bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deep Level Generation-Annihilation in Nitrogen Doped FZ Crystals
Authors: Abe T. , Harada H. , Ozawa N. , Adomi K. 
Published: March 2011

ABSTRACTNitrogen atoms exist in silicon as non-reactive nitrogen molecules. This is concluded from two I-R absorption experiments: one is the nitrogen isotope effects on N- N pairs and the other is silicon isotope shifts at 10 K. Intrinsic resistivities (over 20 K ohm-cm) are obtained by annealing at 1000°C, 1 min. in N2 in both p- and n-type nitrogen doped thin wafers. Resistivity increases are due to deep- level generations: 0.66 eV above the valence band for p-type and mainly 0.44 eV below the conduction band for n-type material. These deep levels are considered to be formed by nitrogen pairs and divacancies which are incorporated during growth. Since divacancies are easy to out diffuse to the wafers surface, the deep levels are also irreversibly removed. Diffusion coefficient of Si intersititialswici'ch are annihilated with divacancies in the lattice are calculated as 6×10−6cm2/s and 2×10−6cm2/s at 900°C and 1000°C respectively. Migration energy of Si interstitials is about 4.5 eV.
Off-Center N and O in Silicon
Authors: Hjalmarson Harold P. , Jennison Dwight R. , Binkley J. S. 
Published: March 2011

ABSTRACTThe pseudo Jahn-Teller effect and chemical rebonding are both considered as mechanisms that drive substitutional atoms, such as N in Si, off-center. By use of an effective Hamiltonian technique, impurities forming very deep levels, such as Si:N, are found to be susceptible to off-center displacement by the pseudo Jahn-Teller effect. Using a Hartree-Fock technique, we find two classes of N displacements which depend on the relaxation of the nearest-neighbor Si atom “cage”. For outward relaxation of the four nearest neighbors, the N displaces by 0.05 Å in the [111] direction and retains sp3 bonding; this mechanism appears equivalent to the pseudo Jahn-Teller effect. For inward relaxation of the “cage” by 0.45 Å the N displaces by 0.75 Å in the [111] direction and forms a trigonal sp2 bond; this is a chemical rebonding mechanism. Additional cluster calculations suggest that inward relaxation of the “cage” is likely. Similar calculations for 0 revealed a <100> displacement of approximately 1.1Å.
Rheology and Component Interactions in Tape Casting Slurries
Authors: Morris John R , Cannon W Roger 
Published: March 2011

AbstractRheology and the component interactions which affect rheology were studied for a tape casting composition similar to commercial systems. Viscosity measurements at different shear rates were compared to measured tape properties to determine if high or low shear rate rheological behavior controls tape characteristics. Relative viscosity was measured to assess the contribution of each component to the stability of the dispersion.
Kinetics and Mechanisms of Creep in Hot Isostatically Pressed Niobium Carbide
Authors: Nixon Robert D. , Davis Robert F , Bentley James 
Published: March 2011

AbstractConstant compressive stress creep experiments in the temperature and stress ranges of 1730K - 2100K and 16 MN/m2 - 70 MN/m2 on HIPed NbC0.74 have revealed stress exponents of 2.0 under stress levels of 16–54 MN/m2 at all temperatures investigated and 3.2 under stress levels of 54–70 MN/m2 at 1830K. The activation energy of steady state creep is approximately 230 kJ/mol in the temperature range of 1730K - 1930K under 48–54 MN/m and 470 kJ/mol in the temperature range of 1900K - 2100K under 64 MN/m2. TEM of the annealed but uncrept material reveals grown-in dislocation subboundaries. At 1730K and under 34–54 MN/m2, these subboundaries become single dislocations and dipoles. At 1830K and under 54–70 MN/m the subboundaries evolve into simple tilt boundaries which are occasionally knitted, indicating more glide activity at higher stresses. At 1930K and under 34–54 MN/m , hexagonal subboundaries form, but are not as well defined as in the annealed material. At 2100K and under 16–30 MN/m2, the subboundaries are well-defined hexagonal networks which become polygonized under higher stresses on 64 MN/m2. The experimental and TEM results indicate that at low temperatures (below 0.5 Tm = 2073K) and at all stresses, creep occurs by dislocation glide which is accompanied by subgrain and high angle boundary interaction. At high temperature (above 0.5 Tm), strain occurs by glide and subboundary movement; recovery occurs by climb in the subboundary.
The Defect Structure of Yttria Stabilized Zirconia
Authors: Catlow C.R.A. , Chadwick A.V. , Cormack A.N. , Greaves G.N. , Leslie M. , Moroney L.M. 
Published: March 2011

AbstractWe present results of EXAFS and computer simulation studies of the defect structure of yttria-stabilised zirconia. The results are analysed in terms of dopant-vacancy association models for this phase.
Structure of Dislocations and Interfaces in Non-Metallic Crystalline Materials
Authors: Carter C. B. 
Published: March 2011

AbstractThe present understanding of the structure of grain boundaries and phase boundaries in ceramic materials is briefly reviewed with a view to extracting general conclusions on the structure of such interfaces. Examples of experimental studies of grain boundaries in alpha-alumina, spinel and germanium are discussed together with illustrations of the wustite/spinel and sesquioxide/spinel interface. In the oxide systems discussed here, both the grain boundaries and phase boundaries can facet even in the case where the anion sublattice is effectively undisturbed, this observation emphasises the influence of the cations on the selection of the boundary plane.
The Structure of Surface Steps on Low-Index Planes of Oxides.
Authors: Susnitzky D.W. , Simpson Y. Kouh , De Cooman B.C. , Carter C.B. 
Published: March 2011

AbstractSurface steps have been observed on low-index planes of alpha-alumina and spinel. The steps were produced by annealing both bulk and perforated thin foil single crystals. A comparative study of bright-field TEM and dark-field REM of the same crystals makes it possible to construct models for the surface structure. Many faceted steps can be observed on the (0001), {0112}, {1010} and {1120} surfaces of alpha-alumina and on the {100} surface of spinel. A detailed study of step faceting and step facet movement during reheating is presented.
Thermal Expansion Measurements by Photodetector Based Laser Beam Position Change Determination
Authors: Vikram C. S. , Agrawal D. K. , Roy R. , McKinstry H.A. 
Published: March 2011

AbstractA new method for thermal expansion measurements is described. The technique is based on rotation of a laser beam reflected from a probe bar caused by uneven thermal expansions of sample and reference rods. At a distance, the reflected gaussian laser beam is observed with a small photodetector (much smaller than the beam cross-section). The measurement of minute beam position change thus results in related low thermal expansion measurement capability. Experimental arrangement and the sensitivity are described. Some results are also reported.
Synthesis of Metallo-Organic Compounds for Mod Powders and Films
Authors: Vest G.M. , Singaram S. 
Published: March 2011

AbstractThis paper gives the synthesis of several metallo-organic (MO) compounds. The MO compounds have been synthesized so that thermal decomposition produces fine metal oxide powders, or films ⋍0.1 to 0.3 μm thick without going through the powder stage. The Metallo-organic decomposition (MOD) process differs from the SOL-GEL process in that a gel is never formed, and the compound requirements are considerably different. Ferroelectric BaTiO3 and PbTiO3 powders were formed at 600°C and 450°C respectively, which are much lower temperatures than those required by conventional techniques. Defect free tetragonal PbTiO3 films have been formed 1 to 2 μm thick over an area of 1 cm × 1 cm at ⋍470°C, which is 20 to 30°C below its Curie Temperature.
Influence of Transition Metals on The Defect and Optical Properties of Yttrium Aluminum Garnet
Authors: Rotman S. R. , Tuller H. L. 
Published: March 2011

AbstractThe electrical and optical properties of single crystals of Ni, Ni + Zr, and Fe doped Y3Al5O12(YAG) were studied as a function of temperature, atmosphere and composition. The often dramatic changes in properties observed for these materials are interpreted in terms of the underlying defect structure of these materials. Defect formation and migration energies are derived as well as the position of energy states within the gap.
The Application of Transmission Electron Microscopy to the Study of Ti-Diffused Lithium Niobate
Authors: Twigg M. E. , Maher D. M. , Holmes R. J. , Nakahara S. , Sheng T. T. 
Published: March 2011

AbstractTransmission electron microscope studies of Ti-doped, congruent lithium niobate (LiNbO3) have shown that extended structural faults are only present within the Ti diffused layer (i.e. the wave guiding region). Structural faults have not been observed in undoped control crystals of congruent and stoichiometric LiNbO3. Therefore, it appears that the introduction of Ti is responsible for the formation of these defects. The chemical driving forces which may be controlling the formation of structural faults are discussed.Diffraction contrast experiments, which have been interpreted in terms of two-beam dynamical theory for a centrosymmetric crystal, indicate that the faults are tensile in nature (i.e. formed by removing a plane of atoms – so-called intrinsic faults) and have a displacement vector of the type c/12/001] when indexed in the hexagonal coordinate system. That is, the displacement vector is along the c-axis. The detailed crystallographic character of the fault planes is not clear; both (118) and (1 1 12) planes have been confirmed from trace analyses and therefore the fault has a shear component. Additional contrast experiments will be required in order to clarify this feature of structural faults in Ti-doped LiNbO3.Since the extent of these structural faults is tens of microns, they are clearly potential scattering sites for photons. In this regard, a systematic understanding of their origin and thermal stability is crucial to integrated optical device technologies based on LiNbO3 and on the Ti-doped waveguide fabrication technique.
Dilute Aqueous Dispersions of Zro2 And Al2O3
Authors: De Liso Evelyn M. , Cannon W. Roger , Srinivasa Rao A. 
Published: March 2011

AbstractColloidal interactions in a heteroparticulate mixture of zirconia and alumina in water were studied for use in a transformation toughened alumina composite. The microelectrophoresis technique was used to measure the mobility of three zirconia powders and an alumina powder. The electro-phoretic mobility and particle size data were used to calculate total potential energy curves. The maximum height of the total potential energy barrier was used to predict the stability of a zirconia/alumina mixture. Theoretical predictions were compared to experimental results obtained from sedimentation and rheology measurements carried out as a function of pH of the dispersion. For a 5 v/o aqueous zirconia/alumina system stable dispersions were made at pH 3 and pH 5.
Glass Optical Guided-Wave Technology
Authors: Miyashita T. 
Published: March 2011

AbstractRecent advances of glass materials and fabrication processes will be reviewed in the field of guided-wave technology. A variety of optical fibers and guided-wave devices are in development by using high-silica and non-silica glasses. Following the successful development of silica fiber, a new family of optical fibers is being investigated by using non-silica glasses such as fluoride and chalcogenide glasses, which operate at mid-infrared wavelength range and offer the potential of ultra-low loss. High-silica channel waveguides are fabricated by processing a SiO2TiO2 planer waveguide on a silicon substrate. These are applied to various guided wave optical circuits such as switch and wavelength-division multi/demultiplexer, which would be used for the construction of optical communication systems. The materials and processing techniques influencing optical guided-wave performance are described.
Effects of Irradiation on the Electrical Properties of Alpha-Quartz Crystals
Authors: Ling S. , Lim B. S. , Nowick A. S. 
Published: March 2011

AbstractA study is made of irradiation effects on α-quartz crystals using the techniques of electrical conductivity and dielectric loss measurements. The initial radiation-induced conductivity (RIC) induced by X-ray irradiation over the temperature range from 94 to 250 K is found to have a nearly constant activation energy of 0.29 ± 0.02 eV. Since a large RIC still results from irradiation at temperatures too low for alkalis to be liberated, it is proposed that the RIC is due to holes (as small polarons) rather than to alkalis. The dielectric loss measurements in Na-swept quartz are used to follow the changes in the relaxation peaks due to the Al-Na defect as a function of radiation dose and annealing. At the same time a low-temperature “irradiation peak” is studied. Restoration of the main Al-Na peak during annealing occurs in two stages: one near 500 K and the other above 600 K. From the observed behavior of the irradiation peak in various crystals, it is concluded that this peak is probably due to alkali centers. Finally, a defect model interpreting the two annealing stages is presented.
Surface Modification of Sic by Ion Implantation
Authors: Wood Susan , Spitznagel J. A. , Choyke W. J. , Bradshaw J. , Greggi J. , Doyle N. J. 
Published: March 2011

AbstractPredominantly 6H <0001> SiC single crystals have been implanted with nitrogen and aluminum at 300°K. The effects of implantation and post-implantation annealing at 573–1173°K have been characterized by Rutherford backscattering/channeling, microhardness measurements and transmission electron microscopy. Even at 1173°K, defect annealing was inhibited in amorphized regions. Progressive damage recovery as the anneal temperature was increased was otherwise generally observed. Fluences predicted by the critical damage energy of 2 × 1021 keV/cm3 did not quite produce amorphization to x = 0. In the as-implanted specimens, decreasing hardness was observed with increasing fluence. Significant surface softening (∼ 33% hardness reduction) was achieved at the highest aluminum fluence (5 × 1015 Al/cm2) and was stable at temperatures < 893°K.
R-Curve Behavior and The Mechanical Properties of Transformation-Toughened ZrO2-Containing Ceramics
Authors: Steinbrech R. W. , Heuer A.H. 
Published: March 2011

AbstractCurrent understanding of R-curve behaviour and the strength-toughness relationship of transformation-toughened ZrO2-containing ceramics is reviewed. If the toughness increases with crack, extension along an R-curve, a maximum in strength versus toughness is observed, which is related to the crack instability criterion for R-curves. An analytical expression from a well-known “wake” theory of crack tip shielding due to McMeeking and Evans is used to compute R-curves and strength/toughness relations, which are compared with experiment.
Properties of Yttria Stabilized Tetragonal Zirconia Polycrystals
Authors: Matsumoto Roger L. K. , McEntire B. J. 
Published: March 2011

AbstractThe properties of yttria stabilized tetragonal zirconia polycrystalline ceramic fabricated from commercial powders are described. The fracture strength, fracture toughness, density, and low temperature aging effects, are studied for sintered and hot isostatically pressed ceramics. The role of alumina as an additive to the material and its influence on properties is also discussed.
X-Ray Photoelectron Spectroscopy of In-Situ Fractured Reaction Bonded Silicon Nitride
Authors: Donley M. S. , Stoebe T. G. , Thomas M. T. 
Published: March 2011

AbstractThe grain boundary chemistry of reaction bonded silicon nitride (RBSN) and the effects of iron species and content on this chemistry are investigated using X-ray photoelectron spectroscopy (XPS). Data are reported for semiconductor grade RBSN, Fe-doped semiconductor grade RBSN, and metallurgical grade RBSN specimens. Results indicate that the grain boundaries have an elemental composition of Si, N, O, and C, with important chemical differences depending on the purity of the starting material. In the RBSN made from metallurgical grade silicon, the grain boundaries have a distinct “oxide-like” layer, with a subregion of Si3N4. No distinct oxide layer was observed in the RBSN made from semiconductor-grade silicon, where the O appears to be uniformly incorporated into the Si3N4.
Processing and Properties of Reaction Bonded Silicon Nitride Made from Laser Synthesized Silicon Powders
Authors: Haggerty J. S. , Garvey G. , Lihrmann J-M. , Ritter J.E. 
Published: March 2011

AbstractLaser synthesized silicon powders have been used to make reaction bonded silicon nitride samples. Maximum hardness (11.3 GNm−2), fracture toughness (3.6 MNm−3/2), pore size (Hg porosimetry 50–300Å radius) and strength (∼460 MNm−2) values reflect the superior microstructures that are observed. With anaerobic anhydrous processing, these powders nitride to completion in less than 7 hours at 1400°C.
The Hardness Of Ion Implanted Ceramics
Authors: Oliver W. C. , McHargue C. J. , Farlow G. C. , White C. W. 
Published: March 2011

AbstractIt has been established that the wear behavior of ceramic materials can be modified through ion implantation. Studies have been done to characterize the effect of implantation on the structure and composition of ceramic surfaces. To understand how these changes affect the wear properties of the ceramic, other mechanical properties must be measured. To accomplish this, a commercially available ultra low load hardness tester has been used to characterize Al 2O3 with different implanted species and doses. The hardness of the base material is compared with the highly damaged crystalline state as well as the amorphous material.
Clean-Room and Co2-Laser Processing of Ultra High-Purity Al2O3
Authors: Morris P.A. , French R.H. , Coble R.L. , Tebbe F.N. , Chowdhry U. 
Published: March 2011

AbstractClean-room powder processing, furnace firing, and CO2-laser heating techniques to produce high-purity Al2O3 ceramics were applied to a new source of high-purity Al2O3 ( 〉13 ppm total and 〉8 ppm cation detected impurities). The chemical analyses of the material after each stage of processing and firing indicate that the procedures used in this work give no detectable contamination of the material. The microstructure of a CO2-laser ultra high-purity Al2O3 is illustrated. Densification is incomplete for this material. Calcination and deagglomeration were not optimized. Procedures, such as these are required to control the trace impurity contents in a fired ceramic material
Energy Changes During Crack Extension in Compression
Authors: El-Rahman M. , Shrive N. G. 
Published: March 2011

ABSTRACTMuch is known about the tensile fracture, both brittle and ductile: theories are well developed. There is no equivalent theory for compressive failure. A generalized theorem has been developed based on the concept of cohesive strength and the fact that tensile stresses frequently develop around the surface of voids in a material subject to compression. The theory does not produce criteria on critical flaw size. The latter should result from an energy criterion. It is shown, however, that modelling compression cracks as zero width flaws results in no energy change as the crack extends: an anomalous result compared with experimental findings. Allowing compression cracks to have finite width results in strain energy reduction as the ‘crack’ gets larger. A three-dimensional ellipsoid has been used as a model of a compression ‘crack’. Strain energy reduction in the medium, due to the presence of the void, is shown to depend on both its shape and its size. Initial estimates of a compressive G - a compressive energy release rate as the ‘crack’ extends - also suggest a dependence on both size and shape of the cavity. The results indicate further investigation is warranted.
Strain Rate Effects on Concrete and Reinforcements, and their Contributions to Structures
Authors: Takeda Jin-ichi 
Published: March 2011

ABSTRACTThis paper deals with the rate effects on concrete and reinforcements, especially unfavorable effects for the dynamic design of concrete or reinforced concrete structures. The rate effects on concrete are divided into two effects, the rate effect on stress-strain relations and that on fracture criteria of concrete which bringsabout occasionally the unfavorable and brittle fractures of concrete and reinforced concrete structures.It is also described that the brittle fractures are usually caused by the rapid propagation of cracks generated in concrete under the high rate loadings, which can be said to be one of the rate effects on concrete.
Effects of Loading Rate on Cracking of Cement Paste in Compression
Authors: Darwin David , Attiogbe Emmanuel K. 
Published: March 2011

ABSTRACTSubmicroscopic cracking within cement paste is studied for monotonic and short-term sustained loading. Loading times range from 1.25 minutes to 4 hours. Water cement ratios of 0.3 and 0.5 are used. Specimens are loaded to preselected strains and immediately unloaded. The specimens are then sliced with a diamond saw and viewed in a scanning electron microscope. Crack traces are cataloged based on length, width and orientation. The crack traces are converted to three dimensional crack distributions, which are in turn used to determine the degree of softening due to cracking. The results indicate that for loading to a fixed strain, slow loading results in less cracking than rapid loading. However, at the same stress-strength ratio, rapid loading results in fewer cracks. The results indicate that the role of submicroscopic cracking in the nonlinear behavior of cement paste increases with strain rate.
An Impact Damage Model of Concrete
Authors: Kobayashi A. S. , Hawkins N. M. , Du J. J. 
Published: March 2011

ABSTRACTDynamic fracture of two impact loaded, plain concrete, three-point bend specimens was simulated using a dynamic finite element model. A three-segment fracture process zone, which was established in a previous static analysis, together with a tensile overload fracture criterion were used to propagate the crack from the tension side of the unnotched beams. Reasonable agreement between the measured and computed velocities at two points on one beam and estimated and computed average crack velocities was obtained.
Response of Confined Concrete to Cyclic Loading at Various Slow Strain Rates
Authors: Perry S. H. , Al-Shaikh A. H. , Cheong H. K. 
Published: March 2011

ABSTRACTTests have been undertaken in the Imperial College concrete laboratories to study the effect of cyclic loading upon the compressive strength, the stress-strain relationship and the energy absorption and dissipation characteristics of concrete prisms at variable strain rates. Comparison is made with prisms loaded monotonically at similar strain rates. Prisms were confined by high-tensile steel bolts inserted horizontally in two orthogonal directions through pre-formed ducts, and the annular space between ducts and bolts was grouted with high strength epoxy resin. Both steel and concrete deformational response was measured. Significant enhancement of the strength and ductility of the concrete was obtained. Specimens displayed large energy absorption and dissipation capacity under cyclic loading. The validity of an envelope curve to describe cyclic behaviour is discussed.