Yttrium Aluminum Garnet Y3Al5O12 Research Articles

SiC ceramics production by spark plasma sintering from a coal fly ash residue after high-pressure NH4HSO4-and-H2SO4 leaching

In this article, a novel method for SiC production from a residue of coal fly ash (CFA) after high-pressure leaching with a mixture of NH4HSO4 + H2SO4 is proposed. A thermodynamic analysis showed that SiC can be obtained at >1500 °C, and titanium carbide (TiC) and ferrosilicon (FeSi) can form as byproducts. Carbothermal reduction of the CFA residue with carbon in the range 1300–1500 °C with holding time 1–3 h was investigated. X-ray phase analysis (XRD) indicated that SiC forms at >1425 °C. Iron compounds in the form of Fe3Si and Fe5Si3 were detected by Mössbauer spectroscopy in a sample sintered at 1500 °C. The possibility of SiC production by a two-step procedure was demonstrated. First, a SiC powder was obtained from the CFA residue and carbon at 1500 °C, then SiC was mixed with yttrium aluminum garnet Y3Al5O12 and processed by spark plasma sintering at 1750–2000 °C, holding time 5 min, and pressure 50 MPa. Ceramic samples obtained at 1850 and 1900 °C with compressive strength of 350 ± 17.5 & 416 ± 20.8 MPa and Vickers hardness of 17.89 ± 0.89 & 15.97 ± 0.79 GPa, respectively, proved to be comparable to the best reported SiC + yttrium aluminum garnet ceramics. Thus, this study presents an original method for ceramics production from solid waste of coal-fired power plants; this approach will allow to create a comprehensive technology for utilizing 100 % of CFA.

Thermochromic properties of some colored oxide materials

The thermochromic properties up to 500 °C of some colored, commercial and non-toxic oxides were studied. It includes Bi2O3, Fe2O3, In2O3, WO3, Er2O3, YAG:Ce (Ce doped yttrium aluminum garnet Y3Al5O12) and YInMn-Blue (Mn doped yttrium indium oxide YInO3). From the CIELAB colorimetric parameters (L*a*b*), evolution of the color contrast ΔE with temperature was calculated. It allowed estimating that most of these oxides change color reversibly with increasing temperature, the strongest thermochromism being found for Bi2O3 (ΔE ∼ 65 at 500 °C). Two exceptions were identified: i) Er2O3 which stayed almost identically pink with ΔE<7 even at 500 °C and ii) WO3 which original color was not recovered upon cooling back to room temperature. While the color change of the other oxides was gradual with increasing temperature, YAG:Ce compound behaved differently since its thermochromicity abruptly started above 300 °C. DSC analyses did not allow detecting any physico-chemical event in relation with these peculiarities. The obtained datasets for all these compounds can be used for anticipating the thermochromic properties of these powders and the blends made out of them.

Contribution of the hybrid component to the structure and properties of ceramics based on metastable phases Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

The paper presents results of the study of the effect of doping with yttrium oxide on ceramics of the composition (γ + θ) Al2O3 + nY2O3 (n = 0, 1, 2, 3 wt%), sintered at 1550°C for 2 h, from powders of the specified composition annealed at temperatures of 500 , 800, 1000°С. X-ray diffraction analysis established the formation in ceramics of yttrium aluminum garnet Y3Al5O12 (YAG) and a metastable phase of the same composition with a tetragonal lattice type in powders at temperatures above 1200°C. The effect of YAG on the physical and mechanical properties was established: high properties were demonstrated by ceramics of the composition α-Al2O3 + 2wt% Y2O3, obtained from a powder annealed at 1000°C. In addition, high physical and mechanical properties were observed in ceramics of the composition α-Al2O3 + 0wt% Y2O3, obtained from a powder annealed at 800°C. The effect of the so-called “mutual protection against crystallization” was discovered, which consists in the mutual inhibition of crystallization processes in powders of the Al2O3 – Y2O3 system.

YAG Laser Rod 3D Corrective Process Optimization through Tool Influent Function Shape Inspection

Due to the increasing demands on the quality of solid-state laser active media production based on yttrium aluminum garnet Y3Al5O12 in the form of rods with precisely machined faces, the possibilities of applying subaperture 3D corrective polishing in this segment of optical production were studied. For the considered laser rod diameters of up to 10 mm, the corrective process had to be optimized to achieve a stable, suitably shaped tool influence function at the full width at half maximum of approximately 1.5 mm, enabling 3D shape corrections with sufficient lateral resolution. For this purpose, a number of experiments were performed using both tools based on a flexible elastic membrane inflated by compressed air and tools with a viscoelastic head, and the effect of the tool-polished surface interaction was studied and analyzed.

Volatile impurities in the structure of Y3Al5O12 garnet synthesized in water fluid

The mechanism of synthesis of fine-crystalline yttrium aluminum garnet Y3Al5O12 (YAG) in sub- and supercritical conditions of water medium was studied. It was found that, under subcritical conditions, the initial oxides are hydroxylated to form yttrium hydroxide, boehmite, and agglomerates of nanoscale YAG crystals and, under supercritical conditions, the nanoscale crystals are recrystallized yielding micron YAG crystals with well-formed faces. Two-stage synthesis in sub- and supercritical water fluid allows obtaining cerium-doped YAG crystals with high photoluminescence intensity. The gas content, gas release, degassing kinetics, and water diffusion coefficients in YAG at high temperatures were determined using the method of kinetic thermodesorption mass spectrometry. Water, carbon-containing substances and oxygen play a significant role in degassing. It was concluded that the ordering of the crystal structure occurs due to the appearance of solid-phase mobility of the oxide structure and changes in the state of hydroxyl groups. Knowing the content of volatile impurities and the temperature dependence of the diffusion coefficient allows us to develop the technology of high-temperature sintering of YAG crystals in order to obtain high-quality transparent ceramics.

First-principles study of the formation energies and positron lifetimes of vacancies in the Yttrium-Aluminum Garnet Y3Al5O12

Lattice vacancies are a major concern for the use of the Y3Al5O12 garnet (YAG) in optical applications. They are known to trap charge carriers preventing them from reaching luminescence centers. This reduces useful photon emission and deteriorates performance. Recent efforts to characterize such defects include experimental works by positron-annihilation spectroscopy (PAS) where extensive positron trapping was reported and attributed to defects made up of both cation and oxygen vacancies. The present study reports first-principles calculations for monovacancy and divacancy defects in YAG by means of conventional and two-component density-functional theory. The defect formation energies and corresponding charge-transition levels in the gap were initially determined. The ability of the lower-energy defects to act as positron-trapping centers was then examined. Corresponding positron lifetimes and binding energies to defects were calculated and compared to the experimental PAS data. The lifetimes of aluminum monovacancies agreed well with experiment if gradient corrections are included in the electron-positron correlation. Association of oxygen with aluminum vacancies was found to lead to stable negatively-charged divacancy complexes which also trap positrons. These defects are characterized by longer positron lifetimes, in agreement with the experimental observations.

Application of High-Frequency Electron Paramagnetic Resonance/Electron Spin Echo for the Identification of the Impurity Composition and Electronic Structure of Ceramics Based Garnets

Electron paramagnetic resonance (EPR) spectra of Ce3+, Yb3+, Cr3+, and Gd3+ impurity ions in yttrium aluminum garnet Y3Al5O12 (YAG) ceramics were detected and identified at frequency of 94 GHz. The advantage of measuring the EPR spectra in the high-frequency range compared to the standard EPR technique is shown, which makes it possible to separate the EPR spectra characterized by different anisotropic g-factors and also to isolate the EPR signals due to the splitting of the fine structure for centers with high-spin states. In ceramics with a high content of magnetic Gd3+ ions, EPR and electron spin echo (ESE) spectra of multi-ionic gadolinium complexes were observed, and EPR spectra of complexes with the maximum number of exchange-coupled gadolinium ions are seen at low temperatures. The temperature dependences of the EPR spectra indicates ferromagnetic ordering of exchange-coupled complexes of gadolinium.

Vanadium in yttrium aluminum garnet: Charge states and localization in the lattice

Incorporation of the V3+ and V4+ ions into the yttrium aluminum garnet Y3Al5O12 (YAG) lattice has been studied by the correlated optical absorption and electron paramagnetic resonance (EPR) measurements. Only the V3+ ions at both octahedral and tetrahedral aluminum sites are found in as-grown crystals. However, annealing in air leads to the transformation of the V3+ to V4+, whereas annealing in the hydrogen atmosphere remains the V3+ concentration almost unchanged. Spin Hamiltonian parameters of the V3+ and V4+ ions at the tetrahedral sites including the zero field splitting and 51V hyperfine constants are determined using high-frequency, up to 300 GHz, EPR measurements. By using the spin Hamiltonian parameters, the ground state energy levels splitting of the V3+ and V4+ ions were calculated in the framework of the crystal field theory. The g and hyperfine tensors suggest that electron density around the tetrahedral V3+ ion is distributed strongly inhomogeneously resulting also in large (40%) reduction of the spin-orbit coupling constant whereas the tetrahedral V4+ ion exhibits weaker covalent bounding with surrounding ligands. Furthermore, the obtained EPR data on vanadium ions allow to improve identification of the optical absorption peaks in YAG:V crystals.

Применение высокочастотного ЭПР/ЭСЭ для идентификации примесного состава и электронной структуры керамик на основе гранатов

Electron paramagnetic resonance (EPR) spectra of Ce3+, Yb3+, Cr3+, and Gd3+ impurity ions in yttrium aluminum garnet Y3Al5O12 (YAG) ceramics were detected and identified at frequency of 94 GHz. The advantage of measuring the EPR spectra in the high-frequency range compared to the standard EPR technique is shown, which makes it possible to separate the EPR spectra characterized by different anisotropic g-factors and also to isolate the EPR signals due to the splitting of the fine structure for centers with high-spin states. In ceramics with a high content of magnetic Gd3+ ions, EPR and electron spin echo (ESE) spectra of multi-ionic gadolinium complexes were observed, and EPR spectra of complexes with the maximum number of exchange-coupled gadolinium ions are seen at low temperatures. The temperature dependences of the EPR spectra indicates ferromagnetic ordering of exchange-coupled complexes of gadolinium.

The influence of stopping power and temperature on latent track formation in YAP and YAG

Transmission electron microscopy techniques were used to analyse the effect of swift heavy ion irradiation on both yttrium aluminium perovskite (YAP) YAlO3, and yttrium aluminium garnet (YAG) Y3Al5O12 single crystals. The crystals were irradiated with Kr, Xe and Bi ions with energies ranging from 107 to 1030 MeV. These ions have electronic stopping powers in the range from 11 to 41 keV/nm. The ion fluences were all within the non-overlapping regime for latent ion tracks i.e. 1011–1012 cm−2. A number of crystals were also irradiated at different temperatures of 80, 300 and 1000 K at a fixed stopping power. Latent ion tracks with an amorphous core were observed in all samples. The track diameters were seen to increase with increasing stopping power. Track diameters only increase by a significant amount as a result of irradiation temperature at 1000 K, whereas the diameters at 80 and 300 K differ only slightly. Ion tracks in YAG were also found to be larger than those in YAP at comparable stopping powers. It was found that on average 10 keV/nm of extra energy input is required to produce ion tracks in YAP with diameters similar to those in YAG. The results also suggest that the complexity of the crystal structure plays a significant role in the formation of ion tracks in these crystals.

YAG:Ce-Phosphor Scintillators for Optical Fiber Radiation Sensors With High Temporal Resolution

A miniature optical fiber real-time X-ray radiation sensor based on plastic optical fiber coupled with a fast decay time trivalent cerium-activated yttrium aluminum garnet Y3Al5O12 (YAG:Ce) scintillator material is reported. The YAG material was tested in powder and ceramic form. Three separate sensors were irradiated three times on a Siemens Artiste linear accelerator (linac). The measured light output of the YAG:Ce ceramic to the detector at the distal end of the fiber is 4.52 times greater than the YAG:Ce powder, and its output intensity detected by photon counter is further increased 2.52 times using a two-layer highly reflective Teflon tape. The sensor made with YAG:Ce powder shows excellent repeatability, being a maximum of 0.36 %, but the value using YAG:Ce ceramic exhibits orientation sensitivity when located in orthogonal positions relative to the X-ray beam. To the best of our knowledge, the work described in this letter is the first instance of the direct high temporal resolution detection of the individual (circa 3.9 ms) output of X-ray light pulses of clinical linacs. The experimental results of pulsewidths are in good agreement with the manufacturer’s stated value of $3.45~\pm ~0.21~\mu \text{s}$ .

Influence of Sulfate Ion on Phase and Dispersion of Y&lt;sub&gt;3&lt;/sub&gt;Al&lt;sub&gt;5&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; Nanopowders with the Co-Crystallization Method

Yttrium aluminum garnet Y3Al5O12 (YAG) nanopowders were synthesized from co-crystallized precursors of Y2(SO4)3, Al(NO3)3-Al2(SO4)3 and Y(NO3)3 with a three-layer core-shell structure. X-ray diffraction (XRD) pattern indicated that too much was detrimental to the synthesis of pure phase YAG because of the serious separation between Y2(SO4)3 and Al(NO3)3-Al2(SO4)3. Transmission electron microscopy (TEM) revealed that was beneficial for the dispersion of the powders owing to the high decomposition temperature of . The powders with the n()/n(Y3+) mole ratio of 1.5/3 calcined at 1050°C showed good sintering activity.

Heat-Treatment-Induced Evolution of the Mesostructure of Finely Divided Y3Al5O12 Produced by the Sol–Gel Method

A method was developed for the low-temperature sol–gel synthesis of one of the most popular components of functional and structural materials—nanostructured yttrium aluminum garnet Y3Al5O12—using precursors from the class of alkoxoacetylacetonates produced from the corresponding acetylacetonates. It was determined that increasing duration of heat treatment of yttrium-aluminum-containing xerogen in air to 6 h reduces the crystallization temperature of the Y3Al5O12 phase from 920–930 to 750–800°C, which was confirmed by IR spectroscopy and X-ray powder diffraction analysis. The microstructure of nanocrystalline yttrium aluminum garnet obtained at 800°С was studied; it was found that the size of crystallites is 30–40 nm, the size of particles is 30–50 nm, and the size of pores is 20–30 nm. Small-angle neutron scattering demonstrated that, in the powders synthesized at 700–800°C, there is structural ordering of the short-range type, whereas in the nanocrystalline samples heat-treated at a higher temperature (850°С), there is no such ordering.

Relaxation of the environment of Gd3+ and Eu2+ impurity ions in the Y3Al5O12 garnet

The second-rank spin Hamiltonian parameters of Gd3+ and Eu2+ orthorhombic centers in crystals of the yttrium aluminum garnet Y3Al5O12 have been analyzed within the framework of the superposition model for the zero-field splitting of the ground state. It has been shown that the description of the experimental data in this model is possible only under the assumption of relaxation of the ligand environment of the paramagnetic impurity.

Luminescence of yttrium–aluminum garnet crystals with Eu2+ impurity ions

Luminescence of yttrium-aluminum garnet Y3Al5O12: Eu,Si samples is studied. It is found that luminescence is associated with Eu2+ ions, but does not correspond to intracenter 4f65d1–4f7 transitions. Measurements of the excited state lifetime point to the luminescence mechanism involving charge-transfer states.

Preparation of SiC–MgAl2O4–Y3Al5O12-MWCNTs nanocomposites by spark plasma sintering

Fabrication a composite materials based on silicon carbide (SiC) reinforced with multi-walled carbon nanotubes (MWCNTs) with addition of magnesium alumina spinel MgAl2O4, and yttrium aluminum garnet Y3Al5O12 by spark plasma sintering are presented.Two series of composites differing by the particle size of starting SiC were prepared. Mechanical characteristics of composites including microhardness, fracture toughness and flexural strength are determined.

Anion-Exchange Synthesis of Yttrium-Aluminum Garnet Powders

A new method is proposed for synthesizing yttrium-aluminum garnet Y3Al5O12 powder. The method consists in anion exchange coprecipitation of yttrium and aluminum from chloride solutions by the anionite Purolite A-300 in the OH-form and calcination at 900 °C of the precursor formed. The product was investigated by means of XPA, DSC, IR-spectroscopy, and electron microscopy. The Y3Al5O12 particle size was 300 nm.

Organically modified clays as rheology modifiers and dispersing agents for epoxy packing of white LED

We develop a new class of polyetheramine-modified organoclays that enable the homogenous dispersion of inorganic phosphorescent phosphor powder, yttrium aluminum garnet Y3Al5O12 (YAG), in epoxy, which can then be used for packing of light-emitting diode (LED) devices. The organoclays are prepared from the ionic exchange reaction of sodium montmorillonite (Na+-MMT) with poly(oxypropylene) (POP) diamines of sufficiently high molecular weight, which are found to be effective for homogenizing YAG in the two-component epoxy system involving an anhydride curing agent and an aliphatic epoxy resin. By adding the POP-diamine-based organoclays, the viscosity of the anhydride/epoxy resins is greatly enhanced and the resin shows a non-Newtonian shear-thinning behavior. Because of the high viscosity that retards the molecular motion, the micrometer-scaled YAG particles can remain dispersed in the resins for a fairly long time without precipitation during the curing process. We investigate the rheological properties of the organoclays as the thickening agent and applied the organoclays to fabricate YAG particle-dispersed epoxy for packing of blue light LED that mixes the yellow light of the well-dispersed YAG particles to form uniform white illumination.

The effect of N3− substitution for O2− on optical properties of YAG:Ce3+ phosphor

In the present work, yttrium aluminum garnet Y3Al5O12−xN2x/x (YAGN) was obtained using aluminum nitride (AlN) as a source of aluminum. YAGN was doped with the Ce3+ ions (YAGN:Ce) in concentrations from 0.5 to 14 mol%. According to XRD analysis, the crystal structure of YAG is maintained with traces of Al2O3. Scanning electron microscope (SEM) studies showed that the nitrogen atoms are not quite uniformly incorporated into grains, which may easily lead to the formation of a number of various Y3+ sites. This means that Ce3+ ions can also occupy sites of different nitrogen/oxygen ratios. The probability of Ce3+entering different sites changes with the dopant concentration. The emission and excitation spectra of Ce3+ exhibit concentration dependence. For concentrations in the range 0.5–7% emission bands are extended to longer and shorter wavelengths in comparison to the typical emission of Ce3+ in YAG. With the increase in the concentration of active ions (10–14 mol%) excitation bands show further widening, and the emission bands shift gradually toward longer wavelengths, reaching the value of 45 nm for 14 mol%. The usefulness of these phosphors for application in white LED technology is discussed on the basis of the quantum efficiency of the emissions, luminescence decay times, and thermal quenching of the Ce3+ emission.

Yttrium aluminium garnet under pressure: Structural, elastic, and vibrational properties from ab initio studies

The structural, elastic, and vibrational properties of yttrium aluminum garnet Y3Al5O12 are studied under high pressure by ab initio calculations in the framework of the density functional theory. The calculated ground state properties are in good agreement with the available experimental data. Pressure dependences of bond length and bulk moduli of the constituent polyhedra are reported. The evolution of the elastic constants and the major elastic properties, Young and shear modulus, Poisson's ratios, and Zener anisotropy ratio, are described. The mechanical stability is analyzed, on the light of “Born generalized stability criteria,” showing that the garnet is mechanically unstable above 116 GPa. Symmetries, frequencies, and pressure coefficients of the Raman-active modes are discussed on the basis of the calculated total and partial phonon density of states, which reflect the dynamical contribution of each atom. The relations between the phonon modes of Y3Al5O12 and the internal and external molecular modes of the different polyhedra are discussed. Infrared-active modes, as well as the silent modes, and their pressure dependence are also investigated. No dynamical instabilities were found below 116 GPa.