SNMS and XRD investigations of laser deposited YSZ buffer layers

Summary Secondary Neutral Mass Spectrometry (SNMS) and X-Ray Diffraction (XRD) were used to find optimum parameters for the in-situ pulsed laser deposition of ZrO₂/Y₂O₃ (YSZ) buffer layers on silicon (100) substrates. Homogeneous and nearly stoichiometric concentration depth profiles were found by SNMS for the laser deposited YSZ films. A peak of the SiO intensity during profiling of the YSZ/Si interface points to a SiO₂ intermediate layer. An increasing Y-deficit of the YSZ films was found by decreasing the laser energy density at the target. Epitaxial growth of the YSZ thin films was observed at an oxygen partial pressure lower than 10^–3 mbar, a substrate temperature of 600–800°C and a laser energy density at the target of about 8 J/cm².     

Thiophene and Cyclohexane Conversion on Alumina Supported Ni and NiMo Catalysts

A two-stage packing of a 30 wt.% Ga₂O₃/Al₂O₃ catalyst and a mixture catalyst of 30 wt.% Ga₂O₃/Al₂O₃ with 10 wt.% of Mn₂O₃ is shown to be quite efficient to NO selective reduction by a lower hydrocarbon under lean conditions. A high NO reduction conversion was observed in the temperature range of 200-600°C.     

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS

A strong Al⁺ and a minor Ti⁺ peak without a proportional increase of the O⁺ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating μm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI⁺). SI⁺ and SI^– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al⁺, O^–, AlO^–, and AlO₂ ^– ions sputtered from massive Al₂O₃. Similarly, and depending on stoichiometry, also Ti⁺ from mixed sintered, microscopically inhomogeneous Al₂O₃-TiO₂-SiO₂ pellets has been identified to be partly SI⁺. The subtraction of an assumed contribution of ionized secondary neutrals (SN⁺) suggests that SI⁺ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI⁺ contributions does not build up on μm-thin insulating layers. Therefore, we have to conclude that the Al⁺ and Ti⁺ peaks in the sputter time profiles of the μm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O⁺ deficiency cannot have been caused by SI⁺. Instead, their more probable origin is the inhomogeneous Al₂O₃ interlayer itself. Together with the residues of a topmost TiO₂ layer which has strongly been depleted in O by preferential sputtering, the relative O⁺ deficiency may be explained without assuming SI⁺ contributions. Received: 22 February 1999 / Revised: 1 July 1999 / Accepted: 6 July 1999     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS

A strong Al⁺ and a minor Ti⁺ peak without a proportional increase of the O⁺ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating μm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI⁺). SI⁺ and SI^– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al⁺, O^–, AlO^–, and AlO₂ ^– ions sputtered from massive Al₂O₃. Similarly, and depending on stoichiometry, also Ti⁺ from mixed sintered, microscopically inhomogeneous Al₂O₃-TiO₂-SiO₂ pellets has been identified to be partly SI⁺. The subtraction of an assumed contribution of ionized secondary neutrals (SN⁺) suggests that SI⁺ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI⁺ contributions does not build up on μm-thin insulating layers. Therefore, we have to conclude that the Al⁺ and Ti⁺ peaks in the sputter time profiles of the μm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O⁺ deficiency cannot have been caused by SI⁺. Instead, their more probable origin is the inhomogeneous Al₂O₃ interlayer itself. Together with the residues of a topmost TiO₂ layer which has strongly been depleted in O by preferential sputtering, the relative O⁺ deficiency may be explained without assuming SI⁺ contributions. Received: 22 February 1999 / Revised: 1 July 1999 / Accepted: 6 July 1999     

Analysis of thermally induced solid-solid interactions in vanadia-alumina system

V₂O₅/Al₂O₃ solids of varying compositions were prepared, dried at 100°C and calcined in air at 400–1000°C. The solid-solid interactions between the mixed oxides were investigated by means of DTA, TG and XRD techniques.The results revealed that ammonium metavanadate and aluminium hydroxide decomposed at 260 and 290°C, respectively, to yield an ammonium vanadium intermediate compound and Al₂O₃ as solids. The intermediate compound readily decomposed at 360°C to give V₂O₅.Solid V₂O₅ generally catalyses the crystallization of Al₂O₃ to an extent proportional to its amount present. The solid-solid interactions between Al₂O₃ and V₂O₃ to produce AlV₂O₄ and AlVO₄ took place at 750 and 900°C. These solids decomposed entirely at 1000°C, producing V₂O₅ and alpha-corundum. The pure Al₂O₃ samples employed existed as amorphous solids even when heated in air at 750°C, but in the presence of V₂O₅ (7–18 wt.%) they crystallized to thetaalumina at 600°C. The pure solid alumina crystallized at 1000°C to a mixture of theta and kappa-alumina. In the presence of V₂O₅, alpha-corundum together with kappa and theta phases was obtained on heating at 900°C.     

Improved adhesion of copper on Al2O3

Summary Improved methods for Al₂O₃ metallization by Cu are described. Good adhesion between Cu and Al₂O₃ substrate depends on the formation of chemical bonds between the substrate and the metallic layer. The temperature needed for the formation of a CuAl₂O₄ spinel interface is reduced from 1050°C to 900°C by the addition of various oxides. The adhesion between the CuAl₂O₄ interface and deposited Cu is stronger then the tensile strength of pure Cu. Plasma techniques for the formation of a Cu containing interface are also described. Bombardment of a Cu film with Xe⁺ ions in a rf-glow discharge implants Cu atoms into the substrate to a depth of 5 nm, as determined by SIMS depth profiling. Methods for reduction of the CuAl₂O₄ surface for subsequent metallization are also presented.     

Series of compositions Bi2(M′xM1−x)4O9 (M′, M=Al, Ga, Fe; 0≤x≤1) with mullite-type crystal structure: Synthesis, characterization and O/O exchange experiment

Series of compositions Bi₂(M′_xM_1−x)₄O₉ with x=0.0, 0.1,…, 1.0 and M′/M=Ga/Al, Fe/Al and Fe/Ga were synthesized by dissolving appropriate amounts of corresponding metal nitrate hydrates in glycerine, followed by gelation, calcination and final heating at 800 °C for 24 h. The new compositions with M′/M=Ga/Al form solid-solution series, which are isotypes to the two other series M′/M=Fe/Al and Fe/Ga. The XRD data analysis yielded in all cases a linear dependence of the lattice parameters related on x. Rietveld structure refinements of the XRD patterns of the new compounds, Bi₂(Ga_xAl_1−x)₄O₉ reveal a preferential occupation of Ga in tetrahedral site (4 h). The IR absorption spectra measured between 50 and 4000 cm⁻¹ of all systems show systematic shifts in peak positions related to the degree of substitution. Samples treated in ¹⁸O₂ atmosphere (16 h at 800 °C, 200 mbar, 95% ¹⁸O₂) for ¹⁸O/¹⁶O isotope exchange experiments show a well-separated IR absorption peak related to the M-¹⁸O_c-M vibration, where O_c denotes the common oxygen of two tetrahedral type MO₄ units. The intensity ratio of M-¹⁸O_c/M-¹⁶O_c IR absorption peaks and the average crystal sizes were used to estimate the tracer diffusion coefficients of polycrystalline Bi₂Al₄O₉ (D=2×10⁻²² m²s⁻¹), Bi₂Fe₄O₉ (D=5×10⁻²¹ m²s⁻¹), Bi₂(Ga/Al)₄O₉ (D=2×10⁻²¹ m²s⁻¹) and Bi₂Ga₄O₉ (D=2×10⁻²⁰ m²s⁻¹).     

Über den Mechanismus der Polymerisationsreaktionen

Zusammenfassung Beim Erhitzen gefällter Kieselsäure zeigen sprunghafte Änderungen in der Emanationsabgabe Umwandlungen bei etwa 570⁰ bzw. 870⁰ C an.Calciumoxyd reagiert mit SiO₂ erst nach 900⁰ C.Die Umwandlung eines -Al₂O₃ in Korund erfolgt zwischen 840⁰ und 950⁰ C. Diese Umwandlang schreitet von außen nach dem Inneren des Al₂O₃-Partikels vor; daraus wird auf einen größeren Energieinhalt der Atome an der Oberfläche der Partikeln gegenüber jenen in deren Innerem geschlossen.Kobaltcarbonat zeigt auf Aluminiumhydroxyd bis etwa 400⁰ C keinen Einfluß; zwischen 400⁰ und 800⁰ C tritt eine den Austritt der Emanationsatome stark blockierende Wirkung ein. Die Oberfläche des entstehenden -Al₂O₃ wird stark verdeckt bis nach 800⁰ C, also beim Beginn der —-Umwandlung, ein E.V.-Anstieg einsetzt: Das Kobaltoxyd reagiert mit dem Al₂O₃ unter Bildung von Thenardsblau und der Beginn der Reaktion ist mit einer starken Auflockerung verbunden.CaCO₃ wirkt auf die Oberfläche von Al₂O₃ nach 600⁰ C stark ein. Zu Beginn der Reaktion von CaO mit Al₂O₃ tritt eine starke Auflockerung der Al₂O₃-Oberfläche ein.Die Bildung von Calciumferrit erfolgt zwischen 550⁰ und 600⁰ C unter erheblicher Erhöhung der Dispersität beim Beginn der Reaktion.Für Unterstützungen zu großem Dank verpflichtet bin ich den Herren Professoren H.Mark und St.Meyer.     

Pd/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the selective liquid-phase hydrogenation of acetylene to ethylene

The structure of Ga₂O₃–Al₂O₃ supports and Pd/Ga₂O₃–Al₂O₃ catalysts and the performance of these catalysts in liquid-phase acetylene hydrogenation have been investigated. The deposition of Ga(NO₃)₃ onto Al₂O₃ by impregnation followed by calcination of the impregnated support at 600°C yields γ-Ga₂O₃–Al₂O₃ solid solutions containing up to 50 wt % Ga₂O₃. X-ray diffraction characterization of model palladium catalysts and their temperature-programmed reduction with hydrogen have demonstrated that, while palladium in Pd/Ga₂O₃ is in the form of a Pd₂Ga alloy, in the Pd/γ-Ga₂O₃–Al₂O₃ catalyst there is no direct interaction between PdО and Ga₂O₃ particles and palladium is in the monometallic state. The introduction of 10–20 wt % gallium oxide into Al₂O₃ lowers the activity of the supported palladium catalyst relative to that of the initial Pd/Al₂O₃ but increases the ethylene yield by enhancing the ethylene formation selectivity.     

A Ga2O·11Al2O3 nanonet prepared by interfacial reaction growth approach and its application in fabricating GaN nanowires

A Ga₂O·11Al₂O₃ nanonet was synthesized by using Ga₂O₃ powder as the precursor to generate Ga₂O vapor in H₂ atmosphere which further reacted with Al₂O₃ at 730 °C to form Ga₂O·11Al₂O₃ at the interfaces of a porous anodic aluminum oxide (AAO) template. The prepared Ga₂O·11Al₂O₃ nanonet then served as a Ga₂O-stablizing reservoir to fabricate single crystal GaN nanowires. The residual Ga₂O₃ powder at the surface of the produced Ga₂O·11Al₂O₃ nanonet and the metallic Ga or Ga₂O from the Ga₂O·11Al₂O₃ decomposition reacted with ammonia to yield GaN nanowires at 780 °C. The reaction mechanisms were investigated.     

High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5

Phase transitions in MgAl₂O₄ were examined at 21-27 GPa and 1400-2500 °C using a multianvil apparatus. A mixture of MgO and Al₂O₃ corundum that are high-pressure dissociation products of MgAl₂O₄ spinel combines into calcium-ferrite type MgAl₂O₄ at 26-27 GPa and 1400-2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al₂O₃ corundum and a new phase with Mg₂Al₂O₅ composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg₂Al₂O₅ phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å³, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O₆ octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O₆ octahedra. The structure is related with that of ludwigite (Mg, Fe²⁺)₂(Fe³⁺, Al)(BO₃)O₂. The molar volume of the Mg₂Al₂O₅ phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al₂O₃ corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl₂O₄ among various A²⁺B³⁺₂O₄ compounds.     

A simple and easy one-step fabrication of thin BaZr0.1Ce0.7Y0.2O3−δ electrolyte membrane for solid oxide fuel cells

A green BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) electrolyte layer was deposited on porous anode substrate (BZCY:NiO = 35:65, in weight ratio) by a suspension spray. In this process, the suspension was prepared by directly ball-milling the mixed BaCO₃, CeO₂, ZrO₂ and Y₂O₃ powders in ethanol for 24 h. Then the bi-layers were co-sintered at 1400 °C for 5 h in air to obtain dense and uniform electrolyte membrane in the thickness of 10 μm. With Nd_0.7Sr_0.3MnO_3−δ cathode, a fuel cell was assembled. It was tested from 600 °C to 700 °C using humid hydrogen as fuel and air as oxidant. The cell at 700 °C exhibited 1.02 V for open circuit voltage (OCV), 450 mW/cm² for peak output and 0.18 Ω cm² for electrode polarizations under open circuit conditions, respectively. The results indicate that it is feasible to fabricate thin electrolyte membrane for solid oxide fuel cells (SOFCs) by this simple, cost-effective and efficient technique.     

Non-random cation distribution in hexagonal Al0.5Ga0.5PO4

Based on powder X-ray diffraction and ³¹P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) investigations of mixed phosphate Al_0.5Ga_0.5PO₄, prepared by co-precipitation method followed by annealing at 900 °C for 24 h, it is shown that Al_0.5Ga_0.5PO₄ phase crystallizes in hexagonal form with lattice parameter a=0.491(2) and c=1.106(4) nm. This hexagonal phase of Al_0.5Ga_0.5PO₄ is similar to that of pure GaPO₄. The ³¹P MAS NMR spectrum of the mixed phosphate sample consists of five peaks with systematic variation of their chemical shift values and is arising due to existence of P structural units having varying number of the Al³⁺/Ga³⁺ cations as the next nearest neighbors in the solid solution. Based on the intensity analysis of the component NMR spectra of Al_0.5Ga_0.5PO₄, it is inferred that the distribution of Al³⁺ and Ga³⁺ cations is non-random for the hexagonal Al_0.5Ga_0.5PO₄ sample although XRD patterns showed a well-defined solid solution formation.     

New compounds A 3+ Te6+M 33+ X 25+ O14 (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca3Ga2Ge4O14 structure

Compounds A₃⁺Te⁶⁺M₃³⁺X₂⁵⁺O₁₄ (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca₃Ga₂Ge₄O₁₄ structure (sp. gr. P321) were prepared by solid-phase synthesis at 600–850°C in air. The compounds melt incongruently or decompose in the solid state.     

Synthesis of Ag-Colloids in Sol-Gel Derived SiO2-Coatings on Glass

Ag colloid-containing coatings on soda lime glass and fused silica are prepared via the sol-gel process. To incorporate Ag⁺-ions in the coatings homogeneously, they are stabilized by a functionalised silane (aminosilane) and then mixed with the basic sol prepared from 3-glycidoxypropyl trimethoxysilane (GPTS) and tetraethoxysilane (TEOS). Crack-free and transparent coatings with a thickness of 0.5 to 1.2 m, are obtained by heat treatment between 120°C and 600°C. The Ag-colloid formation was monitored by UV-VIS spectroscopy as a function of temperature. The investigations reveal that the substrate has a deciding influence on the Ag-colloid formation caused by alkali diffusion from the substrate into the coating. High resolution transmission electron microscopy (HRTEM) investigations prove that poly-crystalline Ag_xO_y-nanoparticles are formed during thermal densification in the coatings and that this change is accompanied by a vanishing of the yellow colour of the coatings. A post-heat treatment in a reducing atmosphere (90% N₂, 10% H₂) turns back the yellow colour and single-crystalline Ag-colloids can be detected by HRTEM. A suitable choice of the temperature and time conditions allows the control of the colloid size during heat treatment in a reducing atmosphere. For comparison, ion-exchange experiments have been carried out which showed that a spontaneous Ag-colloid formation was achieved in the soda lime substrate at 400°C. Since Ag containing SiO₂-coatings remained colourless after thermal treatment between 400°C and 600°C in air, on soda lime substrates, a remarkable diffusion of Ag⁺ into the substrate was excluded.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Mechanochemical-thermal preparation and structural studies of mullite-type Bi2(GaxAl1−x)4O9 solid solutions

A series of Bi₂(Ga_xAl_1−x)₄O₉ solid solutions (0≤x≤1), prepared by mechanochemical processing of Bi₂O₃/Ga₂O₃/Al₂O₃ mixtures and subsequent annealing, was investigated by XRD, EDX, and ²⁷Al MAS NMR. The structure of the Bi₂(Ga_xAl_1−x)₄O₉ solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi₂(Ga_xAl_1−x)₄O₉ series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the ²⁷Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi₂(Ga_xAl_1−x)₄O₉. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga₂O₃/Al₂O₃ oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X‐ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel‐type structure; also shown by γ‐Al₂O₃ and γ‐Ga₂O₃. The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m² g^?1 for the mixed oxide having Ga:Al = 9:1 up to 370 m² g^?1 for that having Ga:Al = 1:9. High resolution MAS NMR showed that Ga³⁺ and Al³⁺ ions occur at both tetrahedral and octahedral sites in the spinel‐type structure of the mixed metal oxides, although there is a preferential occupation of tetrahedral sites by Ga³⁺ ions. A proportion of penta‐coordinated Al³⁺ ions was also found. IR spectra of carbon monoxide adsorbed at 77 K showed that the mixed metal oxides have a considerable Lewis acidity, related mainly to tetrahedrally coordinated metal ions exposed at crystal surfaces. The characteristic infrared absorption band of coordinated (adsorbed) CO appears in the range 2205–2190 cm^?1, and its peak wavenumber is nearly independent of Ga:Al ratio in the mixed gallia‐alumina oxides.