Preparation of Yttrium Aluminum Garnet Powders by Modified Alkoxy-derived Process

Three compounds exist in the system Al₂O₃-Y₂O₃:yttrium aluminum garnet (YAG, Y₃Al₅O₁₂), yttrium aluminum perovskite (YAP, YAlO₃), and yttrium aluminum monoclinic (YAM, Y₄Al₂O₉)^[1]. Among these compounds, YAG has received the most attention due to its good optical properties. Single crystal YAG is best known as a solid-state laser host material.     

Influence of hydrolysis method on the sol-gel formation of the yttria-alumina system with use of alcoholates

The influence exerted by hydrolysis methods and introduction of a hydrolyzing agent into the systems formed by the alkoxide technology, which uses yttrium salts and alumium secondary butylate as the initial components, was determined. It was found that the hydrolysis stage affects the conditions of the subsequent thermal treatment, the phase formation in the system, and the granulometric composition of the prepared powders. The most favorable conditions for formation of yttrium aluminum garnet are achieved upon excess water hydrolysis in the presence of an aqueous solution of yttrium salt.     

Thermogravimetric study of yttrium isopropoxide and dispersant burnout in aluminum nitride ceramic processing

Yttrium isopropoxide, an yttrium oxide precursor, is sometimes used as a sintering aid for producing aluminum nitride ceramics. In the present work, this sintering aid was used with isopropanol as the solvent and polyethyleneimine as the dispersing agent. After initial ball milling and drying steps, the burnout behaviour of samples taken from isostatically pressed pellets was studied by thermal analysis in nitrogen and air. In addition to the milled and pressed pellets, each component was also analyzed separately. Complete conversion to yttrium oxide, with no residual carbon, would be a desirable property of this system. However, during the preparation of the aluminum nitride pellet, there was only partial yttrium isopropoxide decomposition. The nitrogen burnout residue contained carbon formed from the yttrium isopropoxide and dispersant overlapping thermal decomposition, mostly from an intermediary decomposition stage of the former that occurs between 300 and 550°C. The residual carbon content and the previous yttrium isopropoxide decomposition were estimated by thermogravimetry.     

YAlC: A Bonding Chameleon with Heteropolyacetylene Features

YAlC was prepared by a flux method. It crystallizes as a partially filled‐up TlI structure, showing remarkable structural aspects at the border between Zintl phases and intermetallics. This novel ternary aluminide–carbide exhibits a unique one‐dimensional multi‐center bond and a polyacetylene‐related aluminum carbide substructure. The different functionalities of aluminum and of yttrium are quite remarkable. While the latter behaves more like a trivalent ion, aluminum contributes considerably to covalent bonding with carbon. Still yttrium d states contribute, but hardly in a directed manner.     

Mg-Y合金的电子理论研究

添加稀土元素Y,可以显著提高镁合金的力学性能特别是高温力学性能。通过固体与分子经验电子理论(EET)对Mg-Y合金进行了价电子结构分析：纯金属晶体计算结果显示Y应处于第五杂阶,证实了Mg应处于第三杂阶。对比Mg-Al合金,阐明了Y优于Al在镁合金中的固溶强化作用的电子理论依据是键能得到增强;同时用电子理论解释了Mg24Y5中间相在镁合金中具有显著强化作用的原因是Y原子占据八面体中心位置,Mg—Y键有效强化了合金基体。     

Synthesis,Characterization and Luminescence Properties of YAG:RE (Ce,Sm and Gd) Nanophosphor by Cathodic Electrodeposition Method

Russian Journal of Electrochemistry - YAG:RE (RE: Ce, Sm and Gd) phosphors were synthesized via a novel method based on cathodic electrodeposition of a mixture of yttrium, aluminum and some rare...     

Structural parameters of the close environment of group III metal ions in aqueous solutions of their salts

Published data obtained by various research methods and our own experimental results on the structural characteristics of the nearest environment of aluminum, gallium, indium, thallium, as well as scandium, yttrium and lanthanum ions in aqueous solutions of their salts under ambient conditions are summarized. The structural parameters, like coordination number, interparticle distance, parameters of the second coordination sphere and the types of ion association are discussed. The hydrate complexes of the ions of aluminum and gallium subgroups are compared.     

Reactions of niobium silicide melt with refractory ceramics

Vaporization of a multicomponent Nb?Si-based melt with ceramic materials containing yttrium, zirconium, hafnium, and gadolinium oxides is studied. The high-temperature reactions of the alloy and ceramics at 1795?2510 K involve reduction of yttrium, zirconium, hafnium, and gadolinium oxides, accompanied by an increase in the partial pressures of GdO, YO, ZrO, and HfO compared with the partial pressures of the same oxides over individual ceramic samples. Ceramics oxidized titanium, silicon, aluminum, and niobium to oxides.     

Dynamic study of ammonium dawsonite doped with yttrium transformation at elevated temperatures

Co-precipitation of alumina/YAG precursor from aluminum and yttrium nitrates solution with ammonium carbonate results in dawsonite (NH₄Al(OH)₂CO₃). Its crystallographic parameters differ from the compound precipitated without the yttrium additive. It indicates that yttrium ions become incorporated into the dawsonite structure. The DSC/TG and X-ray measurements show decomposition of dawsonite at elevated temperature resulting in γ-Al₂O₃ which transforms to δ and θ modifications at still higher temperatures. The full transformation to α-Al₂O₃ and YAG occurs at temperatures higher than 1,230 °C.     

ICP-AES analysis of aluminum isopropoxide,yttrium, and neodymium oxide nanopowders

A technique has been developed for analysis of impurities in precursors of the optic ceramics: aluminum isopropoxide, yttrium and neodium oxide nanopowders (weight fraction of Nd ≤5%) by atomic-emission spectroscopy with inductively coupled plasma. In the case of aluminum isopropoxide, the effect of matrix is compensated by applying Bi as an internal standard. The detection limits of impurities were found to be 10^?5–10^–6 wt.%.     

Preparation of inorganic crystalline compounds induced by ionizing,UV and laser radiations

Results on preparation of nickel, zinc, yttrium, aluminum and cobalt oxides, zinc peroxide and hydroxide, yttrium and lutetium aluminum garnets and cobalt(II) aluminate via irradiation of aqueous solutions containing soluble metal salts and radical scavengers (formate anion or propan-2-ol) are summarized in this paper. Various physico-chemical and structural properties of prepared compounds (e.g. crystallinity, specific surface area, particle size) are also reported.All used variants of radiation method are rather convenient and simple, and yield nano-scale powder materials with interesting characteristics. Prepared materials generally have high chemical purity, high specific surface area and narrow distribution of particle size (ranging in tens of nm).Generally, accelerated electrons, gamma, and UV radiation yield materials with comparable properties and structural characteristics, but UV-radiation seems to be the most convenient for preparation of intricate compounds such as synthetic garnets and spinels, while ionizing radiation is better for preparation of compounds doped with foreign ions.Among discussed compounds, only zinc oxide, peroxide and hydroxide were prepared directly via irradiation. For preparation of other crystalline oxidic compounds, mild heat treatment of amorphous or weakly crystalline solid phase was necessary.     

First-principles calculations for the cooperative transitions of Yb3+ dimer clusters in Y3Al5O12 and Y2O3 crystals

A first-principles multielectron method is applied to the calculations for the cooperative transitions of trivalent ytterbium ions (Yb3+) in yttrium aluminum garnet (Y3Al5O12; YAG) and yttrium sesquioxide (Y2O3) crystals. The method is based on a molecular-orbital method, in which the overlap between the Yb 4f and the oxygen 2p orbitals is directly considered through a self-consistent procedure. A Yb2(3+) two-ion model and a (Yb2O14)22- dimer cluster embedded in the point charges of the YAG lattice are compared. The 4f-2p overlaps in the cluster model is needed to explain the cooperative transition probability originating from electric dipole transitions. A (Yb2O10)14- dimer molecule in Y2O3 lattice produces larger electric dipole transition probabilities than the case of YAG. The smaller coordination number in Y2O3 produces the larger 4f-2p overlaps, which result in the larger transition probabilities.     

Preparation of nanostructured thin films of yttrium aluminum garnet (Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>) by Sol—Gel technology

The synthesis of hydrolytically active heteroligand coordination compounds [M(C₅H₇O₂)_3–x(C₅H₁₁Oⁱ)_x] (where M = Al³⁺ and Y³⁺) using aluminum and yttrium acetylacetonates has been studied. The gel formation kinetics in their solutions upon hydrolysis and polycondensation has also been studied. Thin films of a solution of these precursors have been applied to polished sapphire substrates by dip coating. The crystallization of nanostructured yttrium aluminum garnet (Y₃Al₅O₁₂) films during heat treatment of xerogel coatings under various conditions has been studied. How the phase composition, microstructure, and particle size depend on the synthesis parameters has been recognized.     

Coating of Y2O3:Eu3+ particles with alumina by a humid solid state reaction at room temperature

Humid solid state reaction at room temperature was utilized for the first time to coat Y(2)O(3):Eu(3+) particles with alumina. The particles were studied with an X-ray photoelectron spectrometer (XPS), a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS). XPS results show that the yttrium and europium contents are decreased and that the aluminum content is the highest except for that of oxygen after coating. SEM and EDS results show that particles are coated with a thin shell of alumina.     

Stereochemistry of lactide polymerization with chiral catalysts: new opportunities for stereocontrol using polymer exchange mechanisms

The synthesis of chiral aluminum and yttrium alkoxides and their application for lactide polymerization are reported. The complexes (SalBinap)MOR [4, M = Al, R = (i)Pr; 5, M = Y, R = (CH(2))(2)NMe(2)] are synthesized by reacting the ligand (SalBinap)H(2) [2,2'-[(1,1'-binaphthalene)-2,2'-diylbis(nitrilomethylidyne)]bisphenol] with the appropriate metal trisalkoxide. While enantiomerically pure yttrium complex 5 did not effect stereocontrol in the polymerization of either meso- or rac-lactide, homochiral 4 was found to exhibit excellent stereocontrol in a range of lactide polymerizations. Enantiomerically pure 4 polymerizes meso-lactide to syndiotactic poly(lactic acid) (PLA), while rac-4 polymerizes meso- and rac-lactide to heterotactic and isotactic stereoblock PLA, respectively. On the basis of the absolute stereochemistry of ring-opening of meso-lactide using (R)-4, a polymer exchange mechanism is proposed to account for the PLA microstructures resulting from rac-4.     

ULTRAVIOLET RESONANCE RAMAN SPECTROSCOPY OF BACTERIORHODOPSIN

Ultraviolet resonance Raman spectra of bacteriorhodopsin have been obtained using 229 nm excitation from a hydrogen-shifted neodymium yttrium aluminum garnet (Nd: YAG) laser. High signal-to-noise spectra are observed exhibiting vibrational bands at 762, 877, 1011, 1175, 1356, 1552 and 1617 cm-1 which are assigned to scattering from tryptophan and tyrosine side chains. This demonstrates the feasibility of using UV resonance Raman spectroscopy to monitor aromatic amino acid structural changes during the bacteriorhodopsin photocycle.     

Electron-phonon interactions in ce3+-doped yttrium aluminum garnet nanophosphors

Ce 3+-doped yttrium aluminum garnet nanophosphors with sizes near 30 and 250 nm have been synthesized by using chemical gelation and solvothermal methods, respectively. The size-dependent electron-longitudinal-optical-phonon coupling is investigated by fitting measured photoluminescence spectra within the framework of the Brownian oscillator model. Results show that the coupling strength is in a decreasing order from the bulk material to the nanophosphors of much smaller sizes.     

Reversible chain transfer between organoyttrium cations and aluminum: synthesis of aluminum-terminated polyethylene with extremely narrow molecular-weight distribution

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).     

Characterization of yttrium aluminum garnet /YAG/ using 14 MeV neutron activation

A non-destructive method for the analysis of yttrium, aluminum and oxygen in Yttrium Aluminum Garnet /YAG/ by 14 MeV neutron activation analysis has been developed and evaluated. The fast neutron induces primarily /n, 2n/, /n, p/ or /n, / reactions with yttrium, aluminum, and oxygen to produce isotopes with measurable characteristic gamma-ray spectra. Concentrations of Y, Al and O were determined on the basis of calibrated nuclear decay emission spectra recorded on selected standards. After each analysis the crystal was returned to the furnace for further adjustments of the growth parameters, and any resultant elemental variations were observed in the next analysis. The accuracy of this method was determined by repeated analyses with various YAG crystals from a series of separate furnace runs.     

Properties of epoxy polymers filled with nanopowders

The complex character of the effect of aluminum oxide and zirconium dioxide nanopowders that differ in their thermal prehistory, the specific surface value of particle sizes, phase composition, and the content of alloying additive of yttrium oxide on the stress-strain, thermophysical, tribotechnical, and adhesion properties of epoxy polymers is revealed. The effect depends on the chemical nature of the fillers, the sizes and specific surfaces of their particles, and the presence of alloying additive and other factors.