce³⁺ ions substitute Ca²⁺ sites in CSS, where Nd³⁺ and Yb³⁺ ions emit the NIR light in 900–1100 nm and their excitation efficiencies at ∼450 nm are greatly enhanced by utilizing the energy transfer from Cr³⁺ to Nd³⁺/Yb³⁺ ions. Ce³⁺ ions can further enhance the absorption of CSS:Cr³⁺/Ln³⁺ phosphors to the blue light, and at the same time contribute to the visible emission in 480–650 nm. Furthermore, CSS:Cr³⁺/Ln³⁺ phosphors show good thermal stability, and approximately 79% of the initial emission intensity is sustained at 150 °C. A phosphor-converted LED (pc-LED) prototype is fabricated by integrating the as-prepared phosphor CSS:Cr³⁺/Ln³⁺ and the commercial phosphor CaAlSiN₃:Eu²⁺ with the blue LED chip, showing a super broadband emission ranging from 450 to 1100 nm. This finding shows the potential application of CSS:Cr³⁺/Ln³⁺ phosphors in broadband NIR pc-LEDs or super broadband LED sources with visible to NIR light output.     

Coincidence Doppler broadening spectroscopy in polyvinyl chloride after doping with Al2O3

Coincidence Doppler broadening of annihilation radiation (CDBAR) and Vickers hardness techniques were performed to study pure Al₂O₃, pure polyvinyl chloride (PVC), and doped PVC with different concentrations of Al₂O₃ (10–50%). The CDBAR ratio curves with respect to pure PVC were presented and reflect the momentum distribution of all the samples. The peak around 14.5 ×10^?3 m_oC in the CDBAR ratio curves suggests a large contribution of positron annihilation with the Al₂O₃. There is a linear correlation between the height of this peak and the Al₂O₃ concentration. The S‐ and W‐parameters were extracted from the CDBAR spectra and increase with increasing the Al₂O₃ concentration showing discontinuity at 30% of Al₂O₃ concentration on PVC. The present data confirmed that there is no positronium formation in pure Al₂O₃ as a result of smaller S‐parameter. The Vickers hardness increases with increasing the Al₂O₃ concentration in PVC showing a linear dependence with two different slopes depend on the Al₂O₃ concentration range. A correlation between the Vickers hardness (macroscopic data) and the W‐parameter (microscopic data) was observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of Al/Sr ratio on the luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

Recent studies have brought out many phosphors like Eu²⁺, Dy³⁺-doped alkaline earth aluminates. The trivalent Dy³⁺ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission.In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu²⁺ and Dy³⁺ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis.A variety of strontium aluminates, such as SrAl₂O₄, Sr₄Al₂O₇, Sr₃Al₂O₆, Sr₃Al₂(Eu, Dy, Y)O_7.5, Al₅(Eu, Dy, Y)O₁₂, Sr₄Al₁₄O₂₅, SrAl₁₂O₁₉ and (Eu, Dy, Y)AlO₃ have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl₄O₇ phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl₂O₄ phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition.     

Overcoming the cyan gap for full-spectrum lighting using cation-substitution-induced rigid Ca2YZr2Al3O12:Ce3+

Mixing multicolor phosphors for simulating the full spectrum of sunlight illumination is a popular solution to obtain high-quality white light. However, there is still a need to overcome the cyan gap in the emission spectrum. In this work, a series of garnet Ca₂Y_0.94–xLu_xZr_2–yHf_yAl₃O₁₂:6%Ce³⁺ (abbreviated as CY_0.94–xLu_xZr_2–yHf_yA:Ce³⁺) cyan phosphors are designed and prepared by substituting Y³⁺ and Zr⁴⁺ in Ca₂YZr₂Al₃O₁₂:6%Ce³⁺ with Lu³⁺ and Hf⁴⁺ with smaller ionic radius and larger mass. Under 405 nm violet light excitation, the optimized Ca₂Y_0.88Lu_0.06Hf₂Al₃O₁₂:6%Ce³⁺ (CY_0.88Lu_0.06Hf₂A:Ce³⁺) shows a bright cyan emission band in the range of 430–750 nm with the peak at 477 nm. Importantly, the emission intensity and thermal stability properties of CY_0.88Lu_0.06Hf₂A:Ce³⁺ were significantly improved by 58% and 47% compared to those of pure Ca₂YZr₂Al₃O₁₂:Ce³⁺. Small and heavy cation substitution could induce highly stable rigid structure, thus enhancing emission intensity and stability. The color rendering index increases from 84.5 to 92.0 after supplementing CY_0.88Lu_0.06Hf₂A:Ce³⁺ phosphor in white light-emitting diode devices combining commercial red, green, and blue phosphors with a violet chip, indicating its practical application in full-spectrum lighting. The present study provides promising strategies for the design and development of efficient cyan materials for high-quality full visible spectrum light-emitting diode lighting.     

Structural studies on Ca3Al4MgO10 (C3A2M)—A ternary phase in the system CaO–Al2O3–MgO

In a sequence of temperature-dependent solid-state reactions in the system CaO–Al₂O₃–MgO the formation of the ternary phase Ca₃Al₄MgO₁₀ or C₃A₂M has been studied. Whereas the compound could not be prepared at 1200°C, a yield of 85 wt.-% of Ca₃Al₄MgO₁₀ was obtained at 1320°C (incongruent melting point: 1330°C). Powder diffraction data compare well with results of previous investigations from the 1960s. Single crystals of Ca₃Al₄MgO₁₀ could be retrieved from the sinter-pellets. Basic crystallographic data are as follows: orthorhombic symmetry, space group Pbcm, a = 5.14073(8), b = 16.7576(2), c = 10.70977(16) Å, V = 922.61(2) ų, Z = 4. Using synchrotron diffraction data it was possible to solve the crystal structure. Least-squares refinements resulted in a residual of R(|F|) = 0.021 for 1000 independent observed reflections with I > 2σ(I) and 97 parameters. The structure contains [TO₄]-tetrahedra (T=Al,Mg) forming a three-dimensional (3-D) framework whose topological characteristics have been determined. Al-Mg distributions on the different T-sites have been studied. The calcium cations are located in voids of the network. More than 50 years after its first observation our investigation clarifies the crystal structure of a compound belonging to a system that is of relevance for several fields of materials science.     

Synthesis of iron aluminates and a new modification of aluminum oxide under shock waves from explosives (Review)

The results of an x-ray diffraction investigation of iron aluminate with unit cell parameter a = 8.090(4) Å, cation-defective iron aluminate Fe_0.5Al_2.23O₄ with a = 8.002 Å, and a new modification of aluminum oxide synthesized under shock waves from explosives containing aluminum are presented. Aluminum oxide can crystallize in the hexagonal system in a primitive lattice with a = 9.151(1) Å, c = 7.945(2) Å, V = 576 ų or in a tetragonal system in a primitive lattice with one-half the volume — a = 7.941(2) Å, c = 4.575(1) Å, V = 288 ų.     

Preparation and Application of Strong Near‐Infrared Emission Phosphor Sr3SiO5:Ce3+,Al3+,Nd3+

This work investigated the near‐infrared (NIR) emission properties of mCe³⁺, xNd³⁺ codoped Sr_3?m?x(Si_1?m?xAl_m+x)O₅ phosphors. Samples with various doping concentrations were synthesized by the high‐temperature solid‐state reaction. Al³⁺ ions have the ability to promote Ce³⁺ ions to enter into the Sr²⁺ sites and to improve the visible emission of Ce³⁺. Thus the NIR emission of Nd³⁺ is enhanced by the energy‐transfer process, which occurred from Ce³⁺ to Nd³⁺. The device based on these NIR emission phosphors is fabricated and combined with a commercial c‐Si solar cell for performance testing. Short‐circuit current density of the solar cell is increased by 7.7%. Results of this work suggest that the Sr_2.95Si_0.95Al_0.05O₅:0.025Ce³⁺, 0.025Nd³⁺ phosphors can be used as spectral convertors to improve the efficiency of c‐Si solar cell.     

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

A new kind of structural and functional integration ceramic matrix composite material was prepared from high-performance alumina (Al₂O₃) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al₂O₃ fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al₂O₃ fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al₂O_3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter-bundles of Al₂O₃ fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al₂O_3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m^1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al₂O_3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X-band. In conclusion, Al₂O_3f/SiCN composite can serve as a high-temperature structural material with excellent microwave absorption properties for aerospace applications.     

Dissolution mechanism of alumina inclusions into CaO–SiO2–Al2O3–FetO–MgO slag via a converter tapping process

Reducing the amount of inclusions during the steelmaking process as much as possible and much earlier plays a vital role in improving the quality of steel products. To reveal the dissolution mechanism of inclusions in slag during the converter tapping process, some comparison experiments were conducted by adding isolated spherical alumina balls as inclusions in CaO–SiO₂–Al₂O₃–Fe_tO–MgO slag, and Fe_tO content up to 10% was contained in slag. The results showed that the dissolution rate of alumina balls in the slag was mainly affected by the diffusion of Al₂O₃, and the diffusion coefficients of Al₂O₃ were 4.2 × 10^–11, 7.5 × 10^–11, and 1.5 × 10^–10 m²/s at 1500℃, 1550℃, and 1600℃, respectively. In addition, the upgraded diffusion-distance-controlled dissolution model (DDD-Model), in which Fe_tO content was introduced and applied in the study. The results illustrated that the Al₂O₃ inclusion apparent dissolution rate was improved by a high Fe_tO content, increasing CaO/SiO₂ and raising the temperature as soon as possible at the early stage of the converter tapping process. It is not necessary to increase the Fe_tO content in the slag to enhance the dissolution rate of the Al₂O₃ inclusion at the last tapping stage. The predicted complete dissolution time of spherical Al₂O₃ inclusions with 1000 µm in diameter based on the upgraded DDD-Model was approximately 1796 s during the actual converter tapping process.