bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical vapor deposition of superconducting Bi-Sr-Ca-Cu-O films using fluorocarbon-based precursors
Authors: Nemoto Masanori , Yamanaka Mitsugu
Published: September 2007

Superconducting Bi-Sr-Ca-Cu-O thin films have been prepared for the first time by chemical vapor deposition using triphenyl bismuth and fluorocarbon-based chelates such as bis(hexafluoroacetylacetonate)strontium, bis(hexafluoroacetylacetonate)calcium, and bis(hexafluoroacetylacetonate)copper. After annealing in air, x-ray diffraction data reveal that the films deposited on (001) SrTiO3 substrates have preferential orientation of their crystalline c-axis perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of superconductivity at 80 K and zero resistivity at 50 K.
The production of high performance YBa2Cu3O7 using nitrogen dioxide
Authors: Leary Kevin J. , Jacobson Howard W. , Levoy Nancy F. , Lapalomento Richard A. , Askew Thomas R. , Flippen Richard B. , Keller Steven W. , Stacy Angelica M.
Published: September 2007

Energy Dispersive X-ray Spectroscopy (EDS) was used to show that the elemental homogeneity of YBa2Cu3O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen at 950°C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO3)2, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa2Cu3O7.
The chemistry and superconducting properties of species in the system Bi-Ca-Sr-Cu-O
Authors: Arendt R. H. , Garbauskas M. F. , Schilling L. L.
Published: September 2007

Experimental results are presented on efforts to maximize the content of the phase responsible for the 110 K superconducting transition, Bi2Ca2Sr2Cu3O2 or (2223), in the system Bi–Ca–Sr–Cu–O. It was found that the content of this phase depends not only on the initial composition of the reacting mixture, but also on the presence of PbO, the temperature of reaction, and the duration of the reaction.
Crystal chemistry of the compound Sr2Bi2CuO6
Authors: Roth R. S. , Rawn C. J. , Bendersky L. A.
Published: September 2007

The compound Sr2Bi2CuO6 should nominally be the phase with n = 1 of the high Tc superconducting series Sr2Bi2CanO4+2n. However, the superconducting phase with n = 1 (with no CaO) occurs only with a gross deficiency in SrO content. Instead, at the composition Sr2Bi2CuO6, a different phase is formed with an x-ray diffraction pattern considerably different from that expected for the n −1 member of the series. This phase has been found, by a combination of electron diffraction and single crystal and powder x-ray diffraction, to have a commensurate lattice with monoclinic symmetry, space group C2/m or Cm, a = 24.473 (2), b = 5.4223 (5), c = 21.959 (2)A, and β = 105.40 (1)°. The actual composition of this phase may be deficient in CuO by as much as 1.0 mole %.
Influence of oxygen atmosphere on the crystal growth of copper(II) oxide
Authors: Milliken Edward C. , Cordaro James F.
Published: September 2007

Single crystal growth of CuO, synthetic tenorite, was accomplished in oxygen atmosphere by the chemical vapor transport technique. We present the first systematic study of the growth of CuO in various partial pressures of oxygen. Crystals were grown using trace, 0.1, and 0.5 atm partial pressures of oxygen. The growth temperatures used were 820 and 865 °C. Typical dimensions of the crystals obtained were 1 × 2 × 0.25 mm. We have shown that the stoichiometry of single crystal CuO can be controlled during the growth process. The crystals exhibited cation deficient stoichiometry, Cu1−xO, with x increasing from less than 0.005 with no added oxygen, up to 0.05 with 0.5 atm O2 when grown at 865 °C.
Electrocatalysis of Pt-Fe alloys produced by ion beam mixing
Authors: Fernandes M. G. , Thompson D. A. , Smeltzer W. W. , Davies J. A.
Published: September 2007

Ion beam mixing using 120 keV Fe+ ions at doses varying from 3.0 to 20 ⊠ 1015 cm2 was carried out on Pt–Fe bilayer samples over a temperature range from 298 to 523 K to produce alloys of various compositions. The mixing was characterized using Rutherford backscattering with 2 MeV 4He+ ions and transmission electron microscopy. Ion beam mixing and thermal anneals led to grain growth of the polycrystalline films and to formation of Pt3Fe as an alloy phase. At T ≤ 373 K, mixing was athermal and took place by ballistic collisional processes. At T ≥ 473 K, iron migrated rapidly into platinum; the observed activation energy of 0.3 eV suggested that diffusion was of the short-circuit type controlled by lattice vacancy and grain boundary transport. The surface Pt concentration in the mixed films remained high at ∼90 at. %. This resulted in a reduction of ∼25% in the cathodic overpotential compared to pure Fe electrodes for H2 evolution in 30 wt. % KOH solution. An ion beam mixed Pt–Fe surface layer was more stable than Fe coated with evaporated Pt; this is attributed to improved Pt–Fe adhesion as a result of the ion beam mixing process.
Microencapsulation of silicon nitride particles with yttria and yttria-alumina precursors
Authors: Garg Ajay K. , De Jonghe Lutgard C.
Published: September 2007

Procedures are described to deposit uniform layers of yttria and yttria-alumina prccursors on fine powders and whiskers of silicon nitride. The coatings were produced by aging at elevated temperatures aqueous systems containing the silicon nitride core particles, yttrium and aluminum nitrates, and urea. Optimum concentrations of the core particles, in relation to the reactants, were established to promote surface deposition of the oxide precursors. Polymeric dispersants were used effectively to prevent agglomeration of the solids during the microencapsulation process. The morphology of the powders was characterized using scanning and transmission electron microscopy. The mechanisms for the formation of the coated layers are discussed. A description is provided that allows qualitative assessment of the experimental factors that determine microencapsulation by a slurry method.
The instability of polycrystalline thin films: Experiment and theory
Authors: Miller K. T. , Lange F. F. , Marshall D. B.
Published: September 2007

Dense polycrystalline thin films of ZrO2 (3 and 8 mol % Y2O3) were produced by the pyrolysis of zirconium acetate precursor films, which were deposited on single crystal Al2O3 substrates by spin-coating aqueous solutions of zirconium acetate and yttrium nitrate. Dense films were heat treated to encourage grain growth. With grain growth, these films broke into islands of ZrO2 grains. Identical areas were examined after each heat treatment to determine the mechanism that causes the polycrystalline film to uncover the substrate. Two mechanisms were detailed: (a) for a composition which inhibited grain growth and produced a polycrystalline film with very small grains, the smallest grains would disappear to uncover the substrate, and (b) for a composition which did not inhibit grain boundary motion, larger grains grew by enveloping a smaller grain and then developed more spherical surface morphologies, uncovering the substrate at three grain junctions. In both cases, the breakup phenomenon occurred when the average grain size was larger than the film thickness. Thermodynamic calculations show that this breakup lowers the free energy of the system when the grain-size-to-film-thickness ratio exceeds a critical value. These calculations also predict the conditions needed for polycrystalline thin film stability.
Interfacial energy states of moisture-exposed cracks in mica
Authors: Wan Kai-Tak , Aimard Nicholas , Lathabai S. , Horn Roger G. , Lawn Brian R.
Published: September 2007

Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = WE, with G the Griffith mechanical-energy-release rate and WE the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, WE is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.
Is Y1Ba2Cu3O7 stiff or soft?
Authors: Ledbetter Hassel , Lei Ming
Published: September 2007

Using several measured and calculated physical properties, we argue that the high-Tc metal-oxide superconductor Y1Ba2Cu3O7 is elastically soft compared with BaTiO3 or SrTiO3. We conclude that the bulk modulus equals approximately 107 GPa, despite several high-pressure x-ray diffraction studies that report values up to approximately 200 GPa. Part of the argument uses an ionic-crystal-model calculation of the bulk modulus.
Preliminary investigation of a NiAl composite prepared by cryomilling
Authors: Whittenberger J. Daniel , Arzt Eduard , Luton Michael J.
Published: September 2007

An attempt has been made to improve the high temperature mechanical strength of the B2 cubic crystal structure intermetallic NiAl by dispersion strengthening. Prealloyed Ni–51 (at.%) Al was cryomilled with a Y2O3addition to form an yttria dispersoid within the intermetallic matrix. Following milling, the powder was hot extruded to full density and machined into test coupons. Compression testing between 1200 and 1400 K indicated that the cryogenic process yielded the strongest NiAl based material tested to date: creep resistance was six times better than NiAl and twice that of a NiAl particulate composite containing 10 vol.% TiB2. Surprisingly, transmission electron microscopy revealed that the second phase was inhomogeneously distributed. Furthermore, x-ray analysis indicated that the second phase was not Y2O3but rather AIN.
Nucleation of alpha alumina in boehmite gel
Authors: Pach Ladislav , Roy Rustum , Komarneni Sridhar
Published: September 2007

Transformation of boehmitc-derived alumina gel to α–Al2O3 in unseeded gels is strongly influenced by the parent phase, θ-Al2O3. In seeded gels the perfect structure of the epitaxial substrate (α–Al2O3, 0.3 wt. %) influences the surrounding defect θ-phase resulting in (a) fewer imperfections due to lower transformation enthalpy to α–Al2O3, and (b) multiple nucleation sites of α–Al2O3 at the α–Al2O3 seed surface. The rate of transformation expressed for the same number of α–Al2O3 nuclei in unseeded and seeded gels indicates that it is faster in the unseeded gel than in the seeded gel.
An atomic model of crack tip deformation in aluminum using an embedded atom potential
Authors: Hoagland R. G. , Daw M. S. , Foiles S. M. , Baskes M. I.
Published: September 2007

The atomic configuration at the tip of a mode 1 crack in aluminum is modeled by means of molecular dynamics calculations using an embedded atom potential. This potential intrinsically incorporates many-body contributions. This paper is concerned with the characteristics of the atomic displacement fields in comparison to the linear elastic predictions and dislocation emission phenomena. Three crack/crystal orientations are examined in which the crack plane–crack propagation directions are (010)-[100], (10)-[110], and (10)-[111]. The first two models behaved in a brittle fashion as dislocation emission did not occur for reasons associated with the use of periodic boundary conditions parallel to the crack front. For the models which remained atomically sharp, the positions of the atoms near the crack tip in equilibrium configurations are different from the linear elastic predictions but, to first order, retain an r1/2 dependence, with smaller K, and with the origin displaced behind the physical crack tip. This near tip region is also observed to be elastically softer than in the far field. Dislocation emission readily proceeds in the (10)-[111] model by the sequential emission of partials with attendant nonzero uz displacements. The blunting is characterized by the creation of two corner defects that separate as emission occurs and relaxation of the strains in the region initially confronted by the crack tip. Additional features of the results are discussed.
The decay of carbon, luminescence in liquid-encapsulated Czochralski-grown semi-insulating GaAs
Authors: Teh C. K. , Tuszyński J. , Weichman F. L.
Published: September 2007

In undoped liquid-encapsulated Czochralski-grown semi-insulating gallium arsenide (LEC SI GaAs), the carbon acceptor, CAS, is responsible for the ∼1.49 eV emission due to donor-acceptor (D–A) pair radiative recombination. We have studied the effect of different carbon concentrations on the line shape and decay kinetics at and near the D–A emission peak for temperatures ranging from 4.2 to 34 K. The photoluminescence decay has been found to follow a double exponential law at the early stage of the decay but follows a power law of the form L(t)αT−p at a later stage. Analysis of the temperature dependence of the exponential components gives two activation energies of ≃5.7 and ≃15 meV. We find that the 5.7 meV is most likely associated with SiGa shallow donor, while the 15 meV is due to a more indirect process involving an EL2 related donor cluster near 20 meV. The exponent, p, of the power-law decay is found to be both temperature (T) and concentration dependent of the form p = βT −1, where β is a linear function of the concentration of the acceptors, CAs, in the temperature range of 18  T < 30 K. A promising, simplified model based on a continuous set of trapping levels is presented and compared to the experiments. Some aspects of the observed exponential and power law decays are predicted by the theory.
Dependence of the properties of laser deposited tin oxide films on process variables
Authors: Godbole V. P. , Vispute R. D. , Chaudhari S. M. , Kanetkar S. M. , Ogale S. B.
Published: September 2007

In this paper we report the influence of process variables, viz., substrate temperature, oxygen partial pressure, and external electric field bias, on phase precipitation and microstructure of tin oxide films as revealed by small-angle x-ray diffraction and conversion electron Mössbauer spectroscopy.
The effect of ion induced damage on the hardness, wear, and friction of zirconia
Authors: Fleischer E. L. , Hertl W. , Alford T. L. , Børgesen P. , Mayer J. W.
Published: September 2007

Microhardness measurements were carried out on ion implanted single crystal Y2O3 stabilized cubic ZrO2. Inert gas ions (Ne, Ar, Xe) and N, Si, Ti, and W were implanted up to fluences of 3 × 1017 ions/cm2. Implantation energies were selected to give equivalent ranges. Comparison of the Knoop microhardness values of ZrO2 implanted with various species over a range of fluences showed that the principal variable causing hardness changes is damage energy and not the ion fluence nor the ion species. For all implants studied, the hardness versus damage energy gives a unified plot. At low doses the hardness rises with increasing deposited damage energy to a value 15% higher than that of unimplanted zirconia. With additional damage the hardness drops to a value 15% lower than that of the unimplanted zirconia. Friction and wear measurements in a pin-on-disk assembly showed very different behavior for high dose versus unimplanted ZrO2. The unimplanted samples showed debris with an associated rise in friction. The implanted system showed much less debris and a constant value of friction even after 10 000 cycles.
The fate of selected impurities in the recrystallization of zirconium oxychloride and in its conversion to zirconium tetrafluoride
Authors: Sommers James A. , Fahey Jeff V. , Ewing Kenneth J. , Aggarwal Ishwar D.
Published: September 2007

The fate of Fe, Co, Y, and Ce impurities is determined in the process of recrystallization of zirconium oxychloride and in its subsequent fluorination with aqueous hydrofluoric acid to ZrF4 · H2O. Techniques of gamma ray spectrometry were used to follow radioisotopes introduced at critical steps in the process. All impurities remained in the recrystallization liquor. The liquor and its associated impurities, which is retained on the crystals, can be displaced by acid washing. In fluorination, Fe and Co are rejected while Y and Ce are retained and cannot be removed by washing.
Structural and magnetic properties of random mixture graphite intercalation compounds
Authors: Suzuki Masatsugu , Santodonato Louis J. , Yeh Mildred , Sampere Samuel M. , Smith Andrew V. , Burr Charles R.
Published: September 2007

The structural and magnetic properties of the stage 2 CocNi1−cCl2- and COcFe1−cCl2-graphite intercalation compounds (GICs) for 0 ≤ c ≤ 1 have been studied by x-ray scattering and dc magnetic susceptibility. The stage 2 CocNi1−cCl2-GICs approximate two-dimensional randomly-mixed ferromagnets with XY spin symmetry. The average effective magnetic moment Peff, the Curie-Weiss temperature θ, and the paramagnetic-to-ferromagnetic phase transition temperature Tc have been determined as continuously varying functions of Co concentration c. They indicate that the Co2+ and Ni2+ spins are randomly distributed on the triangular lattice sites of each intercalate layer. They also show that the intraplanar exchange interaction J(Co–Ni) between the Co2+ and Ni2+ spins is enhanced and is larger than the interaction J(Co–Co) between two Co2+ spins and J(Ni–Ni) between two Ni2+ spins. This enhanced interaction, J(Co–Ni), can be expressed as J(Co–Ni) = 1.28 [J(Co–Co) · J(Ni–Ni)]1/2. The stage 2 CocFc1−cCl2-GICs approximate two-dimensional randomly mixed ferromagnets with competing spin anisotropy. The dc magnetic susceptibility results suggest that Co2+, Fe3+ rather than Fe2+ are distributed in the intercalate layer. The repeat distance along the c-axis (d-spacing) versus Co concentration deviates from Vegard's law which states that the d-spacing is proportional to Co concentration. The broad peak of d-spacing observed at c = 0.75 is discussed in terms of the double layer model developed by Jin and Mahanti.
Cold-rolling of Ti-rich TiAl polysynthetically twinned crystals
Authors: Nishitani S. R. , Oh M. H. , Nakamura A. , Fujiwara T. , Yamaguchi M.
Published: September 2007

Polysynthetically twinned crystals of TiAl with a nearly stoichiometric composition have been grown and rolled at room temperature. The maximum total reduction in thickness which is attainable without fracture depends on lamellae orientation with respect to the rolling plane and rolling direction. When specimens are oriented such that shear deformation parallel to the lamellar planes is operative during rolling and its operation causes lengthening of specimens, such specimens can be rolled up to about 50% reduction in thickness. The (111) pole figures are determined for the surface of specimens rolled to several different amounts of reduction, and the formation of surface texture is briefly discussed.
Preparation and characterization of laser-ablated multicomponent chalcogenide thin films
Authors: Islam Didarul , Brient C. E. , Cappelletti R. L.
Published: September 2007

The preparation of multicomponent chalcogenide glassy thin films from bulk targets by laser ablation is described. The film stoichiometries are characterized by proton-induced x-ray emission (PIXE). Compared to single source thermal evaporation, laser ablation is found to preserve starting stoichiometries in the resulting thin films far more accurately. Thermally evaporated films were studied both by PIXE and by energy dispersed x rays (EDX) produced in a scanning electron microscope, and the results of these two analytical techniques compare well.
Indentation fracture of lead magnesium niobate-based multilayer composite structures
Authors: Megherhi M. H. , Dayton G. O. , Shrout T. R. , Mecholsky J. J.
Published: September 2007

The effects of internal electrodes on the fracture properties of relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3multilayer structures were studied. It was observed that the position of the first electrode layer from the surface is critical to the strength and toughness of the multilayer structure. Positioning the electrode close to the surface was found to enhance interaction with cracks which initiate on the multilayer surface. This interaction limits the effective crack length and therefore increases the fracture strength and effective toughness of the composite. Samples indented parallel to the electrodes exhibited higher fracture strengths and toughness than those indented perpendicular to the conducting layers. Both parallel and perpendicular orientations gave higher strength and toughness than the control specimens (without electrodes).
Mechanics modeling using a spring network
Authors: Curtin W. A. , Scher H.
Published: September 2007

A simple spring network model is utilized to investigate stress concentrations and toughness increases for a variety of traditional mechanics problems. The scaling of crack-tip stress with crack size and separation, the shielding due to a low modulus process zone, and the toughness increase from microcracking and transformation process zones are all in good agreement with available analytic or numerical mechanics results. Also, the, process zone growth and attendant R-curve behavior for microcracking and/or transformation toughening is simulated directly using the network model with only a few simple rules. The network model is thus expected to be useful for obtaining easy quantitative results for related problems which are not so easily solved by other means. In addition, the good agreement found here supports the use of the network model for studying problems involving distributed disorder, as discussed in the previous paper.
Composition analysis of thin AlxGa1−xAs layers with TEM and SIMS
Authors: de Jong A. F. , Janssen K. T. F.
Published: September 2007

In this paper two methods for measuring aluminum compositions in very thin (1.5–15 nm), individual AlxGa1–xAs layers are investigated. The transmission electron microscopy (TEM) thickness-fringe method uses the bright-field extinction fringes from a small, cleaved 90° wedge imaged in a [100] orientation. By comparing calculated and experimental extinction fringes, compositions are determined with a sensitivity in x of 0.03, in layers with a thickness of 3.5 nm. With secondary ion mass spectrometry (SIMS), compositions in AlxGa1–xAs layers with a thickness of 15 nm are measured with an accuracy in x between 0.02 and 0.05. Thicker layers (1 μm) with a composition known from x-ray diffraction measurements are used as a reference for both methods. Subsequently, TEM results are compared with SIMS and the reference measurements. The overall agreement is good, but for 0.25 < x < 0.65, the values of x found by TEM are systematically 0.05 too low. Using the SIMS and reference measurements as a calibration, compositions can be determined by TEM with an accuracy between 0.03 (low x) and 0.05 (high x) in layers as thin as 1.5 nm.
Possible evidence for overcoordination at semiconductor grain boundaries
Authors: Krakow W. , Levi A. A. , Pantelides S. T.
Published: September 2007

The structure of a near coincidence Ge tilt grain boundary, containing a step, has been derived from a high resolution electron micrograph. There are two possible interpretations of portions of this interface, one of which is the existence of a sheet of fivefold coordinated atoms between the Σ = 19 and Σ = 27 coincidence misorientations. This finding may represent the first experimental evidence that overcoordinated atoms are present at semiconductor grain boundaries free of a screw dislocation.
Homogeneous fabrication and densification of zirconia-toughened alumina (ZTA) composite by the surface-induced coating
Authors: Jang Hyun M. , Moon Jong H.
Published: September 2007

This article proposes a new scheme for fabricating homogeneous Al2O3–ZrO2 composite, in which a thermodynamic theory of interfacial electrochemical phenomena is applied. The theory predicts that a heterogeneous Al2O3 interface in colloidal dispersion can induce an enhanced concentration of the ionic species needed for a selective formation of the ZrO2 precursor at the Al2O3/aqueous solution interface. Based on this proposition, a homogeneous Al2O3–ZrO2 composite powder was fabricated by a surface-induced coating of the fine ZrO2 precursor on the kinetically stable colloid particles of Al2O3. The composite prepared by the surface-induced coating was characterized by a uniform spatial distribution of the dispersed ZrO2 phase and by the absence of large ZrO2 grains formed from hard ZrO2 agglomerates. The composite also showed highly uniform grain size distribution of both the dispersed ZrO2 and the matrix Al2O3 phases. The uniform grain size distribution of the matrix phase indicates that the homogeneous coating of the fine ZrO2 particles is effectively pinning the Al2O3 grain boundaries.
Dispersion and consolidation of silicon nitride whisker in aqueous suspension
Authors: Hirata Yoshihiro , Nakagama Susumu , Ishihara Yoshimi
Published: September 2007

Characteristics of aqueous silicon nitride whisker suspension and the packing nature of whiskers during consolidation (sedimentation or filtration) were investigated in order to control the microstructure and density of a whisker compact. Silicon nitride whiskers (average size 0.4 μm × 3.7 μm) coated by SiO2 film were well dispersed at pH 10.5 due to the strong repulsion force among negatively charged whiskers. Low viscosity suspension of highly charged whiskers showing Newtonian behavior formed a dense whisker compact with a narrow pore size distribution of small pores. The density increase of green compact was accompanied by the orientation of whiskers where the direction in length of whiskers was perpendicular to the direction of filtration. Application of an external pressure (isostatic pressing) to porous whisker compacts consisting of network structure of randomly packed whiskers or whiskers of low orientation increased the green density.
Production of hydroxyapatite-glass compacts by hydrothermal hot-pressing technique
Authors: Yamasaki N. , Yanagisawa K. , Kakiuchi N.
Published: September 2007

Low-temperature sintering (under 350°C) of hydroxyapatite was attempted by a hydrothermal hot-pressing technique. The effects of borosilicate glass addition on the characteristics of the solidified body (mechanical strength, microstructure, crystal structure, pore distribution, etc.) and on the densification process during hydrothermal reaction were investigated. The borosilicate glass increased the mechanical strength of the solidified body; compression of 50% content of apatite was 2100 kg/cm2. It is also shown that water acts as a good catalyzer during solidification under hydrothermal conditions, and micropores can increase toughness of the solidified body due to the adsorption of stress. These hydrothermal hot-pressing solidification processes are so similar to sintering with liquid phase under pressure that the initial kinetics was discussed by means of the velocity measurement of shrinkage rate. In addition, these reactions may proceed in water, and are then discussed from the point of view of a heterogeneous reaction between powder and aqueous solution. It was proposed that the solidification process was due to viscous flow with rearrangement of grains in the solidified body, and the rate-determining step followed a core model of extraction from solid to solution.
Substrate bias effects during R-F sputtering of Y-Ba-Cu-O films
Authors: Drehman A. J. , Dumais M. W.
Published: September 2007

Y-Ba-Cu-O films were made by R-F diode sputtering using a single oxide target. It was found that if a small negative bias is applied to the substrate, the etching associated with reactive sputtering is significantly reduced. This results in better composition control and uniformity, which are quite important for the formation of superconducting thin films. Films deposited on strontium titanate, when annealed in oxygen, become superconducting with zero resistance at 89 K.
Preparation of small particle stabilized zirconia by aerosol pyrolysis
Authors: Pebler A. R.
Published: September 2007

Yttria stabilized zirconia powder was synthesized by aerosol pyrolysis of an Y-Zr-nitrate solution. The particles were spherical and had a narrow size distribution, peaking at 0.4 μm. Material made by this process is phase-pure (cubic) and has high chemical purity.
SEM and electrical studies of current induced superconducting-resistive transitions in Y1Ba2Cu3O7−x thin films
Authors: Frenkel A. , Chang C. C. , Clausen E. , Venkatesan T. , Lin P. S. D. , Wu X. D. , Inam A. , Lalevic B.
Published: September 2007

We studied the electrical current induced superconducting-resistive transitions in laser deposited c-axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films. Comparative studies of I-V characteristics of thin film bridges with different geometries at temperatures below Tc and SEM voltage imaging of current induced resistive regions in the same samples were performed. The I-V curves of these bridges had two nonlinear regimes, a gradual and an abrupt transition to the normal state. We concluded that the gradual nonlinear transition is caused by imperfections in the sample such as film and substrate defects, film thickness variation, etc., and by dissipative effects such as flux motion and superconductor/normal-metal/superconductor type behavior. The abrupt transition to the normal state in the I-V curve is ascribed to Joule heating. The SEM mapping provides a direct image of the above effects and is useful for material or device characterization and for studying the transport properties of high Tc films.
Flexible stainless steel foil as a substrate for superconducting Y-Ba-Cu-O films
Authors: Witanachchi S. , Patel S. , Zhu Y. Z. , Kwok H. S. , Shaw D. T.
Published: September 2007

As-deposited superconducting Y-Ba-Cu-O films have been grown on stainless steel substrates by the plasma assisted laser deposition technique. Low interfacial diffusion of iron at the 550°C growth temperature enables us to produce superconducting films with critical temperatures up to 83 K and critical currents up to ∼4 × 103 A/cm2 (40 K). Dependence of the superconducting properties of the Y-Ba-Cu-O films on the surface condition of the mirror finished stainless steel substrate has been studied. Critical temperature and critical current of the films have been improved by heat-treating the substrate and incorporating buffer layers. Variation of the critical current with the bend radii of the film is discussed.
Solid-state reaction of Ru powder in molten AlxBi1−x
Authors: Johnson R. W. , Garland C. M.
Published: September 2007

We describe a low-temperature solid-state interdiffusion technique that allows reaction between spatially separated reacting species and its application in the Al–Ru alloy system. This technique uses a liquid-metal solvent (Bi) as a medium for the transfer of Al to the surface of Ru powder where reaction occurs with the formation of nanocrystalline AlxRu1−x product phases. X-ray diffraction measurements are used to follow the time and temperature dependence of the reaction. Cross-sectional transmission electron microscopy allows direct imaging of the growth and morphology of the AlxRu1−x product phases.
Brittle fracture and grain boundary chemistry of microalloyed NiAl
Authors: George E. P. , Liu C. T.
Published: September 2007

The room-temperature tensile properties, fracture mode, and grain boundary chemistry of undoped stoichiometric NiAl, as well as NiAl doped with boron, carbon, and beryllium, have been investigated, Pure, stoichiometric NiAl fractures with limited tensile ductility in a predominantly intergranular manner. Auger analyses revealed that the grain boundaries in NiAl are extremely clean and free of any segregated impurities, indicating that they are intrinsically brittle. Boron, when added to stoichiometric NiAl at a bulk level of 300 wt. ppm, segregates to the grain boundaries and suppresses intergranular fracture. However, there is no attendant improvement in tensile ductility because boron is an extremely potent solid solution strengthener in NiAl, more than doubling its yield strength. As a result, any potential benefit of improving grain boundary strength is more than offset by the increase in yield strength. Unlike boron, both carbon (300 ppm) and beryllium (500 ppm) are ineffective in suppressing intergranular fracture in NiAl, and Auger analyses of the C-doped alloy revealed that carbon did not affect the fracture mode because it did not segregate to the grain boundaries. Although neither beryllium nor carbon suppressed grain boundary fracture, their effects on the tensile ductility of NiAl were quite different: the ductility of the Be-doped alloy was higher than that of the B-doped alloy because beryllium, unlike boron, has a rather modest strengthening effect in NiAl, whereas the C-doped alloy was brittle like the B-doped alloy, because carbon is a potent solid solution strengthener, just like boron. These observations were rationalized by considering a hard-sphere model for interstitial and substitutional sites in NiAl. It was concluded that boron and carbon occupy interstitial sites, whereas beryllium dissolves substitutionally. In all the alloys that were investigated, the Ni and Al contents of the grain boundaries were not significantly different from the bulk levels, and no evidence was found for B–Ni cosegregation.
The location of tantalum atoms in Ni3(Al, Ta)
Authors: Lin Hui , Pope David P.
Published: September 2007

An x-ray powder diffraction method was used to determine the location of tantalum atoms in Ni3Al. A series of Ni3(Al, Ta) alloys were produced with tantalum contents ranging from 0.1 to 3.0 at.%. Fine powders with average particle sizes less than 80 μm were made from melt-spun ribbons by a grinding process. The values of the intensity of the (100) superlattice peak normalized to that of the (200) fundamental peak as a function of tantalum content agreed with the calculated values, assuming that tantalum atoms substitute on aluminum sites, not on nickel sites, and also assuming small amounts of anti-site defects exist in the ordered fee structure of Ni3(Al, Ta) alloys. It is concluded from our experiments that tantalum atoms substitute for aluminum in Ni3Al. The long-range order parameters thus calculated of the Ni3(Al, Ta) alloys are generally above 0.84 and below 0.95, except for Ni75Al24.8Ta0.2, at which composition the long-range order parameter is close to unity.
Evolution of the microstructure of cobalt during diffusionless transformation cycles
Authors: Munier A. , Bidaux J. E. , Schaller R. , Esnouf C.
Published: September 2007

Differential scanning calorimetry and transmission electron microscopy have been used to study thermal fatigue due to diffusionless phase transformation cycling in pure cobalt. Thermal cycling through the allotropic (hcp ↔ fcc) transformation results in a temperature shift of the calorimetric peaks, which means a delay of the transformation. In addition, the transformation enthalpy, which is greater on heating than on cooling, diminishes when the number of transformation cycles increases. This is interpreted as being due to an evolution of the microstructure. Transmission electron microscopy shows the appearance of transformation-induced defects, which are mainly sessile dislocations. We can interpret the calorimetry results (enthalpy evolution and transformation delay) as due to the interactions between interface dislocations and these sessile dislocations.
Transmission electron microscopy studies of bismuth films
Authors: Nahm S. , Salamanca-Riba L. , Partin D. L. , Heremans J.
Published: September 2007

We have studied the structure of Bi films grown on BaF2 substrates as a function of the distance from the interface with the substrate. Close to the interface the films show a polycrystalline structure and probably contain some amorphous regions. The crystallite size increases as the distance from the interface increases. At distances ≥90 nm the film becomes single crystalline and has the (111) trigonal direction normal to the film surface. Our structural data relate very well to mobility measurements performed on samples grown under the same conditions. Our results suggest that the carrier mobility is higher at distances ≥90 nm from the interface, where the film is single crystalline, than close to the interface, where it is polycrystalline.
Electrical performance and reaction kinetics of silicone gels
Authors: Wong C.P.
Published: September 2007

Silicone gels are becoming more accepted as protective coatings for Very Large Scale Integrated circuits (VLSI) against severe environments due to their excellent electrical, thermal, and mechanical properties. Recent studies indicate that high performance silicone gels in low-cost, non-hermetic plastic packaging may replace conventional hermetic ceramic packaging. This paper describes the use of the soft silicone gels as coatings on Integrated Circuit (IC) devices, and the correlation between the material's cure temperature and cure time versus their adhesion and electrical reliability during 85°C, 85% RH and bias accelerating testing. In addition, the reaction kinetics of the silicone gel based on the Differential Scanning Calorimetry (DSC) study of the uncured sample will be reported.
Electron microscopy of vapor phase deposited diamond
Authors: Williams B.E. , Kong H.S. , Glass J.T.
Published: September 2007

Thin carbon films grown from a low pressure methane-hydrogen gas mixture by microwave plasma enhanced CVD have been examined by electron microscopy. Previously reported transmission electron microscopy (TEM) of the diamond films has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. In this study, high resolution electron microscopy (HREM) has been utilized to lattice image individual defects in these polycrystalline diamond films. Interpretation of the images from these defects is not trivial and reported image simulations have been utilized to understand further these defects. Fivefold multiply twinned particles have also been examined and it was found that the 7.5° misfit present in such particles has been accommodated at the twin boundaries rather than by elastic deformation. This creates a twin boundary coincident with a low angle grain boundary which has been termed a “tilted twin boundary”. The density of defects in these particles is generally high; however, a dramatic reduction in the defect density near the twin boundaries was observed. This defect reduction is significant because if its origin can be determined, this information may be useful in producing higher quality diamond films.
Temperature and reactive etching effects on the microstructure of microwave plasma deposited diamond films
Authors: Harker Alan B. , DeNatale Jeffery F.
Published: September 2007

In the microwave induced plasma deposition of diamond from methane-hydrogen-oxygen mixtures, the variables available for controlling the microstructure of the resulting films are the plasma composition and density, the substrate surface properties, and the temperature. It has been demonstrated that the competition between nucleation site formation and the rate of reactive plasma etching is the critical feature in the development of the film microstructure on silicon substrates. On diamond substrates, the favorable lattice match dominates and homo-epitaxial films are formed over a wide temperature range. Raman scattering studies also demonstrate that the reactive etching of the diamond surface by oxygen-containing species is critical to the removal of non-diamond carbon species over the temperature range 450–1050 °C.
Microstructure and conversion electron Mössbauer studies of M decrease in Fe3O4 films
Authors: Ortiz C. , Hwang C. , Morrish A. H. , Zhou X. Z.
Published: September 2007

This paper analyzes the influence of the deposition conditions (substrate temperature and oxygen flow) on the magnetic moment of Fe3O4 films grown by reactive RF sputtering. With conversion electron Mössbauer spectroscopy and transmission electron microscopy of specific microstructures we have identified different mechanisms which can contribute to the decrease of M in our samples: decrease of average grain size (superparamagnetism) and distortion of the lattice which may induce mispopulation of tetrahedral and octahedral sites and decrease of crystalline quality.
MASS-NMR structural analysis of barium aluminofluorophosphate glasses with and without nitridation
Authors: Fletcher Joseph P. , Risbud Subhash H. , Kirkpatrick R. James
Published: September 2007

The local structure of barium-aluminofluorophosphate (Ba–Al–P–O–F) glasses was investigated using high resolution magic-angle sample spinning nuclear magnetic resonance (MASS-NMR) spectroscopy. The 27Al spectra show three different aluminum environments [Al(4), Al(5), and Al(6)] in these glasses. Changes were observed due to the addition of fluorine and nitrogen. 31P results indicate only one type of phosphorus environment which shifts with fluorine additions. The 19F spectra suggest that fluorine has both Ba and Al as nearest neighbors.
Sol-gel processing of strontium-barium niobate ferroelectric thin film
Authors: Xu Ren , Xu Yuhuan , Chen Ching Jih , Mackenzie John D.
Published: September 2007

Ferroelectric thin film of strontium-barium niobate was successfully fabricated by the sol-gel technique. The films were made on several types of substrate, including quartz, single crystal silicon wafer, and glass slides. The processing temperature was as low as 700 °C. The film obtained with thickness of 3000 Å was dense, transparent, and showed excellent ferroelectricity.
Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries
Authors: Babcock S. E. , Larbalestier D. C.
Published: September 2007

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.
Equilibrium phase diagram for the system PbO-CaO-CuO
Authors: Kitaguchi Hitoshi , Takada Jun , Oda Kiichi , Miura Yoshinari
Published: September 2007

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb-Sr-Ca-Cu-O system, phase equilibria in the system PbO-CaO-CuO have been studied, mainly by x-ray diffraction analysis and thermal analysis. Temperature versus composition diagrams were established for the systems PbO-CuO(Cu2O) and PbO(PbO2)–CaO in air. Three invariant points were detected in these systems: a eutectic reaction (PbO + Ca2PbO4 = L) at 847 ± 6°C, a peritectic reaction (Ca2PbO4 = L + CaO) at 980 ± 2°C, and a eutectic reaction (PbO + CuO = L) at 789 ± 3°C. For the system PbO(PbO2)-CaO-CuO, subsolidus phase equilibrium in air was established. The liquidus was also examined at 780, 800, and 820°C, and a ternary (PbO-Ca2PbO4-CuO) eutectic point was detected at 772 ± 6°C.
Effect of an oxide dispersion on the hydrogen embrittlement of a Ni3Al base alloy
Authors: Camus G.M. , Duquette D.J. , Stoloff N.S.
Published: September 2007

The susceptibility of a hot isostatically pressed Ni3AI, Cr, Zr alloy to hydrogen embrittlement has been studied. The base alloy and a second alloy containing 5 vol. % Y2O3 particles were tested by cathodically charging with hydrogen prior to or simultaneously with tensile testing. Embrittlement of both alloys was noted under both charging conditions, but was much more severe for simultaneous charging. Intergranular fracture due to hydrogen was noted in the base alloy, while the dispersoid-containing alloy failed along prior particle boundaries. The results are explained by a dislocation transport mechanism in which hydrogen is delivered to interior fracture sites by mobile dislocations. Much greater penetration of hydrogen is achieved under simultaneous charging conditions.
Room-temperature epitaxy of Cu on Si(111) using partially ionized beam deposition
Authors: Bai P. , Yang G-R. , You L. , Lu T-M. , Knorr D.B.
Published: September 2007

The epitaxial growth of Cu on Si(111) substrate at room temperature was achieved using the Partially Ionized Beam (PIB) deposition technique in a conventional (10−4 Pa) vacuum without prior in situ cleaning of the substrate or post-annealing of the film. The beam contained ≍2% of Cu self-ions, and a bias of 0 to 4.2 kV was applied to the substrate during deposition. X-ray diffraction studies showed the existence of a twin structure in the epitaxial Cu layer deposited at 1 kV. A mechanism of epitaxial growth of Cu(111) on Si(111) substrate via an η″—Cu3Si intermediate phase is proposed. Based on the crystal structure of η″—Cu3Si, it is demonstrated that the geometrical lattice matching concept provides a simple picture of lattice continuity at the interface in this epitaxial system.