bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization Phases of the Zr41Ti14Cu12.5Ni10Be22.5 Alloy After Slow Solidification
Authors: Wei Q. , Wanderka N. , Schubert-Bischoff P. , Macht M-P. , Friedrich S.
Published: March 2008

A systematic study was carried out on the equilibrium phases after slow solidification of the Zr41Ti14Cu12.5Ni10Be22.5 alloy. The crystalline microstructure of the slowly cooled melt of the alloy shows “polygons” and “plates” embedded in a fine-grained two-component matrix. To analyze the crystal structure of the different components, microdiffraction technique combining convergent beam electron diffraction and conventional selected-area electron diffraction were used. The stoichiometry of these phases was confirmed by field ion microscopy with atom probe and energy-dispersive x-ray analysis in a transmission electron microscope. The polygons were determined to be cubic (a = 1.185 nm) with space group Fm3m (cF116). The plates were found to be tetragonal (a = 0.37 nm, c = 1.137 nm) with space group I4/mmm (tI6). Its composition is (Cu + Ni)(Zr + Ti)2. One phase of the fine-grained two-component matrix was rich in Ti and poor in Be; the other one was rich in Be and poor in Ti. The Ti-rich phase was determined to be hexagonal (a = 0.536 nm, c = 0.888 nm) with space group P63/mmc.
Synthesis of Carbon Tubes Using Microwave Plasma-assisted Chemical Vapor Deposition
Authors: Zhang Qing , Yoon S. F. , Ahn J. , Gan Bo , Rusli  , Yu Ming-Bin
Published: March 2008

Carbon tubes were successfully produced using microwave plasma-enhanced chemical vapor deposition on silicon, quartz, and ceramic substrates. The carbon tubes, about 80–100 nm in diameter and a few tens of microns in length, were formed under methane and hydrogen plasma at 720 °C with the aid of iron oxide particles. In this approach, an average tube density of about 109 cm−2 was obtained. The crooked and nonuniform diameters of some tubes suggested that they were composed of incompletely crystallized graphitic shells due to existing defects. The characteristic of the tubes grown upward on the silicon substrate accounted for a remarkably large electron field emission current of 0.1 mA/cm2 from the surface of the tube sample at a low turn-on field of 3 V/μm.
Effects of Interstitial Additions on the Structure of Ti5Si3
Authors: Williams J. J. , Kramer M. J. , Akinc M. , Malik S. K.
Published: March 2008

Changes in the structure of Ti5Si3 were measured by x-ray and neutron diffraction as carbon, nitrogen, or oxygen atoms were systematically incorporated into the lattice. Additionally, the lattice parameters and variable atomic positions of pure Ti5Si3 were determined to be a = 7.460 Å, c = 5.152 Å, xTi = 0.2509, and xSi = 0.6072. The measured trends in lattice parameters as carbon, nitrogen, or oxygen atoms were added to Ti5Si3 showed that most of the previous studies on supposedly pure Ti5Si3 were actually contaminated by these pervasive light elements. Also, oxygen and carbon additions were shown to strongly draw in the surrounding titanium atoms—evidence for bonding between these atoms. The bonding changes that occurred on addition of carbon, nitrogen, or oxygen acted to decrease the measured anisotropic properties of Ti5Si3, such as thermal expansion.
A Study of Microindentation Hardness Tests by Mechanism-based Strain Gradient Plasticity
Authors: Huang Y. , Xue Z. , Gao H. , Nix W. D. , Xia Z. C.
Published: March 2008

We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicronlength scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model. In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework.
Processing and Characterization of High-conductance Bismuth Wire Array Composites
Authors: Huber T. E. , Graf M. J. , Foss C. A. , Constant P.
Published: March 2008

We fabricated Bi nanowire array composites with wire diameters from 30 to 200 nm by high-pressure injection (HPI) of Bi melt into porous anodic alumina templates. The composites were dense, with Bi volume fraction in excess of 50%. The parallel Bi nanowires, whose length appeared to be limited only by the thickness of the host template (up to 55 μm), terminated at both sides of the composite in the Bi bulk. The individual Bi nanowire crystal structure was rhombohedral, with the same lattice parameters as that of bulk Bi; the wires in the array were predominantly oriented with the trigonal axis along the wire length. Low contact resistance was achieved by bonding the composite to copper electrodes.
Metalorganic Chemical Vapor Deposition of Nickel Films from Ni(C5H5)2/H2
Authors: Kang Jin-Kyu , Rhee Shi-Woo
Published: March 2008

Nickel thin films were deposited with Ni(C5H5)2 \NiCp2, bis(cyclopentadienyl)nickel, nickelocene]/H2 at various temperatures and H2/Ar ratios. The deposition rate, resistivity, purity, crystal structure, and surface morphology of the nickel film were investigated. Also, thermal analysis was done to find out the dissociation characteristics of NiCp2, and Fourier transform infrared spectroscopy diagnostics were carried out to study the gas phase reaction kinetics of NiCp2. Nickel films deposited at higher temperatures (>225 °C) had high carbon content and high resistivity. At higher temperatures, thermal decomposition of NiCp2 and subsequent decomposition of Cp induced a large amount of carbon incorporation into the film. At lower temperatures (<190 °C), the slow dissociation of NiCp led to some extent of carbon incorporation in the film. Nickel films deposited at around 200 °C showed carbon content lower than 5% and lower resistivity because of the effective dissociation of Ni–Cp and desorption of Cp from the surface. Nickel films deposited with hydrogen addition showed higher purity, crystallinity, and lower resistivity due to the removal of the carbon on the surface.
Crystal growth and structure analysis of Sm2−xCexCuO4
Authors: Takeda H. , Okuno M. , Ohgaki M. , Yamashita K. , Matsumoto T.
Published: March 2008

The phase diagram of the Sm2O3–CuO system was investigated by the combination of the differential thermal analysis and the quench method. The results showed that Sm2CuO4 incongruently melts at about 1220 °C, and that the solid Sm2CuO4 exists in equilibrium with the liquid consisting of 81–95 mol% CuO in the range of 1060–1220 °C. On the basis of the phase diagram, Sm2−xCexCuO4 single crystals were grown by the traveling solvent floating zone method. The crystal structure [space group I4/mmm, a = 3.917(1), c 4 11.899(2) Å] has been refined using single-crystal x-ray diffraction data with a precision corresponding to an R index of 0.02.
Structure and chemical characteristics of tin oxide films prepared by reactive-ion-assisted deposition as a function of oxygen ion beam energy
Authors: Song Seok-Kyun , Kim Daeil , Kim Steven , Koh Seok-Keun , Jung Hyung-Jin , Lee Jeong-Young , Baik Hong-Koo
Published: March 2008

Tin oxide films were deposited on amorphous SiO2/Si and Si (100) substrates by ion-assisted deposition (IAD) at various ion beam potentials (VI) at room temperature and a working pressure of 8 × 10−5 torr. The structural and chemical properties of the as-grown tin oxide films were investigated to determine the effects of the oxygen ion/atom arrival ratio (Ri). X-ray diffraction patterns indicated that the as-grown films with different average energy per atom (Eave) showed different growth directions. The as-grown films with oxygen/Sn ratio (NO/NSn) of 2.03 and 2.02 had preferred orientation of (101) and (002), respectively. In addition, the as-grown film with low Ri was amorphous. Comparison of the observed d spacings with those for standard SnO2 samples, indicated that the crystalline as-grown films had compressive and tensile stress depending on Eave. In transmission electron microscopy analysis, a buffer layer of amorphous tin oxide was observed at the interface between the substrate and the film, and the crystalline grains were grown on this buffer layer. The crystalline grains were arranged in large spherical clusters, and this shape directly affected surface roughness. Rutherford backscattering spectroscopy spectra showed that the tin oxide thin films were inhomogeneous. The density of films decreased and the porosity and oxygen trapped in the films increased with increasing Ri. The densest film had about 6% porosity.
Huge magnetic hardening ascribed to metastable crystallites during first stages of devitrification of amorphous FeSiBNbSn alloys
Authors: Cremaschi V. , Arcondo B. , Sirkin H. , Vázquez M. , Asenjo A. , Garcia J. M. , Abrosimova G. , Aronin A.
Published: March 2008

A huge magnetic hardening (i.e., increase of coercivity from 5 A/m up to 4.4 kA/m) was reported for Fe75Si11B10Nb3Sn alloy ribbons during their very first stage of crystallization from an initial amorphous state. In contrast, Fe78Si11B10Sn1 showed no such hardening, while a moderate hardening was observed for Fe76Si11B10Nb3. This outstanding change was ascribed to the generation of metastable nanocrystallites that disappear upon heating at higher temperatures. A noticeable softening was then recovered (with a decrease of coercivity down to 0.8 kA/m) once the optimum homogeneous conventional nanocrystalline phase was achieved. Both structure and magnetic evolutions are followed by different techniques.
Thermal stability of RuO2, BaxSr1−xTiO3/RuO2, and BaxSr1−xTiO3/Pt/Ti/SiO2on Si(100)
Authors: Kang T. S. , Kim Y. S. , Je Jung Ho
Published: March 2008

The thermal stability of RuO2/Si(100) films in air was studied using ex situ synchrotron x-ray scattering. The (110) textured RuO2 film showed good thermal stability due to the low surface and strain energies. However, the RuO2 films of high strain and surface energies were transformed to three-dimensional islands during annealing up to 800 °C. We also studied, during the post annealing process, the interface roughness of BaxSr1−xTiO3 (BST)/RuO2/Si(100) and BST/Pt/Ti/SiO2/Si(100) structures comparatively, using in situ synchrotron x-ray scattering. The interfaces of the BST/RuO2/Si were thermally stable up to 500 °C, and the deterioration of the interfaces above 500 °C was attributed to the crystallization of amorphous BST film. Meanwhile, the interfaces of the BST/Pt/Ti/SiO2/Si were significantly degraded even at the low temperature of 350 °C, mainly due to the formation of the Pt–Ti alloy and the Ti oxidation.
Local environment of iron and uranium ions in vitrified iron phosphate glasses studied by Fe K and U LIII-edge x-ray absorption fine structure spectroscopy
Authors: Karabulut M. , Marasinghe G. K. , Ray C. S. , Day D. E. , Waddill G. D. , Allen P. G. , Booth C. H. , Bucher J. J. , Caulder D. L. , Shuh D. K. , Grimsditch M. , Saboungi M-L.
Published: March 2008

The local structure of iron and uranium ions in a series of iron phosphate glasses with the general composition (40 – x)Fe2O3–xUO2–60P2O5 and (1–x–y)(40Fe2O3–60P2O5)– xUO2–y(Na2O or CaO) was investigated using Fe K-edge and U LIII-edge x-ray absorption fine structure spectroscopy. Replacing Fe2O3 by UO2 in the glass caused more distortion in the coordination environment of Fe(III) ions. Extended x-ray absorption fine structure fits revealed that the Fe–P bonds observed in the base glass also existed in all the waste-loaded glasses. X-ray absorption near-edge structure showed that the uranium ions were predominantly present as U(IV) in the glasses. Uranium ions were coordinated to approximately 8 ± 1 oxygen atoms and 2.5 ± 0.6 phosphorus atoms at an average distance of 2.47 ± 0.02 and 3.8 ± 0.02 Å, respectively. There were no Fe–U or U–Fe neighbors observed, indicating that uranium ions occupied voids in the glass away from the PO4 units. These conclusions were supported by Mössbauer, x-ray photoelectron, and Raman spectroscopic data.
Inhomogeneities in acid-catalyzed titania–silica and zirconia–silica xerogels as revealed by small-angle x-ray scattering
Authors: Mountjoy G. , Rigden J. S. , Anderson R. , Wallidge G. W. , Newport R. J. , Smith M. E.
Published: March 2008

The small-angle x-ray scattering (SAXS) technique was used to investigate inhomogeneities on the scale of 10 to 600 Å in acid-catalyzed titania–silica and zirconia–silica xerogels. SAXS of (TiO2)x(SiO2)1−x and (ZrO2)x(SiO2)1−x xerogels with x < 0.1, in which there was no phase separation, showed the presence of two types of inhomogeneity. For Q < 0.05 Å−1 there was a clear departure from Porod scattering which showed that xerogel powder particle surfaces were rough. For 0.1 < Q < 0.4 Å−1 there was a plateau feature corresponding to micropores within the silica-based network, and this feature changes with heat treatment. SAXS of xerogels with x > 0.3 showed the presence of phase-separated regions of metal oxide, which were initially amorphous and crystallized at higher temperatures. A (TiO2)0.18(SiO2)0.82 xerogel that was not initially phase separated became phase separated after heat treatment at 750 °C due to reduced solubility of Ti in the silica network.
Microstructure observations of silicon carbide nanorods
Authors: Peng H. Y. , Zhou X. T. , Lai H. L. , Wang N. , Lee S. T.
Published: March 2008

The microstructures of β-SiC nanorods synthesized by hot-filament chemical vapor deposition were studied in detail by high-resolution electron microscopy. Two distinct types of nanorods were identified. The longer nanorods (lengths > 0.1 mm) contained globules at their tips and a relatively low density of stacking faults perpendicular to their [111] growth direction. It was also observed that SiC nanorods that grew along [100] direction contained no planar defects. Meanwhile, Ni was found to be an effective catalyst for SiC nanorod growth. The short nanorods (lengths < 50 nm), which contained no globules at their ends, can grow along [111], [100], or [112] direction. The growth of these nanorods was interpreted by a two-dimensional vapor–solid mechanism.
Mechanical properties of niobium disulfide and its hydrated sodium cation intercalation compound
Authors: Lepienski C. M. , Meruvia M. S. , Veiga W. , Wypych F.
Published: March 2008

Mechanical properties of 2H–NbS2 and its intercalation derivative Nax(H2O)yNbS2 were measured by using nanoindentation techniques. The intercalation chemical process was conducted in solution and the cation–hydrated derivative produced was [Nax(H2O)yNbS2]. It was observed that the intercalation process occurs through the crystal edges producing a wave intercalation's front that moved as the reaction proceeded. The hardness and elastic modulus presented very low values in the intercalated region. The load × displacement curves from nanoindentation tests suggested that intercalation of hydrated sodium ions through the edges caused layer separation even in the nonintercalated region at the center of the crystal. It is important to emphasize that no similar studies were found in the literature about this theme. Intercalation process is very important in several areas, like solid-state batteries, and mechanical properties of these kinds of materials are not completely understood. This study is a new approach to understanding the mechanical behavior of layered materials submitted to an intercalation process.
Morphology and microstructural properties of TiO2 nanopowders doped with trivalent Al and Ga cations
Authors: Depero L. E. , Marino A. , Allieri B. , Bontempi E. , Sangaletti L. , Casale C. , Notaro M.
Published: March 2008

The effects of doping on the morphological and microstructural properties of TiO2 nanopowders produced by laser pyrolysis were investigated mainly by x-ray diffraction (XRD) and electron microscopy. Samples of TiO2 powders were prepared by doping with different trivalent cations (Al and Ga). The powders were calcined at different temperatures in the range 400–1000 °C for 18 h, as well as at constant T = 700 °C up to 160 h. After each thermal treatment, XRD patterns were collected. The analysis of XRD patterns allowed us to estimate the microstrains and average crystallite size and to observe the evolution of the microstructural parameters with temperature. Both Al and Ga inhibited the crystallite growth of TiO2 anatase and the rutile phases, this effect being larger in the Al-doped powders.
Microwires coated by glass: A new family of soft and hard magnetic materials
Authors: Zhukov A. , González J. , Blanco J. M. , Vázquez M. , Larin V.
Published: March 2008

The Taylor–Ulitovski technique was employed for fabrication of tiny ferromagnetic amorphous and nanocrystalline metallic wires covered by an insulating glass coating with magnetic properties of great technological interest. A single and large Barkhausen jump was observed for microwires with positive magnetostriction. Negative magnetostriction microwires exhibited almost unhysteretic behavior with an easy axis transverse to the wire axis. Enhanced magnetic softness (initial permeability, μι, up to 14000) and giant magneto impedance (GMI) effect (up to 140% at 10 MHz) was observed in amorphous CoMnSiB microwires with nearly zero magnetostriction after adequate heat treatment. Large sensitivity of GMI and magnetic characteristics on external tensile stresses was observed. Upon heat treatment, FeSiBCuNb amorphous microwires devitrificated into a nanocrystalline structure with enhanced magnetic softness. The magnetic bistability was observed even after the second crystallization process (increase of switching field by more than 2 orders of magnitude up to 5.5 kA/m). Hard magnetic materials were obtained as a result of decomposition of metastable phases in Co–Ni–Cu and Fe–Ni–Cu microwires fabricated by Taylor–Ulitovski technique when the coercivity increased up to 60 kA/m. A magnetic sensor based on the magnetic bistability was designed.
Synthesis of transparent magnetic particle/organic hybrid film using iron–organics
Authors: Yogo Toshinobu , Nakamura Tomoyuki , Sakamoto Wataru , Hirano Shin-ichi
Published: March 2008

A transparent magnetic particle/organic film was synthesized from an iron–organic compound. Iron(III) 3-allylacetylacetonate (IAA) was polymerized followed by in situ hydrolysis yielding an iron oxide particle/oligomer hybrid. The sizes of magnetic particles were dependent upon the hydrolysis conditions of the IAA oligomers. A nanometer-sized ferrimagnetic iron oxide particle/oligomer hybrid showed a magnetization curve with no coercive force at 300 K and that with Hc of 200 Oe at 4.2 K, respectively. The magnetization versus H/T curves at 300 and 77 K were superimposed on each other and satisfied the Langevin equation. The transparent hybrid film showed a magnetization curve at room temperature. The absorption spectrum of the film was shifted to higher energy by 0.14 eV compared with that of bulk magnetite. The absorption edge of the film was blue-shifted.
A study on barium ferrite particles prepared by chemical coprecipitation
Authors: Ng W. K. , Ding J. , Chow Y. Y. , Wang S. , Shi Y.
Published: March 2008

Chemical coprecipitation was employed to prepare fine particles of barium ferrite with high coercivity (450 kA/m). Magnetic properties of the bonded barium ferrite magnet were measured at different temperatures. The results were found to be fairly close to the theoretical values based on the Stoner–Wohlfarth model. Mechanical milling was utilized to prepare ultrafine dispersed barium ferrite particles. NaF was introduced as a dispersing agent during milling and subsequent heat treatment. The dispersed particles were compacted and then subjected to die upsetting at room temperature. A weak anisotropy in the coercivity and remanence was found in the directions parallel and perpendicular to the compaction direction.
The roles of ammonia and ammonium bicarbonate in the preparation of nickel particles from nickel chloride
Authors: Xia B. , Lenggoro I. W. , Okuyama K.
Published: March 2008

The roles of NH3· H2O and NH4HCO3in the preparation of Ni particles from NiCl2· 6H2O aqueous solution by ultrasonic spray pyrolysis were investigated. The results showed that both ammonia and ammonium bicarbonate had a remarkable influence on the solution chemistry and the resulting particles, and could significantly modify the reaction pathway. After the addition of these additives to the precursor solution, intermediate NiO was formed initially, followed by reduction to metallic Ni in the presence of a reductive gas. H2is a powerful reducing agent; however, metallic Ni could also be obtained in the absence of H2in the carrier gas. In the latter case, it was shown that NH3 was primarily responsible for Ni formation. A description of the mechanisms and processes of Ni formation during spray pyrolysis is proposed.
Formation of carbon nanostructures with Ge and SiC nanoparticles prepared by direct current and radio frequency hybrid arc discharge
Authors: Oku Takeo , Hirata T. , Motegi N. , Hatakeyama R. , Sato N. , Mieno T. , Sato N. Y. , Mase H. , Niwano M. , Miyamoto N.
Published: March 2008

Carbon nanocage structures with Ge and SiC nanoparticles were synthesized by direct current and radio frequency (dc-rf) hybrid arc discharge of C, Ge, and Si elements. High-resolution images showed the formation of Ge and SiC nanoparticles and nanowires encapsulated in carbon nanocapsules and nanotubes. The growth direction of the Ge nanowires was found to be 〈111〉 of Ge, and a structure model for Ge/C interface was proposed. The present work indicates that the various carbon nanostructures with semiconductor nanoparticles and nanowires can be synthesized by the dc-rf hybrid arc-discharge method.
Effect of sensitizing Cr3+ion on optical parameters of Nd-doped yttrium calcium oxyborate crystals
Authors: Xia H. R. , Guo M. , Wang J. Y. , Wei J. Q. , Hu X. B. , Liu Y. G.
Published: March 2008

Pure, Nd doped, and Nd–Cr bidoped yttrium calcium oxyborate Yca4O(BO3)3(YCOB), NdxY1−xCa4O(BO3)3(NYCOB) withx= 0.86, and Cr:NdxY1−xCa4O(BO3)3(Cr:NYCOB) withx= 0.45 and a small amount of Cr3+ions crystallized with a fluorapatite-type structure in the monoclinic system. The unit cell constants werea= 0.8076(7),b= 1.6020(10), andc= 0.3527(2) nm with the angle β of 101.23° for the NYCOB andz= 2. The measured absorption spectra of NYCOB and Cr:NYCOB were compared to Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric-dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agreement. The experiments showed that the Cr3+ions were introduced into the crystalline lattice as a sensitizer to absorb the excitation energy and transfer it to the Nd3+ions in the lattice structure.
Nonagglomerated, submicron α–Fe2O3 particles: Preparation and application
Authors: Jungk H-O. , Feldmann C.
Published: March 2008

Spherical particles of α–Fe2O3 80 to 100 nm in size were prepared with the polyol method. Scanning electron microscopy, x-ray powder diffraction, and measurements of the diffuse reflection were used to characterize the powder material. The characteristic red color of hematite was adjusted after brief heating (250 °C, 15 min) which did not lead to further particle growth. The polyol method turned out to be suited for the preparation of quite concentrated (up to 20 wt%) and very stable suspensions of submicron Fe2O3 particles. Based on such suspensions, the red emitting phosphor Y2O2S:Eu was coated as a model substrate. As a result, very homogeneous coatings of α-Fe2O3 on the phosphor material were realized. Individual iron oxide particles on the phosphor surface confirm the presence of nonagglomerated Fe2O3 particles in the polyol medium.
Pulsed laser deposition of oriented V2O5 thin films
Authors: McGraw Jeanne M. , Perkins John D. , Hasoon Falah , Parilla Philip A. , Warmsingh Chollada , Ginley David S. , Mateeva Eli , Readey Dennis W.
Published: March 2008

We have found that by varying only the substrate temperature and oxygen pressure five different crystallographic orientations of V2O5 thin films can be grown, ranging from amorphous to highly textured crystalline. Dense, phase-pure V2O5 thin films were grown on SnO2/glass substrates and amorphous quartz substrates by pulsed laser deposition over a wide range of temperatures and oxygen pressures. The films' microstructure, crystallinity, and texturing were characterized by electron microscopy, x-ray diffraction, and Raman spectroscopy. Temperature and oxygen pressure appeared to play more significant roles in the resulting crystallographic texture than did the choice of substrate. A growth map summarizes the results and delineates the temperature and O2 pressure window for growing dense, uniform, phase-pure V2O5 films.
Low temperature chemical synthesis of nanocrystalline Pb(Mg1/3Nb2/3)O3 and (1–x)Pb(Mg1/3Nb2/3)O3–xPb(Fe1/2Nb1/2)O3 (x = 0.1, 0.2, and 1) ceramics
Authors: Das R. N. , Ray J. C. , Pramanik P.
Published: March 2008

Nanocrystalline (20 nm) lead magnesium niobate (PMN) powders were prepared via a chemical process. This process involved the addition of aqueous niobium tartrate, lead-ethylenediaminetetraacetic acid, and magnesium-polyvinyl alcohol complex to produce a homogeneous solution. After the complete evaporation of the resulting homogeneous solution, the complexes decomposed and produced a black, fluffy precursor material. The precursor material on calcination up to 850 °C/2 h produced nanocrystalline PMN powders with the corresponding average particle size 20 nm. PMN powders modified with lead iron niobate (PFN) (1 – x)PMN–xPFN (x = 0.1, 0.2, and 1) were also prepared using this route and investigated through x-ray diffraction studies.
Synthesis of filled skutterudite compounds: BayFexCo4−xSb12
Authors: Chen L. , Tang X. , Goto T. , Hirai T.
Published: March 2008

Ba-filled skutterudite compounds, BayFexCo4−xSb12, were synthesized by a two-step solid reaction method. A binary compound of Sb3Ba and a ternary compound of FexCo1−xSb2 were first synthesized at 900 and 973 K, respectively. The presynthesized Sb3Ba and FexCo1−xSb2 were then mixed with Sb and heated at 973 K in an Ar atmosphere. The resulting powder was of single phase with a composition of BayFexCo4−xSb12, having skutterudite structure with the Sb–dodecahedron voids fractionally filled by Ba. The lattice constant of BayFexCo4−xSb12 increased with Ba and Fe content. The maximum filling fraction of Ba (ymax) in BayFexCo4−xSb12 was found to be greater than that of Ce or La in LnyFexCo4−xSb12, especially in the lower Fe content region. The ymax varied from 0.35 to near 1.0 when Fe content (x) changed from 0 to 4.
High-temperature interfacial reaction of an Al thin film with single-crystal 6H–SiC
Authors: Lee Byung-Teak , Shin Yang-Soo , Kim Jin Hyeok
Published: March 2008

Interfacial reactions between an Al thin film and a single-crystal (001) 6H–SiC substrate were investigated using x-ray diffraction and cross-sectional transmission electron microscopy. Aluminum thin films were prepared by radio-frequency magnetron sputtering method on 6H–SiC substrates at room temperature and then annealed at various temperatures from 500 to 900 °C. A columnar-type polycrystalline Al thin film was formed on a 6H–SiC substrate in the as-deposited sample. No remarkable microstructural change, compared to the as-deposited sample, was observed in the sample annealed at 500 °C for 1 h. However, it was found that the Al layer reacted with the SiC substrate at 700 °C and formed an Al–Si–C ternary compound at the Al/SiC interface. Samples annealed at 900 °C showed a double-layer structure with an Al–Si mixed surface layer and an Al–Si–C compound layer below in contact with the substrate.
Thin SiO2 coating on ZnS phosphors for improved low-voltage cathodoluminescence properties
Authors: Park W. , Wagner B. K. , Russell G. , Yasuda K. , Summers C. J. , Do Y. R. , Yang H. G.
Published: March 2008

A significant improvement (40–60%) was reported in the low voltage (100–1000V) cathodoluminescence efficiency of ZnS phosphors coated with SiO2 by the sol-gel technique. The properties of the coatings were found to be critically dependent upon the precursor concentration, pH value and the temperature of the solution with optimum performance being obtained for a SiO2 concentration of 1.0 wt%, pH values between 7–9, and a solution temperature of 83 °C. The efficiency curves exhibited a characteristic voltage dependence which was analyzed by a one-dimensional numerical model. Enhanced low voltage efficiency was attributed to a reduction of surface recombination and the actual shape of the efficiency curve was determined by the interplay between the reduction of surface recombination and energy losses in the SiO2 coating.
Fabrication of highly ordered ZnO nanowire arrays in anodic alumina membranes
Authors: Li Y. , Cheng G. S. , Zhang L. D.
Published: March 2008

Highly ordered ZnO nanowire arrays were fabricated by oxidizing the metal Zn that was electrodeposited in the pores of anodic alumina membranes (AAMs). The diameters of ZnO nanowires range from 15 to 90 nm. Atomic force microscope, x-ray diffraction, and transmission electron microscopy observations indicate the polycrystalline ZnO nanowires were uniformly assembled into the hexagonally-arranged nanochannels of the AAM. A green emission band caused by the singly ionized oxygen vacancy in the ZnO nanowires was also reported.
Phase evolution, microstructure, and gas-sensing characteristics of the Sb2O3–Fe2O3 system prepared by coprecipitation
Authors: Zhang Tianshu , Hing P. , Zhang Ruifang , Zhang Jiancheng , Li Young
Published: March 2008

Precursor powders with antimony-to-iron (Sb/Fe) atomic ratios ranging from 0 to 2.0 were prepared by chemical coprecipitation. The origin of enhanced gas-sensing behavior at a higher calcining temperature was investigated, based on phase evolution and microstructure characterized by means of thermal analysis, x-ray diffraction, Brunauer–Emmett–Teller surface area measurement, and electron microscopy. Only one iron–antimony oxide (i.e., FeSbO4) could be obtained under present experimental conditions. Pure FeSbO4 exhibited a high gas sensitivity, only when calcining temperature was below 600 °C. A rapid crystallite growth, as well as hard agglomeration, occurred in pure FeSbO4 powder calcined at 600–1000 °C, and thus led to poor gas-sensing behavior. However, there existed an optimal Sb/Fe ratio range (i.e., 0.25 to 0.65) in which crystallite growth of both α–Fe2O3 and FeSbO4 could be efficiently depressed up to 800 °C. The samples (with Sb/Fe ratio in the range 0.25–0.65) calcined at 600–800 °C displayed a high sensitivity to liquid petroleum gas due to their large specific surface area and poor crystallinity.
Investigation of the mechanism of sol-gel formation in the Sr(NO3)2/citric acid/ethylene glycol system by solution state 87 Sr nuclear magnetic resonance spectroscopy
Authors: Li Xiaohua , Agarwal Vishal , Liu Meilin , Rees William S.
Published: March 2008

The polymerization mechanism of a modified Pechini process was investigated by 87Sr nuclear magnetic resonance spectroscopy for the mixed solution of strontium nitrate, citric acid, and ethylene glycol. The C-ratio (the ratio of citric acid to metal ions in the polymer complex) is suggested to have a strong influence on the quality of the derived film. An analysis of the chemical shift variation, as a function of C-ratio, indicates the presence in the solution of two species: solvated strontium ions and strontium ions bound to the polymer complex, with a stoichiometry of 1:7. A polymeric precursor model based on this stoichiometry is proposed. Through a relaxation rate study of the strontium sites, it was found that the polymerization mechanism is predominantly bimolecular within the concentration region being studied. The equilibrium rate constant for the polymerization was calculated to be 104 s−1. A kinetic study of the fast cation exchange between the two identified strontium sites indicates that the inhomogeneity of the polymeric network leads to film cracking during pyrolysis.
Reaction sintering and mechanical properties of B4C with addition of ZrO2
Authors: Kim Hae-Won , Koh Young-Hag , Kim Hyoun-Ee
Published: March 2008

The effect of ZrO2 addition on sintering behavior and mechanical properties of both hot-pressed and pressureless-sintered B4C was investigated. The addition of ZrO2 improved the densification behavior of B4C remarkably via a reaction with the B4C to form ZrB2 at elevated temperatures. When B4C was densified at 2000 °C by hot pressing, only a small amount (approximately 2.5 vol%) of ZrO2 was necessary to achieve a full densification. Excellent mechanical properties (hardness, elastic modulus, flexural strength, and fracture toughness) were observed in those specimens. As the amount of ZrO2 was increased further, the mechanical properties were reduced, except for the fracture toughness, apparently due to the formation of too much ZrB2 in the specimen. Without the applied pressure, larger amounts of ZrO2 should be added to obtain a body with high relative density. When the B4C was sintered at 2175 °C with addition of 10 vol% ZrO2, the specimen has a density higher than 95% of the theoretical, and hardness and flexural strength of 25 GPa and 400 MPa, respectively.
Surface stress model for intrinsic stresses in thin films
Authors: Cammarata R. C. , Trimble T. M. , Srolovitz D. J.
Published: March 2008

A simple model was presented for intrinsic stress generation in thin films resulting from surface stress effects. This mechanism can explain the origin of compressive stresses often observed during island growth prior to coalescence, as well as intrinsic compressive stresses reported for certain continuous, fully grown films. In some cases, surface stress effects may contribute to a sudden change in the intrinsic stress during island coalescence.
Time-of-flight study of electrical charge mobilities in liquid-crystalline zinc octakis(β-octoxyethyl) porphyrin films
Authors: Yuan Yang , Gregg Brian A. , Lawrence Marcus F.
Published: March 2008

Time-of-flight measurements performed on micron-thick films of liquid-crystalline zinc octakis(β-octoxyethyl) porphyrin indicated that charge carriers possess significantly high drift mobilities, attaining approximately 0.01 cm2 V−1s −1 and 0.008 cm2 V−1s −1 for holes and electrons, respectively, at room temperature. Upon heating the samples from 300 to 420 K, causing the porphyrin to go from the solid-crystalline to the discotic mesophase, the mobilities did not decrease drastically, and remained at values slightly larger than half those observed at room temperature. Charge transport in this material conformed to the Scher–Montroll model, which attributes a distribution of hopping times to the propagation of the initially formed charged carrier packet. Analysis of the “universal” plots prescribed by this model yielded a dispersion factor of 0.5 for both charge carriers.
Piezoelectric and dielectric reliability of lead zirconate titanate thin films
Authors: Polcawich Ronald G. , Trolier-McKinstry Susan
Published: March 2008

This work was directed toward developing a database for the long-term reliability of the transverse piezoelectric coefficient d31 under both unipolar and bipolar drive. Under unipolar drive, the films showed excellent reliability, with 99% of the devices surviving to 109 cycles. However, both aging and low amplitude bipolar drive resulted in rapid degradation of d31 due to backswitching of the ferroelectric domains. Both thermal and ultraviolet (UV) imprint prevented backswitching and resulted in improved aging and bipolar degradation behavior. Additionally, the UV imprinted samples showed nonlinear aging due to the presence of an internal space charge field that developed from photo-induced charge carriers.
Induction-field-activated self-propagating high-temperature synthesis of AlN–SiC solid solutions in the Si3N4–Al–C system
Authors: Kata D. , Ohyanagi M. , Munir Z. A.
Published: March 2008

The synthesis of AlN–SiC solid solutions from Si3N4, Al, and C was investigated using the induction-field-activated/self-propagating high-temperature synthesis/static pseudo-isostatic compaction technique. Careful x-ray diffraction analyses were made on the products of combustion to determine reaction routes. Optical microscopy as well as scanning electron microscopy with an electron probe microanalysis was used for microstructural analysis. It was found that initially molten aluminum reacted with silicon nitride producing an Al–Si alloy. At higher temperatures, aluminum evaporated from the Al–Si liquid and the synthesis of AlN via a vapor phase process took place. Subsequently, dissolution of AlN into molten Si resulted in the formation of an AlN–SiC solid solution from the Al–N–Si–C liquid phase. However, below 1850 °C, the resulting solid solution of 4AlN–3SiC was not fully crystallized. Combustion temperatures above or equal to 1850 °C were required to prepare a highly crystallized solid solution with a morphology exhibiting hexagonal platelets. Based on these observations, a model for the formation of AlN–SiC solid solution is proposed.
Solid-phase epitaxial growth of oxide buffer materials for Rba2Cu3O7−y(R: rare earth and Y) superconductor
Authors: Yamagiwa K. , Matsumoto K. , Hirabayashi I.
Published: March 2008

We prepared various oxide buffer films on single-crystalline oxide substrates using chemical solution deposition to investigate general interfacial problems of buffer layers for coated conductors, such as epitaxial relationships between buffer material and the substrate. We found that (i) interfaces between the films and the substrates having the same crystal structure were compatible, even in a range of misfit value up to 7%, showing in-plane alignment; however (ii) interfaces between the films and substrates of other combinations of interface structures, with and without occupying tetragonal sites, narrow the range of the epitaxial growth. The former results (i) can be explained by the arrangement of oxygen ions, but for the latter cases (ii), cation arrangement is also important in forming a compatible interface as well as an anion arrangement. The general tendency is largely explained by the ionic arrangement at the interface. The interface structure becomes unstable by the electrostatic repulsive force since the distance between cations at the interface becomes shorter than that in each original crystal structure.
Energetics of oxidation of oxynitrides: Zr–N–O, Y–Zr–N–O, Ca–Zr–N–O, and Mg–Zr–N–O
Authors: Molodetsky I. , Navrotsky A. , DiSalvo F. , Lerch M.
Published: March 2008

The enthalpies of oxidation, δHox, of oxynitrides YyZr1−yO2x−0.5y−2/3xNx(0.016 <x< 0.2), CayZr1−yO2x−y−2/3xNx(0.03 <x< 0.14), MgyZr1−yO2x−y−2/3xNx(0.146 <x< 0.28), and Zr–O–N (β-type and γ phases) are measured using drop solution calorimetry in molten sodium molybdate (3Na2O · 4MoO3) at 973 K. Linear relations between the enthalpy δHoxand nitrogen content were found in all oxynitrides. They indicate that, within the experimental range of nitrogen concentrations, sites occupied by nitrogen ions are energetically equivalent in a given substitutional series. The enthalpies normalized per mole of nitrogen, δHnox, for compounds of Y–Zr–N–O, Ca–Zr–N–O, and Zr–N–O are similar, about −500 kJ/(mol of N). A more exothermic value of δHnox, of about −950 kJ/(mol of N), is seen in Mg–Zr–N–O compounds. The energetics of vacancy formation in zirconium oxynitrides was determined and compared to the energetics of vacancy formation in yttria- and calcia-stabilized zirconia. The enthalpy of vacancy formation (enthalpy of formation relative to end members normalized per vacancy) in zirconium oxynitrides (−190.5 ± 27.0 kJ/mol of Vö) is more exothermic than that in yttria- and calcia-stabilized zirconia (−105 ± 7.2 and −91.4 ± 3.8 kJ/mol of Vö, respectively). This is consistent with the higher tendency for long-range ordering in zirconium oxynitrides compared to stabilized zirconia. Some technological implications of the results are briefly discussed.
Hydrothermal synthesis of multiwall carbon nanotubes
Authors: Gogotsi Yury , Libera Joseph A. , Yoshimura Masahiro
Published: March 2008

Multiwall open-end and closed carbon nanotubes with the wall thickness from several to more than 100 carbon layers were produced by a principally new method— hydrothermal synthesis—using polyethylene/water mixtures in the presence of nickel at 700–800 °C under 60–100 MPa pressure. An important feature of hydrothermal nanotubes is a small wall thickness, which is about 10% of the large inner diameter of 20–800 nm. Closed nanotubes were leak-tight by virtue of holding encapsulated water at high vacuum and can be used as test tubes for in situ experiments in transmission electron microscope (TEM). Raman microspectroscopy analysis of single nanotubes shows a well-ordered graphitic structure, in agreement with high-resolution TEM. The hydrothermal synthesis has the potential for producing multiwall nanotubes for a variety of applications. The fabrication of nanotubes under hydrothermal conditions may explain their presence in coals and carbonaceous rocks and suggests that they should be present in natural graphite deposits formed under hydrothermal conditions.
Production of Al–Ti–C grain refiner alloys by reactive synthesis of elemental powders: Part II. Grain refining performance of alloys and secondary processing
Authors: Brinkman H. J. , Zupanič F. , Duszczyk J. , Katgerman L.
Published: March 2008

This article, Part II in a series, reports on the grain refining performance of the Al–Ti–C alloys produced by reactive synthesis. Grain refinement was tested as a function of the following parameters in the reaction synthesis process: Ti content, Ti/C ratio, and cooling rate after the reaction. The grain refining performance of the alloys in the as-synthesized condition was limited due to either a shortage of TiC particles or an insufficient amount of aluminum matrix. Dilution of the alloys to a nominal composition of 3 wt% Ti, followed by extrusion improved the grain refinement to the level of commercially available Al–Ti–C grain refining alloys. A prerequisite for successful secondary processing is that the conversion of carbon is completed in the reaction synthesis; otherwise Al4C3 is formed rather than TiC.
Study on preparation, growth mechanism, and optoelectronic properties of highly oriented WSe2 thin films
Authors: Tsirlina T. , Lyakhovitskaya V. , Fiechter S. , Tenne R.
Published: March 2008

Recently, highly oriented WSe2 thin films, with the c axis of the crystallites perpendicular to the substrate, were reproducibly obtained by interposing a Ni/Cr thin layer between the substrate and a WO3 precursor film. In the present work the preparation conditions were varied to elucidate the growth mechanism of such films. A model for the growth mode is proposed. Based upon this analysis, WSe2 thin films with improved crystalline and electronic properties were obtained. The photoresponse spectrum for photoelectrochemical cells with the WSe2 electrode immersed into a selenosulfate solution was measured. Quantum efficiency of 0.1% was calculated from this spectrum.
YBa2Cu3O7-y−coated conductors with high engineering current density
Authors: Paranthaman M. , Park C. , Cui X. , Goyal A. , Lee D. F. , Martin P. M. , Chirayil T. G. , Verebelyi D. T. , Norton D. P. , Christen D. K. , Kroeger D. M.
Published: March 2008

Short segments of YBa2Cu3O7-y (YBCO) coated conductors were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with a layer sequence of CeO2/YSZ/Ni using an ex situ BaF2 precursor process. Pulsed laser deposition (PLD) was used to deposit both YSZ and CeO2 layers. The YBCO films were grown using e-beam coevaporated Y–BaF2–Cu precursors followed by postannealing. An overall engineering current density, JE, of 28,000 A/cm2 and critical current, Ic, of 147 A/cm width at 77 K were achieved for a 1.6-μm-thick YBCO film. This result demonstrates the possibility of using both the ex situ BaF2 precursor approach and the RABiTS process for producing long lengths of high-JE coated conductors.
Poly(vanadium–molybdenum acid) xerogel thin films fabricated by the sol-gel process and their humidity-sensing properties
Authors: Tong Maosong , Dai Guorui , Wu Yuanda , He Xiuli , Yan Wei , Gao Dingsan , Volkov Victor , Zakharova Galina
Published: March 2008

Thermogravimetric analysis, x-ray photoelectron spectroscopy, and x-ray diffraction results and the humidity sensing properties of poly(vanadium–molybdenum acid) H2V9.5Mo2.5O32.0 · 8.8H2O xerogel thin films, which were fabricated by the sol-gel process, are described in this paper. The conductance and the capacitance of the thin films strongly depend on the relative humidity. Different electrodes have different influences on the humidity-sensing properties of the thin films.
Epitaxial growth at PZT/Ir interface
Authors: Okuwada Kumi , Yoshida Ken-ichi , Saitou Tomoko , Sawabe Atsuhito
Published: March 2008

Surface oxidation of an iridium film and the possibility of epitaxial growth of PZT spin-coated film on sputtered iridium were investigated. The free surface on the iridium film oxidized over 400 °C with random orientation. Nevertheless, both the PZT(111)/Ir(111) and PZT(100)/Ir(100) interfaces were realized using the highly oriented iridium layer. These results suggest that PZT nucleation has priority over iridium surface oxidation.
Nanoscale mechanical patterning for the selective deposition of nanostructures
Authors: Friesen C. A. , Hayes J. R.
Published: March 2008

In this paper, we describe a new method for creating nanostructures, and demonstrate its use by depositing Au, Ni, and Zn on a SiO2 passivated Si substrate. The method combined the spatial control of electron-beam lithography with the ease of fabrication of self-assembled arrays. The technique enabled the selective electrochemical deposition of nanostructures by creating specific nucleation sites by nanoindentation. This offered the possibility of accurately creating nanostructures ranging in size from one to hundreds of nanometers. We showed that it is possible to electrically isolate the nanostructures from the substrate and each other by a thermal oxidation process. In principle, this technique allowed fabrication of quantum devices of any geometry.
Optimization of chemical vapor infiltration with simultaneous powder formation
Authors: Ditkowski A. , Gottlieb D. , Sheldon B. W.
Published: March 2008

A key difficulty in isothermal, isobaric chemical vapor infiltration is the long processing times that are typically required. With this in mind, it was important to minimize infiltration times. This optimization problem was addressed here, using a relatively simple model for dilute gases. The results provided useful asymptotic expressions for the minimum time and corresponding conditions. These approximations were quantitatively accurate for most cases of interest, where relatively uniform infiltration was required. They also provided useful quantitative insight in cases where less uniformity was required. The effects of homogeneous nucleation were also investigated. This does not effect the governing equations for infiltration of a porous body; however, powder formation can restrict the range of permissible infiltration conditions. This was analyzed for the case of carbon infiltration from methane.