Temperatures In Oxygen Atmosphere Research Articles

Spark plasma sintering of SnO2 based varistors

In this research, for the first time, SnO2-based varistors were fabricated via spark plasma sintering technique (SPS) and the microstructure and electrical properties of these varistors were investigated. Furthermore, the effect of post-annealing temperature in oxygen atmosphere on electrical properties of the SPSed samples was studied. The SPS process was performed at the sintering temperatures of 600, 650, and 700 ᵒC for 15 min with a maximum pressure of 90 MPa under vacuum condition. The SPSed sample which was sintered at 650 ᵒC possessed maximum density of 98% and the ultra-fine-grained microstructure with the mean grain size of 380 nm. Surprisingly, all SPSed samples exhibited Ohmic behavior with very low electric resistances. After post-annealing in oxygen atmosphere, Ohmic to non-Ohmic transition was observed in SPSed samples. The oxygen deficiency during the SPS process was responsible for the Ohmic characteristic of SPSed samples. Post-annealing of SPSed samples in the oxygen atmosphere resulted in Schottky barriers formation through oxygen adsorption at grain boundaries. The sample post-annealed at 1050 ᵒC presented the best non-Ohmic parameters including high breakdown electric field of 4500 V/cm and the nonlinear coefficient of 13. These electrical parameters are comparable with the conventional-sintered samples which was sintered at 1300 ᵒC and its breakdown electric field and nonlinear coefficient were equal to 900 V/cm and 8, respectfully.

Untwinned YBa2Cu3O7−δ thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates

We have grown untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) films on (110) MgO substrates that were pre-annealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear, in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.

Titanium hydride—a stable support for Pt catalysts in oxygen reduction reaction

A new class of conductive and dimensionally stable surface-modified TiH2 particles prepared by ultra-sonication method is proposed as a non-carbon support for Pt catalysts. Thermal analysis results indicated good thermal stability of these materials at high temperatures in oxygen atmosphere. TiH2 particles are discovered to be stable at potentials higher than 1.5 V in O2-saturated H2SO4 solution. It is also found that the surface-modified TiH2 exhibits a modest electrocatalytic activity toward oxygen reduction reaction. Accelerated durability measurements show that Pt catalysts supported on sonicated TiH2 exhibited superior stability than standard Vulcan XC-72 carbon. High corrosion resistance and thermal stability render better chemical stability and structural integrity to surface-modified TiH2 particles at elevated temperatures.

Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere

The growth and thermal stability of textured iridium thin films used as bottom electrode in electronic devices based on ferroelectric materials were investigated. The thin films were grown using the dc magnetron sputtering technique. The Ir layers directly deposited on SiO2/Si substrates present a mixed (111) and (200) orientations, while the films grown on Ti seed layers exhibit a strong preferred (111) orientation favoured by good matching with the titanium lattice. The substrate temperature during the growth of iridium/titanium stack has a significant effect on the surface morphology of the iridium layer and its thermal stability. The as-grown surface of 20-nm-thick Ir films is smooth, having a root-mean-square (rms) roughness of 0.7 nm. After thermal annealing the Ir film shows an increased surface roughness due to the formation of agglomerations. The change in the surface morphology of the Ir layer is due to titanium diffusion and its oxidation. Thicker and better crystallised iridium thin films annealed in oxygen atmosphere at 700 °C show a good thermal stability with only a slight modification of the surface morphology. Within the limits of experimental error, there is no change in the electrical resistivity before and after thermal annealing. The rms roughness has not varied significantly and the XPS investigation shows no traces of titanium oxide on iridium surface. Ir/Ti stack deposited under the optimum conditions could be successfully used as electrode in devices based on oxide thin films.

Nanoindentation study of nickel manganite ceramics obtained by a complex polymerization method

The chemical synthesis of nickel manganite powder was performed by a complex polymerization method (CPM). The obtained fine nanoscaled powders were uniaxially pressed and sintered at different temperatures: 1000–1200°C for 2h, and different atmospheres: air and oxygen. The highest density was obtained for the sample sintered at 1200°C in oxygen atmosphere. The energy for direct band gap transition (Eg) calculated from the Tauc plot decreases from 1.51 to 1.40eV with the increase of the sintering temperature. Indentation experiments were carried out using a three-sided pyramidal (Berkovich) diamond tip, and Young's modulus of elasticity and hardness of NTC (negative temperature coefficient) ceramics at various indentation depths were calculated. The highest hardness (0.754GPa) and elastic modulus (16.888GPa) are exhibited by the ceramics sintered at highest temperature in oxygen atmosphere.

Intrinsic reactivity analysis of soot removal in LNT-catalysts

The soot removal process in presence of a series of LNT-catalysts, and different reaction atmospheres, has been studied, using thermogravimetric analysis coupled to mass spectrometry (TG-MS) time-resolved experiments. Kinetic parameters have been estimated, using a distribution function of activation energy: where the frequency factor was correlated approximately with the activation energies which enable the decoupling of the processes involved in the regeneration by soot removal over those synthesized catalysts. It was found that soot removal is a sequential process that is strongly dependent on the formulation and surface structure of the catalyst and atmosphere of reaction. K-containing LNT catalysts showed a high activity in the soot removal process by gasification (Ea≈70–90kJmol−1), promoted by surface hydroxylated centers, decreasing the ignition temperature in oxygen atmosphere. NO+O2 atmosphere, more oxidizing than O2, provokes in addition a reduction in the soot removal temperature due to a direct reaction between soot and NO2 (gas) and/or the adsorbed NOx onto the catalyst surface.

SrCoOx薄膜中的氧空位效应研究

本文中我们采用脉冲激光沉积技术在SrTiO3(001)基底上制备出钙铁石结构的SrCoO2.5(BM-SCO)外延薄膜，在氧气氛围、不同温度下对样品进行后退火工艺处理，使薄膜发生由钙铁石相到钙钛矿相(P-SCO)的拓扑相变。研究结果表明薄膜的磁性和微结构在相变温度(250℃)附近发生很大的变化。当退火温度为250℃ ≤ T < 600℃时，薄膜由BM-SCO转变为BM-SCO与P-SCO的共存相(Mix-SCO)，薄膜的磁性明显增强，由反铁磁性转变为铁磁性(Tc~180 K)。当退火温度达到600℃时，完全转变为钙钛矿型SrCoO3–δ。XPS拟合结果显示，退火后Co的价态发生变化，从Co3+转变为Co4+，即薄膜中的部分氧空位被填充。故退火后钙钛矿型SrCoO3–δ的氧含量(3–δ)约为2.75。 In this work, we grew brownmillerite SrCoO2.5 (BM-SCO) epitaxial thin films on (001) SrTiO3 substrates by pulsed laser deposition and performed post-annealing at various temperatures in oxygen atmosphere for topotactic conversion into the perovskite phase (P-SCO). The results show that the magnetic properties and microstructure of the films have a great change near the critical temperature (250˚C). When a BM-SCO film was annealed in lower temperature (250˚C ≤ T < 600˚C), a mixed-phase of BM-SCO and P-SCO (Mix-SCO) was observed, and oxygen intercalation drove the antiferromagnetic phase to ferromagnetic phase (Tc~180 K). We also found that in post-annealing under 600˚C a complete phase transition from the brownmillerite SrCoO2.5 to the perovskite SrCoO3–δ was exhibited. XPS fitting results clearly indicate a change in the Co valence state from 3+ toward 4+. So some oxygen vacancies in the films are filled. Therefore, we conclude that the oxygen concentration (3–δ) in perovskite SrCoO3–δ by post-annealing is about 2.75.

The Increment Valuated of Natural Ruby by Heat Treatment

This research aims to investigate the effects of heat treatment on color and clarity of ruby. The ruby were heated at 1200, 1300, 1400, 1500 and 1600°C in oxygen atmosphere for 40 hours, respectively. Each ruby before heated and after heated, the color measurement by spectrophotometer, to observe color changing and clarity. Found that, the samples had beautiful red and clarity more than before heated. So that, heat treatment of ruby at high temperature in oxygen atmosphere, could to increment valuated of natural ruby.

Fully filamentized HTS coated conductor via striation and selective electroplating

A simple, cost-effective method involving top-down mechanical scribing, oxidation and bottom-up electroplating has been successfully developed to fabricate fully filamentized HTS coated conductors. The copper stabilizer layer is selectively electroplated on the superconducting filaments while the striations remain copper-free due to the formation of a resistive oxide layer in between filaments by oxidation of the striated grooves at elevated temperature in oxygen atmosphere. Magnetization AC loss measurements, performed in a frequency range of 45–500Hz at 77K, confirmed the expected N-fold reduction in AC loss of the filamentized tapes with no significant degradation in critical current beyond that due to the material removal from the striations (N – number of filaments). A considerable reduction in coupling AC loss was observed after high temperature annealing/oxidation of the striated tapes. Furthermore, a significant reduction in eddy current loss was achieved with selective copper electroplating, as evidenced by analyzing the field and frequency dependence of magnetization AC loss, as well as by comparing the AC loss performance of striated samples to that of non-striated samples after electroplating of copper stabilizer.

Structural and functional properties of Al:ZnO thin films grown by Pulsed Laser Deposition at room temperature

Current research on transparent conductive oxides (TCOs) is focusing on indium-free TCOs, such as Al-doped ZnO (AZO), as an alternative to indium–tin oxide. In this work, AZO thin films were grown by Pulsed Laser Deposition at room temperature in oxygen atmosphere. The O2 pressure was varied from 0.01Pa to 10Pa, highlighting the effects of defect formation and oxygen vacancies on the film properties. Structural properties were characterized by X-ray diffraction and Scanning Electron Microscopy, while functional properties were characterized by measurement of electrical conductivity, Hall mobility, carrier density and optical transmission. At an optimal deposition pressure of 2Pa, optical transparency in the visible range and minimum resistivity (4.5∙10−4Ωcm) were found, comparable to state-of-the-art TCOs. Mean value of visible transparency was shown to increase with increasing pressure, up to 88% at a deposition pressure of 10Pa.

Hard and Flexible Nanocomposite Coatings using Nanoclay-Filled Hyperbranched Polymers

The combination of hardness, scratch resistance, and flexibility is a highly desired feature in many coating applications. The aim of this study is to achieve this through the introduction of an unmodified nanoclay, montmorillonite (Na(+)MMT), in a polymer resin based on the hyperbranched polyester Boltorn H30. Smooth and transparent films were prepared from both the neat and the nanoparticle-filled hyperbranched resins. X-ray diffraction (XRD) and transmission electron microscopy (TEM) corroborated a mainly exfoliated structure in the nanocomposite films, which was also supported by results from dynamic mechanical analysis (DMA). Furthermore, DMA measurements showed a 9-16 degrees C increase in Tg and a higher storage modulus-above and below the T(g)-both indications of a more cross-linked network, for the clay-containing film. Thermogravimetric analysis (TGA) demonstrated the influence of the nanofiller on the thermal properties of the nanocomposites, where a shift upward of the decomposition temperature in oxygen atmosphere is attributed to the improved barrier properties of the nanoparticle-filled materials. Conventional coating characterization methods demonstrated an increase in the surface hardness, scratch resistance and flexibility, with the introduction of clay, and all coatings exhibited excellent chemical resistance and adhesion.

“ In situ” XPS study of band structures at Cu 2O/TiO 2 heterojunctions interface

In an attempt to investigate influence of the defects on electronic structure of Cu 2O/TiO 2 heterojunctions, thin Cu 2O layers were successively deposited on TiO 2 that has different levels of defect concentrations, and the resultant band bending and offset characteristics were studied by in situ X-ray photoelectron spectroscopy (XPS). The TiO 2 substrates with defects were prepared by Ar + sputtering, followed by annealing at different temperatures in oxygen atmosphere. Presence of the defects in TiO 2 surface dramatically influences on the band bending and band offset at the interface: more defects are on TiO 2 surface, less band bending are at the interface, inducing smaller conduction band offsets. On the reduced TiO 2 surface, Cu 2O was disproportionately decomposed to form CuO and Cu.

Effects of heat-treatment on critical current of BSCCO-2212 superconductor

Bi2Sr2Ca1Cu2Ox (BSCCO-2212) tubes were fabricated by melt and solidification process. BSCCO-2212 powder compact was melted in a resistance furnace using a Pt crucible and poured in a rotating cylindrical mold. The solidified BSCCO-2212 tube samples were heat-treated at various temperatures in oxygen atmosphere. The current–voltage curves at 77K of the samples were obtained by transport measurement, and the microstructure was investigated by scanning electron microscope. It was found that the critical current (Ic) of the BSCCO-2212 samples was dependent on the heating schedule regarding the grain growth of the BSCCO-2212 plates and the formation of the second phase.

Oxygen ion implantation in Strontium Bismuth Tantalate thin films

Strontium Bismuth Tantalate (SBT) ferroelectric thin films have attracted considerable attention for the development of non-volatile ferroelectric random access memories (NV-FRAMs). These films, however, have a critical problem: a high processing temperature ( > 700oC) is required for the crystallization of the perovskite phase. The thermal evolution of the SBT films prepared by Chemical Solution Deposition (CSD) techniques showed the formation of an intermediate oxygen-deficient fluorite phase at ~ 550oC. The SBT perovskite phase crystallizes at higher temperatures. To favor an earlier perovskite crystallization, SBT thin films were implanted with oxygen ions pulses produced by a Plasma Focus (1 kJ). The samples were annealed at different temperatures in oxygen atmosphere and characterized by GI-XRD and Atomic Force Microscopy techniques. It was found that oxygen addition into the SBT structure promotes a better crystallization of the perovskite phase.

Synthesis and Characterization of Hollow and Non‐Hollow Monodisperse Colloidal TiO2 Particles

Monodisperse spherical hollow and non‐hollow titania particles of variable sizes are produced in a sol–gel synthesis from Ti(EtO)4 in ethanol. Hollow spherical particles of rutile were obtained by coating colloidal polystyrene beads with a titanium oxide hydrate layer and subsequently calcination at elevated temperatures in oxygen atmosphere. The non‐hollow titania particles were produced in the presence of salt or polymer solution. The influence of different salt ions or polymer molecules on the size and on the size distribution of the non‐hollow particles was investigated. Nitrogen absorption measurements revealed that the addition of polymers yields porous titania colloids.

Synthesis and characterization of 9.5/65/35 PLZT prepared from the polymeric precursors

The 9.5/65/35 PLZT was prepared from the polymeric precursors (the Pechini and partial oxalate process) and by sintering in two stages in an oxygen atmosphere. After thermal treatment at 400°C, the powders were calcinated and sintered at 1200°C with slow heating and cooling rates. The second stage of sintering consisted of hot pressing at the same temperature in oxygen atmosphere. After calcination of PLZT powders obtained by both methods, as well as after sintering of PLZT obtained by Pechini process, the paraelectric cubic phase was formed. After sintering of PLZT obtained by partial oxalate procedure, small tetragonality of crystal structure was observed. After hot pressing PLZT was pseudocubic. SEM microstructural analyses were carried out of the sintering and hot pressed samples and indicated the small grain size less than 2 μm.

Mechanically induced oxidation of SrFeO 3−δ

The nonstoichiometric strontium–iron oxide SrFeO 3−δ (2.5 ≤ 3 − δ ≤ 3.0) exhibits richness of equilibrium states over a broad range of temperatures and oxygen partial pressures. Its oxidation induced by ball milling was investigated. The mechanical treatment of the material at room temperature in oxygen atmosphere was found to cause the reaction. However, the product differs from compounds obtained by annealing, due to crystal imperfections introduced by milling. The changes in the oxygen stoichiometry, the crystal structure, and the morphology of the powder are discussed.

Effect of oxygen deficiency on the Raman spectra and hyperfine interactions of nanometer SnO 2

The Raman and Mössbauer spectra of nano-SnO 2 specimens with crystallite size 3–16 nm were measured at room temperature. Specimens were annealed at different temperatures in oxygen atmosphere and vacuum respectively. Both the Raman and Mössbauer spectra of the specimens consist of crystalline and interface (or surface) components. The effects of oxygen deficiency on the Raman spectra are presented and correlated with the changes of the Sn-O bond properties, which were obtained from the corresponding Mössbauer spectra.

Structural analysis of superconducting NdBa 1.5Sr 0.5Cu 3o 7−δ

Two samples of NdBa 1.5Sr 0.5Cu 3O 7−δ with δ<0.1, prepared by the solid state reaction, were subjected to two different annealing conditions. Based on Rietveld refinement of powder neutron diffraction (PND) patterns, the occurrence of a single phase with tetragonal symmetry was found for the sample, which was annealed at high temperature in oxygen atmosphere (T-sample). The other sample, which was heated at high temperature in argon atmosphere followed by low temperature annealing in oxygen atmosphere, however, showed coexistence of both orthorhombic and tetragonal symmetries (O/T-sample). Refinement of powder X-ray diffraction data of the T-sample indicated cation disorder between Sr and Nd ions at the ( 1 2 , 1 2 , z ) and the rare earth sites, respectively. The relation to oxygen disorder is discussed. Superconducting transition temperatures, obtained by electrical resistance measurements, were T c ( R = 0) = 83 K and T c ( R = 0) = 71 K for the O/T-and T-sample, respectively. The lower T c for the T-sample is correlated with an elongated bond distance between the Cu(2) ion and apical oxygen.

Effect of quenching on the magnetic properties of RBa 2Cu 3O 7−y (r=rare earth) compounds

The RBa 2Cu 3O 7−y (R = Nd, Sm, Eu, Dy, Ho and Er) compounds have been prepared in the orthorhombic superconducting (SC) form by slow-cooling the samples to room temperature in oxygen atmosphere and in the tetragonal non-superconducting (non-SC) form by fast quenching to liquid nitrogen temperatures. Magnetic susceptibility measurements reveal a slight increase in the susceptibility of the non-superconducting samples over that of the superconducting samples above 100K. This may be due to a small magnetic moment on copper in non-SC samples. Crystal field effects are evident in the susceptibility of some of the non-SC compounds.