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Oxygen Partial Pressure (oxygen + partial_pressure)
Kinds of Oxygen Partial Pressure Selected AbstractsEffect of Oxygen Partial Pressure During Firing on the High AC Field Response of BaTiO3 DielectricsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Ichiro Fujii The effect of oxygen partial pressure during firing on the high field dielectric response of formulated and undoped BaTiO3 ceramics was investigated. For formulated ceramics, the dielectric constant of both oxygen- and air-fired samples increased almost linearly with the amplitude of the ac-driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sublinear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sublinearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move. [source] Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO3 Melt Using an Aerodynamic LevitatorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009Malahalli S. Vijaya Kumar The Yb2O3,Fe2O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10,1 Pa. Two kinds of metastable phases, with space groups of P63cm and P63/mmc, were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced Po2. The crystal structure of the as-solidified samples changed from orthorhombic Pbnm to hexagonal P63cm and P63/mmc with decreasing Po2. X-ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as-solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric,differential thermal analysis (TG-DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb,Fe,O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+, which has an ionic radius larger than that of Fe3+, decreases the tolerance factor and therefore destabilizes the perovskite structure. [source] ChemInform Abstract: Impact of Oxygen Partial Pressure on the Ruddlesden,Popper Series Nd2-2xSr1+2xMn2O7: Oxygen Vacancy Formation and Ordering.CHEMINFORM, Issue 41 2001Julie E. Millburn Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] High-Temperature Stability of Lanthanum Orthophosphate (Monazite) on Silicon Carbide at Low Oxygen Partial PressuresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Michael K. Cinibulk The stability of lanthanum orthophosphate (LaPO4) on SiC was investigated using a LaPO4 -coated SiC fiber at 1200°,1400°C at low oxygen partial pressures. A critical oxygen partial pressure exists below which LaPO4 is reduced in the presence of SiC and reacts to form La2O3 or La2Si2O7 and SiO2 as the solid reaction products. The critical oxygen partial pressure increases from ,0.5 Pa at 1200°C to ,50 Pa at 1400°C. Above the critical oxygen partial pressure, a thin SiO2 film, which acts as a reaction barrier, exists between the SiC fiber and the LaPO4 coating. Continuous LaPO4 coatings and high strengths were obtained for coated fibers that were heated at or below 1300°C and just above the critical oxygen partial pressure for each temperature. At temperatures above 1300°C, the thin LaPO4 coating becomes morphologically unstable due to free-energy minimization as the grain size reaches the coating thickness, which allows the SiO2 oxidation product to penetrate the coating. [source] Heat treatment induced structural and optical properties of rf magnetron sputtered tantalum oxide filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007S. V. Jagadeesh Chandra Abstract Rf magnetron sputtering technique was employed for preparation of tantalum oxide films on quartz and crystalline silicon (111) substrates held at room temperature by sputtering of tantalum in an oxygen partial pressure of 1x10 -4 mbar. The films were annealed in air for an hour in the temperature range 573 , 993 K. The effect of annealing on the chemical binding configuration, structure and optical absorption of tantalum oxide films was systematically studied. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Floating zone growth of CuO under elevated oxygen pressure and its relevance for the crystal growth of cupratesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005G. Behr Abstract CuO single crystals have been grown from the melt by a floating zone method with optical heating at elevated oxygen pressures 3.5 to 5.5 MPa and growth rates as high as 10 mm/h. Melting experiments and recalculated Cu-O phase diagram data show that CuO melts incongruently. The melting temperature increases and the concentration difference between the melt and the CuO phase decreases for rising oxygen partial pressure. Accordingly, increasing the oxygen partial pressure improves the growth process by reducing both the significant oxygen loss during melting as well as the composition difference at the growth interface. The results on CuO provide important information for the crystal growth of more complex cuprates. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Testing a Vapour-fed PBI-based Direct Ethanol Fuel CellFUEL CELLS, Issue 5 2009J. Lobato Abstract This work is focused on the application and performance of a high temperature PBI-based direct ethanol fuel cell, studying the influence of some operating variables such as the temperature, ethanol concentration and oxygen partial pressure. An increase in the temperature resulted in an improvement of the cell performance due to the enhanced electrodic kinetic and electrolyte conductivity. An ethanol/water weight ratio between 0.25 and 0.5 was found to be suitable for providing both enough water and fuel availability to make the ethanol oxidation possible. Measurements of the ethanol crossover at different temperatures and concentrations were carried out. An intermittent lifetime test showed that the cell, after several hours, was able to reach stability. Moreover, its performance was completely reversible with no perceptible losses for 7,days. Finally, tests using bio-ethanol as fuel were performed, with no significant power losses. This final feature is of special interest from a practical ,green' point of view. [source] Fabrication and Electrochemical Properties of Epitaxial Samarium-Doped Ceria Films on SrTiO3 -Buffered MgO SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Simone Sanna Abstract Thin films of samarium-oxide-doped (20,mol%) ceria (SDC) are grown by pulsed-laser deposition (PLD) on (001) MgO single-crystal substrates. SrTiO3 (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite-structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400,775,°C) in a wide range of oxygen partial pressure (pO2) values (10,25,1,atm) in order to separate ionic and electronic conductivity contributions. At 700,°C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7,×,10,2,S cm,1, down to pO2 values of about 10,15,atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation-reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure. [source] Electronic Manifestation of Cation-Vacancy-Induced Magnetic Moments in a Transparent Oxide Semiconductor: Anatase Nb:TiO2ADVANCED MATERIALS, Issue 22 2009Shixiong Zhang Nb-doped anatase TiO2 thin films grown by pulsed-laser deposition show Kondo scattering in elctronic-transport measurements, providing evidence for the formation of magnetic moments. The origin of magnetism is attributed to cation (Ti) vacancies, confirmed by X-ray absorption spectroscopy and first-principle calculations. The Ti vacancies are controlled by oxygen partial pressure during growth. [source] Tribology,Structure Relationships in Silicon Oxycarbide Thin FilmsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010Joseph V. Ryan Silicon oxycarbide is a versatile material system that is attractive for many applications because of its ability to tune properties such as chemical compatibility, refractive index, electrical conductivity, and optical band gap through changes in composition. One particularly intriguing application lies in the production of biocompatible coatings with good mechanical properties. In this paper, we report on the wide range of mechanical and tribological property values exhibited by silicon oxycarbide thin films deposited by reactive radio frequency magnetron sputtering. Through a change in oxygen partial pressure in the sputtering plasma, the composition of the films was controlled to produce relatively pure SiO2, carbon-doped SiC, and compositions between these limits. Hardness values were 8,20 GPa over this range and the elastic modulus was measured to be between 60 and 220 GPa. We call attention to the fit of the mechanical data to a simple additive bond-mixture model for property prediction. Tribological parameters were measured using a ball-on-disk apparatus and the samples exhibited the same general trends for friction coefficient and wear rate. One film is shown to produce variable low friction behavior and low wear rate, which suggests a solid-state self-lubrication process because of heterogeneity on the nanometer scale. [source] Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas BuffersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006Abdul-Majeed Azad High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source] Oxidative degradation of 4-nitrophenol in UV-illuminated titania suspensionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2001Jimmy Lea Abstract An internally-irradiated annular photoreactor has been used to investigate the oxidative degradation of aqueous 4-nitrophenol with titania as the photocatalyst. Reaction runs were performed over a 3-h period and in practically all cases, complete degradation was possible within about 2,h. The kinetics was determined as a function of nitrophenol concentration, oxygen partial pressure, catalyst loading, pH, temperature and light intensity. The reaction was characterised by a relatively low activation energy of 7.83,kJ,mol,1 although transport intrusions were negligible. Rate decreased almost exponentially with pH while a quadratic (maximum) behaviour with respect to both oxygen pressure and nitrophenol concentration is symptomatic of self-inhibition possibly due to the formation of intermediates which competitively adsorb on similar sites to the reactants. Increased catalyst dosage also improved the reaction rate although the possible effects of light scattering and solution opacity caused a drop at loadings higher than about 1.20,g,dm,3. Rate, however, has a linear dependency on light intensity, suggesting that hole,electron recombination processes were negligible at the conditions investigated. © 2001 Society of Chemical Industry [source] Catalytic wet air oxidation of phenol using active carbon: performance of discontinuous and continuous reactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2001Frank Stüber Abstract Catalytic wet air oxidation (CWAO) of an aqueous phenol solution using active carbon (AC) as catalytic material was compared for a slurry and trickle bed reactor. Semi-batchwise experiments were carried out in a slurry reactor in the absence of external and internal mass transfer. Trickle-bed runs were conducted under the same conditions of temperature and pressure. Experimental results from the slurry reactor study showed that the phenol removal rate significantly increased with temperature and phenol concentration, whereas partial oxygen pressure had little effect. Thus, at conditions of 160,°C and 0.71,MPa of oxygen partial pressure, almost complete phenol elimination was achieved within 2,h for an initial phenol concentration of 2.5,g,dm,3. Under the same conditions of temperature and pressure, the slurry reactor performed at much higher initial rates with respect to phenol removal than the trickle bed reactor, both for a fresh active carbon and an aged active carbon, previously used for 50,h in the trickle bed reactor, but mineralisation was found to be much lower in the slurry reactor. Mass transfer limitations, ineffective catalyst wetting or preferential flow in the trickle bed alone cannot explain the drastic difference in the phenol removal rate. It is likely that the slurry system also greatly favours the formation of condensation polymers followed by their irreversible adsorption onto the AC surface, thereby progressively preventing the phenol molecules to be oxidised. Thus, the application of this type of reactor in CWAO has to be seriously questioned when aiming at complete mineralisation of phenol. Furthermore, any kinetic study of phenol oxidation conducted in a batch slurry reactor may not be useful for the design and scale-up of a continuous trickle bed reactor. © 2001 Society of Chemical Industry [source] The potential role of plant oxygen and sulphide dynamics in die-off events of the tropical seagrass, Thalassia testudinumJOURNAL OF ECOLOGY, Issue 1 2005J. BORUM Summary 1Oxygen and sulphide dynamics were examined, using microelectrode techniques, in meristems and rhizomes of the seagrass Thalassia testudinum at three different sites in Florida Bay, and in the laboratory, to evaluate the potential role of internal oxygen variability and sulphide invasion in episodes of sudden die-off. The sites differed with respect to shoot density and sediment composition, with an active die-off occurring at only one of the sites. 2Meristematic oxygen content followed similar diel patterns at all sites with high oxygen content during the day and hyposaturation relative to the water column during the night. Minimum meristematic oxygen content was recorded around sunrise and varied among sites, with values close to zero at the die-off site. 3Gaseous sulphide was detected within the sediment at all sites but at different concentrations among sites and within the die-off site. Spontaneous invasion of sulphide into Thalassia rhizomes was recorded at low internal oxygen partial pressure during darkness at the die-off site. 4A laboratory experiment showed that the internal oxygen dynamics depended on light availability, and hence plant photosynthesis, and on the oxygen content of the water column controlling passive oxygen diffusion from water column to leaves and below-ground tissues in the dark. 5Sulphide invasion only occurred at low internal oxygen content, and the rate of invasion was highly dependent on the oxygen supply to roots and rhizomes. Sulphide was slowly depleted from the tissues when high oxygen partial pressures were re-established through leaf photosynthesis. Coexistence of sulphide and oxygen in the tissues and the slow rate of sulphide depletion suggest that sulphide reoxidation is not biologically mediated within the tissues of Thalassia. 6Our results support the hypothesis that internal oxygen stress, caused by low water column oxygen content or poor plant performance governed by other environmental factors, allows invasion of sulphide and that the internal plant oxygen and sulphide dynamics potentially are key factors in the episodes of sudden die-off in beds of Thalassia testudinum. Root anoxia followed by sulphide invasion may be a more general mechanism determining the growth and survival of other rooted plants in sulphate-rich aquatic environments. [source] Temperature-dependent changes in energy metabolism, intracellular pH and blood oxygen tension in the Atlantic codJOURNAL OF FISH BIOLOGY, Issue 6 2003F. J. Sartoris The effect of acute increase in temperature on oxygen partial pressure (Po2) was measured in the gill arches of Atlantic cod Gadus morhua between 10 and 19° C by use of oxygen microoptodes. Oxygen saturation of the gill blood under control conditions varied between 90 and 15% reflecting a variable percentage of arterial or venous blood in accordance with the position of each optode in the gill arch. The data obtained suggested that arterial Po2 remained more or less constant and arterial oxygen uptake did not become limiting during warming. A progressive drop in venous Po2, however, was observed at >10° C indicating that excessive oxygen uptake from the blood is not fully compensated for by circulatory performance, until finally, Po2 levels fully collapse. In a second set of experiments energy and acid,base status of white muscle of Atlantic cod in vivo was measured by magnetic resonance (31P-NMR) spectroscopy in unanaesthetized and unimmobilized fish in the temperature range between 13 and 21° C. A decrease in white muscle intracellular pH (pHi) with temperature occurred between 10 and 16° C (,pH per ° C = ,0·025 per ° C). In white muscle temperature changes had no influence on high-energy phosphates such as phosphocreatine (PCr) or ATP except during exposure to high critical temperatures (>16° C), indicating that white muscle energy status appears to be relatively insensitive to thermal stress if compared to the thermal sensitivity of the whole animal. The data were consistent with the hypothesis of an oxygen limitation of thermal tolerance in animals, which is set by limited capacity of oxygen supply mechanisms. In the case of Atlantic cod circulatory rather than ventilatory performance may be the first process to cause oxygen deficiency during heat stress. [source] Effects on acid-base balance, methaemoglobinemia and nitrogen excretion of European eel after exposure to elevated ambient nitriteJOURNAL OF FISH BIOLOGY, Issue 3 2002C.-Y. Huang Haemoglobin, methaemoglobin, blood nitrite concentration and acid-base balance were measured in European eel Anguilla anguilla following exposure to 0 (control), 0·142, 0·356, 0·751 and l·549 mM nitrite in fresh water for 24 h. Blood GOT (glutamate oxaloacetate transaminase) and GPT (glutamate pyruvate transaminase) activities and whole animal ammonia-N and urea-N excretions were also measured. Blood nitrite, methaemoglobin, PO2 (oxygen partial pressure), GOT, and whole animal ammonia-N excretion and urea-N excretion increased directly with increasing ambient nitrite concentrations, whereas blood pH, PCO2, and HCO,3 were inversely related to ambient nitrite concentration. An accumulation of nitrite in the blood of A. anguilla following 24 h exposure to elevated ambient nitrite as low as 0·751 mM increased its blood methaemoglobin, PO2, GOT and nitrogen excretion, but decreased its PCO2 (carbon dioxide partial pressure), HCO,3 and functional haemoglobin. [source] Influence of Ca content and oxygen partial pressure on microstructural evolution of (Co,Ca)O at elevated temperaturesJOURNAL OF MICROSCOPY, Issue 1 2006J. KUSINSKI Summary Ca-doped (1, 1.7, 5 and 10 mol% CaO) cobalt oxide single-crystal samples, with an [001] orientation, were annealed at elevated temperatures of 1000,1200 °C for different times and at different oxygen partial pressures. The microstructure was examined by means of transmission light and electron microscopy. High-temperature X-ray diffractometry was used, with the aim of determining the temperature of the CoO , Co3O4 transition in these materials. Extensive precipitation of Ca-free Co3O4 spinel crystals was observed with increasing Ca content and oxygen activity. It is suggested that the electrical conductivity changes in this material may be related to this precipitation, because it changes the electronic state of cobalt cations. [source] Electrical Properties of Gadolinium,Europium Zirconate CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Xiao-Liang Xia (Gd1,xEux)2Zr2O7 (0,x,1.0) ceramics are prepared via a solid-state reaction process at 1973 K for 10 h in air. (Gd1,xEux)2Zr2O7 (0.2,x,1.0) ceramics exhibit an ordered pyrochlore-type structure; however, Gd2Zr2O7 has a disordered defect fluorite-type structure. Raman spectroscopy analysis indicates that the degree of structural ordering increases with the increase of Eu content. The electrical properties of (Gd1,xEux)2Zr2O7 ceramics are investigated using complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz from 623 to 923 K. Electrical conductivity obeys the Arrhenius equation. Both the activation energy and the preexponential factor for grain conductivity decrease with increasing europium content from Gd2Zr2O7 (x=0) to Eu2Zr2O7 (x=1.0). The measured electrical conductivity of (Gd1,xEux)2Zr2O7 ceramics increases with increasing Eu content and temperature. Electrical conductivity of the pyrochlore-type materials is higher than that of the defect fluorite-type material in (Gd1,xEux)2Zr2O7 solid solution systems. The electrical conductivity of (Gd0.4Eu0.6)2Zr2O7 is almost independent of oxygen partial pressure from 1.0 × 10,4 to 1.0 atm. The high ionic transference number of (Gd0.4Eu0.6)2Zr2O7 ceramic at different temperatures proves that conduction is purely ionic with negligible electronic contribution. [source] Effect of Oxygen Partial Pressure During Firing on the High AC Field Response of BaTiO3 DielectricsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Ichiro Fujii The effect of oxygen partial pressure during firing on the high field dielectric response of formulated and undoped BaTiO3 ceramics was investigated. For formulated ceramics, the dielectric constant of both oxygen- and air-fired samples increased almost linearly with the amplitude of the ac-driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sublinear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sublinearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move. [source] Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO3 Melt Using an Aerodynamic LevitatorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009Malahalli S. Vijaya Kumar The Yb2O3,Fe2O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10,1 Pa. Two kinds of metastable phases, with space groups of P63cm and P63/mmc, were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced Po2. The crystal structure of the as-solidified samples changed from orthorhombic Pbnm to hexagonal P63cm and P63/mmc with decreasing Po2. X-ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as-solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric,differential thermal analysis (TG-DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb,Fe,O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+, which has an ionic radius larger than that of Fe3+, decreases the tolerance factor and therefore destabilizes the perovskite structure. [source] High-Temperature Stability of Lanthanum Orthophosphate (Monazite) on Silicon Carbide at Low Oxygen Partial PressuresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Michael K. Cinibulk The stability of lanthanum orthophosphate (LaPO4) on SiC was investigated using a LaPO4 -coated SiC fiber at 1200°,1400°C at low oxygen partial pressures. A critical oxygen partial pressure exists below which LaPO4 is reduced in the presence of SiC and reacts to form La2O3 or La2Si2O7 and SiO2 as the solid reaction products. The critical oxygen partial pressure increases from ,0.5 Pa at 1200°C to ,50 Pa at 1400°C. Above the critical oxygen partial pressure, a thin SiO2 film, which acts as a reaction barrier, exists between the SiC fiber and the LaPO4 coating. Continuous LaPO4 coatings and high strengths were obtained for coated fibers that were heated at or below 1300°C and just above the critical oxygen partial pressure for each temperature. At temperatures above 1300°C, the thin LaPO4 coating becomes morphologically unstable due to free-energy minimization as the grain size reaches the coating thickness, which allows the SiO2 oxidation product to penetrate the coating. [source] Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3 -Based Dielectrics: Part 1.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Defect Energies Under Ambient Air Conditions Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO3 powder samples. Through fabricating the BaTiO3 materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature (T), and oxygen partial pressure (PO2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T. From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO2 partial-Schottky defects (BaTi1,,O3,2,) and the BaO partial-Schottky defects (Ba1,,TiO3,,), and showed discontinuous changes in the two-phase region. The formation enthalpy and entropy for the partial-Schottky defect reactions was evaluated to be 2.32±0.1 eV and 10.15±0.7 kB for the BaO partial-Schottky defect, and 2.89±0.1 eV and 8.0±1.5 kB for the TiO2 partial-Schottky defects equilibrated under air annealing conditions. [source] Titanium Silicon Carbide Pest Induced by NitridationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Haibin Zhang The thermal stability of bulk Ti3SiC2 in high-purity nitrogen was investigated. It was surprising to observe that Ti3SiC2 underwent rapid and catastrophic disintegration above 1300°C, although this material was thermally stable below this temperature. This degradation was unexpected and extremely serious, and has been termed "Ti3SiC2 pest." This phenomenon was related to the volume change associated with the formation of mixtures of TiCx, Ti(C, N)x, and TiN, which caused internal tensile stresses and cracked the resulting layers. "Ti3SiC2 pest" could be prevented by increasing oxygen partial pressure in nitrogen. [source] Effect of Oxygen Partial Pressure During Liquid-Phase Sintering on the Dielectric Properties of 0.9MgTiO3,0.1CaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Hee-Kyun Shin Microstructural evolution and microwave dielectric properties of liquid-phase-sintered 0.9MgTiO3,0.1CaTiO3 dielectric ceramic material have been investigated as a function of oxygen partial pressure () during sintering. Sintering in a weakly reducing atmosphere (=10,14 atm) generally increased the density, permittivity, quality factor (Q×f), and the temperature coefficient of resonance frequency (,f), but further reducing atmosphere down toof 10,14 atm generally decreased Q×f and ,f. When the 5 wt% lithium borosilicate glass-added specimen was sintered at 950°C and=10,14 atm, it demonstrated a permittivity of 18.8, Q×f of 19 000 GHz, and ,f of 10 × 10,6 K,1. [source] Formation of High-Quality, Epitaxial La2Zr2O7 Layers on Biaxially Textured Substrates by Slot-Die Coating of Chemical Solution PrecursorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Sung-Hun Wee Crystallization studies were performed of epitaxial La2Zr2O7 (LZO) films on biaxially textured Ni,3at.%W substrates having thin Y2O3 (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c -axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850°,950°C in flowing one atmosphere gas mixtures of Ar,4% H2 with an effective oxygen partial pressure of P(O2),10,22 atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100°C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures. [source] Processing Dependence of Texture, and Critical Properties of YBa2Cu3O7,, Films on RABiTS Substrates by a Non-Fluorine MOD MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Y. Xu YBa2Cu3O7,, (YBCO or Y123) films on rolling-assisted biaxially textured substrates (RABiTS) were prepared via a fluorine-free metallorganic deposition (MOD) through spin coating, burnout, and high temperature anneal. The effects of substrate texture and surface energy of the CeO2 cap layer were investigated. Except for the commonly accepted key factors, such as the textures of substrate and buffer layers, we found some other factors, for example, the deposition temperature of the cap layer, are also critical to the epitaxial growth of Y123 phase. With the CeO2 cap layer deposited at relative high temperature of 700°C, a critical current density, Jc, over 1 MA/cm2 has been demonstrated for the first time on Ni-RABiTS by a fluorine-free MOD method. Whereas for samples with CeO2 cap layers deposited at a lower temperature of 600°C, even though XRD data showed a better texture on these buffer layers, texture degradations of YBCO grains under the optimized processing conditions were observed and a lower oxygen partial pressure around 40 ppm was necessary for the epitaxial growth of Y123 phase. As a result, Jc fell to 0.45 MA/cm2 at 77 K. The observed phenomena points to the change of surface energy and reactivity of the CeO2 cap layer with respect to the CeO2 deposition temperature. In this paper, the YBCO phase diagram was also summarized. [source] PO2 Dependence of the Diffuse-Phase Transition in Base Metal Capacitor DielectricsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Daniel E. McCauley The diffuse-phase transition in BaTiO3 -based dielectrics for capacitor applications has been studied with respect to its dependence on oxygen partial pressure during sintering. Understanding the mobility of this transition is critical in developing next generation dielectrics for ultra thin (,1 ,m) applications while maintaining the appropriate temperature stability and insulation resistance. Historically, a heterogeneous core/shell microstructure was developed to maintain temperature stability. However, in fired grains of ,250 nm (required for layers ,1 ,m) a well-defined core/shell structure is very difficult to establish. The results from this study demonstrate that careful control of the diffuse-phase transition addresses some of these problems. [source] Solubility of Silver and Palladium in BaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Shao-Ju Shih Silver, palladium, and their alloys are frequently used as electrode materials for BaTiO3 (BT) based dielectrics. However, the electrodes and dielectrics usually are cofired at high temperatures, and silver and palladium can dissolve into the BT during cofiring. In the present study, the solubility of silver and palladium into BT after cofiring was determined. Three measurement techniques were used to determine solubility: chemical analysis, structural analysis, and dielectric analysis. The solubility of the silver in the BT was low, 450 ppm, after cofiring at 1290°C for 2 h in air. The diffusion distance of the silver ions into the BT was >5 ,m. The solubility of the palladium in the BT was even lower, 50 ppm at 1290°C, and the diffusion distance was ,1 ,m. The solubility of both the silver and the palladium in the BT decreased as the oxygen partial pressure of the sintering atmosphere decreased. These results demonstrated that both silver and palladium solutes act as acceptors for BT. [source] Revisit to the Origin of Grain Growth Anomaly in Yttria-Doped Barium TitanateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Jung-Kun Lee In this study, the effect of atmosphere during calcining and sintering of Y2O3 -doped BaTiO3 was investigated to reveal the origin of the anomaly of grain growth and conductivity as a function of Y2O3 content. Samples with various atmospheric histories were prepared. Microstructural and electrical variations were observed using SEM, dielectric (,r vs T) and thermopower measuring techniques, and impedance spectroscopy. An abrupt decrease in grain growth and a transition from semiconducting to insulating behavior were observed when the Y2O3 concentration exceeded 0.3 mol% and the samples were heat-treated in an O2 atmosphere. In contrast, the samples treated under N2+ 5% H2 atmosphere revealed neither grain growth anomaly nor conductivity anomaly even though the Y2O3 concentration was much greater than 3 mol%. The undoped BaTiO3 samples also demonstrated increased average grain size with increased oxygen partial pressure. Therefore, it was suggested that the grain growth anomaly did not result from the formation of cation vacancies V,Ba or V,,Ti. To investigate the origin of the grain growth anomaly, the Curie temperature, concentration of free electrons, and impedance spectra were measured. The grain growth anomaly and conductivity anomaly were associated with abrupt changes in all the measurements. These abrupt changes could be explained by the partial incorporation of donor dopants. Consequently, the origin of the anomaly in the microstructure and electrical properties are discussed in terms of grain-boundary segregation of the donor dopant. [source] Electrical Properties of Cerium-Doped BaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Jin Hyun Hwang The high-temperature equilibrium electrical conductivity of Ce-doped BaTiO3 was studied in terms of oxygen partial pressure, P(O2), and composition. In (Ba1,xCex)TiO3, the conductivity follows the ,1/4 power dependence of P(O2) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P(O2) where electron compensation prevails at low P(O2). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3, indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1,yCey)O3. The Curie temperature (Tc) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter. [source] | ||||||||||||||||||||||||||||||||||