Wide Range Of Oxides Research Articles

Interfacial Symmetry-Breaking Effects in the Quantum Paraelectric SrTiO3

Oxides lacking a center of symmetry are highly desired, as they usually have fascinating physical properties. However, there are limited numbers of noncentrosymmetric media in nature and most of them do not have multiple functionalities integrated. Here, using the bulk photovoltaic effect as the probing technique, we demonstrate that, at interfaces with a wide range of oxides, strontium titanate (${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$) is polar, i.e., with broken inversion symmetry in the quantum paraelectric phase. Studies comprising conductivity and the bulk photovoltaic effect on ${\mathrm{La}\mathrm{Al}\mathrm{O}}_{3}/{\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ thin films further show that excessive electronic band bending screens the induced polarity, revealing that appropriate band bending at the interface is the key parameter to control symmetry breaking. Inheriting high carrier mobility from ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$, the polar interface under illumination at low temperatures is conductive or metallic, permitting multifunctionality coupling between the oxides and ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$. Our studies show that significant photovoltaic effects can be generated at the polar interfaces, especially in the quantum-paraelectric phase of ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$, thus giving practical design strategies for multifunctional devices.

A promising engineering strategy for water electro-oxidation iridate catalysts via coordination distortion.

Here, we study the relationship between the coordination structure of IrO6 and OER activity in a wide range of oxides with systematic comparisons. The results reveal that distorted IrO6 is more conducive to OER activity. Specifically, for a given material, regulating the transformation of the IrO6 octahedron from D4h compression to D4h elongation causes electrons near the EF level to become more delocalized, which is very beneficial for reducing the energy of the rate determining step. Our findings will guide the design and preparation of more efficient iridium-based OER catalysts.

FT-IR spectroscopy study of HNCO adsorption and hydrolysis over oxide-based samples dedicated to deNOx processes

HNCO adsorption monitored by FT-IR spectroscopy was performed over a wide range of oxides from various acid-base and redox properties: SiO2, Al2O3, TiO2, ZrO2, CeO2, CeO2-ZrO2, WO3/CeO2-ZrO2. HNCO adsorbed dissociatively in the whole studied samples. A correlation with pyridine ν8a wavenumbers revealed that HNCO dissociation mainly involved weak Lewis acid sites (LAS) location. The significant isocyanate adsorption capacity of titania and zirconia was evidenced. HNCO hydrolysis reaction was also investigated. Among the various studied samples, CeO2-ZrO2 and WO3/CeO2-ZrO2 presented the higher HNCO hydrolysis rate, with ammonia formation from room temperature. For all studied samples, NCO groups were evidenced as intermediate species of HNCO hydrolysis.

Diamonds, Super‐Reduced and Crustal Minerals in Chromitites of the Hegenshan and Sartohay Ophiolites, Central Asian Orogenic Belt, China

The Central Asian Orogenic Belt (CAOB) is a huge tectonic mélange that lies between the North China Craton and the Siberian Block. It is composed of multiple orogenic belts, continental fragments, magmatic and metamorphic rocks, suture zones and discontinuous ophiolite belts. Although the Hegenshan and Sartohay ophiolites are separated by nearly 3000 km and lie in completely different parts of the CAOB, they are remarkably similar in many respects. Both are composed mainly of serpentinized peridotite and dunite, with minor gabbro and sparse basalt. They both host significant podiform chromitites that consist of high‐Al, refractory magnesiochromite with Cr#s [100Cr/(Cr+Al)] averaging >60. The Sartohay ophiolite has a zircon U‐Pb age of ca. 300 Ma and has been intruded by granitic plutons of similar age, resulting in intense hydrothermal activity and the formation of gold‐bearing listwanites. The age of the Hegenshan is not firmly established but is thought to have formed in the Carboniferous.Like many other ophiolites that we have investigated in other orogenic belts, the chromitites in these two bodies have abundant diamonds, as well as numerous super‐reduced and crustal minerals. The diamonds are mostly, colorless to pale yellow, 200–300 μm across and have euhedral to anhedral shapes. They all have low carbon isotopes (δ14C = −18 to −29) and some have visible inclusions. These are accompanied by numerous super‐reduced minerals such as moissanite, native elements (Fe, Cr, Si, Al, Mn), and alloys (e.g., Ni‐Mn‐Fe, Ni‐Fe‐Al, Ni‐Mn‐Co, Cr‐Ni‐Fe, Cr‐Fe, Cr‐Fe‐Mn), as well as a wide range of oxides, sulfides and silicates. Grains of zircon are abundant in the chromitites of both ophiolites and range in age from Precambrian to Cretaceous, reflecting both incorporation of old zircons and modification of grains by hydrothermal alteration.Our investigation confirms that high‐Al, refractory chromitites in these two ophiolites have the same range of exotic minerals as high‐Cr metallurgical chromitites such as those in the Luobusa ophiolite of Tibet. These collections of exotic minerals in ophiolitic chromitites indicate complex, multi‐stage recycling of oceanic and continental crustal material at least to the mantle transition zone, followed by uprise and emplacement of the peridotites into relatively shallow ophiolites.

Atomistic origins of pressure-induced changes in the OK-edge x-ray Raman scattering features ofSiO2andMgSiO3polymorphs: Insights fromab initiocalculations

Despite its fundamental importance in condensed matter physics and geophysical implications, establishing the systematic and direct link between the pressure-induced structural changes in crystalline and noncrystalline low-$z$ oxides and their corresponding evolution in O $K$-edge core-electron excitation features under extreme compression has been challenging. Here we calculated the site-resolved partial density of states and O $K$-edge x-ray Raman scattering (XRS) spectra for two of the important oxide phases in the Earth's lower mantle, $\mathrm{MgSi}{\mathrm{O}}_{3}$ bridgmanite and post-bridgmanite, up to 120 GPa using ab initio calculations, revealing the electronic origins of the O $K$-edge features for oxides under compression. The absorption threshold $({E}_{A})$ and band gap increase linearly with a decrease in the O-O distance in diverse $\mathrm{Si}{\mathrm{O}}_{2}$ and $\mathrm{MgSi}{\mathrm{O}}_{3}$ high-pressure phases $[{E}_{A}(\mathrm{eV})\ensuremath{\approx}\ensuremath{-}10.9{d}_{\text{O-O}}(\AA{})+34.4]$, providing a predictive relationship between the ${E}_{A}$ and the O-O distances in the oxide at high pressure. Despite densification, upon isobaric phase transition from bridgmanite to post-bridgmanite at 120 GPa, a decrease in band gap results in a decrease in edge energy because of an increase in O-O distance. The oxygen proximity is a useful structural proxy of oxide densification upon compression, as it explains the pressure-induced changes in O $K$-edge XRS features of crystalline and amorphous $\mathrm{Si}{\mathrm{O}}_{2}$ and $\mathrm{MgSi}{\mathrm{O}}_{3}$ at high pressures. These results can be applied to studies of the pressure-bonding transitions in a wide range of oxides under extreme compression.

A comprehensive study of oxidative stress in sudden hearing loss.

Little is known about the association between idiopathic sudden sensorineural hearing loss (ISSNHL) and oxidative stress. We investigated changes in a wide range of oxidants and antioxidants to create a comprehensive picture of oxidative imbalance. In the peripheral blood of 50 ISSNHL patients and 50 healthy subjects, total oxidant status (TOS), total antioxidant status (TAS), paraoxonase (PON), thiol/disulphide levels were measured. Moreover, a global oxidative stress index, reflecting both oxidative and antioxidant counterparts, was also calculated. One-way analysis between oxidative markers and severity of hearing loss were evaluated. The ISSNHL patients showed significantly higher TOS levels than controls (6.02±3.17 vs. 4.5±2.22; p=0.018). The oxidative index was also significantly higher in patients than controls (0.39±0.19 vs. 0.3±0.14; p=0.035). TAS, PON, native thiol, and total thiol were not altered. There was no statistical significance between oxidative markers and severity of hearing loss. The binary logistic regression model revealed that disulphide and TOS were associated with ISSNHL. There are alterations in a wide array of oxidants and antioxidants, with balance shifting toward increased oxidative stress in ISSNHL. Our findings may suggest endothelial dysfunction in ISSNHL etiopathogenesis.

Rapid solid-state metathesis route to transition-metal doped titanias

Rapid solid-state metathesis (SSM) reactions are often short-lived highly exothermic reactions that yield a molten alkali halide salt that aids in product growth and crystallization. SSM reactions may also produce kinetically stabilized structures due to the short (seconds) reaction times. This report describes the investigation of rapid SSM reactions in the synthesis of transition-metal doped titanias (M–TiO2). The dopant targeted compositions were ten mol percent and based on elemental analysis, many of the M–TiO2 samples were close to this targeted level. Based on surface analysis, some samples showed large enrichment in surface dopant content, particularly chromium and manganese doped samples. Due to the highly exothermic nature of these reactions, rutile structured TiO2 was observed in all cases. The M–TiO2 samples are visible colored and show magnetic and optical properties consistent with the dopant in an oxide environment. UV and visible photocatalytic experiments with these visibly colored rutile M–TiO2 powders showed that many of them are strongly absorbent for methylene blue dye and degrade the dye under both UV and visible light illumination. This work may open up SSM reactions as an alternate non-thermodynamic reaction strategy for dopant incorporation into a wide range of oxide and non-oxides.

Improved description of metal oxide stability: Beyond the random phase approximation with renormalized kernels

The renormalized adiabatic PBE (rAPBE) method has recently been shown to comprise a significant improvement over the random phase approximation (RPA) for total energy calculations of simple solids and molecules. Here we consider the formation energies of 19 group I and II metal oxides and a few transition-metal oxides. The mean absolute error relative to experiments is 0.21 eV and 0.38 eV per oxygen atom for rAPBE and RPA, respectively, and thus the rAPBE method greatly improves the description of metal-oxygen bonds across a wide range of oxides. The failure of the RPA can be partly attributed to the lack of error cancellation between the correlation energy of the oxide on the one hand and the bulk metal and oxygen molecule on the other hand, which are all separately predicted much too negative by the RPA. We ascribe the improved performance of the rAPBE to its significantly better description of absolute correlation energies which reduces the need for error cancellation. The rAPBE is just one out of an entire class of renormalized exchange-correlation kernels which should be further investigated.

Oxidative coupling of N-hydroxyphthalimide with toluene

Oxidative C-O-coupling of N-hydroxyphthalimide (NHPI) with toluene was studied. The reaction occurred in different organic solvents with a wide range of oxidants, such as (NH4)2Ce(NO3)6, PhI(OAc)2, KMnO4, Mn(OAc)3·2H2O, Pb(OAc)4, and Co(OAc)2/O2, to afford N-benzyloxyphthalimide in yield of 11–75%. Phthalimide-N-oxyl radicals, generated under the reaction conditions, could eliminate the hydrogen atom from the benzyl fragment of alkylarene at room temperature. Probably, formation of the product of the oxidative coupling occurred via recombination of benzyl and phthalimide-N-oxyl radicals.

Increased oxidative stress and altered antioxidants status in patients with chronic allergic rhinitis

Background: Allergic rhinitis is an inflammatory disorder of the upper airways. Although several oxidants and antioxidants are likely to be involved, alterations in only limited parameters have been studied. Objective: In this study an attempt has been made to study the oxidant-antioxidant imbalance by investigating changes in a wide range of oxidants and antioxidants in the blood. Methods: Blood samples were obtained from 39 chronic allergic rhinitis patients (males 24, females 15), aged 20-70 (mean age 36.33 ± 2.03) years and 53 individuals (36 males, 17 females); aged 24 to 64 (mean age 45.42 ± 1.36) years. Duration of allergic rhinitis was 1.77 ± 0.237 years. In the study group, nasal symptoms were scored and the results were recorded. The patients were classified as having perennial Allergic rhinitis (PAR) if they had had at least 2 rhinitis symptoms (sneezing, rhinorrhea, nasal obstruction, itching) for at least 6 months a year in the previous 2 years and if they had a positive skin prick test response to at least 1 clinically significant perennial allergen (e.g., house dust mites, molds, cockroach, cockroach excrement grass and tree pollen, cat and dog epithelia and molds, or animal dander). They had no other allergic diseases except persistent allergic rhinitis diagnosed by the physical and history examination. Erythrocyte lipid peroxidation, erythrocyte antioxidants viz., glutathione, glutathione reductase, superoxide dismutase, catalase and plasma antioxidants viz., ceruloplasmin, glutathione-S-transferase, vitamin C, total antioxidant activity were estimated in the above two groups. Results: Erythrocyte lipid peroxidation (0 hour, p < 0.01) and superoxide dismutase (p < 0.01) were significantly higher, whereas plasma vitamin C (p < 0.001), ceruloplasmin (p < 0.05) and total antioxidant activity (p < 0.001) were significantly lower in chronic allergic rhinitis patients when compared to controls. Plasma Glutathione S transferase and erythrocyte catalase, glutathione, and glutathione reductase remained unchanged from normal subjects. Conclusion: The changes in different parameters indicate an imbalance in the oxidant and antioxidant status in chronic allergic rhinitis patients. Further studies are required to investigate the potential for antioxidant supplements to be used as routine therapy in chronic allergic rhinitis patients. Capsule summery: The study shows that the body is trying to cope for the oxidative stress by altering the enzyme levels. But external supplement may also be required as the total antioxidant levels are very much depleted.

Ab Initio Calculation of Elastic Constants of Ceramic Crystals

An effective computational scheme to calculate the complete set of independent elastic constants as well as other structural parameters including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio for crystals is reported. The scheme is based on the stress–strain analysis approach with the appropriate selection of strain governed by symmetry consideration. The first principles Vienna ab initio simulation package (VASP) is used in stress calculations. Comprehensive tests were performed for α‐SiO2 and spinel MgAl2O4 with different exchange‐correlation potentials, and different sets of computational parameters to investigate the relative accuracies of the calculations. A wide range of oxides, nitrides, and carbonate crystals with different crystal symmetries were chosen to test the scheme under both LDA and GGA approximations at zero temperature and pressure. Some of these calculations for large complex crystals are believed to be attempted for the first time. The calculated elastic constants show quite good agreement with the existing experimental data for almost all the examined systems with the exception of the relatively soft material such as α‐SiO2 and the C14 parameter of some trigonal crystals expressed in the hexagonal form such as in α‐Al2O3. Other structural properties derived from the elastic constants also show good agreements with the measured values.

Markers of protein oxidation: different oxidants give rise to variable yields of bound and released carbonyl products

Exposure of proteins to radicals in the presence of O 2 gives both side-chain oxidation and backbone fragmentation. These processes can be interrelated, with initial side-chain oxidation giving rise to backbone damage via transfer reactions. We have shown previously that alkoxyl radicals formed on the C-3 carbons of Ala, Val, Leu, and Asp residues undergo β-scission to give backbone α-carbon radicals, with the release of the side- chain as a carbonyl compound. We now show that this is a general mechanism that occurs with a wide range of oxidants. The quantitative significance of this process depends on the extent of oxidation at C-3 compared with other sites. HO , generated by γ radiolysis, gave the highest total carbonyl yield, with protein-bound carbonyls predominating over released. In contrast, metal ion/H 2O 2 systems, gave more released than bound carbonyls, with this ratio modulated by EDTA. This is ascribed to metal ion – protein interactions affecting the sites of initial oxidation. Hypochlorous acid gave low concentrations of released carbonyls, but high yields of protein-bound material. The peroxyl radical generator 2,2′-azobis(2-amidinopropane) hydrochloride, and a peroxynitrite generator, 3-morpholinosydnonimine hydrochloride, gave lower overall carbonyl yields, with released carbonyls predominating over protein-bound species similar to that observed with metal ion/H 2O 2 systems.

Use of Polymeric and other Organic Additives in Ceramic Slurry Processing for Casting—A Review

Polymeric and other organic additives are used in ceramic slurry processing for a wide range of oxides, carbides, nitrides etc as dispersants, flocculants, binders, wetting agents and antifoaming agents. The performance of the additives in effecting the desired purpose depends mainly on their chemical nature and functionality, the nature of mineral surface and the aqueous environment. Therefore, it is necessary to have a thorough understanding of the chemistry of dispersants, flocculants, binders, wetting and antifoaming agents in order to maximize the effectiveness of the polymeric and other organic additives. Apart from the polymeric additives other non-polymeric additives are also used. They may be wetting agents, antifoaming agents or even dispersants.Mutual interactions between the additives in any system are usually considered negligible. In many cases, however, interactions that occur can affect the process and ultimately the product performance. This could be the root cause of some common ceramic defects. This paper presents an overview of the use of polymeric and other organic additives in ceramic slurry processing for casting. The basic principle of interactions between ceramic particle and additives governing the stability of the suspension, wettability of the powder dispersion and workability are also discussed.

Increased oxidative stress and altered levels of antioxidants in asthma

Background: Reactive oxygen species might play an important role in the modulation of airway inflammation. There is evidence of an oxidant-antioxidant imbalance in asthma. Although several oxidants and antioxidants are likely to be involved, alterations in only limited parameters have been studied in isolation. Objective: We investigated changes in a wide range of oxidants and antioxidants to create a comprehensive picture of oxidant-antioxidant imbalance. Methods: In the peripheral blood of 38 patients with bronchial asthma and 23 control subjects, oxidative stress was measured in terms of superoxide anion generation by leukocytes, lipid peroxidation products, total nitrates and nitrites, total protein carbonyls, and total protein sulfhydrils in plasma. Antioxidant status was evaluated by measuring red blood cell superoxide dismutase and catalase activity, total blood glutathione, and glutathione peroxidase activity in red blood cells and leukocytes and total antioxidant capacity in plasma. Results: Asthmatic patients showed increased superoxide generation from leukocytes, increased total nitrites and nitrates, increased protein carbonyls, and increased lipid peroxidation products and decreased protein sulfhydrils in plasma, indicating increased oxidative stress. They also showed increased superoxide dismutase activity in red blood cells and increased total blood glutathione and decreased glutathione peroxidase activity in red blood cells and leukocytes. Red blood cell catalase activity and the total antioxidant capacity of plasma were not altered. Conclusion: There are alterations in a wide array of oxidants and antioxidants, with balance shifting toward increased oxidative stress in asthma. Therapeutic augmentation of the antioxidant defenses might be beneficial. (J Allergy Clin Immunol 2003;111:72-8.)

Metal organic chemical vapor deposition (MOCVD) of oxides and ferroelectric materials

The electrical properties of thin-film oxides span a tremendous range from insulating to superconducting. As a consequence, they are now finding an increasing number of applications in electronics and opto-electronics, both as stand-alone layers and for the provision of added functionality to electronic circuits, especially silicon. The modified precursor delivery technologies (e.g. aerosol or liquid delivery or injection techniques) coupled with improved precursors, and better engineering of the deposition kit, have transformed the prospects for the deposition of these materials by MOCVD. It is now possible to exploit the many traditional advantages of MOCVD, especially over other routes to thin-film oxide deposition. A wide range of oxides and particularly complex ferroelectric oxides are being produced on substrates of up to 200 mm in diameter. This paper highlights the progress and real advantages that MOCVD has for thin-film oxide deposition, including the design of improved precursors. Examples of the deposition of dielectric layers and lead-based ferroelectric layers for uncooled thermal imaging, and MEMS actuation applications are presented.

Prediction of the chemiluminescent behavior of pharmaceuticals and pesticides.

The present paper deals with the first attempt to apply molecular connectivity calculations to predict a chemical property with analytical usefulness: the chemiluminescent behavior of substances when reacted with common oxidants in a liquid phase. Preliminary evidence when searching for new direct CL methods consisted of the examination of analyte reaction with a wide range of oxidants and media. This task, which results in time-consuming and trial-and-error expensive procedures, is necessary due to ensure empirical or theoretical rules for CL prediction are available. On the other hand, in quantitative structure-activity relationship studies, molecular connectivity is a topological method capable of describing the structure of a molecule by means of numbers named indices; subsequent regression in relation to the experimental values of the physical, chemical, or biological properties yields a series of functions called connectivity functions. Discriminant analysis was applied to 200 either chemiluminescent or nonchemiluminescent substances found either bibliographically or in an experimental screening. The method used for the selection of descriptors was a stepwise linear discriminant analysis from the Snedecor F-parameter. The classification criterion used was the minimum value of Mahalanobis. The quality of the discriminant function was calculated through the Wilks U-statistical parameter. Finally, the function was applied to a database including of more than 50,000 structurally heterogeneous compounds. The theoretical predictions were faced with the empirical evidence obtained through a continuous-flow manifold.

Bonding of stabilised zirconia (Y-TZP) by means of nano Y-TZP particles

A technique has been developed for bonding conventionally produced plates of yttria stabilised tetragonal zirconia polycrystals (Y-TZP) to one another by using nano-sized particles of the same chemical composition as an interlayer. The latter was in the form of a disc partially pre-consolidated at elevated temperature. Bonding was performed under carefully controlled conditions of hot pressing. Sound bonds were obtained as determined by ultrasonic examination and bend tests. The temperatures used for bonding were perhaps up to 400°C less than would have been required for powder of conventional size (several μm). The bonds obtained should have the additional advantages of preserving the physical and corrosion-resistant properties of the plates being joined. The technique should be applicable to a wide range of oxides, non-oxide ceramics, intermetallic and inorganic compounds.

The Production of Copper–Arsenic Alloys (Arsenic Bronze) by Cosmelting: Modern Experiment, Ancient Practice

Cosmelting experiments to produce copper–arsenic alloys were carried out by Lechtman in 1984. The experiments included crucible and furnace smelting techniques utilizing ores collected in the Peruvian Andes. Smelting charges consisted of mixtures of copper oxide ore with either copper sulpharsenide or iron sulpharsenide ore. The experimental furnaces were constructed to resemble furnaces excavated at Batán Grande, a large ore smelting site on the Peruvian north coast where copper–arsenic alloys were produced during the Middle Horizon and later.The cosmelting experiments yielded coherent copper–arsenic alloy ingots over a wide range of oxide: sulpharsenide ore mixtures. Crucible/furnace charges containing ratios of between 2:1 and 4:1 oxide:sulpharsenide mineral produced clean metal, fully separated from slag or matte byproducts. The sulphide ores were not roasted prior to smelting; no flux was added to the charges.Study of the metal ingots, mattes, and slags helps determine the chemical and thermodynamic reactions and the phase separation mechanisms that took place inside the smelting enclosures. The copper–arsenic alloys found in ancient artefacts could have been made easily, deliberately or accidentally, by cosmelting procedures.

Chemical oxidation of a neutral electrochemically prepared polythiophene film

AbstractNeutral polythiophene films obtained by NH4OH compensation of electrochemically polymerized samples were re‐oxidized chemically to the metallic state by a wide range of oxidants. The electrochemically and chemically oxidized polythiophene films were found to be quite stable in air. Results of IR, SEM and WAXS studies are described and discussed. The feasibility of chemical re‐oxidation of neutral electrochemically prepared polythiophene films offers a convenient means to produce flexible highly conductive polythiophene films.

X-ray spectrometry in the eighties

X-ray fluorescent spectroscopy anno 1983 is a superb analytical technique which allows precisions of one part in 2000. The main impediments to reaching this accuracy are sampling and sample preparation. Nevertheless, very accurate results can be obtained on a wide variety of materials. After fusion, a wide range of oxides can be analyzed using one calibration. Recent advances in analytical instrumentation will further contribute to improved performance for specific analytical problems. the scandium side window tube is the first of a series of side window tubes which will greatly enhance light element performance. The developement of multilayer technology shows great promise for the improvement of light to ultra-light element dispersion. Advances in detector technology will mainly be reached through selecting gas detectors per element range, and the use of high resolution gas detectors such as the gas scintillation proportional counter. Data treatment will show improvements through the increased use of fundamental parameter methods using theoretical alphas, on-line fundemental parameter calculations, or a combination of both. In addition, there will be a strongly increasing use of laboratory management systems which handle the automatic logging of samples and combine the XRF results with results from other techniques. Hardware in Energy Dispersive Spectroscopy (EDS) has not shown major changes in recent years. The use of room temperature HgI 2 detectors with a resolution around 400 eV could be usefull for sorting or identification applications. In the field of EDS, some extremely usefull software packages have been developed. These include packages for the analysis of samples without standards, and packages to analyse coatings.