Amorphous Oxide Phase Research Articles

이온선 스퍼터 증착법에 의하여 제조된 CrOx의 전기적 특성

The influences of ion beam energy and reactive oxygen partial pressure on the physical and crystallographic characteristics of transition metal oxide compound(CrOx) film were studied in this paper. Chromium oxide films were deposited onto a cover-glass using ion Beam Sputter Deposition(IBSD) technique according to the various processing parameters. Crystallinity and grain size of as-deposited films were analyzed using XRD analysis. Thickness and Resistivity of the films were measured by <TEX>$\alpha$</TEX>-step and 4-point probe measurement. According to the XRD, XPS and resistivity results, the deposited films were the cermet type films which had crystal structure including amorphous oxide(a-oxide) phase and metal Cr phase simultaneously. The increment of the ion beam energy during the deposition process led to decreasing of metal Cr grain size and the rapid change of resistivity above the critical <TEX>$O_2$</TEX> partial pressure.

The novel low temperature synthesis of nanocrystalline MgAl 2O 4 spinel using “gel” precursors

Nanocrystalline MgA1 2O 4 was synthesized by pyrolysis of the homogeneous spinel precursor, Mg(C 4H 5O 2) 2·(H 2O):Al 2(OH) 3(C 3H 3O 2) 3·(H 2O) 2:NH 4(C 3H 3O 2)·(H 2O). The spinel precursor gel is composed of a mixture of magnesium and aluminum acrylate salts dissolved in an ammonium acrylate gel. The reaction of acrylic acid with magnesium hydroxide in water produced magnesium methacrylate, and a similar reaction of basic aluminum acetate produced the aluminum salt of acrylic acid. The reaction of acrylic acid with ammonium hydroxide produced the ammonium acrylate gel. Ammonium acrylate gel was found to absorb many times its own weight of water. Although similar properties have been identified in PMMA and in the polymer of sodium acrylate, only the ammonium acrylate gel exists as an unpolymerized monomer. The spinel precursor gel is a pre-ceramic material that yields an amorphous oxide phase at 425°C that begins to crystallize to the MgAl 2O 4 spinel at 600°C and is fully crysta1line at 1030°C with a uniform particle size of 7–100 nm. The spinel precursor gel and the nanocrystalline MgA1 2O 4 spinel were characterized by XRD and TEM.

Platinum and molybdenum oxide deposited carbon electrocatalyst for oxidation of hydrogen containing carbon monoxide

Carbon-supported Pt/MoO x catalysts for use in PEFC anodes were prepared and their catalytic activity for the oxidation of CO-contaminated H 2 was examined based on the fuel cell performance in PEFC single cell arrangements. Based on the XRD pattern and XPS measurements of the prepared Pt/MoO x /C catalysts, it was found that the deposited MoO x exists as an amorphous oxide phase. The MoO x phase shows a redox peak at around 0.45 V, which was revealed by the cyclic voltammogram of the Pt/MoO x /C in sulfuric acid solution. The PEFC performance of the cell with Pt/MoO x /C was improved under 100 ppm CO-contaminated H 2 conditions compared to the Pt/C catalyst, and was almost comparable to the PtRu(1:1)/C catalyst.

Distribution of uranium- and thorium series radionuclides in mineral phases of a weathered lateritic transect of a uranium ore body

A surficial, weathered 400 m long profile of the Ranger One ore body #3 (Northern Territory, Australia) has been characterised to a depth of 10 m in terms of the total uranium, 238 U , 234 U , 232 Th , 230 Th and 228 Th distributions, and measurements of other geochemically important elements. The characterisation was limited to the <106 μm material, where effects of different mineralogical composition were found to be small. The distribution was classified in terms of successive extractions for amorphous oxide phases (e.g., ferrihydrites), crystalline oxides (e.g., goethite, hematite), and resistate material. It was concluded that the observed uranium concentration and isotopic ratio structures are an image of the outline of the ore body at the surface. These structures are the result of several physical and chemical processes which dominate at the Foot wall and at the ore body surface. The processes involve the formation of amorphous iron oxides, α-recoil enhanced mobilisation and transport of 234 U , 230 Th and 228 Th , precipitation due to evaporation of ground- and interstitial water, and the adsorption of uranium and thorium within a time frame less than that required for 234 U/ 238 U and 230 Th/ 234 U to achieve secular radioactive equilibrium. The mineralogical composition of the soil is to some extent responsible for local variations in the measured properties. The differences in chemical speciation and behaviour of uranium and thorium enhance the variability in the 230 Th/ 234 U activity ratios. The monsoonal climatic and hydrological variations intensify some of the observed effect.

Preparation and optical transmittance of titanium hydride (deutende) films by rf reactive sputtering

Microstructure of the titanium hydride (deutende) films prepared by rf reactive sputtering with Ar and H 2 (or D 2) gases were examined by X-ray diffraction measurements, scanning electron microscopy, Rutherford backscattering spectrometry and elastic recoil detection analysis. In addition, their optical measurements were also carried out in visible and infra-red regions. It was found that the hep Ti structure (α-TiH x ) was mainly formed at high rf power. With decreasing rf power, however, the fcc CaF 2 structure (δ-TiH x ) was obtained. The films have a smooth surface at a short time of deposition for 1–10 min, and these films are used for optical measurements. The films show wide absorption over visible and infra-red regions, although the films include a large amount of O atoms, which may suggest the presence of the amorphous titanium oxide phase.

XPS and transmission electron microscopy of themulticomponent hydride-forming alloys

The photoelectron spectrograms of the Ni2p, Ni3p, Co3p, Mn2p, Al2p,Ols and Cls in LaNi 4.6Mn 0.4, LaNi 4.5Al 0.5, MmNi 3.5Co 0.7Al 0.8, and Zr3d, Ti2p, V2p, Ni2p, Co2p, Ols, and Cls inZr 0.9VCo 0.55Ni 0.55 and Zr 0.59Ti 0.41V 0.53Cr 0.22 Fe 0.20Co 0.27Ni 0.78 have been obtained.In a surface layer about 2–2.5 nm of both alloys, the main part of nickel atoms are in metallic state(Ni 0) and only a third of them in oxidized state (Ni +2, Ni +3). At the same time the concentration of nickel in surface layer of Zr-containing alloy is muchlower as compared with Mm-containing alloy. The chemical state of Co and V atoms is similar toNi atoms state, but their concentrations, especially of V, in surface layer is lower than that ofnickel. The results of XPS have been compared with those of transmission electron microscopy ofthe thin foils of La- and Zr- based alloys. Dark field microphotographs of the oxidized alloysindicate presence of two different phases, which, according to electron microdiffraction, arenickel-based alloy and oxide. On the first stage of oxidation on the surface of foil the fine nickelparticles (about 10 nm) and amorphous oxide phase appear. Complete oxidation of the foil leadsto formation of eutectic-like structure of mixture of metallic and oxide phase. Some difference ofthe oxidized layer structure of investigated alloys have been observed.

Initial growth of Al 2 O 3 on NiAl(001)

O3 films were prepared by oxygen exposure at room temperature and subsequent annealing. The initial stages of oxidation such as the reconstruction of the clean NiAl(001) surface, oxygen adsorption on the bare surface, and finally the growth of the ordered Al2O3 films on a NiAl(001) have been explained on the basis of scanning tunnelling microscopy (STM) measurements. The main result is the identification of the oxide growth of ordered Al2O3 as a thermally activated, fast, local ordering process of a precovered amorphous oxide phase arising from oxygen stimulated Al segregation after exposure at room temperature. The surface morphology is determined by the density of the disordered Al2O3 nuclei in the amorphous oxide phase which can be controlled by oxygen exposure.

A comparison of cesium-containing heteropolyacid and sulfated zirconia catalysts for isomerization of light alkanes

The heteropolyacid H3PW12O40 and its cesium salts CsxH3-xPW12O40 (x = 1, 2, 2.5, 3) were synthesized, characterized and tested as catalysts for hydrocarbon reactions. All samples were characterized by a variety of techniques including elemental analysis, X-ray diffraction, dinitrogen adsorption, thermal gravimetric analysis and ammonia sorption. Results from these methods confirmed that pure cesium salts were prepared without significant contamination by amorphous oxide phases. Incorporation of cesium into the heteropolyacid decreased the acidic protons available for catalysis, increased the specific surface area, and increased the thermal stability. The heteropolyacids were tested as catalysts for butane skeletal isomerization, pentane skeletal isomerization and 1-butene double bond isomerization. For comparison, the activity of sulfated zirconia, a well-studied strong acid catalyst, was also evaluated for the three probe reactions. On a per gram basis, the Cs2HPW12O40 sample was the most active heteropolyacid, presumably due to its high surface area. This sample was more active than sulfated zirconia for pentane skeletal isomerization and 1-butene double bond isomerization. However, sulfated zirconia was more effective for butane skeletal isomerization. Since the pentane and 1-butene reactions were monomolecular in nature, whereas butane isomerization was bimolecular, restrictions inside the micropores of the heteropolyacid may inhibit the formation of long chain intermediates. Interestingly, trace butenes were required to initiate butane isomerization reactions on sulfated zirconia, whereas heteropolyacids catalyzed the reaction in the absence of butenes.

Effect of Electron Beam Irradiation-Enhanced Diffusion on A W-Aluminum Oxide-Ti/Cu Multilayer

AbstractTungsten, aluminum oxide and Ti films were deposited onto a Cu substrate by means of a rf magnetron sputtering method. TEM thin foils for cross-sectional irradiation were prepared using a focused ion beam (FIB). Electron irradiation was carried out in a Hitachi H- 1300 electron microscope at I MV. The specimen temperatures during irradiation were 300, 473, 623 and 703K. The phases of W, aluminum oxide and Ti films were identified from selected area diffraction patterns as bcc, amorphous and hcp phases, respectively. The phases of W and Ti did not change due to irradiation. However, the amorphous aluminum oxide phase transformed to crystalline γ-Aluminum oxide. Electron irradiation caused no change in the composition of the interface of W/aluminum oxide, but diffusion was enhanced on the interfaces of aluminum oxide/Ti and Ti/Cu.

Mixed Si/C/M/O ceramics from 2,5-disilahexane/metal carbonyl (MFe and Co)

Reactions of 2,5-disilahexane with cobalt or iron carbonyl were performed in order to prepare cobalt or iron organosilicon ceramic precursors. Characterization of their structure by NMR and IR spectroscopies indicates the presence of mixed oligomeric and molecular species. Pyrolysis under argon at 1000 °C gives multiphase ceramics in high yields. Part of the CO ligands were incorporated during the thermal decomposition. Materials were characterized by X-ray, Raman, TEM and magnetic susceptibility analyses. For cobalt and iron, formation of metal-rich nodules included in a homogeneous matrix is observed for the sample pyrolyzed at 1000 °C. Crystalline Fe3Si or Co2Si are detected and the presence of amorphous oxide or oxycarbide phases is consistent with the high oxygen level. Between 1200 °C and 1400 °C, a carbothermal reduction process occurs at different temperatures for the iron and the cobalt precursors. Elimination of CO and SiO occurs with modification of the ceramic phases. Formation of SiC and silicides (FeSi for I and CoSi for II) is observed. Melting of the Fe3Si phase leads to the formation of spherical metallic particles.

XPS and transmission electron microscopy of the multicomponent hydride-forming alloys for electrochemical applications

Photoelectron spectra of the Ce4d, Ni2p, Ni3p, Co3p, Al2p, O1s, C1s in Mm(Ni,Co,Al) 5 and Zr3d, Ti2p, V2p, Ni2p, O1s, C1s in Zr 1− X Ti X (Ni,V,Co,Cr) 2 alloys have been obtained. In the surface layer, about 2–2.5 nm of both alloys, the main part of the nickel atoms are in the metallic state (Ni 0) and only a third of them in oxidized states (Ni +2, Ni +3). At the same time the concentration of nickel in surface layer of Zr-content alloy is much smaller when compared with Mm-content alloy. The chemical state of the Co and V atoms is similar to the Ni atoms state, but their concentrations, especially of V, in the surface layer is smaller than that of nickel. The results of XPS have been compared with the data of transmission electron microscopy of the thin foils of La- and Zr- based alloys. Dark field microphotographs of the oxidized alloys indicate the presence of two different phases, which, according to electron microdiffraction, are nickel-based alloy and oxide. In the first stage of oxidation on the surface of the foil, fine nickel particles (about 10 nm) and an amorphous oxide phase appear. Complete oxidation of the foil leads to the formation of a eutectic like structure consisting of a mixture of metallic and oxide phases. Some difference in the oxidized layer structure of the investigated alloys has been observed.

Synthesis of yttrium iron garnet precursor particles by homogeneous precipitation

Yttrium iron garnet (YIG) precursor particles were obtained by homogeneous precipitation in a nitrate salt solution by a reaction involving the thermal decomposition of urea. Chemical analysis indicated that solid phases were initially precipitated with sequential iron ion content. The precipitate formed was an amorphous mixed iron oxide phase. The complex composition and the thermal decomposition of the precipitate were studied by thermogravimetry-differential thermal analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform-infrared spectroscopy. Precipitate morphology was observed by SEM and TEM. Fine-grained single-phase yttrium iron garnet (YIG:Y3Fe5O12) powders were obtained by calcination of the precipitate at 1200 °C. YFeO3 intermediate compound was formed at 600 °C prior to the final crystallization of YIG.

Reactive sputter-deposition and characterization of lead oxide films

Lead and lead oxide containing films have been deposited on various substrates by radio frequency sputtering of a lead target in pure argon and argon–oxygen discharges. The sputter-deposited films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analyses, and the x-ray diffraction technique. The composition, deposition rate, and crystalline structure of films were investigated as functions of the oxygen content (1.5%–50%) in the gas phase and sputtering power (50–200 W). The O/Pb atom number ratio increased rapidly up to one as the oxygen content in the discharge was varied from 1.5% to 6%. The films deposited under these conditions were composed of metallic lead, yellow orthorhombic β-PbO and PbO1.57 phases in variable proportions. Amorphous and noncataloged lead oxide phases were also formed for oxygen contents in the discharge higher than 6%. The effect of the composition of the deposited material on the residual stresses developed in the films was determined and related to the morphology of films examined by scanning electron microscopy. The friction properties of lead and lead oxide containing films deposited on stainless steel disks were determined by alumina ball-on-disk tribological tests conducted in air at a sliding speed of 3 cm s−1 under a load of 2 N. The friction coefficient was investigated as a function of the sliding distance, film thickness, and surface roughness of tribological disks and test temperature.

Thermal decomposition of co-precipitated oxide hydrates of zirconium and manganese

The thermal decomposition of mixed ZrMn oxide hydrates containing 0–0.3 mol of manganese was examined by means of simultaneous TG and DTA. When heated, these mixed hydroxides decompose to an amorphous oxide phase and subsequently crystallize to a cubic phase. These changes are accompanied by a broad endothermic peak at around 165–180°C and an exothermic peak between 450 and 700°C. The temperature at which the crystallization occurs depends on the manganese content. A linear increase was observed between manganese content and crystallization (exothermic peak) temperature. The enthalpy of crystallization, however, showed a decreasing trend (from 28.7 to 12.1 kJ mol −1) with increasing manganese content within this range. Since no amorphous manganese oxide was formed when manganese oxide hydrate alone was heated, it is apparent that optimum concentrations of manganese (0.1–0.3 mol) in amorphous zirconia decrease the enthalpy of crystallization, thereby stabilizing zirconia in the cubic phase at low temperatures.

High-Energy Milling of WO3 Oxides: Amorphization and Reaction with Cs2CO3

Abstract Three WO3 oxides with ReO3-, pyrochlore-, and hexagonal-type structures have been studied in nonreactive and reactive grinding conditions by high-energy ball milling. In nonreactive grinding conditions, pyrochlore- and hexagonal-type WO3 oxides amorphize by collapse of the oxide structure. Monoclinic WO3 cannot be amorphized in these experimental conditions: the effect of high-energy ball milling is to decrease the crystallite size to a limit value. In reactive grinding conditions WO3 + Cs2CO3 mixtures lead to the formation of a lacunar cubic pyrochlore-type cesium tungstate. The reaction kinetics are strongly influenced by the WO3 oxide structure and its behavior in nonreactive grinding. The mechanochemical reactivity is higher for monoclinic WO3 and seems to depend on the presence of intercrystallite boundaries rather than on the amorphous oxide phase.

Transmission electron microscopy study of ball-milled GaSb powder mixture

Powders of mechanically ground (MG) Ga + 88 at% Sb were investigated by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), high resolution electron microscopy (HREM), selected area diffraction (SAD) and energy dispersive X-ray analyses (EDS). In ball milling we obtained two nonequilibrium phases stable at room temperature, i.e. amorphous antimony oxide and high-temperature antimony (HT) oxide Sb 2O 3. The formation of amorphous oxide phase in grain boundaries and development of HT Sb 2O 3 in its lamellar form from the amorphous region of the sample milled for 16 h was observed by HREM and controlled also with qualitative EDS. The model of appearance of HT Sb 2O 3 from the amorphous region of the sample is proposed from structural analyses carried out by HREM and SAD. For different milling rates the observed microstructure showed a layered structure and nanocrystalline grain sizes.

Geochemical mapping in Newfoundland and Labrador: its role in establishing geochemical baselines for the measurement of environmental change

Abstract Geochemical mapping based on the analysis of grab samples of organic sediment from more than 40,000 lakes to promote mineral exploration in Newfoundland and Labrador, Canada, was completed in 1987. The usefulness of the resulting regional geochemical data in defining the natural geochemical background for environmental purposes is only now being examined in detail. Questions to be addressed include assessing the magnitude and nature of any widespread contamination of the sediments in relation to naturally occurring levels, how well the data reflect bio-available levels and concentrations in more environmentally critical media such as surface water and soil, and how grab samples of lake sediment reflect anthropogenic chemical change. The stratigraphic variation of trace-elements has been investigated in a relatively undisturbed part of Newfoundland in cores from five lakes selected from the regional geochemical maps to exhibit wide ranges in concentration of several trace elements. Except for extractable Pb, which was enriched up to two-fold in the uppermost 10–20 cm of three cores, the stratigraphic variations of trace-element concentrations in the upper 1–1.5 m of sediment, due to local environmental fluctuations over time, are generally much smaller than geochemical variation between lakes due to the primary geochemical composition of the local bedrock. Preliminary element-speciation studies of the sediments have shown that significant proportions of a wide range of elements (i.e., Cu, Ni, Co, Zn, Y, Dy, La, Cd, Ce, Pb, Mn, V, Fe, Cr, Mo, Ba and Li) are held in acid-leachable organic and amorphous oxide phases of the sediments, indicating their geochemical mobility and potential bio-availability under acid conditions. The geochemical reflection in lake sediment of significant human disturbance of the landscape (urbanization) was studied in the city of St. John's, Newfoundland. Several elements were enriched in the inner-city lakes relative to the local background, most notably Pb which is from 5 to 10 times higher in grab samples of sediment from lakes in the urban core than the upper limit of its natural background for the area. Comparative studies between sediment and water in urban lakes indicate that the spatial distributions of several elements (e.g. Na, Sb, Mg, Pb, K, Cr, Ba, Ti and Sr) are significantly correlated between the two media.

Formation, structure and electrochemical properties of IrO 2-RuO 2 oxide electrodes

Composition and structure of the xRuO 2· (1− x) IrO 2 anode coatings obtained by pyrolysis of Ru and Ir chlorides have been studied by X-ray and IR analysis. Spectrophotometry and voltammetry of the initial solutions allowed us to establish the redox interaction of ruthenium hydrochlorides and Ir(IV) complexes with the formation of mixed (RuIV RuIV IrIII) complexes. In the range A (0< x⩽0.3) aggregates of partially hydrated Ru and Ir complexes coexist with the mixed ‘molecular’ forms. As a result the rutile type solid solutions formed in the coatings of the A region are more microheterogeneous and contain microregions enriched by Ru or Ir oxides. Another type of microheterogeneity is associated with incomplete crystallinity of the films and the presence of hydrated amorphous oxide phases on the surface of the crystallites of rutile solid solutions (Ru,Ir)O 2. All Ru x Ir 1− x O 2 electrodes demonstrate lower activity in O 2 evolution reactions and lower rates of charge storage processes in comparison with RuO 2 and IrO 2 electrodes. This may be associated with the peculiarities of the interaction of Ir and Ru ions on the surface of hydrated phases, and at the same time may explain higher corrosion stability of the RuO 2-component under O 2 evolution conditions.

Surface oxygen artifacts on aluminum nitride

Aluminum nitride (AlN)is an increasingly important electronic ceramic with oxygen as an important bulk impurity. Quantitative microanalysis of oxygen to determine its precise distribution is a necessary step in characterization of the ceramic that may be complicated due to surface oxidation. AlN is thermodynamically unstable compared to the oxide (Al2O3) at room temperature in the presence of environmental oxygen or water and may thus be expected to form a thin, possibly passive oxide film similar to the oxide layer of pure aluminum metal. Such an oxide layer has been used to explain anomalies in oxygen quantification in AlN by neutron activation methods [1] but reflecteion high energy electron diffraction studies [2] failed to reveal either crystalline or amorphous oxide phases forming at room temperature.Electron diffraction techniques in the transmission electron microscope were used to examine thin AlN sections for possiblecrystalline surface layers. A ceramic AlN sample was prepared using conventional techniques for the preparation of thin foils with final thinning accomplished by ion milling.

The effect of boron on ZSM-5 zeolite shape selectivity and activity: II. Coincorporation of aluminium and boron in the zeolite lattice

ZSM-5 zeolite samples have been synthesized in the presence of NaAlO 2 and NaBO 2 to yield a crystalline phase of almost unchanged Al + B site population, but with increased B Al ratio. The presence of boron in the zeolitic lattice is evident by MAS NMR. Transformation of boron (upon NH 3 sorption) within trigonal and tetrahedral symmetries, which is revealed by IR spectroscopy as persistence and disappearance of the trigonal BO stretching mode at 1385 cm −1, together with the appearance of the &z.tbnd;SiOB skeletal vibration at 920 cm −1 for the zeolite as synthesized, confirms the incorporation of boron by synthesis with no evidence of occluded amorphous boron oxide phase. IR spectroscopy reveals a distinct absorption at 3700 cm −1 assigned to Brønsted sites associated with lattice boron. NH 3 sorption, studied by IR spectroscopy and microcalorimetry, reveals weak acidity for boron-associated sites; however, they do certainly sorb ammonia. Kinetic data of 3-Me-pentane sorption suggest a role for lattice boron in modifying the interior part of the zeolite, which is also indicated by catalysis of toluene disproportionation as improved selectivity toward p-xylene formation. Zeolite modification by the present method, although exhibiting a minor effect on ZSM-5 shape selectivity, has a major role in drastically decreasing the zeolite acidity and hence activity.