bluuebunny/crossref_metadata_2025 huggingface dataset:
A photoluminescence technique for characterizing the GaInAsP channeled substrate buried heterostructure wafer for lasing wavelength
Authors: Swaminathan V. , Green C. A. , Huo D. T. C. , Brelvi M.
Published: September 2007

A photoluminescence technique to characterize, for lasing wavelength, the channeled substrate buried heterostructure wafer grown for fabricating lasers for undersea transmission applications, is described. The technique consists of photopumping a piece from the as-grown wafer at 80 K to achieve lasing action and determining the lasing wavelength at 300 K after correcting for the temperature shift of the bandgap. By comparing the optically determined wavelength against the lasing wavelength measured on the device, the accuracy of the technique to predict wavelength is found to be ± 20 nm. The factors that limit the accuracy are discussed.
Ion implantation in β-SiC: Effect of channeling direction and critical energy for amorphization
Authors: Edmond J. A. , Davis R. F. , Withrow S. P. , More K. L.
Published: September 2007

Damage in single-crystal β-SiC(100) as a result of ion bombardment has been studied using Rutherford backscattering/channeling and cross-section transmission electron microscopy. Samples were implanted with Al (130 keV) and Si (87 keV) with doses between 4 and 20 × 1014 cm−2 at liquid nitrogen and room temperatures. Backscattering spectra for He+ channeling as a function of implantation dose were initially obtained in the [110] direction to determine damage accumulation. However, the backscattered yield along this direction was shown to be enhanced as a result of uniaxial implantation-induced strain along [100]. Spectra obtained by channeling along this latter direction were used along with the computer program TRIM to calculate the critical energy for amorphization. The results for amorphization of β-SiC at liquid nitrogen and room temperature are ∼ 14.5 eV/atom and ∼ 22.5 eV/atom, respectively.
Preferential leaching and natural annealing of alpha-recoil tracks in metamict betaflte and samarskite
Authors: Lumpkin G. R. , Ewing R. C. , Eyal Y.
Published: September 2007

Leaching experiments on naturally occurring, metamict betafite and samarskite minerals in a bicarbonate-carbonate solution show strongly enhanced release to the solution of short-lived 228Th relative to its parent isotope 232Th (by a factor of 3 to 6), but only slightly enhanced dissolution (by a factor of 1.2 to 2) of long-lived 234U and 230Th relative to 238U and 232Th, respectively. The betafite (a complex Ca–U–Ti–Nb oxide of the pyrochlore group, A2−mB2X6Y0−1.H2O) and samarskite (a complex Y–Fe–U–Nb oxide with varying stoichiometry between AB O4 and AB2O6) are x-ray and electron diffraction amorphous having experienced doses of 2.2–2.8 × 1017 alpha-decay events/mg (24–31 dpa) and 3.8–4.4 × 1017 alpha-decay events/mg (39–45 dpa), respectively. The isotopic fractionation is attributed to the radiation damage created by the alpha-decay events. Individual alpha-recoil tracks are preserved for some time as disordered regions of higher chemical reactivity in already fully damaged, aperiodic areas that result from the alpha-decay events. The annealing time of the alpha-recoil track within the aperiodic atomic array of the metamict state is calculated to be 29 300 ± 8100 years for samarskite and 42 700 ± 13 700 years for the betafite. These data plus data on an earlier studied betafite sample (annealing time = 2000 ± 1300 years) give an average annealing time of 25 000 ± 21 000 years. The variation in calculated annealing time is due, in part, to post-metamict alteration of the sample, particularly for the betafite. The wider range of values for the betafite is attributed to its greater degree of alteration. These results demonstrate that recoil nuclei of alpha-decay events may be selectively leached from damaged, aperiodic phases, but that these tracks are subject to low-temperature annealing in short periods of time relative to the age of the samples (∼ 500 m.y.). The same phenomena are expected in actinide-containing nuclear waste form glasses.
Mechanisms of ductility improvement in L12 compounds
Authors: Izumi Osamu , Takasugi Takayuki
Published: September 2007

The present article first describes some characteristics of structure, chemistry, and electronic (bond) nature for grain boundaries in the A3B Li2-type intermetallic compounds. Next, the phenomenological aspects for the grain boundary brittleness of the Li2-type intermetallic compounds are reviewed with respect to the combination of the constituent atoms, the alloying effect, the stoichiometry effect, and a role of impurity or gaseous atoms. It is emphasized that the brittleness of grain boundaries in the intermetallic compounds is directly controlled by the atomistic and electronic structures at grain boundary regions. Based on these systematic investigations, it is suggested that the brittleness of the Li2-type intermetallic compounds can be manipulated by appropriate control of composition and the corresponding electrochemical bond environment at grain boundary planes and by control of test environment. Furthermore, some examples of the materials development are described.
Stochastic model of staging in graphite intercalation compounds
Authors: Miyazaki Hiroshi
Published: September 2007

A stochastic model is presented for staging transitions in graphite intercalation compounds. Three types of kinetic processes are introduced into the domain model of Daumas and Herold, and a one-dimensional Monte Carlo simulation is carried out within the framework of a single-column model to study the time evolution of the system for a variety of cases of staging transitions. Results of Monte Carlo simulations from stage 3 to stage 2 after a sudden change of chemical potential show that the staging transition depends sensitively on the final value of the chemical potential μf, temperature of the system, and the kinetic coefficients. When μf is taken in a certain range in the phase diagram, the time evolution of the structure factor demonstrates the coexistence and no significant broadening of peaks corresponding to the initial and final stage states. For other values of μf, it is observed that the staging transitions proceed via disordered states and in some cases the final states are also disordered. Similar results are obtained for staging transitions from stage 4 to stage 3. Simulations are also made for staging transitions in which the start is from stage 4 and suddenly μ changes to a value in the stage-2 stable region. It is found that the system transforms either directly into a stage-2 state or into a metastable stage-3 state without showing evidence of further transition into a final stage-2 state, depending upon the values of μf, and kinetic coefficients. A discussion is presented on the possibility of observing an intermediate metastable stage-3 state during the transition from stage 4 to stage 2.
The reaction of reference commercial nuclear waste glasses during gamma irradiation in a saturated tuff environment
Authors: Bates John K. , Ebert William L. , Fischer Donald F. , Gerding Thomas J.
Published: September 2007

The effects of gamma irradiation on groundwater and the reaction between groundwater and glass have been investigated at radiation exposure rates of 2 × 105 1 × 103 and 0 R/h. These experiments, which bound the conditions that may occur in a high-level nuclear waste repository located in tuff, have been performed using the actinide-containing glasses ATM-lc and ATM-8, and have been performed for time periods up to 278 days. The experimental results indicate that when only the repository groundwater is present, the pH of the system remains near-neutral, regardless of the radiation field, due to the buffering capacity of the solution. When glass is added to the system, the subsequent reaction is governed by the solution chemistry, which results from a complex interaction between radiolysis products, glass reaction products, and groundwater components. While no long-term reaction trends have been extracted from the current data, it is noted that there are no outstanding differences in the reaction of the glasses as measured by the release of the soluble components B, Mo, and Na, as a function of radiation exposure rate. However, there is a marked difference in the amount of U, Np, and Pu released from the glasses as a function of radiation exposure rate. This difference can be correlated with the pH values of the leachate, with more basic solutions resulting in lower actinide release.
Kinetics of the oxidation of Ba2 YCu3Ox ceramics
Authors: O'Bryan H. M. , Gallagher P. K.
Published: September 2007

The kinetics of the oxidation of dense and porous samples of Ba2 YCu3Ox ceramic have been determined by gravimetric analysis at 400–700 °C. At 600 °C and above, the rate decreases as the thickness of the oxidized layer increases. At 500 °C and below, the kinetics show a linear relation that indicates that the oxidized layer does not protect the ceramic. Dilatometric, microscopic, and high-temperature x-ray data suggest that fractures in the oxide layer at the lower temperatures are caused by the large volume decrease that accompanies the change in oxygen stoichiometry.
Intercalation of mixed chloride–fluorides of antimony in graphite
Authors: Datars W. R. , Zaleski H. , Ummat P. K.
Published: September 2007

The intercalation of SbCl4F and SbCl3F2 into graphite is described. The c-axis identity period, measured by (00/) x-ray diffraction, is 9.30, 12.69, and 16.04 Å for stages 1, 2, and 3, respectively, of SbCl4 F-intercalated graphite. The c-axis identity period for stage 1 SbCl4F-intercalated graphite is 8.85 Å. Mass spectroscopy shows that the molecule in SbCl4F-intercalated graphite is a (SbCl4F)4 tetramer. The molecule in SbCl3F2-intercalated graphite is a (SbCl3F2)4 tetramer. Mossbauer measurements show that Sb is in a 5 + state in SbCl4F-intercalated graphite.
Interfacial phenomena involving liquid metals and solid oxides in the Mg–Al–O system
Authors: Weirauch D. A.
Published: September 2007

The wetting of ceramic surfaces by aluminum alloys has been reexamined using a chemical system where interfacial reactions and oxide film effects could be isolated. The system Al–Mg–O was chosen since it is technologically important and high-purity, well-characterized materials are readily available. Magnesium alloyed with the aluminum sessile drop and silicon picked up from the experimental apparatus cause an initial reduction in contact angle by altering the protective nature of the oxide film formed on the sessile drop. Evidence of spreading is observed as an intermediate process in the reactive sessile drop pairs. Reaction products formed between the Al–Mg alloys and sapphire (Al2O3), spinel (MgAl2O4), or periclase (MgO) can be interpreted with predicted phase equilibria and the measured loss of magnesium from the sessile drop. Only the rate of the periclase alloy interaction was rapid enough to result in a continuous product layer after 24 h at 800 °C. The volatilization of all of the magnesium from the sessile drop resulted in the formation of a true Al–Al2O3interface. The contact angle for a true Al–Al2O3interface is 88 ± 5 deg at 800 °C. The liquid-solid interfacial energy is 1688 ergs/cm2.
Growth kinetics of ZnO prepared by organometallic chemical vapor deposition
Authors: Souletie P. , Wessels B. W.
Published: September 2007

Zinc oxide films were deposited using the reactants dimethyl zinc and tetrahydrofuran. Growth kinetics were determined from the dependence of the growth rate on substrate temperature and reactant partial pressure. A complex temperature dependence was observed over the temperature range of 300–500 °C. For a deposition temperature of 400 °C, the growth kinetics were modeled using a bimolecular surface reaction rate-limited mechanism. The layers were characterized using x-ray diffractometer and Auger spectroscopy measurements.
Degradation of Y–Ba–Cu–O in a high-humidity environment
Authors: Garland M. M.
Published: September 2007

Changes in ac susceptibility of the high-Tc superconductor Y–Ba–Cu–O have been used to investigate the degradation of this material in the presence of high humidity. It is found that the fraction of YBa2Cu3O7 in a sample decreases exponentially with time when the sample is kept at 98% relative humidity and 20 °C. The time constant is approximately 22 days.
Structural phase transition study of Ba2YCu3O6+x in air
Authors: Wong-Ng W. , Cook L. P. , Chiang C. K. , Swartzendruber L. J. , Bennett L. H. , Blendell J. , Minor D.
Published: September 2007

A structural phase transition study of Ba2YCu3O6+x (x = 0 to 1) has been conducted on a series of 13 quenched samples. These samples were prepared from an orthorhombic material by annealing at temperatures from 400 to 1000 °C in air, followed by rapid quenching. All quenchings were performed by using a liquid-nitrogen-cooled copper cold well with a continuous flow of cooled helium gas. Various measurements including x-ray diffraction, thermogravimetric analysis, Meissner effect, and scanning electron microscopy were carried out in order to correlate the nature of the phase transition with erystallographic data, superconductivity, and annealing temperature. The phase transition from Ba2YCu3,O7 to Ba2YCu3O6 appears to involve two orthorhombic regions: region A with a <b ≈ c/3 below approximately 600 °C and region B with cell parameters of a < b < c/3 from & 600 to 708–720 °C. The transformation from orthorhombic to tetragonal takes place in the temperature range of 708–720 °C. This transition appears to be a second-order, order-disorder type.
Laser-induced multicrystallization events of thin germanium films
Authors: Ortiz C. , Rubin K. A. , Ajuria S.
Published: September 2007

The crystallization kinetics of thin (35 and 60 nm) amorphous as-deposited Ge films were studied using diffraction limited laser beam irradiation and laser pulses between 30 ns and 1 ms. The recrystallization of crystalline as-deposited films was also studied for similar laser conditions. Crystallization was observed for pulses as short as 50 ns. It was concluded that the irradiation of amorphous thin films with small beam spots (∼ 1μm) gives a very different crystallization morphology from that observed previously for larger beam diameter and same laser pulse length. In the present case for short irradiation times, the nucleation process dominates over crystal growth. Temperature calculations allow the understanding of these results by showing that only the small spot irradiation sustains the material at high temperature for times comparable to the pulse width. Laser irradiation of as-deposited crystalline films produced grains with significantly fewer defects than grains crystallized from as-deposited amorphous films.
Variable strain energy in amorphous silicon
Authors: Sinke W. C. , Roorda S. , Saris F. W.
Published: September 2007

Different Raman experiments on structural relaxation ofa-Si anda-Ge are reviewed and discussed in relation to calorimetric measurements ona-Ge. On the basis of the correlation found between results from Raman spectroscopy and results from calorimetry in the case ofa-Ge and of the strong similarity betweena-Si anda-Ge in terms of their Raman spectra, it is suggested that the strain energy ina-Si may vary considerably with preparation conditions and subsequent treatments. Under this assumption thea-Si Gibbs free energy versus temperature has been constructed for material in different initial states of relaxation. It is shown that the melting temperature of amorphous silicon should increase when relaxation occurs during the heating phase prior to melting. Thus differences in apparent melting temperature, as observed under different laser heating conditions, may be explained.
The body-centered-cubic-type icosahedral reciprocal lattice of the Al–Cu–Fe quasi-periodic crystal
Authors: Ebalard S. , Spaepen F.
Published: September 2007

We show that the Al–Cu–Fe stable icosahedral crystal has an almost perfect icosahedral symmetry, and a reciprocal lattice of the body-centered cubic type.
Self-diffusion and impurity diffusion of fee metals using the five-frequency model and the Embedded Atom Method
Authors: Adams J. B. , Foiles S. M. , Wolfer W. G.
Published: September 2007

The activation energies for self-diffusion of transition metals (Au, Ag, Cu, Ni, Pd, Pt) have been calculated with the Embedded Atom Method (EAM); the results agree well with available experimental data for both mono-vacancy and di-vacancy mechanisms. The EAM was also used to calculate activation energies for vacancy migration near dilute impurities. These energies determine the atomic jump frequencies of the classic “five-frequency formula,” which yields the diffusion rates of impurities by a mono-vacancy mechanism. These calculations were found to agree fairly well with experiment and with Neumann and Hirschwald's “Tm” model.
Elastic Green's function for a composite solid with a planar interface
Authors: Tewary V. K. , Wagoner R. H. , Hirth J. P.
Published: September 2007

The elastic plane-strain Green's function is calculated for a general anisotropic composite solid with a plane interface and a line load parallel to the composite interface. The interface may be between two different solids or between different orientations of the same solid such as a grain boundary. The equations of elastic equilibrium are solved by the Fourier transform method. Analytical expressions are obtained for the Green's function in real as well as Fourier space. These expressions should be useful for calculations of elastic properties of a composite solid containing defects. Two sum rules are also derived for matrices which constitute the Green's function and the stress tensor. These sum rules can serve as numerical checks in detailed computer simulation calculations.
The effect of grain size on microstructure and stress relaxation in polycrystalline Y1Ba2Cu3O7−δ
Authors: Shaw T. M. , Shinde S. L. , Dimos D. , Cook R. F. , Duncombe P. R. , Kroll C.
Published: September 2007

We have used transmission electron microscopy and optical microscopy to examine the effect that grain size and heat treatment have on twinning and microcracking in polycrystalline Y1Ba2Cu3O7−δ. It is shown that isothermal oxygenation heat treatments produce twin structures consisting of parallel twins, with a characteristic spacing that increases with increasing grain size. Slow cooling through the temperature range where the orthorhombic-to-tetragonal transformation induces twinning, however, produces a structure consisting of a hierarchical arrangement of intersecting twins, the scale of which appears to be independent of grain size. It is also shown that the microcracking induced by anisotropic changes in grain dimensions on cooling or during oxygenation can be suppressed if the grain size of the material is kept below about 1 μm. The results are examined in the light of current models for transformation twinning and microcracking and the models used to access the effect other processing variables such as oxygen content, doping or heat treatment may have on the microstructure of Y1Ba2Cu3O7−δ.
The characterization of an SCS6/Ti–6Al–4V MMC interphase
Authors: Jones C. , Kiely C. J. , Wang S. S.
Published: September 2007

Using TEM, Auger spectroscopy, EDX, and convergent beam electron diffraction, a thorough characterization of the interphase region between SCS6 fibers and Ti–6Al–4V matrix in a metal matrix composite has been performed. The interphase region is shown to be very complex, consisting of numerous layers of varying compositions and thicknesses. The chemical interaction of the fiber and matrix results in a 0.5–1.5 μm thick TiC layer. Evidence for the existence of a Tix Siy (C) layer is also presented. The SCS6 overlayer on the fibers has inhibited any chemical interaction between the matrix and the SiC filament itself, 60% of the interphase region originating from the SCS6 protective coating. In situ fracture experiments (in an Auger spectrometer) reveal that fracture takes place between the TiC and an amorphous carbon layer.
A study of native oxides of β–SiC using Auger electron spectroscopy
Authors: Chaudhry M. Iqbal
Published: September 2007

Thermal and anodic oxide films of beta silicon carbide are analyzed using Auger electron spectroscopy. Auger depth-composition profiles are obtained in order to determine the chemical composition of the oxide films. The position and shape of silicon spectral peaks are used to estimate the chemical bonding of the oxide constituents. It is found that the wet thermal oxide is almost stoichiometric but contains about 14% carbon. Dry oxide, on the other hand, has less than 3% carbon but is highly nonstoichiometric. The carbon content in the anodic oxide is 12%. Anodic oxide films, like dry-oxide films, are nonstoichiometric. A model of the SiC oxidation process is presented.
Carbon films from polyacrylonitrile
Authors: Renschler C. L. , Sylwester A. P. , Salgado L. V.
Published: September 2007

Polyacrylonitrile (PAN) films have been fabricated by both spin and solvent casting techniques, and pyrolyzed to produce carbon films in the thickness range of 200–50000 Å. These films have higher electrical conductivities than carbon films produced from most other precursors at similar temperatures. The chemical structure of the films at different stages of processing was investigated by UV, IR, Raman, and XPS spectroscopies. An extra degree of control over the final electrical conductivity was obtained by varying the PAN content of copolymer precursors. Oxidation rates and an activation energy were determined. Finally, processing techniques are described which allow both dry and wet film transfer and lithographic patterning.
Partial substitution of 18O in YBa2Cu3O7: Investigations of inhomogeneities and their effect on Tc
Authors: Ham William K. , Keller Steven W. , Michaels James N. , Stacy Angelica M. , Krillov Dimitry , Hodul David T. , Fleming Ronald H.
Published: September 2007

The possibility of site-selective substitution of 18O into YBa2Cu3O7 was explored. Samples containing various quantities of 18O were prepared by processing in 18O2 both at 950 °C and at 400 °C. The samples were characterized by secondary ion mass spectroscopy (SIMS), temperature programmed desorption (TPD) and reduction (TPR), Raman spectroscopy, and magnetization measurements. Measurements of the shifts in the Raman active modes with 18O substitution and of the ratios of 18O to 16O by TPD, TPR, and SIMS show that even for temperatures as low as 400 °C and times as short as 2 h. 18O is not substituted exclusively into the chain site (O1) in YBa2Cu3O7. In addition, there is no consistent variation in the shifts in Tc with the degree of substitution; therefore, the isotope effect for a sample with 100% 18O cannot be predicted by a linear extrapolation of data obtained for samples with partial 18O substitution. The mechanism of oxygen substitution, the difficulties of measuring the true magnitude of the oxygen isotope shift, and the meaning of the small isotope shift are discussed.
The melting point depression of tin in mechanically milled tin and germanium powder mixtures
Authors: Koch C. C. , Jang J. S. C. , Gross S. S.
Published: September 2007

A melting point depression, δTM, has been observed for Sn in Ge/Sn (50 at.% Sn) dispersions which were prepared by mechanical milling of Ge and Sn powders. Sn and Ge are immiscible and form a fine dispersion of the pure components when milled in a high energy ball mill. The magnitude of δTM, as measured by DSC, increases with milling time, i.e., with refinement of the dispersion. Melting is observed to begin as low as 36 °C below the equilibrium bulk melting temperature. The magnitude of δTM is reduced by about 25% after melting the Sn. Subsequent remelts do not change δTM further. Impurities cannot account for δTM. While stored energy of cold work may contribute to 25% of δTM before Sn is melted, it is concluded that the major contribution to δTM comes from the nucleation of disorder/melting at the Ge/Sn interfaces.
Chemical vapor deposition of silicon dioxide barrier layers for conductivity enhancement of tin oxide films
Authors: Ellis Frank B. , Houghton Jim
Published: September 2007

Silicon dioxide for use as a diffusion barrier between soda lime glass and fluorine-doped tin oxide is deposited uniformly by atmospheric chemical vapor deposition from silane. oxygen, and nitrogen using a simple single-slot injector head. With a sufficiently thick silicon dioxide layer, the conductivity of the tin oxide is greatly improved by reducing the diffusion of sodium into the tin oxide as it is deposited between about 500 to 600 °C. Based upon the conductivity of thin lightly doped tin oxide films, it appears that at least 250 nm of silicon dioxide deposited on soda lime glass are required to essentially eliminate the diffusion of sodium into the tin oxide. However, only about 10 nm of silicon dioxide are required to obtain almost the full benefit of 250 nm thick films for moderately doped tin oxide films approximately 500 nm thick, The silicon dioxide deposition process is examined between 350 and 580 °C. The activation energy for the deposition is about 27 kJ/mole. Peak and average film deposition rates greater than 50 nm/sec and 10 nm/sec, respectively, may be obtained. The dependence of the film growth rate on the silane, oxygen, and propylene (an inhibitor) concentration is examined. The deposition rate is found to be limited by the rate of gas-phase reactions. Deposition conditions which yield high silane utilization and good film uniformity are discussed. The origin of undesirable by-product powder is studied. At low silane concentration, powder is mainly formed as the gases cool due to condensation from intermediate species.
Kinetics of structural relaxations in the glassy semiconductor a–Se
Authors: Kasap S. O. , Yannacopoulos S.
Published: September 2007

It has recently been suggested that the rate of structural relaxations in amorphous chalcogenide glasses is inversely proportional to the viscosity and the latter obeys the Vogel-Tammann-Fulcher relationship. In this paper, Differential Scanning Calorimetry (DSC) and Thermomechanical Analysis (TMA) experiments examining the glass transformation in a–Se are reported which have been carried out over as wide range of heating rates as practically possible on the available instrumentation covering more than three decades of heating rate variation from r = 0.05 °C/min to r = 100 °C/min. The observed glass transformation temperatures in DSC and TMA ranged from 30 °C to 65 °C. The a–Se films were vapor deposited by thermal evaporation onto A1 substrates (at ∼70 °C) under identical conditions and well aged over an equal period of time so that all the films had an identical initial structure. Analysis of the glass transition temperature, Tg, vs heating rate, r, data obtained from the DSC endotherms shows that the structural relaxation rate is non-Arrhenius and can be described reasonably well by a Vogel expression of the form exp[–A/(T – T0)] which may have a weak structure dependent factor of the form exp[–c(H – HE)] where (H – HE) is the deviation of the structural enthalpy from its equilibrium value. It was found that a phenomenological single parameter Vogel description for the retardation time over the whole temperature range accessed leads to A and T0 values comparable with those obtained from the Vogel analysis of the viscosity-temperature data of Cukiermann and Uhlmann (1972), as well as the recent thermomicrohardness data of the present authors (1989). Furthermore, it is shown that the wide differences reported for the crystallization activation energy in a–Se can be readily interpreted by a viscosity limited crystallite growth rate. The Vogel interpretation is also found to be consistent with the temperature dependence of the mean dielectric relaxation time in the Debye loss observed by Abkowitz, Pochan, and Pochan (1980). It is suggested that in the elemental chalcogenide a–Se, the relaxation rate of enthalpy, microhardness, and dielectric polarization, as well as the crystallization rate, all scale inversely with the viscosity. TMA measurements, on the other hand, although still interpretable in terms of a Vogel behavior, did not indicate a softening behavior which paralleled the viscosity.
Effects of dopants on PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 composition
Authors: Yan M. F. , Ling H. C. , Rhodes W. W.
Published: September 2007

We studied the effects of 15 dopants on the dielectric properties of the Pb1–x–yMgxNb2yO1+4y perovskite system. The investigated dopants are Ba, Ag, La, Bi, and Nd, which substitute in the Pb sublattice, and Co, Ni, Zn, Mn, Cr, Dy, Al, Fe, Zr, and Ti, which substitute in the sublattice occupied by Mg and Nb. While the dielectric constants of Pb1−x–yMgxNb2yO1+4y) are not affected by Al, Zr, and Ni dopants, their dielectric constants are increased by Ti dopant and decreased by other dopants. The rates of change in the Curie temperatures of Pb1–x–y MgxNb2yO1+4y with different dopant concentrations were quantitatively measured. The relative effectiveness of these dopants in altering the Curie temperature is correlated to the bond strengths between oxygen and the dopants in either the Pb sublattice or the Mg/Nb sublattice. The effects of these dopants on the dissipation factors and electrical resistivities were investigated. Cobalt and manganese oxides were identified as the most effective dopants in reducing the dissipation factor and lanthanum and barium oxides are effective in increasing the resistivity. We have also observed that zinc oxide promotes densification and reduces the temperature coefficient of capacitance in these compositions. Ternary and quaternary systems based on selected combinations of these dopants were prepared and characterized. Compositions in the Pb(Zn⅓Nb⅔)O3 + Pb(Co⅓Nb⅔O3 + PbTiO3 + Pb1–x–yMgxNb2yO1+4y quaternary systems were shown to be promising candidates for capacitor applications. Furthermore, multilayer capacitors of these promising compositions were fabricated and they were shown to have favorable device properties.
Alumina powders via a controlled precipitation of aluminum acetate
Authors: Ayral A. , Droguet J. C.
Published: September 2007

A new method of producing alumina powder is described. Aluminum basic acetate is first synthesized from alkoxide precursor. The chemical reactions which control the precipitation of this salt are followed, using IR spectroscopy. Alumina powder is obtained by further thermal decomposition, and the thermal evolution of the precipitate is studied.
On the atomic structure of the Nb/Al2O3 interface and the growth of Al2O3 particles
Authors: Kuwabara M. , Spence J. C. H. , Ruhle M.
Published: September 2007

The growth mechanism for small precipitates of Al2O3 formed by internal oxidation in the Nb–Al2O3 interface is studied in detail. The observations show that the Nb (001)/Al2O3 (00.1) interface is almost atomically flat and that there are no interface compounds. We suggest that the final layer on the Al2O3 side of this interface consists of oxygen atoms. The effects of image forces on misfit dislocations are found to result in a standoff distance between dislocation cores and the interface, in good agreement with the recent theory. The implications of this for the strength of metal-ceramic bonding are discussed.
Application of freeze-fracture technique for analyzing the structure of lubricant greases
Authors: Magnin A. , Piau J. M.
Published: September 2007

The freeze-fracture technique has been developed to study solid-liquid dispersions. In this technique, a sample of dispersion is frozen, then fractured. A replica of the fracture surface is made and observed using a scanning electron microscope. The physical form of the solid thickener in dispersion can be studied, and the structure of the thickener can be revealed as well as a combination of rupture properties of the solid and the frozen liquid. The application of this technique is on lubricant greases. Greases are two-phase dispersed systems composed of mineral oil gelled with solid particles of soap. Three lithium 12-hydroxystearate greases are examined. Two different kinds of washing of the replica are used, the first eliminating the liquid phase. The configuration of soap particles and the network formed by them are observed, and artifacts such as twisting soap fibers are avoided. The second washing eliminates the solid and liquid phase. Examination of the fracture surface of the soap provides information on crystalline arrangement. The observed structures by freeze fracture are related to the thermal treatments during grease manufacture. The results are compared with the observations obtained from an electron transmission microscope analysis after preparation by the usual dispersion technique.
Mechanoelectric transduction in bone
Authors: Chakkalakal Dennis A.
Published: September 2007

The cells in living bone are embedded in a charged, organic-inorganic solid permeated by ionic fluids flowing through a complex network of channels (diameter ∼10−1–102μm). The solid matrix, which has a high degree of composite material organization beginning at the macromolecular level, has even finer pores of diameter ≳10−3μm containing extracellular fluids. Since bone cells are thus bathed in fluid environments of varying ionic composition and concentration, it is likely that the physiology of bone depends on its electrical and electromechanical properties. This hypothesis is supported by the known effects of externally applied mechanical and electrical signals on physiological functions. Contrary to the earlier perception of bone as an insulating material, it is now recognized that the fluid content of bone endows it with physiologically significant conductivity. Mechanoelectric transduction in bone, at low frequencies, is most likely an electrokinetic process associated with the solid-fluid interfaces in bone. Electromechanical properties of bone have been determined experimentally by measurements of stress-generated potentials and streaming potentials in wet bone specimens and electrophoretic mobility of bone particles. Interpretation of results has been difficult due to the complexity of the solid-fluid interfaces in bone and the often undefinable alterations of the pores and interfaces due to specimen preparation. This paper is a review of the present state of knowledge of mechanoelectric transduction in bone and its physiological significance.
Laser-induced forward transfer: A new approach for the deposition of high Tc superconducting thin films
Authors: Fogarassy E. , Fuchs C. , Kerherve F. , Hauchecorne G. , Perrière J.
Published: September 2007

We propose in this work a new approach, named laser-induced forward transfer, for the rapid deposition and patterning in a clean environment of high Tc superconducting thin films. A stoichiometric high Tc compound is initially deposited in a thin layer on an optically transparent support by laser evaporation or another more conventional technique. By irradiating under vacuum or in air the precoated layer with a strongly absorbed single laser pulse through the transparent support, we are able to remove the film from its support to be transferred onto a selected target substrate, held in contact to the original film. Using this technique, we have successfully transferred with one single pulse, provided by an excimer or a Nd:YAG laser, YBaCuO and BiSrCaCuO precoated thin films on various substrates. The Rutherford backscattering spectrometry experiments do not show any strong modification in the composition of the transferred layer against the source material, and the superconducting phases for the two types of compounds were obtained after subsequent thermal annealing carried out in a furnace around 850–900 °C in O2. For the BiSrCaCuO films transferred onto MgO substrates, we have measured an onset critical temperature of about 90 K with a zero resistance at 80 K.
Kinetic paths of B2 and DO3order parameters: Experiment
Authors: Anthony L. , Fultz B.
Published: September 2007

Rapidly quenched powders of Fe3Al were subjected to thermal annealings at temperatures well below the critical temperatures for B2 and DO3ordering. X-ray diffractometry was used to measure the subsequent evolution of B2 and DO3long-range order. It was found that the relative rates of change of B2 and DO3order parameters were temperature dependent; hence at different temperatures the alloy passed through different states of order en route to thermal equilibrium. These temperature dependences of “kinetic paths” can be understood in terms of a theory of kinetic paths based on the kinetic master equation. The theory indicates that the temperature dependence of the observed kinetic paths originates from having first-nearest-neighbor interactions that are stronger than second-nearest-neighbor interactions. This seems consistent with previous thermodynamic analyses of critical temperatures of Fe3Al.
Effect of chromium on properties of Fe3Al
Authors: McKamey C. G. , Horton J. A. , Liu C. T.
Published: September 2007

The effects of the addition of chromium on several properties of Fe3Al, including tensile strength and ductility, fracture behavior, and slip and dislocation characteristics, were studied. Alloying with up to 6 at. % chromium results in an increase in room temperature ductility from approximately 4% to 8–10%. Along with this increase in ductility, the addition of chromium produces a change in fracture mode from transgranular cleavage to a mixed mode of intergranular-transgranular cleavage, and a change in slip behavior from coarse straight slip to fine wavy slip. These phenomena are discussed in terms of the effect of chromium on the antiphase boundary energies and dislocation characteristics.
Electrical charge injection and storage in off-stoichiometric SiO2 films
Authors: López M. , Falcony C.
Published: September 2007

The injection and storage characteristics of electrical charge in off-stoichiometric SiO2 films have been studied using two types of capacitor structures: (A) a simple capacitor formed with an off-stoichiometric SiO2 film deposited on either p- or n-type silicon substrate and a metallic (Al) contact, and (B) a structure similar to (A) but with a thin (100 Å or 500 Å) SiO2 layer between the Si substrate and the off-stoichiometric SiO2. The flat band voltage shifts measured from high frequency capacitance versus voltage curves of these devices were used to study the accumulation of charge in the off-stoichiometric SiO2 layer induced by applied voltage pulses. The width of these pulses was in the range of 10 ms to 100 μs and the amplitude was in the range of 0 to 80 volts. The role of the SiO2 layer in the (B) type structures is to inhibit or reduce charge injection to or from the Si substrate at low applied voltage amplitudes. This effect originates initial shifts of the flat band voltage of opposite polarity to those observed in the case of (A) type structures. The relaxation of the stored charges was monitored by measuring the shifts of the flat band voltage as a function of time when both electrical contacts were connected to ground potential.
Monte Carlo simulations for sintering of particle aggregates
Authors: Madhavrao L. Rao , Rajagopalan Raj
Published: September 2007

A new Monte Carlo simulation procedure is developed for the initial stages of sintering of randomly packed particles. This simulation takes into account the possibility of crack initiation due to the stresses generated by the sintering particles and can accommodate both localized stresses and stress propagation. This procedure is used to investigate the sintering of two-dimensional aggregates of copper particles, and the results are compared with the results of model experiments available in the literature. The two-dimensional simulations presented here lead to shrinkage in area, decreases in perimeter, and particle rearrangements that are physically consistent with the expected behavior and experimental results. The proposed procedure can be extended to accommodate more complex features of sintering and to account for the material-dependent effects of stresses. It can also be used as a probe of sintering of bulk materials with random microstructure and to identify and design model experiments.
Crystallization kinetics of BaO–Al2O3–SiO2 glasses
Authors: Bansal Narottam P. , Hyatt Mark J.
Published: September 2007

Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system have been studied by differential thermal analysis (DTA), x-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt. %) 10BaO–38Al2O3–51SiO2–1MoO3 (glass A) and 39BaO–25Al2O3–35SiO2–1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3 · 2SiO2) and hexacelsian (BaO · Al2O3 · 2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 °C. It undergoes structural transformation into the orthorhombic form at ∼300 °C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.
Formation of percolation networks in ion-irradiated Ag–Co solid films
Authors: Ding J. R. , Liu B. X.
Published: September 2007

Percolation networks were observed in an immiscible Ag–Co alloy system after the Ag30Co70 alloy films were irradiated to a dose of 1 × 1016 Xe+/cm2 with 200 Kev Xe+ at room temperature. Fractal dimension D as well as percolation threshold Pc were calculated and exhibited good agreement with the results of the percolation theory. The mechanism of the formation of the ion-induced percolation structures is also discussed.
Raman studies of reactive DC-magnetron sputtered thin films of YBaCuO on MgO
Authors: Sheng K. C. , Lee S. J. , Shen Y. H. , Wang X. K. , Rippert E. D. , Van Duyne R. P. , Ketterson J. B. , Chang R. P. H.
Published: September 2007

Raman spectroscopy was employed to study Y–Ba–Cu–O films prepared by multilayer, reactive sputtering from separate Y, Cu, and Ba0.5Cu0.5 targets. A set of films having the composition YxBa2CuyOz with 0.7 < x < 1.8 and 2.8 < y < 3.5 and critical temperature with zero resistance, Tc(R = 0), ranging from 25 to 90 K was studied with the Raman technique. The correlation between Raman data and critical temperature, Tc, was investigated. This technique provides important information concerning the film crystallinity, homogencity, and impurity content (including other phases) which is useful in judging the quality of high Tc superconducting films. We also found that the rapid thermal annealing process is a very efficient way to reduce chemical reactions between the film and the substrate.
Characterization of hydrofluoric acid treated Y–Ba–Cu–O oxides
Authors: Jia Q. X. , Anderson W. A.
Published: September 2007

Effects of hydrofluoric acid (HF) treatment on the properties of Y–Ba–Cu–O oxides were investigated. No obvious etching of bulk Y–Ba–Cu–O and no degradation of zero resistance temperature were observed even though the oxides were placed into 49% HF solution for up to 20 h. Surface passivation of Y–Ba–Cu–O due to HF immersion was verified by subsequent immersion of Y–Ba–Cu–O in water. A thin layer of amorphous fluoride formed on the surface of the Y–Ba–Cu–O during HF treatment, which limited further reaction between Y–Ba–Cu–O and HF, and later reaction with water. Thin film Y–Ba–Cu–O was passivated by HF vapors and showed no degradation in Tc-zero after 30 min immersion in water. The properties of the surface layer of Y–Ba–Cu–O oxide after HF treatment are reported from Auger electron spectroscopy, x-ray diffraction, and scanning electron microscopy studies.
Oxidation kinetics of Pb–Sn alloys
Authors: Konetzki R. A. , Chang Y. A. , Marcotte V. C.
Published: September 2007

The solid state oxidation kinetics of Pb–Sn single-phase (2.5 at. % Sn) and eutectic alloys were studied with Auger Electron Spectroscopy combined with sputter depth profiling. The single-phase samples were oxidized in air in the temperature range 22 °C to 250 °C, while the eutectic samples were oxidized from 22 °C to 175 °C. Both alloys oxidize logarithmically between 22 °C and 90 °C and parabolically at temperatures greater than 120 °C. The activation energies for the parabolic oxidation of the single-phase and eutectic alloys are 69.5 and 67.1 ± 8 kJ/mole, respectively.
Effective properties of a periodic chiral arrangement of identical biaxially dielectric plates
Authors: Lakhtakia A. , Varadan V. K. , Varadan V. V.
Published: September 2007

A periodically inhomogeneous medium is constructed by stacking up unit cells made of (identical) structurally chiral slabs. Each structurally chiral slab is comprised of a certain number of identical biaxially anisotropic plates, the consecutive optic axes describing either a right- or a left-handed spiral. The characteristic matrix of the unit cell is obtained and used with the Floquet-Lyapunov theorem to obtain the electromagnetic fields in the periodic medium. When the unit cell thickness is very small compared to the principal wavelengths in the biaxial plates, the periodically inhomogeneous biaxial medium is shown to be equivalent to a homogeneous biaxial medium, the two optic axes of the equivalent medium being dependent on the handedness of the periodic medium.
The interaction of chemical kinetics and diffusion in the dynamics of chemical vapor infiltration
Authors: Middleman Stanley
Published: September 2007

The classical model of Chemical Vapor Infiltration (CVI) treats diffusion and surface reaction in a representative cylindrical pore. Two significant modifications to that approach are presented herein. One accounts for more complex chemistry by allowing for both gas-phase and surface reactions which lead to film growth. The other couples the pore model to a reactor model for the region external to the porous preform. The results demonstrate that it is possible to select chemical schemes that yield densification from the interior to the exterior of the preform, thus avoiding premature trapping of interior voids.
Kinetics and mechanism of laser-driven powder synthesis from organosilane precursors
Authors: Rice G. W. , Woodin R. L.
Published: September 2007

Laser-driven synthesis of refractory powders from the organosilicon compounds ((CH3)3Si)2NH and ((CH3)3Si)2O has been studied as prototypical of powder syntheses from large molecules. A cw CO2 laser is used for powder syntheses and pulsed TEA CO2 laser-driven homogeneous pyrolysis is used to study the initiation chemistry. Initial decomposition of the organosilanes by Si–C bond cleavage initiates free radical chain reactions which produce organosilicon polymers and subsequent refractory phases. A qualitative model is proposed which provides a framework for understanding the parameters influencing powder synthesis from large molecules.
Diffusion of OH− during hydration of YBa2Cu3O7-y by exposing to water vapor
Authors: Ikuma Yasuro , Yoshimura Masahiro , Kabe Shigeru
Published: September 2007

The hydration of YBa2Cu3O7-y in water vapor was investigated at various values of y and at two different PH2O by measuring the weight of the specimen. The reaction was relatively insensitive to the values of y and was extensive in the water vapor pressure of 2.7 kPa at room temperature and 140 °C. This was due to the decomposition of YBa2Cu3O7-y by reacting with H2O. The weight gain was also detected in the water vapor pressure of 270 Pa. The weight gain under lower water vapor pressure was supposed to be controlled by diffusion of OH− in YBa2Cu3O7-y. The diffusion coefficient calculated from the measurement was compared favorably with the oxygen diffusion coefficient.