Small angle X-ray scattering study of spinodal decomposition in B2O3---PbO---Al2O3 glass

SAXS measurement for 80B₂O₃·15PbO·5Al₂O₃ (wt%) glass can be performed with high accuracy. SAXS spectra were obtained for glasses which had been heat-treated for different lengths of time at 380°C and 400°C. A converging point k′_c and a common curve for k >k′_c were observed in the SAXS spectra of glasses subjected to appropriate aging. This suggests the validity of Cook's modification of Cahn's theory. At the very early stage of the decomposition a relaxation takes place of $\text{?″}\text{and}\text{D}\text{?}$ and the spectra of Cahn-Cook's amplification factor show a typical aspect of the early stage of decomposition after the relaxation. Plots of k³I(k) versus k³ suggest that the interface between the two phases is diffuse and the demixing process is in the early stage of the spinodal decomposition.     

Raman scattering study of crystalline and melting states of BaO·2B2O3

Melting and crystallization scenarios of barium tetraborate BaB₄O₇ (BaO·2B₂O₃) are studied in situ by Raman spectroscopy. It is shown that the scenario depends on the temperature–time history of melt. Crystallization conditions of the beta modification of barium tetraborate (β-BaB₄O₇) from a stoichiometric glass structure BaO·2B₂O₃ were investigated.     

Characterization of chemosynthetic Al2O3-2SiO2 geopolymers

Pure chemosynthetic Al₂O₃-2SiO₂ geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin.     

Synthesis and characterization of MxNb4P2O17

A new series of niobium phosphates with the composition of M_xNb₄P₂₁₇17 (M=Li and Na, X=4; M=Zn, Ca, Mg, Sr and Ba, X=2) have been successfully synthesized. The powder X-ray diffraction (XRD) data of these isostructural compounds, was studied The powder Second Harmonic Generation (SHG) effects of these compounds were about twice of that of KH₂PO₄ (KDP).     

Synthesis and X-ray structural investigation of K2(H5O2)[UO2(C2O4)2(HSeO3)]

The synthesis and X-ray diffraction analysis of K₂(H₅O₂)[UO₂(C₂O₄)₂(HSeO₃)] single crystals have been performed. This compound crystallizes in the triclinic system with the unit-cell parameters a = 6.7665(4) ?, b = 8.8850(4) ?, c = 12.3147(7) ?, α = 94.73°, β = 90.16°, γ = 92.11°, sp. gr. P[`1]P\bar 1, Z = 2, and R = 0.019. The basic structural units are island [UO₂(C₂O₄)₂(HSeO₃)]³⁻ groups, which belong to the AB ₂⁰¹ M ¹ crystallochemical group of uranyl complexes (A = UO₂²⁺, B ⁰¹ = C₂O₄²⁻, and M ₁ = HSeO₃⁻). Uraniumcontaining complexes are linked through K⁺ and H₅O₂⁺ ions and via a system of hydrogen bonds with the participation of oxonium hydrogen atoms in this structure.     

Solvothermal synthesis of K2V3O8 nanorods

A solvothermal route has been developed to synthesize K₂V₃O₈ nanorods via the reduction of V₂O₅ using ethanol as the reducing agent as well as the solvent at 200°C. X-ray diffraction and selected area electron diffraction analysis revealed that the as-synthesized products are of tetragonal structure K₂V₃O₈. Transmission electron spectroscopy image showed that the obtained K₂V₃O₈ comprises rod-like nanocrystallites. The formation mechanism of K₂V₃O₈ was studied.     

Anisotropic vapor phase growth of Ga2O3 crystalline nanobelts

Ga₂O₃ nanobelts were synthesized by gas reaction at high temperature in the presence of oxygen in ammonia. X-ray diffraction and chemical microanalysis revealed that the nanostructures were Ga₂O₃ with the monoclinic structure. Electron microscopy study indicated the nanobelts were single crystalline with broad (0 1 0) crystallographic planes. The nanostructures grew anisotropically with the growth direction of . Statistical analysis of the anisotropic morphology of the nanobelts and electron microscopy investigation of the nanobelt tips indicated that both vapor–solid and vapor–liquid–solid mechanisms controlled the growth process. The anisotropic nature of crystallographic morphology is explained in terms of surface energy.     

A structural study of Y2O3---Al2O3---SiO2 glass employing partial RDFs obtained by anomalous scattering

A structural study of Y₂O₃---Al₂O₃---SiO₂ glass has been performed using the partial radial distribution function (RDF) obtained by anomalous scattering at the Y absorption edge. The partial RDF consists of contributions from atom pairs, such as Y---O, Y---M(Si, Al) and Y---Y, related to the local arrangements around the Y atoms, while those of all of the constituent atom-pairs are convoluted into the ordinary RDF. The M(Si, Al)---O, Y---O, M---M, Y---M, and Y---Y interatomic distances and the coordination numbers around the Al and Y atoms are obtained from the two RDFs. The local structures around the Al and Y atoms in the glass are discussed.     

Study of the structural insertion of Al in the Al2O3-SiO2 and Nd2O3-Al2O3-SiO2 glass systems

Glasses in the Al₂O₃-SiO₂ and Nd₂O₃-Al₂O₃-SiO₂ systems were prepared by the sol-gel method. The gel-glass evolution was studied using near-infrared (NIR) and ultraviolet-visible (UV-VIS) spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The results obtained indicate a relationship between the sample compositions, the treatment temperature and the Al coordination. In the samples of the Nd₂O₃-Al₂O₃-SiO₂ system the densification of the structure, when the treatment temperature increases, leads to the segregation of neodymium oxide particles.     

Structural analysis and devitrification of glasses based on the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives

Glasses, whose basic composition was based on the CaO-MgO-SiO₂ system and doped with B₂O₃, P₂O₅, Na₂O, and CaF₂, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q¹ and Q² silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B₂O₃, Na₂O, and CaF₂ had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO₂ system.     

Catalytic growth of In2O3 nanobelts by vapor transport

Indium oxide (In₂O₃) nanobelts have been fabricated by thermal evaporation of metallic indium powders with the assistance of Au catalysts. The as-synthesized nanobelts are single-crystalline In₂O₃ with cubic structure, and usually tens of nanometers in thickness, tens to hundreds of nanometers in width, and several hundreds of micrometers in length. The room temperature photoluminescence spectrum of In₂O₃ nanobelts features a broad emission band at 620 nm, which could be attributed to oxygen deficiencies in the as-synthesized belts. The formation of In₂O₃ nanobelts follows a catalyst-assistant vapor—liquid–-solid growth mechanism, which enables the controlled growth of individual belts on predetermined sites.     

Observation of Raman scattering from N2 in a silica optical fiber

We have observed Raman scattering from N₂ in a silica optical fiber which had been pressurized in an N₂ atmosphere. The Raman shift is 2190 cm^?1 and the half-width of the line is 90 cm^?1 (fwhm).     

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al₂O₃ and ZrO₂ films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al₂O₃) or 0.6 nm (ZrO₂), the band gaps of the Al₂O₃ and ZrO₂ films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al₂O₃/Si and ZrO₂/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al₂O₃ and Zr 3p3 in ZrO₂ are 2.7 and 2.0 nm, respectively.     

Phase equilibria and growth of β-BaB2O4 crystals in the BaB2O4-Ba2Na3[B3O6]2F system

A complex investigation of the BaB₂O₄-Ba₂Na₃[B₃O₆]₂F cut, which belongs to the ternary mutual Ba, Na//BO₂, F (BaB₂O₄-(NaBO₂)₂-(NaF)₂-BaF2) system, has been performed. The cut is quasibinary, with the following eutectics coordinates: 810 ± 5°C, 85 mol % Ba₂Na₃[B₃O₆]₂F, 15 mol % BaB₂O₄. It is shown that this system can be used to grow bulk β-BaB₂O₄ crystals.     

Influence of CoO addition on phase separation and crystallization of glasses of the ZnO–Al2O3–SiO2–TiO2 system

The evolution of structure, phase composition and spectroscopic properties of CoO-doped (up to 5 mol%) titania-containing zinc aluminosilicate glasses with their heat-treatment has been studied using Raman scattering, small angle X-ray scattering, X-ray diffraction analysis and optical absorption spectra. Addition of cobalt oxide was observed to facilitate amorphous phase separation of the parent glass and gahnite, ZnAl₂O₄, crystallization. Cobalt oxide entered phases formed during low-temperature heat-treatments (720 °C), i.e., amorphous phase, enriched in ZnO, Al₂O₃ and TiO₂ and crystalline phase of gahnite. The absorption of these glass-ceramics was defined mainly by tetrahedral Co²⁺ ions located in gahnite nanocrystals. As the temperature was increased further, traces of anosovite solid solution appeared and then decomposed. Even after high-temperature heat-treatments, a certain portion of Co²⁺ ions remained in amorphous zinc aluminotitanate phase and in octahedral sites of inversed gahnite spinel. In glass-ceramics, the residual high silica amorphous phase contained a small quantity of [TiO₄] centers, which content was smaller in Co:ZAS samples as compared with non-doped glass-ceramics.     

Surface crystallization of β-BaB2O4 phase using a CO2 laser source

This letter describes decrystallization process of the β-BaB₂O₄ phase on the surface of 63BaO-26B₂O₃-11TiO₂ glassy sample when irradiated by a CO₂ laser beam for 30-40 s, using a laser power of ≈1.7 W. An analysis by optical microscopy of the irradiated region showed that the glass surface contained crystallites with the same morphology as those observed after traditional crystallization in an electric furnace. However, the crystal growth rate and the crystallite sizes appeared to be higher than those obtained by heating in an electric furnace. X-ray diffraction of the irradiated region showed a preferential orientation of the β-BaB₂O₄ crystallites on the glass surface.     

X-ray absorption and Raman characterizations of TeO2-Ga2O3 glasses

The thermodynamic properties of transparent glasses prepared in the TeO₂-Ga₂O₃ system were investigated by differential scanning calorimetry. The change of the thermal parameters as a function of the chemical composition is discussed. Raman and both Te L_III and Ga K edge X-ray absorption spectroscopies at room temperature were used to examine the short range order. Analyses of the spectra suggest that the addition of Ga₂O₃ content to the TeO₂ glass matrix induces the transformation of trigonal bipyramids (TeO₄E, E=lone electronic pair 5s² of Te) to trigonal pyramids (TeO₃E) with formation of Te-O-Ga bridging bonds. Furthermore, Ga K edge XANES and EXAFS studies show that Ga atoms exhibit both tetrahedral (GaO₄) and octahedral (GaO₆) environments.     

EPR study of RLi2O.V2O5, RNa2O.V2O5, RCaO.V2O5, and RBaO.V2O5 modified vanadate glass systems

Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa₂O.V₂O₅ system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these lines exhibit dramatic narrowing as R approaches 0.5. In the model proposed here, this narrowing is due to an increase in hopping time for small polarons associated with V⁴⁺ ions in these systems. Increases in polaron hopping times are accompanied by increases in electron spin-spin relaxation times T₂'s, and, an associated narrowing of EPR linewidths. Experiments confirm that spectral widths are limited by electron T₂'s due to the fact that EPR linewidths do not vary with temperature down to 4.2 K. Resolved spectra in RNa₂O.V₂O₅ at R = 0.5 reveal a hyperfine coupling parameter of 0.0177 ± 0.0008 T, corresponding to an upper-limit polaron hopping frequency of 487 ± 20 MHz. By similar analyses, the systems of RCaO.V₂O₅, RBaO.V₂O₅, and RLi₂O.V₂O₅ exhibit comparable polaron hopping frequencies limits of 480 ± 20 MHz, 469 ± 20 MHz, and 468 ± 20 MHz, respectively, when R is near 1.0. In addition to the relaxation effects discussed here, results of modeling of resolved spectra to obtain hyperfine coupling constants A_|| and A_┴, and g_┴ values g_|| and g_┴ are presented and discussed.     

A study of alkali resistance of CaO---Al2O3---SiO2 glasses

The alkali resistance and structure of CaO---Al₂O₃---SiO₂ glasses are studied in this paper. The change of coordination number of aluminum ions in the glasses, caused by corrosion from the cement extract aqueous solution, was determined by means of X-ray fluorescence spectra and infrared absorption spectra. The interrelationship between glass compositions, structure, and alkali resistance is discussed.     

Preparation and characterization of fiber-textured SrAl2O4:Eu films grown using a homo-buffer layer

This paper describes the preparation and characterization of fiber-textured SrAl₂O₄:Eu films on a quartz glass substrate using a homo-buffer layer. The effect of the buffer layer on the crystallinity and adhesion was investigated by cross-section transmission electron microscopy and X-ray diffraction (XRD). The results show that the prepared film was not only well crystallized but also highly textured. The preferred orientation of this textured film was confirmed to be (0 3 1) by pole figure measurement. In addition, this film exhibits excellent optical transparency, with an average transmittance of more than 80% in the visible range.