bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivation of interionic potentials using embedded quantum-mechanical clusters: Cation and anion impurities in MgO
Authors: Pandey Ravindra , Zuo Jun , Kunz A. Barry
Published: September 2007

The ICECAP methodology is used to derive interionic potentials of some cation and anion impurities in MgO, namely, Li+, Na+, K+, Be2+, H−, S2−, and O2−. Analysis is given of the defect energies obtained by using the derived impurity potentials. Based on the available experimental data, comparison is made to justify the reliability of the derived impurity potential for Be2+. The calculated activation energy for Be2+ diffusion comes out to be 1.54 eV as compared to the experimental value of 1.60 eV, which is considered to be very satisfactory.
Effect of PbO evaporation on the composition and dielectric properties of PbO-MgO-Nb2O5 based dielectrics
Authors: Ling H. C. , Jackson A. M. , Yan M. F. , Rhodes W. W.
Published: September 2007

We have studied the weight loss during sintering and the resulting phase constituents and dielectric properties of a series of compositions in the lead-rich region of the PbO:MgO:Nb2O5 phase diagram near the stoichiometric composition of Pb(Mg1/3Nb2/3)O3 (PMN). While a ternary system of PbTiO3–Pb(CO1/3Nb2/3)O3–PMN was used, only the PMN component was varied in composition. The observed weight loss was ascribed to PbO evaporation from the nonstoichiometric PMN component. It was found that the sintered PMN compositions at about 1000°C correspond to the stoichiometric composition with varying amounts of excess MgO. These sintered compositions can be calculated by taking the Nb ion as the controlling cation in forming the PMN unit cell, from which the excess MgO can be determined. The excess PbO in the starting compositions, above the amount needed to form the sintered compositions of Pb(Mg1/3Nb2/3)O3 plus excess MgO, serves as a densification aid during the sintering process. Subsequently, the excess PbO is lost through evaporation. The peak dielectric constant of these compositions varies between 12000 and 18500, with the highest value attained in the sintered composition corresponding to stoichiometric PMN plus 0.229 mole of excess MgO. The optimum processing conditions for this composition are also identified.
Structure and superconductivity of BaBiO3 doped with alkali ions
Authors: Tseng D. , Ruckenstein E.
Published: September 2007

XRD shows that doping BaBiO3 with alkali ions transforms the larger monoclinic parent lattice into a more compact cubic or nearly cubic lattice. This lattice contraction favors the transition from semiconductor to metal. It leads also to superconductivity. Doping BaBiO3 with both K and Rb raises the onset resistivity Tc above those obtained by doping with either K or Rb.
Effect of residual stress and adhesion on the hardness of copper films deposited on silicon
Authors: LaFontaine W. R. , Yost B. , Li Che-Yu
Published: September 2007

Continuous indentation testing was used to measure the hardness as a function of indentation depth, of three micron thick copper films deposited on silicon with an intermediate layer of 20 nm thick chromium or titanium. Three different indenters, a nearly perfect Vickers, a Vickers with a 1.2 μm2 flat, and a Pyramid with a 25 μm2 flat were employed. The hardness data suggest that the titanium interlayer produced significantly greater film/substrate adhesion than the chromium interlayer. A compressive residual stress, which relaxed with time, was detected in the samples with the titanium interlayer.
Optical properties of chemical-vapor-deposited diamond films
Authors: Bi Xiang Xin , Eklund P.C. , Zhang J.G. , Rao A.M. , Perry T.A. , Beetz C.P.
Published: September 2007

Results of room-temperature optical studies on ∼10 micron thick, free-standing diamond films are reported. The films were grown on Si(100) substrates by hot filament-assisted chemical vapor deposition (CVD) from a methane/hydrogen mixture. The as-grown, free surface of the films exhibited a surface roughness of scale σ ∼ 0.2 to 5 microns, depending on the methane/hydrogen mixture, which introduces significant optical scattering loss for frequencies greater than 0.5 eV. Specular reflection and transmission spectra in the range 0.01–10 eV were collected. Below the threshold for interband adsorption near ∼5 eV, the films studied behaved approximately as thin parallel plates of refractive index 2.4, with the rough free surface leading to increasingly larger loss of specular transmission/reflection with decreasing wavelength. Structure in the mid-infrared transmission spectra was observed and attributed to disorder-induced one-phonon absorption, intrinsic multi-phonon absorption, and infrared active –C–H2stretching modes. The strength of the C–H band was observed to increase with increasing methane pressure in the growth chamber. At 5.3 eV, the onset of interband absorption was observed, in good agreement with the value of the indirect bandgap in type IIa (intrinsic) diamond.
Classification and consequences of complex lead perovskite ferroelectrics with regard to B-site cation order
Authors: Randall C. A. , Bhalla A. S. , Shrout T. R. , Cross L. E.
Published: September 2007

From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(Bx′B1−x″)O3], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.
Hole pattern formation in unfired ceramic sheets by pulsed Nd:YAG laser
Authors: Louh Rong-Fuh , Buchanan Relva C.
Published: September 2007

Single shot pulses from a Nd:YAG laser have been used to generate different sized holes and patterns in unfired ceramic sheets for electronic packaging applications. The single shot laser pulses were targeted using a computer controlled deflection system and a programmed pattern. With changes in pulse energy level and profile, the laser beam was also used to sinter line patterns in deposited thin and thick films. The surface radial temperature profile resulting from the laser pulse interaction was also directly mapped using a lacquer thermocoat. Effects of the laser pulse energy and beam spot size on laser/ceramic interactions, morphology, and structure of the drilled holes before and after sintering were examined by SEM. High quality hole patterns (of ∼100 μm hole size) were produced in unfired 100 μm thick ceramic sheets up to 100 μm thick using single shot of laser irradiation with 8 mJ pulse energy and 18 nsec pulse duration.
Microstructure and mechanical properties of multiphase NiAl-based alloys
Authors: Panka D.R. , Nathal M.V. , Koss D.A.
Published: September 2007

The effect of the γ′ phase on the deformation behavior fracture resistance of melt-spun ribbons and consolidated bulk specimens of a series of NiAl-based alloys with Co and Hf additions has been examined. The morphology, location, and volume fraction of the γ′ phase are significant factors in enhancing the fracture resistance of the normally brittle NiAl-based alloys. In particular, the results indicate that a continuous grain boundary film of γ′ can impart limited room temperature ductility regardless of whether B2 or L10 NiAl is present. Guidelines for microstructure control in multi-phase NiAl-based alloys are also presented.
Microstructural studies of laser irradiated graphite surfaces
Authors: Speck J.S. , Steinbeck J. , Dresselhaus M.S.
Published: September 2007

The structure of pulsed laser irradiated graphite surfaces has been elucidated. The pulse fluences range up to 4 J cm−2 with durations no longer than 30 ns. The region exterior to the irradiated spot is littered with ∼0.1 μm diameter carbon spheroids. The boundary region is characterized by both spheroids and torn layers 1–5 μm. in lateral extent. The central region displays carbon spheroids and surface upheavals. The carbon spheroids are attributed to hydrodynamic sputtering of carbon. The surface upheavals and torn carbon layers are attributed to constrained thermal expansion and contraction of the irradiated region. It is estimated that a nearly instantaneous 1000°C temperature change is necessary to cause the observed surface deformation. Pulse fluences in excess of 0.8 J cm−2 cause a thin layer of carbon to melt. This is proven by the fact that the irradiated layer in the solid phase has a turbostratic structure. Electron diffraction experiments and dark-field imaging experiments show that the basal plane grain size of the resolidified material varies from ∼20 Å at the melt threshold to ∼100 Å for samples irradiated with 4.0 J cm−2.
Amorphous-to-polycrystalline phase transformations in Sn-implanted silicon
Authors: Thornton R.P. , Elliman R.G. , Williams J.S.
Published: September 2007

An amorphous-to-fine-grain-polycrystalline phase transformation has been observed during annealing of Sn-implanted Si when the peak Sn concentration exceeds about 2 at.%. At lower Sn concentrations, epitaxial growth is retarded in (100) Si but proceeds to completion with a large fraction of Sn residing on substitutional lattice sites. As the Sn concentration is increased, epitaxy is pre-empted by the sudden transformation of the near-surface Sn-doped region into polycrystalline Si. The time required to initiate the transformation is temperature dependent and is characterized by an activation energy of ∼1.7 eV. Rapid redistribution of Sn has been observed to accompany the transformation. Our observations are shown to be consistent with a melt-mediated crystallization process which is rate limited by Sn diffusion and precipitation in amorphous Si.
Electron microscopic studies of internal gettering of nickel in silicon
Authors: Sinha P.K. , Glaunsinger W.S.
Published: September 2007

The internal gettering of nickel in (100) silicon wafers implanted with 2.5 ⊠ 1015 argon-ions/cm2 at 280 keV has been studied by electron microscopy. Nickel deposited on the back surface is gettered by forming a discontinuous layer of nickel silicide, NiSi2, in the argon-implanted region near the front surface. Electron microdiffraction and high-resolution electron microscopy indicate that the layers of nickel silicide probably grow epitaxially on the undamaged silicon surrounding the silicide.
Growth and characterization of ultrathin cobalt silicide films on Si(211) and (311)
Authors: Phillips Julia M. , Batstone J.L. , Hensel J.C. , Yu Irene , Cerullo M.
Published: September 2007

We have studied the structural and electrical properties of ultrathin cobalt silicide films deposited on Si(211) and (311) and annealed at a variety of temperatures. Transmission electron microscopy reveals two regimes of silicide growth. If more than 10 Å of Co is deposited, textured CoSi forms at low temperatures, which transforms to two epitaxial orientations of CoSi2 at about 500°C. If less than 10 Å of Co is deposited, only one epitaxial CoSi2 orientation is observed, which occurs in discontinuous islands or lines. The resistivities of the thinnest films reflect the degree of continuity of the silicide layers. In thicker films, where disorder is the major factor, the resistivity for intermediate annealing temperatures (∼500°C) depends dramatically on the orientation of the Si substrate, being an order of magnitude lower for Si(311) and (211) than for (111). The differences between these observations and those made on films grown under the same conditions on Si(111) can be understood by noting both the greater tendency of the film to form intermediate phases which are epitaxial on the high symmetry Si(111) surface and the faceting of the CoSi2-Si(311) and (211) interfaces.
Oxide thin films for nanometer scale electron beam lithography
Authors: Hollenbeck J.L. , Buchanan R.C.
Published: September 2007

The exposure response of high resolution oxide resist materials has been examined under high intensity irradiation conditions (∼1 ⊠ 105A/cm2) to determine the relationships among film characteristics, exposure requirements, and ultimate resolution, and to explore further the processes responsible for ablative exposure. Amorphous films of Al2O3, Y2O3, Sc2O3, 3Al2O3·2SiO2, and MgO·Al2O3were deposited by rf sputtering onto substrates cooled to –196°C and found to require an exposure dose of approximately 5 ⊠ 103C/cm2to complete exposure. Amorphous film structure was found to be necessary to achieve rapid removal of material during exposure. Material properties also found to influence irradiation response and help guide the selection of new materials included ionic character, heat of formation, and melting point. Film thickness was found to influence strongly both exposure requirements and resolution, an optimum thickness occurring at approximately 90 nm in amorphous Al2O3. The dose requirement in 90 nm thick amorphous Al2O3was determined to be 2.5 ⊠ 103C/cm2, which is two to three orders of magnitude lower than that of oxide films produced by other techniques. Resolution of the rf sputtered oxide films allowed the production of 5.0 nm holes on 8.1 nm centers. A dedicated STEM was used for exposure studies as well as imaging, microdiffraction analysis, and monitoring of the transmitted beam current, and allowed a qualitative model of the exposure process in rf sputtered oxide resists to be developed.
Mechanical properties of nanophase TiO2 as determined by nanoindentation
Authors: Mayo M. J. , Siegel R. W. , Narayanasamy A. , Nix W. D.
Published: September 2007

Nanoindenter techniques have been used to determine the hardness. Young's modulus, and strain rate sensitivity of nanophase TiO2, which is currently available only in very small quantities and which cannot be tested by most conventional techniques. Hardness and Young's modulus both increase linearly with sintering temperature over the range 25–900°C but come to within only 50–70% of the single crystal values. Strain rate sensitivity, on the other hand, is measurably greater for this material than for single crystal rutile, and the value of strain rate sensitivity increases as the grain size and the sintering temperature are decreased. In its as-compacted form, the strain rate sensitivity of nanophase TiO2 is approximately a quarter that of lead at room temperature, indicating a potential for significant ductility in these ceramic materials. Finally, a significant scatter in hardness values has been detected within individual nanophase samples. This is interpreted as arising from microstructural inhomogeneity in these materials.
Well-defined colloidal tin(IV) oxide particles
Authors: Ocaña Manuel , Matijević Egon
Published: September 2007

Spherical and rod-like SnO2 particles of narrow size distribution have been obtained by aging at 100°C acidified tin(IV) chloride solutions in the presence of urea or formamide. It was shown that spherical particles, the x-ray diffraction of which was characteristic of cassiterite, consisted of a large number of much smaller subunits. The rod-like particles had the same structure, but of higher degree of crystallinity. Infrared spectra of these powders were evaluated in terms of the theory of the average dielectric constant (TADC), in order to gain additional information on the particle morphology and the state of aggregation.
Molecular dynamics simulations of some amorphous and crystalline photonic materials
Authors: Phule Pradeep P. , Deymier Pierre A. , Risbud Subhash H.
Published: September 2007

Constant pressure molecular dynamics (MD) simulations have been used to simulate amorphous and crystalline forms of BaTiO3 and TiO2. Simulation results for pure RaTiO3 and TiO2 glasses show fourfold titanium coordination with a Ti–O bond distance of 1.8 Å, consistent with experimental evidence for the structure of titania doped glasses for all optical switching and ultra low expansivity (ULE) TiO2–SiO2 glasses. Radial distribution function data for crystalline, liquid, and amorphous forms of BaTiO3 were also obtained. The displacement polarization and its contribution to susceptibilities have been calculated by application of an electric field to the simulation cell. The calculated ionic dielectric constants (Ki) for simulated NaCI (crystal), TiO2 glass, and TiO2 (crystal) were 3.34, 5.96, and 19.4 as compared to the experimental values of ≍3.34, 3–10, and 78, respectively. The calculated cubic nonlinear susceptibility (ξ3) values for NaCI (crystal), TiO2 (glass), and TiO2 (crystal) were, respectively, 0.194, 2.175, and 4.68 (x 10−18m2V−2). The increase in ξ3 values is consistent with experimentally observed trends of the linear refractive indices. Improved agreement between experimental and calculated values of susceptibilities and dielectric constant was obtained for materials with higher ionicity.
Advanced epitaxial Si and GexSi1−x multiprocessing for semiconductor device technologies
Authors: Moslehi Mehrdad M. , Davis Cecil J.
Published: September 2007

A single-wafer multiprocessing technology has been developed based on the use of lamp heating and remote microwave plasma process energy sources for fabrication of in-situ-doped homoepitaxial Si and heteroepitaxial Si/GexSi1−x multilayer structures via chemical-vapor deposition. Some effective low-temperature (650°–800°C) processes were developed for in-situ pre-epitaxial growth surface cleaning. These chemical cleaning processes employ GeH4 + H2 or GeH4 + H2 + (HF or HCl) gas mixtures with very small GeH4-to-H2 gas flow rate ratios. Multilayer heteroepitaxial structures with controlled doping and Ge fractions consisting of strained Ge4Si1−x layers were fabricated and characterized.
Oriented BSCCO thick film coatings on polycrystalline MgO
Authors: Spann J. R. , Toth L. E. , Lloyd I. K. , Kahn M. , Chase M. , Das B. N. , Francavilla T. L. , Osofsky M. S.
Published: September 2007

Highly oriented 2212 BSCCO thick films were prepared on polycrystalline MgO substrates using a melt/crystallization technique. Results compare very favorably with those on single crystal materials.1,2 The melting, quenching, and annealing processes were all found to be important in the development of a good microstructure and good superconducting properties. The best results (Jc ∼ 2000 A/cm2 at 64 K and 6000 A/cm2 at 4.2 K) were obtained on films which had been melted, quenched to room temperature, heated to 860°C where they were annealed before slow cooling to room temperature in oxygen, lightly polished, and reannealed at 860°C.
OMCVD of thin films from metal diketonates and triphenylbismuth
Authors: Berry A. D. , Holm R. T. , Fatemi M. , Gaskill D. K.
Published: September 2007

Films containing the metals copper, yttrium, calcium, strontium, barium, and bismuth were grown by organometallic chemical vapor deposition (OMCVD). Depositions were carried out at atmospheric pressure in an oxygen-rich environment using metal beta-diketonates and triphenylbismuth. The films were characterized by Auger electron spectroscopy, Nomarski and scanning electron microscopy, and x-ray diffraction. The results show that films containing yttrium consisted of Y2O3 with a small amount of carbidic carbon, those with copper and bismuth were mixtures of oxides with no detectable carbon, and those with calcium, strontium, and barium contained carbonates. Use of a partially fluorinated barium beta-diketonate gave films of BaF2 with small amounts of BaCO3.
Combined neutron and x-ray powder diffraction study of Fe0.50Co0.48V0.02
Authors: Williams A. , Kwei G. H. , Ortiz A. T. , Karnowski M. , Warburton W. K.
Published: September 2007

The large number of constituent elements and high symmetry of the ordered Fe–Co−V alloys make a complete solution of its structure impossible from a single diffraction experiment. We have carried out a Rietveld refinement of the site occupancies for a partially ordered Fe–Co–V alloy using both neutron and anomalous dispersion x-ray powder diffraction data in order to obtain a complete crystallographic solution to its structure. Contrary to previous assumptions that V occupies both sites randomly or magnetic and Mössbauer studies that suggest that V has a site preference for the Fe sublattice, we find that the V dopant preferentially occupies the Co sites.
Microstructure and tribology of laser mixed Fe/Ti/C multilayered films on AISI 304 stainless steel
Authors: Nastasi M. , Hirvonen J-P. , Zocco T. G. , Jervis T. R.
Published: September 2007

An excimer laser was used to mix Fe/Ti/C multilayered films on 304 stainless steel substrates. The samples were processed at both 1.1 and 1.7 J/cm2 with the number of pulses at each position varied between 1 and 10. Composition, microstructure, phase evolution, and tribological properties were observed to correlate with total laser fluence. Increases in Fe concentration from substrate interdiffusion and loss of C content were observed with increasing total laser fluence. The best tribological properties were observed in films possessing a combination of an amorphous or Fe3C phase plus fine grain TiC following processing at low and intermediate total laser fluence. At higher total fluences a combination of α-Fe, Fe3C, and fine-grain TiC was observed along with degradation in the wear and friction properties. Under optimum laser processing conditions the modified surface had a friction coefficient under dry sliding conditions reduced by a factor of 2 relative to uncoated 304 stainless steel and was significantly more wear resistant. These improvements in wear and friction appear to be related to the reduced chemical reactivity of the amorphous and carbide phases and to the influence of microstructure on improved mechanical properties.
Chalcogenide glasses Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te for infrared optical fibers
Authors: Haruvi-Busnach I. , Dror J. , Croitoru N.
Published: September 2007

Chalcogenide glasses of the systems Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te have been prepared. Several compositions were found suitable for drawing fibers for CO2 laser radiation (λ = 10.6 μm) transmission. The glasses were characterized by x-ray diffraction, DSC (Differential Scanning Calorimetry), SEM with EDX analysis, FTIR spectrometry, density, and microhardness measurements. The glass transition temperature and microhardness of Ge–Se–Sn and Ge–Sn–Se–Te glasses decreased with increasing Sn content, for most of the samples. The region of high IR transparency of Ge–Se–Sn, Ge–Se–Te, and Ge–Sn–Se–Te glasses was slightly expanded (1–2 μm) toward longer wavelengths, compared to Ge–Se glasses, mainly for the glasses containing 70 at.% Se. The intensity of the impurity absorption peak of Ge–O (at λ ∼ 12.8 μm), which usually appears in Ge–Se glasses, was reduced or absent in Ge–Sn–Se–Te glasses. The best fibers were produced with the glass composition Ge–0.8Sn0.2Se3.5Te0.5. An attenuation of 20 dB/m at 10.6 μm, and a transmitted maximum power density of 2.4 ⊠ 106 W/m2 were measured. The mechanical and optical characteristics of these glasses have been related to the glasses structure. Corresponding to the reduced masses of the bonds formed in the Ge–Sn–Se–Te system (in the amorphous region), it is expected that the multiphonon edge is slightly shifted. As a consequence, as was measured, the transparency region has been expanded by less than 2 μm toward longer wavelengths.
Electrochemically lithiated V2O5 films: An optically passive ion storage for transparent electrochromic devices
Authors: Talledo A. , Andersson A. M. , Granqvist C. G.
Published: September 2007

LiyV2O5 films were produced by reactive de magnetron sputtering followed by electrochemical posttreatment in LiClO4. X-ray diffraction showed an orthorhombic structure. Spectrophotometric transmittance and reflectance measurements demonstrated that the luminous and solar absorptance increased moderately when y increased from zero to unity. It is argued that LiyV2O5 is useful as an ion storage material operating in conjunction with electrochromic films.
Carbon fiber reinforced tin-lead alloy as a low thermal expansion solder preform
Authors: Ho C. T. , Chung D. D. L.
Published: September 2007

Tin-lead (40 wt. % Pb) solder-matrix composites containing 8–54 vol.% continuous unidirectional copper plated carbon fibers were fabricated by squeeze casting for use as low thermal expansion solder preforms. The low thermal expansion greatly increased the thermal fatigue life for solder joints between materials with low thermal expansion coefficients. For example, for 29 vol.% fibers, the thermal expansion coefficient was 8 ⊠ 10−6/°C (25–105°C) in the direction parallel to the fibers compared to a corresponding value of 24 ⊠ 10−6/°C for plain solder. The thermal fatigue life for cycling 2 cm long alumina-to-alumina solder joints between 25 and 100°C was increased from 98 to 183 cycles by using 29 vol.% carbon fibers in the composite solder. The fibers also increased the tensile modulus and tensile strength of the solder, but the ductility was decreased. The copper coating on the carbon fibers increased the tensile strength and ductility of the composite.
Small-angle scattering studies of the pore structure of polymer-modified portland cement pastes
Authors: Castaño V. M. , Schmidt P. W. , Hörnis H. G.
Published: September 2007

Small-angle x-ray and neutron scattering experiments were performed in several polymer-containing portland cement pastes with the same w/c ratio. The nature of the results is discussed in terms of the role of the polymer upon the properties of the materials. A comparison with other works seems to indicate that the capillary pores are strongly affected whereas the gel porosity remains unchanged by the polymer solutions.
Elevated temperature properties of Mg–14Li–B particulate composites
Authors: Wolfenstine J. , González-Doncel G. , Sherby O. D.
Published: September 2007

The creep behavior of Mg–14Li particulate composites containing 0,10,20, and 30 vol. % boron particles was evaluated from 230 to 280°C. The results reveal that the creep strength of the particulate composite is increased by a factor of eight over the Mg–14Li matrix with the addition of 30 vol. % boron. The body-centered cubic (bcc) Mg–14Li alloy is shown, however, to be much weaker than hexagonal close-packed (hep) pure magnesium. This difference is attributed to the high rate of atom mobility in the open structure of the Mg–14Li bcc alloy. It is predicted that a Mg–6Li–30B particulate composite, containing an hep matrix structure, will have a higher specific strength at 250°C than the new experimental aluminum base–high iron alloys prepared by rapid solidification processing.
Decomposition of YBa2Cu3O7−x during annealing in CO2/O2 mixtures
Authors: Gao Y. , Merkle K. L. , Zhang C. , Balachandran U. , Poeppel R. B.
Published: September 2007

The stability of YBa2Cu3O7−x superconductors toward reactions with CO2 in CO2/O2 gas mixtures has been studied during annealing at temperatures ranging from 600°C to 950°C. The results show that there are three different types of the reactions. The reaction products of these reactions all include BaCO3 and CuO, while the third product is dependent on the annealing temperature. At 600°C, YBa-carbonates were formed while Y2Cu2O5 and Y2BaCuO5 were formed at 815°C and 950°C, respectively. Transmission Electron Microscopy images show that the reactions started at grain boundaries with the formation of island-type precipitates.
TEM studies on twin boundary in YBa2Cu3O7and YBa2(Cu0.98M0.02)3O7(M = Zn, Al)
Authors: Zhu Yimei , Suenaga Masaki , Xu Youwen
Published: September 2007

High resolution electron microscopy of the twin boundary layers in YBa2(Cu1−xMx)3O7+δforx= 0 and 0.02 and M = Zn and Al showed that the boundary widths are ∼1 nm for the pure and the Zn substituted YBa2Cu3O7and ∼3 nm for the Al substituted oxide. From two beam contract studies and the high resolution images, it was concluded that the respective lattice plane across the boundary is shifted by (⅓–½)·2d(110)along the boundary. The broadening of the layer by the Al substitution is also thought to be a cause for the reduction of the twin boundary energy, leading to an increased twin density.
Threshold displacement and interstitial-atom formation energies in Ni3Al
Authors: Caro A. , Victoria M. , Averback R. S.
Published: September 2007

Threshold displacement energies for atomic displacements along 〈110〉, 〈100〉, and 〈111〉 directions, and formation enthalpies of several symmetric interstitial atom configurations were calculated for Ni3Al by computer simulation using “embedded atom method” potentials. The Ni–Ni (100) dumbbell in the plane containing only Ni atoms has the lowest interstitial-atom enthalpy although the enthalpies of other configurations are similar. Interstitial configurations involving Al atoms all have much higher enthalpies. The anisotropy of the threshold energies in Ni3Al is similar to pure metals and no significant difference in threshold energy was observed for 〈110〉 replacement chains in rows containing all Ni atoms or alternating Ni–Al atoms. Various metastable interstitial atom configurations were observed, including crowd-ions. In addition, the spontaneous recombination volume for some configurations can be much smaller than in pure metals. The consequences of these results for radiation induced segregation and amorphization are discussed.
Kinetics of short- and long-range B2 ordering in the pair approximation
Authors: Fultz B.
Published: September 2007

The kinetic master equation is developed in the pair approximation to study disorder ⇉ B2 order transformations in bee binary alloys. Coupled sets of rate equations for the pair variables are obtained for atom movements by either the direct interchange mechanism or the vacancy mechanism. Numerical integrations provide the nonequilibrium relaxations of short- and long-range order (SRO and LRO) and the vacancy balances between the two sublattices. For binary alloys, disorder ⇉ order transformations were studied for all combinations of interatomic interaction strengths, activation barrier heights, and alloy stoichiometry variations. After a transient vacancy relaxation, all cases began with a quick relaxation of SRO, followed later and independently by the growth of LRO and additional SRO. There were some variations in kinetic path through SRO and LRO, moderate variations in overall kinetics, and large variations in vacancy balance. Some nonphysical aspects of kinetics in the pair approximation are discussed.
Synthesis of ternary alloys Mg2Ni0.75Pd0.25 and studies on its surface properties
Authors: Yunshi Zhang , Jianhua Ji , Huatang Yuan , Shengchang Chen , Da Wang , Taoshi Zang
Published: September 2007

The ternary alloy Mg2Ni0.75Pd0.25 was made by the Replacement-Diffusion Method (RDM). Using x-ray analysis, scanning electron microscopy, AES analysis, and the BET method, the authors were able to characterize the structure of the alloy and study its surface properties. It has been found that the alloy thus obtained has excellent surface properties compared to that prepared metallurgically.
Some titanium germanium and silicon compounds: Reaction and properties
Authors: Thomas O. , d'Heurle F. M. , Delage S.
Published: September 2007

Titanium reacts with pure Ge in two different ways: At low temperatures one observes the formation of Ti6Ge5 with some characteristics typical of diffusion-controlled reaction. Upon completion of this first stage Ti6Ge5 reacts with remaining Ge to form TiGe2, isomorphous with C54 TiSi2, in a process which is clearly controlled by nucleation. The same observations apply to reactions with a Ge alloy containing 25 at.% Si. With an alloy containing 50 at.% Si the two stages become merged, so that while remaining identifiable, they are much less distinct than with the previous conditions. The reaction behavior observed with a Ge alloy containing 80 at.% Si resembles that generally obtained with pure Si: there are no easily identifiable steps between the initial Si–Ti sample and the final one, Si–TiSi2. With both the 50-50 and 80-20 Si–Ge alloys the formation of the C54 structure is preceded by that of the C49 structure (ZrSi2 type), as with pure Si. The gradual merging of the diffusion-controlled reaction and that controlled by nucleation as the concentration of Si in the substrate increases implies that nucleation plays a significant role in the formation of TiSi2, even if that role cannot be easily isolated. Effects due to gas impurities on the path of the metal-substrate reaction have been analyzed. The resistivities of several pure and alloyed phases have been measured. Alloy scattering in the system TiSi2–TiGe2 is briefly discussed.
Structural studies of HgCdTe grown by MOCVD on lattice-matched substrates
Authors: Bevan M. J. , Greggi J. , Doyle N. J.
Published: September 2007

Improved structural quality Hg1−xCdxTe epitaxial films have been grown by metal organic chemical vapor deposition (MOCVD) using the interdiffused multilayer process (IMP) on lattice-matched CdZnTe substrates at temperatures above 400°C with diethyltelluride. Double-crystal rocking curve data with values as low as 25 arcsec correlated with cross-sectional transmission electron micrographs. The process of growing alternate layers of HgTe/CdTe for improved compositional uniformity, and the inherent mismatch, was not detrimental to the structural quality, which was limited by that of the substrate.
Microstructures of diamond formed by plasma-assisted chemical vapor deposition
Authors: Kaae J. L. , Gantzel P. K. , Chin J. , West W. P.
Published: September 2007

The microstructures of five different diamond films formed by plasma-assisted chemical vapor deposition have been studied by transmission electron microscopy. The films were selected for study based on differences in their surface morphologies. The preferred orientations inferred from the symmetries of the crystals observed on the surfaces of these films were consistent with those measured by x-ray diffraction. A general characteristic of all of the diamond film microstructures was stacking faults and microtwins on {111} planes, but the densities and the distributions of the defects varied widely among the films. The observations of microstructure indicate that when a crystal grows so that {100} facets are formed, stacking faults and microtwins are confined to regions near its boundaries, and when a crystal grows so that {111} facets are formed, stacking faults and microtwins are distributed throughout its volume. Under some deposition conditions the defects are confined to bands in the crystal, and coincidence of these defect bands with small steps on the crystal facets suggests that the steps may be caused by the intersection of the bands with the surface.
Equilibrium shape of a buoyant particle
Authors: Marks L. D. , Ajayan P. M.
Published: September 2007

The equilibrium shape of a small particle on a substrate where the particle can sink into the substrate is evaluated.
Microstructure at the interface between AIN and a Ag–Cu–Ti braze alloy
Authors: Carim A. H. , Loehman R. E.
Published: September 2007

The joining of aluminum nitride by active metal brazing with a Ag–Cu–Ti foil has been investigated in cross section by transmission electron microscopy. The reaction of AIN with the braze alloy results in the formation of continuous TiN and (Ti, Cu, Al)6N (η-phase) layers at the interface. AIN grains at the interface often display arrays of dislocations, presumably arising from thermal expansion mismatch between the AIN and the TiN (the coefficients of thermal expansion are 43 ⊠ 10−7/°C and 80 ⊠ 10−7/°C, respectively). The adjoining TiN contains small Cu precipitates and may also contain numerous defects. Titanium preferentially penetrates the AIN grain boundaries, resulting in finger-like TiN intrusions into the substrate, which sometimes cover entire AIN grains in a TiN shell. On the other side of the TiN, a continuous layer of equiaxed, defect-free η–nitride grains is found. Beyond this η–nitride layer is the remaining mixture of metallic Ag and Cu. High-resolution electron microscopy demonstrates that the AIN–TiN and TiN–η boundaries are abrupt and contain no additional crystalline or amorphous intervening phases. Particular orientation relationships are occasionally observed at the AIN–TiN interface; these are not always the ones that produce the minimum lattice mismatch. The implications of the observed morphology with respect to the reaction sequence, transitional phases, and structural integrity of the joint are discussed.
The effect of Ag electrode processing on (Nb, Ba) doped TiO2 ceramics
Authors: Chen Chi-Jen , Wu Jenn-Ming
Published: September 2007

Since the characteristics of the electrode made from Ag paste greatly affect the dielectric properties of (Nb, Ba) doped TiO2 ceramics, the processing condition, i.e., baking temperature, was investigated. Low melting glass binder contained in Ag paste reacted with TiO2 ceramics to form an interface layer between Ag electrode and TiO2 ceramics during baking. The interface layer was identified as Bi2Ti2O7 by x-ray diffraction (XRD), and the thickness of the Bi2Ti2O7 layer was estimated from line profiles of EPMA and dielectric properties. The interface layers were found to increase with baking temperature. Increased baking temperature lowered the relative dielectric constant and dielectric dissipation factor of TiO2 ceramics, while it raised the resistivity. Controlling the baking condition of the Ag paste electrode on TiO2 ceramics resulted in reasonably good dielectric properties and excellent temperature stability.
Rietveld powder structure refinement of Na2Al2Ti6O16; Comparison of synchrotron radiation and conventional x-ray tube datasets
Authors: Toraya H. , Masciocchi N. , Parrish W.
Published: September 2007

The crystal structure of Na2Al2Ti6O16 was refined by the Rietveld method using synchrotron radiation and conventional x-ray powder data, and the agreement factors were Rp = 3.35%, Rwp = 4.30%, and RBragg = 6.39% for synchrotron data. The formula based on the chemical analysis and 16 O atoms is Na1.97Al1.82Ti6.15O16. The crystal data are monoclinic, C2/m, a = 12.1239(3) Å, b = 3.7749(1) Å, c = 6.4180(2) Å, β = 107.59(1)°, V = 280.00(4) Å3, Z = 1, and Dx = 3.82 g cm−3. The site occupancy refinement showed a partial ordering of Al3+ and Ti4+ ions in the two-crystallographically independent octahedral sites.
Additive enhanced nonaqueous electrodeposition of silver on Ba2YCu3O7
Authors: Rosamilia J. M. , Miller B.
Published: September 2007

A nonaqueous plating bath for silver deposition on the Ba2YCu3O7 superconductor has been modified with thiourea to give enhanced coverage of the metal film at low thicknesses. For both porous and high density ceramic substrates, SEM and optical microscopy show nucleation of silver deposits is increased by the additive. The resulting silver-superconductor contact resistances are comparable to those achieved without additives. Adhesion of the deposits and ease of mechanical handling are improved with thiourea. The combination of highly reactive oxidized substrate, nonaqueous solvent, and strongly surface active agent forms a novel extension for electrodeposition science.
High dielectric constant and small temperature coefficient bismuth-based dielectric compositions
Authors: Ling H. C. , Yan M. F. , Rhodes W. W.
Published: September 2007

We have studied the crystal structure and the dielectric properties of a scries of Bi-based ceramic compositions as a function of compositional variation and sintering temperature. These dielectrics have dielectric constants hetween 70 and 165 and their temperature coefficients are within ±500 × 10−6/°C. The precise temperature coefficient can be controlled via compositional changes such that dielectrics with temperature coefficients within ±50 × 10−6/°C are easily obtainable. The room temperature dissipation factor is smaller than 0.001 or equivalently, the Q value is greater than 1000. The electrical resistivity is greater than 1014 ohm-cm. Furthermore, these dielectrics are sinterable below 960 °C, rendering it possible to use silver or high silver metallization as the internal electrode in making the multilayer ceramic capacitors.
On the nature of the oxygen-related defect in aluminum nitride
Authors: Harris J. H. , Youngman R. A. , Teller R. G.
Published: September 2007

The oxygen-related defect in an aluminum nitride (AIN) single crystal and in polycrystalline ceramics is investigated utilizing photoluminescence spectroscopy, thermal conductivity measurements, x-ray diffraction lattice parameter measurements, and transmission electron microscopy. The results of these measurements indicate that at oxygen concentrations near 0.75 at.%, a transition in the oxygen accommodating defect occurs. On both sides of this transition, simple structural models for the oxygen defect are proposed and shown to be in good agreement with the thermal conductivity and lattice parameter measurements, and to be consistent with the formation of various extended defects (e.g., inversion domain boundaries) at higher oxygen concentrations.
Preparation of Cu–Y–Ba alloys by mechanical alloying
Authors: Batalla E. , Zwartz E. G.
Published: September 2007

Preliminary results of producing Cu–Y–Ba metallic precursors to high Tc superconductors by high energy ball milling are reported. Mechanical alloying of Cu, Y, and Ba powders (various stoichiometries) produced either amorphous, mixed crystalline/amorphous, or fine grained crystalline powders, as shown by their x-ray spectra. None of the powders exhibited flux exclusion down to a temperature of 1.4 K. The YBa2Cu3 precursor consisted of a mixture of crystalline phases. After being pressed into a pellet and sintered, it was found to be superconducting at liquid nitrogen temperatures.
Synthesis of YBa2Cu3O7−x fibers from an organic acid solution
Authors: Zhang S. C. , Messing G. L. , Huebner W. , Coleman M. M.
Published: September 2007

A process has been developed for the synthesis of YBa2Cu3O7−x superconducting fibers from an organic acid precursor solution. Through rheology measurements on a series of precursor solutions, the molecular structure was determined and subsequently controlled to allow for fiber drawing. For solutions with a viscosity ⋛10 poise, fibers of 1 to 2 m length and 50 ∼ 100 μm diameter can be hand drawn at ≍80 °C. Processing methods were developed to circumvent deformation of the thermoplastic fibers during heating and to minimize BaCO3 formation during decomposition. Fibers sintered at 850 °C for 1 h in 10−2 atm O2, followed by annealing at 500 °C for 4 h in O2, were fully dense, consisted of submicron grains, and were superconducting.
Grain growth and the microstructural effects on the properties of YBa2Cu3O7−y superconductor
Authors: Chu C. T. , Dunn B.
Published: September 2007

The microstructural development and grain growth of YBa2Cu3O7−y ceramics at 925, 950, and 975 °C were studied. Densification occurred quite rapidly at temperatures below 925 °C. The grain growth of YBa2Cu3O7−y followed a D5 − D50 = Kt relation when sintered at 925 and 950 °C. At 975 °C, the kinetics changed to cubic (D3) behavior, which can be attributed to the formation of a liquid phase at grain boundaries. A trend of decreasing Jc with increasing sintering temperature was observed. Other properties including Tc and the width of the transition were virtually unaffected by the change in microstructure. Without prolonged annealing, a relatively homogeneous oxygen stoichiometry of 6.8 was obtained for fairly dense samples (>93% of theoretical). These results suggest that the oxygenation rate of YBa2Cu3O7−y was quite rapid between the tetragonal phase and the orthorhombic composition of YBa2Cu3O6.8.
Degradation of high-Tc superconductors by annealing in dry and moist atmospheres
Authors: Lee W-K. , Nowick A. S.
Published: September 2007

A study is made of the effects of annealing both La2−xSrxCuO4 (for x = 0, 0.1, and 0.15) and YBa2Cu3O7 in wet and dry O2 atmospheres at various temperatures between 200 and 930 °C. In the case of La2−xSrxSrCuO4, substantial degradation of resistive properties occurs during annealing in moist O2, the degradation being highest at 200 °C and decreasing as the treatment temperature increases. Since the Meissner effect remains unaffected, it is concluded that degradation is due to the formation of a hydroxide species at grain boundaries, which decomposes as the anneal temperature is increased to 930 °C. In the case of YBa2Cu3O7, on the other hand, moisture does not produce degradation for anneals at 200 °C and above, but severe degradation of resistive behavior does occur for dry O2 anneals, with a maximum effect at 500 °C. It is found that this effect results from a contaminant gas, possibly CO2, absorbed by the furnace when it is open to air. Again, the degradation is due to formation of a grain-boundary phase which decomposes by annealing at 930 °C.
Surface morphology of oxygen-implanted wafers
Authors: Nakashima Sadao , Izumi Katsutoshi
Published: September 2007

The surface morphology of SIMOX wafers implanted at 180 keV with doses of 0.4–2.2 ⊠ 101816O+ cm−2 in a temperature range of 400–700 °C has been investigated using transmission electron microscopy (TEM) replica and cross-sectional TEM (XTEM) techniques. Wafer temperature during oxygen implantation strongly affects the morphology. A number of dents are formed on the surface of wafers implanted at temperatures higher than 510 °C with a dose of 1.8 ⊠ 1018 cm−2. Increasing the wafer temperature causes the dents to grow. The dents disappear by a high-temperature anneal of 1260 °C after the implantation. It is found that oxygen implantation through a 50-nm-thick screen oxide film prevents dent formation. A model explaining the dent formation and dent growth is also proposed.
The spontaneous polarization as evidence for lithium disordering in LiNbO3
Authors: Birnie Dunbar P.
Published: September 2007

The ferroelectric to paraelectric phase transition in lithium niobate is examined. The present study focuses on the microscopic mechanism for this phase transition. Literature reports that give insight into this mechanism are reviewed. Two alternate mechanisms for this second order transition have been discussed previously. The phase transition has been proposed to occur by either (a) cooperative displacement of Li ions or (b) statistical disordering of Li between two octahedral sites in the structure. The present study develops a general Landau expression for the second order phase transition. The spontaneous polarization of the lattice is used as an indicator of the extent of transformation. Then both displacement and disordering models are explored. These are compared with the observed spontaneous polarization data. It is concluded that the spontaneous polarization data are indicative of a Li disordering model, rather than a Li displacement model.
Effect of MnO on the microstructures, phase stability, and mechanical properties of ceria-partially-stabilized zirconia (Ce–TZP) and Ce–TZP–Al2O3composites
Authors: Wang J. S. , Tsai J. F. , Shetty D. K. , Virkar A. V.
Published: September 2007

The effects of increasing amounts of MnO additions on the microstructures, phase stability, and mechanical properties of ZrO2–12 mol % CeO2and ZrO2–12 mol% CeO2–10 wt.% Al2O3were studied. MnO suppressed grain growth in ZrO2–12 mol% CeO2, while enhancing the mechanical properties significantly (strength = 557 MPa, fracture toughness = 9.3 MPaat 0.2 wt.% MnO). The enhanced mechanical properties were achieved despite an increased stability of the tetragonal phase, as evidenced by a lower burst transformation temperature (Mb) and a reduced volume fraction of the monoclinic phase on the fracture surface. In ZrO2–12 mol% CeO2–10 wt.% Al2O3, the addition of MnO suppressed the grain size of ZrO2, while promoting grain growth and changing the morphology of Al2O3. More significantly, the stability of the tetragonal ZrO2phase decreased (highMbtemperature) with a concurrent increase in fracture toughness (13.2 MPaat 2 wt.% MnO) and transformation plasticity (1.2% in four-point bending). The widths of the transformation zones observed adjacent to the fracture surfaces showed a consistent inverse relation to the transformation yield stress, as would be expected from the mechanics of stress-induced phase transformation at crack tips. The improvements in mechanical properties obtained in the base Ce–TZP and the Ce–TZP–Al2O3composite ceramics with the addition of MnO are critically examined in the context of transformation toughening and other possible mechanisms.