Reaction of CaAl<Subscript>4</Subscript>O<Subscript>7</Subscript> with (0001)-oriented α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Reactions between thin films of CA₂ and (0001)-oriented α-Al₂O₃ have been studied using a combination of microscopy techniques. Thin films of amorphous CA₂ were deposited on sapphire substrates by pulsed-laser deposition at 900 °C in an oxygen ambient atmosphere. After deposition, the reaction couples were heat treated in air for various times either at 1300 or 1400 °C. Atomic-force microscopy was used to monitor changes in the microstructure of the films. Interfaces between the different regions were examined by transmission electron microscopy (TEM) of cross-sectional samples prepared by focused ion-beam milling. The CA₂ films had dewetted the substrate surface as a result of the heat treatment. An interfacial reaction layer was observed between the dewetted CA₂ droplets and the substrate. The structure of this reaction layer was found to be consistent with γ-Al₂O₃ by computer analysis of high-resolution TEM images. There is a perfect epitaxy between the interfacial layer and the substrate. For the samples heat treated for longer times, hexagonal features were found on the substrate surface. The presence of these features on (0001)-oriented α-Al₂O₃ suggests that CA₆ platelets form by the transformation of the interfacial reaction layer. The results are discussed in relation to the crystallization behavior of the various calcium aluminate phases and the equilibrium-phase diagram of the CaO–Al₂O₃ system.     

Fe effect on the process of intrinsic point defects in α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Fe is a common existing impurity in α-Al₂O₃, and thus the effect of Fe on the process of intrinsic point defects in α-Al₂O₃ has been investigated based on first-principles calculations. It is found that the formation, charge state, relative stability and equilibrium configuration of isolated intrinsic point defects in α-Al₂O₃ will be remarkably influenced by Fe, resulting in the variation of defect process, i.e., the formation of defect complex such as Schottky defect, Frenkel defect and antisite pair in α-Al₂O₃. Generally speaking, depending on the O-condition, the most stable configurations, types and relative proportions of defect complexes will be varied by Fe doping in α-Al₂O₃. From the viewpoint of defect formation energy, Fe is favorable for Frenkel defects and antisite pairs in α-Al₂O₃ under both O-rich and O-deficient conditions; while for Schottky defects, Fe is favorable for the defect formation under the O-rich condition, yet unfavorable under the O-deficient condition.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Catalytic activity of CuO-loaded TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for NO Reduction by CO

The activities in NO + CO reaction of CuO-loaded TiO₂/γ-Al₂O₃ catalysts prepared by precipitation (P), co-precipitation (C-P), or sol-gel (S-G) were examined using a micro-reactor-gas chromatography (GC) system. The study showed higher catalytic activity of 12%CuO/15%TiO₂/γ-Al₂O₃ (P) than that of 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G) or 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) in air condition, compared with higher activity of 12%CuO/15%TiO₂/γ-Al₂O₃ (P) or 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G) than that of 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) in H₂ condition. The specific surface area and crystallite formation had little effect on catalytic activities. H₂-temperature programmed reduction (TPR) revealed four reduction peaks of 12%CuO/15%TiO₂/γ-Al₂O₃ (P), three reduction peaks of 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G), but only one reduction peak of 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P). CuO diffraction peaks were detected only in 12%CuO/15%TiO₂/γ-Al₂O₃ (P), indicating that CuO was highly dispersed on the other two TiO₂/γ-Al₂O₃ catalysts. As a result, 12%CuO/15%TiO₂/γ-Al₂O₃ (P) had the highest activity of reducing NO. During NO + CO reaction, the absorption peaks of intermediate product N₂O were shown at 150 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (P), at 200 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (S-G), and at 100 °C by 12%CuO/15%TiO₂/γ-Al₂O₃ (C-P) after H₂ pretreatment at 400 °C for 1 h.     

Preparation and bactericidal property of MgO nanoparticles on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

After being impregnated in the solution containing Mg(NO₃)₂·6H₂O, -Al₂O₃ was dried and calcined at 500°C which results in the production of a bactericide, highly dispersed MgO loaded on the surface of -Al₂O₃. The threshold value of the monolayer dispersion of MgO on -Al₂O₃ is 14.97%, and MgO crystal formed when the load amount beyond this value. The samples with different load amount were characterized by X-ray Diffraction (XRD), Low-temperature N₂ adsorption-desorption, Inductively Coupled Plasma (ICP) and High Resolution Scan Electronic Microscope (SEM). The results showed that these MgO microcrystals are highly dispersed and have regular size in the range of 4 to 10.8 nm. The specific surface, pore volume and pore size of the sample decreases with the increase of load amount. It is demonstrated that -Al₂O₃ with highly dispersed MgO on the surface is efficient bactericide, and the one with 20% load amount of MgO can kill more than 99% bacteria and spore cells.     

Growth of bulk β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals of high optical quality in the BaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaBaBO<Subscript>3</Subscript> system

Phase equilibria along the BaB₂O₄-NaBaBO₃ join of the BaO-B 2 O 3 -Na 2 O system are studied by differential thermal analysis and modified visual thermal analysis. The join is shown to be suitable for growing - BaB₂O₄ crystal of high optical quality.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 64–69. Original Russian Text Copyright © 2005 by Kokh, Kononova, Fedorov, Bekker, Kuznetsov.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

System ZnO ⋅ B<Subscript>2</Subscript>O<Subscript>3</Subscript>-CuO ⋅ B<Subscript>2</Subscript>O<Subscript>3</Subscript>

Differential thermal analysis and x-ray diffraction data indicate that the ZnO B₂O₃-CuO B₂O₃ join of the ternary system CuO-B₂O₃-ZnO is pseudobinary, with eutectic phase relations and a liquid-liquid miscibility gap in the composition range 25–35 mol % CuO.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 339–340.Original Russian Text Copyright © 2005 by Kasumova, Bananyarly.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Spectroscopic characterisation of local structure in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses doped with gadolinium

Gadolinium doped bismuth borate glasses containing up to 30 mol% Y₂O₃ were prepared by fast melt quenching method. The effect of yttrium on the local order in 3B₂O₃ · Bi₂O₃ and B₂O₃ · Bi₂O₃ glass matrices, particularly on the bismuth sites, was investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) of Gd³⁺ ions. The IR results show that the local structure is more ordered in the glass system with higher bismuth content and the progressive addition of yttrium increases the local disorder in both bismuth–borate glass matrices. The EPR results indicate that Gd³⁺ ions occupy both bismuth and yttrium sites and reflect the same structural disorder like that suggested by IR results.     

Variable—Range hopping in Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

The dc conductivity of the glasses in the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system was studied at temperatures between 223 and 393 K. At temperatures from 300 to 223 K, T^–1/4 (T is temperature) dependence of the conductivity was found, however, both Mott variable-range hopping and Greaves intermediate range hopping models are found to be applicable. Mott and Greaves parameters analysis gave the density of states at Fermi level N (E_F) = 3.13 × 10²⁰–21.01 × 10²⁰ and 1.93 × 10²¹–16.39 × 10²¹ cm^–3eV^–1 at 240 K, respectively. The variable-range hopping conduction occurred in the temperature range T = 300–223 K, since W_D was found to be large (W_D = 0.08–0.14 eV for these glasses) and dominated the conduction at T < 300 K.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.     

Thermal conductivity and heat capacity of α- and β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> single crystals

The thermal conductivity of β- and α-BaB₂O₄ single crystals has been measured at temperatures from 50 to 300 K by a steady-state axial flow technique. The 300-K thermal conductivity of the β-polymorph along and across its c axis is 1.64 ± 0.08 and 1.24 ± 0.06 W/(m K), respectively, and that of the α-polymorph along its c axis is 1.65 ± 0.08 W/(m K). Swirls and twin boundaries have an insignificant effect on the thermal conductivity of α-BaB₂O₄ crystals. The heat capacity of α-BaB₂O₄ measured in the range 56–300 K using adiabatic calorimetry differs little from that of the β-polymorph.     

Formation and Acid–Base Surface Properties of Highly Dispersed η-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanopowders

Highly dispersed η-Al₂O₃-based nanopowders have been prepared via glycine–nitrate combustion followed by heat treatment in air. The resultant materials have been characterized by X-ray diffraction, Fourier transform IR spectroscopy, scanning electron microscopy, simultaneous thermal analysis, and other techniques. We have optimized the glycine-to-nitrate ratio (G/N = 0.2) and found heat treatment conditions for combustion products (isothermal holding at a temperature of 700°C for 6 h) that allow one to obtain single- phase nanocrystalline η-Al₂O₃ powders with an average particle size of 5 ± 1 nm and specific surface area of 54 ± 5 m²/g. The acid–base surface properties of the η-Al₂O₃ nanopowder have been analyzed using pyridine sorption–desorption processes as an example. The specific concentrations of weak, intermediate, and strong Lewis acid centers on the surface of the η-Al₂O₃ nanocrystals have been shown to markedly exceed those on the surface of commercially available γ-Al₂O₃ (A-64). The synthesized nanopowders can thus be used as effective supports of acid catalysts.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.     

Mechanical and acid-etching properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-containing ceramic fillers

The properties of the composite, having a complicated microstructure, are decided by many factors such as those of glass matrix, crystal phases, fillers, and holes. We investigated how the addition of ceramic fillers to the glass matrix affects the mechanical and etching properties of the glass composite by forming new crystal phases. Different amounts of two fillers, ZnO and Al₂O₃, were added to a glass frit consisting of Bi₂O₃–ZnO–B₂O₃. It was sintered at 550 °C for 30 min. Based on the results of this study, the porosity and degree of crystallization of the composites could be controlled by adjusting the content of the ZnO and Al₂O₃ fillers. Therefore, porosity and degree of crystallization formed by the reaction between a glass matrix and fillers influence the mechanical and etching properties of the composite.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Microstructure,interfaces and creep behaviour of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) eutectic ceramic composites

New compositions in the melt-grown eutectic ceramics field are investigated for thermomechanical applications. This paper is focused on the Al₂O₃–Sm₂O₃–(ZrO₂) system. The studied compositions give rise to interconnected microstructures without anisotropy along the growth direction. At variance with the binary eutectic Al₂O₃–SmAlO₃, the homogeneity of the microstructure of the Al₂O₃–SmAlO₃–ZrO₂ ternary eutectic is less sensitive to the growth rate. Interfaces between the alumina and perovskite phases are investigated by high-resolution transmission electron microscopy (TEM). They are semi-coherent. In stepped interfaces, the facets are parallel to dense planes of each phase. The steps have a dislocation character and may accommodate both misfits. The ternary eutectic displays a very good creep behaviour with strain rates very close to those obtained on other previously studied eutectics in the Al₂O₃–RE₂O₃(RE = Y, Gd, Er)–ZrO₂ systems. The deformation micromechanisms are analysed by TEM in the three eutectic phases. After creep, dislocations are present in every phase. The activation of unusual slip systems (pyramidal slip in the alumina phase) shows that high local stresses can be reached. The presence of dislocation networks with low energy configurations is consistent with predominance of dislocation climb processes controlled by bulk diffusion.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.