bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulated structure in Bi2+xSr2−xCu1+yO6+δ
Authors: Hiroi Zenji , Ikeda Yasunori , Takano Mikio , Bando Yoshichika
Published: September 2007

The modulated structure in solid solution Bi2+xSr2−xCu1+yO6+δ (0.1 < x < 0.6, y ∼ x/4) has been investigated by means of powder x-ray diffraction, electron diffraction, and transmission electron microscopy. The [010] component of the modulation vector decreases almost linearly with increasing x, from 5.2b (x = 0.1) to 4.2b (x = 0.5), where b is the unit length of the average structure along the [010] direction, and is little sensitive to excess oxygen content δ. A structure model of the modulation based on a periodic substitution of Sr for Bi and formation of Bi blocks whose size varies with x is proposed. Relations among various modulations appearing in other related phases such as the Pb-substituted 105 K Tc phase are discussed.
Structural and electronic properties of indium-doped YBa2Cu3Oσ
Authors: Weidlich Georg , Goelz Michael , Wang Ruiping , Evenson William E. , Gardner John A. , Keszler Douglas A. , Sommers James A. , Ostenson Jerome E.
Published: September 2007

We have measured x-ray diffraction patterns and Meissner flux exclusion of YBa2Cu3Oσ containing indium. All samples were synthesized at temperatures near 940 °C, and the data indicate the indium atomic solubility to be approximately 3% per formula unit. At the solubility limit Tc is reduced from 92.7 K to 91.3 K relative to undoped samples, and the total magnetic flux excluded is reduced from approximately 40% to about 10%. For samples of formula InxY1−xBa2Cu3Oσ concentrations of other Y–Ba–Cu oxide phases are low and do not depend systematically on x. These results indicate that indium substitutes predominantly for yttrium when x is small.
Compatible phases of the Y2O3–CuO–Cu2O system in air
Authors: Gadalla Ahmed M. , Kongkachuichay Paisan
Published: September 2007

The phase diagram of the Y2O3–CuO–Cu2O system was constructed as a function of temperature in air by means of thermal analysis and x-ray diffraction. The phase Y2Cu2O5 was found to be stoichiometric and melted peritectically at about 1110 °C. A new intermediate phase with the composition YCu2O2.5 was discovered. It exists between 990 and 1105 °C in air and quenching did not preserve it to room temperature. High temperature x-ray diffraction established its pattern and confirmed its peritectic decomposition. Above 1110 °C YCu2O2.5 consists of Y2O3 and liquid. The results of this system are shown on a ternary system as well as on a pseudo-binary phase diagram. The solid state reactions were established. Melting occurs with isothermal oxygen loss or gain, depending on the initial composition.
Flexible Bi2Sr2CaCu2O8+x tapes by metallo-organic deposition
Authors: Hung L.S. , Chatterjee D.K.
Published: September 2007

A metallo-organic deposition technique was employed to grow Bi2Sr2CaCu2O8+x flexible films on unpolished metal foils (stainless steel and silver). Since strong interactions occurred at elevated temperatures between stainless steel and superconducting oxides, HfO2 buffer layers prepared by ion-assisted deposition were used to stabilize the system and Na additions were used to reduce processing temperature and enhance grain growth. The transition of superconducting films on stainless steel was complete around 70–73 K, and the critical current density was about 1000 A/cm2 at 10 K. Silver appears to be an attractive metal support due to its chemical stability and mechanical ductility. The film on silver showed the onset to superconductivity at 77 K, attaining zero resistance at 73 K. The critical current density in zero magnetic field was approximately 27000 A/cm2 at 20 K, comparable to that obtained from MOD films on MgO (100).
Point defect study of CuTi and CuTi2
Authors: Shoemaker J.R. , Lutton R.T. , Wesley D. , Wharton W.R. , Oehrli M.L. , Herte M.S. , Sabochick M.J. , Lam N.Q.
Published: September 2007

The energies and configurations of interstitials and vacancies in the ordered compounds CuTi and CuTi2 were determined using atomistic simulation with realistic embedded-atom potentials. The formation energy of an antisite pair was found to be 0.385 and 0.460 eV in CuTi and CuTi2, respectively. In both compounds, the creation of a vacancy by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an adjacent antisite defect in the case of the Ti vacancy. The vacant Cu site in CuTi was found to be very mobile within two adjacent (001) Cu planes, with a migration energy of 0.19 eV, giving rise to two-dimensional migration. The vacancy migration energy across (001) Ti planes, however, was 1.32 eV, which could be lowered to 0.75 or 0.60 eV if one or two Cu antisite defects were initially present in these planes. In CuTi2, the vacancy migration energy of 0.92 eV along the (001) Cu plane was significantly higher than in CuTi. The effective vacancy formation energies were calculated to be 1.09 eV and 0.90 eV in CuTi and CuTi2, respectively. Interstitials created by inserting either a Cu or Ti atom had complicated configurations in which a Cu 〈111〉 split interstitial was surrounded by two or three Ti antisite defects. The interstitial formation energy was estimated to be 1.7 eV in CuTi and 1.9 eV in CuTi2.
The effect of plastic deformation at near room temperature on the solid state reactions between Ni and Sn
Authors: Martelli S. , Mazzone G. , Vittori-Antisari M.
Published: September 2007

Solid state reactions between Ni and Sn at two compositions, Ni75Sn25 and Ni60Sn40, have been induced by means of near room temperature cold rolling and mechanical alloying. The reaction steps have been monitored by x-ray diffraction and differential scanning calorimetry. At both compositions, the first effect of plastic deformation is the formation of two metastable phases which, by further milling or low temperature thermal treatment, transform into the Ni3Sn4 compound. The chemical composition of the metastable phases has been determined to be close to that of Ni3Sn4 and the crystal structure of one of them appears to be related to that of β–Sn. Differential scanning calorimetry and thermal treatment of samples containing the metastable phases have shown that these phases transform into Ni3Sn4 at about 150 °C and that no other reaction takes place up to this temperature. Upon prolonged milling, a different behavior has been observed for the two compositions. While the Ni60Sn40 mixture eventually forms the Ni3Sn2 compound in agreement with previous results, the final product of mechanically alloying the Ni75Sn25 mixture is a phase whose structure, rather than amorphous as previously hypothesized, in our case can be described as based on that of the disordered high temperature form of the Ni3Sn compound. Differential scanning calorimetry and x-ray diffraction analysis of this sample have shown the formation, at 380 °C, of ordered Ni3Sn with an associated heat release of about 10 kJ/mole.
Interface and mechanical behavior of MoSi2-based composites
Authors: Yang J-M. , Jeng S.M.
Published: September 2007

MoSi2-based composites reinforced with particles, whiskers, and continuous fibers were fabricated using hot pressing and hot isostatic pressing techniques. The microstructure, interface compatability, and interfacial properties between the reinforcements and matrix are discussed. The microstructural parameters which control the mechanical behavior of the MoSi2 composites were characterized. The need for developing a satisfactory reinforced MoSi2 composite for high-temperature structural applications is also addressed.
Compression behavior of TiB2-particulate-reinforced composites of Al22Fe3Ti8
Authors: DiPietro M.S. , Kumar K.S. , Whittenberger J.D.
Published: September 2007

The compression behavior of both the monolithic L12 compound Al22Fe3Ti8 and discontinuous composites obtained by incorporating ∼1 μm TiB2 particles was studied for various volume percent reinforcements as a function of temperature and at high temperatures as a function of strain rate. In this study, by varying the Fe and Ti contents, the nature and volume fraction of the minor phases coexisting with the dominant L12 phase were changed and were examined with and without TiB2 reinforcement. At high strain rates (10−4 s−1), the TiB2 reinforcements significantly enhance ambient and warm-temperature strength, although a crossover is observed at ∼1000 K, above which the monolithic material is stronger than the composite. At slow strain rates (10−7 s−1), representative of creep conditions, however, the TiB2-containing composites retain their superiority at least up to 1200 K. Power law fits of compressive flow stress at 1% strain versus strain rate yielded a stress exponent of ∼3.0 with an activation energy of 310 kJ/mol for the monolithic material. For the particulate composites (20 vol. % TiB2), the corresponding values were ∼5.0 and 465 kJ/mol, suggesting a change in the dominant deformation mechanism.
Electron microscope study of the structure of SrMnO3−x with planar defect
Authors: Shibahara H.
Published: September 2007

Structures of some phases in the SrMnO3−x system accompanied by planar defect were studied using a high resolution electron microscope. A four-layer structure with a hexagonal unit cell was found to have an oxygen deficiency in some degree followed by planar defects normal to the c-axis which are classified into several types. On the basis of observed images showing an irregular stacking along the c-axis in the hexagonal unit, the distribution and the origin of the planar defect are discussed. A structure image showed the transformation of the four-layer phase into a nonstoichiometric state and a shear structure with a displacement vector of occurring between the face-sharing octahedra. Experiment by in situ observation during beam irradiation in an electron microscope indicates the process of the formation of the planar defect. A mechanism for the formation of the planar defect is proposed by which oxygen deficiency in face-sharing octahedra induces the displacement of SrO3 layers and oxygen octahedra which reduce the coordination number of Mn ions and the disruption of face-sharing octahedra.
Hydrogen reduction mechanisms of ilmenite between 823 and 1353 K
Authors: Briggs R.A. , Sacco A.
Published: September 2007

In situ gravimetric measurements and microscopic examinations were used to determine the mechanisms of oxygen removal from synthetic ilmenite disks between 823 and 1353 K. Under a hydrogen atmosphere, iron was observed to form a layer of low porosity on the surface of samples early in the reduction. This created diffusion limitations for hydrogen to the reaction front and for the escape of water vapor. A shrinking core reduction model, modified to include the growth of this iron film, was capable of predicting the conversion-time relationships of ilmenite samples. An activation energy of 43.2 ± 2.6 kcal/gmole was determined to be representative of reaction control over the temperature range 823–1023 K.
High resolution electron microscopy of ion-irradiated GdBa2Cu3O7
Authors: Van Tendeloo G. , Ruault M-O. , Bernas H. , Gasgnier M.
Published: September 2007

GdBa2Cu3O7 crystals were irradiated at room temperature with 200 keV Ne ions and 300 keV Xe ions. In situ standard TEM and further HREM studies show two types of extended defects: (i) mobile extended defects, which account for the preferential defect pinning to twin boundaries reported earlier. These defects are rapidly recovered and difficult to observe by HREM investigations; (ii) stable amorphous areas which are clearly identified by HREM observations. Their overlapping and aggregation conceivably lead to amorphization of the sample.
A TEM study of the microstructures formed during the crystallization of Ni–Zr metallic glasses
Authors: Allem R. , L'Espérance G. , Altounian Z. , Ström-Olsen J.O.
Published: September 2007

The microstructure of two metastable crystalline phases, which are formed during the first step of the crystallization process in Ni–Zr metallic glasses, was investigated by transmission electron microscopy. For the composition Ni33Zr67, crystallites with average size of 150 nm having the face-centered cubic E93 structure are formed. For the Ni42Zr58 composition, 100 nm size crystallites with a simple cubic unit cell, space group Pa3 are formed. The microstructure of the crystallites in the early stage of crystallization of the two phases is similar to globular morphology and internal striations.
Preparation of copper compounds of different compositions and particle morphologies
Authors: Kratohvil Stanka , Matijević Egon
Published: September 2007

Copper compounds of different chemical compositions and particle shapes were prepared by homogeneous precipitation from copper salt solutions in the presence of urea. It was demonstrated that the nature of the anions played an essential role in the properties of the generated solid phase. Thus, Cu(II)-nitrate solutions yielded spherical amorphous particles which had the composition of malachite [Cu2(OH)2CO3], the Cu(II)-chloride solutions gave bipyramidal particles of atacamite [CuCl2 · 3Cu(OH)2], and in Cu(II)-sulfate solutions needle-shaped brochantite [3Cu(OH)2 · CuSO4] or platelets of posnjakite [3Cu(OH)2 · CuSO4 · H2O] were formed. The addition of NaOH to prepared dispersions resulted in a rapid phase transformation of all above solids into needle-like Cu(OH)2. Calcination of various copper basic compounds at 700–800 °C temperature produced CuO, while the particle morphology was retained.
Structure and composition characterization of submicronic mullite whiskers
Authors: Merk N. , Thomas G.
Published: September 2007

Two sets of submicronic mullite whiskers, which have potential applications for fiber reinforced composites or as a thermal insulator, have been characterized to be tetragonal or orthorhombic using x-ray and electron microscopy techniques. The whiskers decompose upon heating under vacuum with a continuous loss of silicon and reduction in oxygen content up to the limit for which pure aluminum metal and α-alumina are formed.
Preparation and characterization of uniform submicrometer metal niobate particles. I. Lead niobate
Authors: Kim Myung Jin , Matijević Egon
Published: September 2007

Colloidal amorphous lead niobate particles of different composition and morphologies were obtained by a metal-chelate decomposition method. The nature of the dispersions depended on the conditions of the preparation of the complexes, pH, aging time, and temperature. The structural and chemical changes of the so prepared powders on calcination were investigated by thermal and x-ray diffraction analyses. Chemical mechanisms of the formation and transformation of the particles are suggested.
Low-temperature oxidation of YBa2Cu3O6.0 with nitrogen dioxide
Authors: Montzka Stephen A. , Hybertson Brooks M. , Barkley Robert M. , Sievers Robert E.
Published: September 2007

Nitrogen dioxide was used to oxidize nonsuperconducting, powdered YBa2Cu3O6.0 to form a material that exhibits the Meissner effect at liquid nitrogen temperature. Nitrogen dioxide treatment at 200 °C for 70 h results in a mixed-phase material containing superconducting YBa2Cu3O6.9 that exhibits onset of superconductivity at 91.5 K and a midpoint at 88 K. During a 70-h exposure of YBa2Cu3O6 to NO2 at 200 °C, a mixture of oxidation and degradation products is formed, including YBa2Cu3O6.9 (61% by weight) and Ba(NO3)2 (23% by weight). Heating the NO2-treated product to 900 °C results in the evolution of NO, NO2, and O2; cooling the sample and annealing at 400 °C in an O2 stream generates the superconducting oxide.
An enhanced rate of the high-Tc phase formation in the Bi–Ca–Sr–Cu–O superconductor by the two-step reaction and rapid heating
Authors: Jang Hyun M. , Moon Jong H. , Shin Hyun J.
Published: September 2007

An alternative synthetic approach was attempted for the fabrication of the Bi–Ca–Sr–Cu oxide superconductor. In this approach a mixed Sr–Ca–Cu oxide powder was first formed, and the resulting powder was subsequently reacted with Bi2O3. With this reaction scheme, problems associated with the low reactivity of CuO and SrCO3 can be partially removed by converting the mixed oxide/carbonate precursors to the reactive Sr–Ca–Cu compound. An enhanced rate of formation of the high-Tc (110 K) phase was observed in the two-step reaction, and this was explained in terms of the low activation free energy path for the formation of the high-Tc phase, which increased the decomposition rate of the remnant CuO. Under the condition of rapid heating, the formation of the high-Tc phase in the one-step reaction was expedited by the Cu-rich liquid phase. However, the liquid phase caused the formation of an insulating layer between the superconducting grains in spite of its catalytic activity in the high-Tc phase formation.
Thermodynamic and structural properties of [001] twist boundaries in gold
Authors: Najafabadi R. , Srolovitz D.J. , LeSar R.
Published: September 2007

We have employed the Local Harmonic (LH) model and the Embedded Atom Method (EAM) to examine the structural and thermodynamic properties of a series of twelve [001] twist boundaries in gold for temperatures between 0 K and 700 K. For the majority of the grain boundary misorientations, metastable structures were observed with grain boundary energies that were typically less than 0.1% larger than the stable structures. Four of the twelve grain boundaries underwent first order structural phase transitions as seen by the crossing of the free energy versus temperature curves for the competing structures. Relatively small cusps or inflections in the grain boundary free energy versus misorientation curves were observed at Σ5 (36.87°) and Σ13 (22.62°) at low temperatures, at Σ13 (22.62°) and Σ17 (28.07°) at intermediate temperatures, and at Σ5 (36.87°) and Σ17 (28.07°) at elevated temperatures. A maximum in the grain boundary entropy versus misorientation was observed at Σ17 (28.07°) for all temperatures, and local minima were observed at Σ5 (36.87°) at low temperature and in Σ13 (22.62°) at high temperature. The excess volume associated with the grain boundary shows a roughly linear dependence on grain boundary free energy at each temperature examined. The room-temperature mean-square vibrational amplitude is approximately 25% larger than that for the bulk at the (002) plane adjacent to the boundary and decays to within 2% of the bulk value by the second (002) plane from the boundary. The room-temperature mean-square vibrational amplitude is dominated by the in-plane (parallel to the grain boundary) vibrations at the (002) plane nearest the grain boundary.
The influence of implanted impurities on the thermally-induced epitaxial recrystallization of CoSi2
Authors: Ridgway M.C. , Elliman R.G. , Petravic M. , Thornton R.P. , Williams J.S.
Published: September 2007

The influence of implanted impurities (B, O, P, Ar, Xe, Pb, and Bi) on the rate of low-temperature (138 °C), solid-phase epitaxial growth (SPEG) of amorphized CoSi2 has been studied. SPEG rates of impurity-implanted CoSi2, as determined from time-resolved reflectivity measurements, were retarded for all impurities compared to that of Si-implanted CoSi2. The extent of retardation varied from a factor of 1.5 for P to 9.4 for Xe. Channeling measurements of impurity-implanted CoSi2 indicated that Xe and Bi atoms were located on nonsubstitutional lattice sites while ∼40% of Pb atoms occupied either substitutional sites or vacant interstitial cation sites following annealing. The presence of impurities did not affect the CoSi2 post-anneal crystalline quality, and no significant impurity diffusion was apparent at 138 °C from secondary-ion mass spectrometry measurements.
Stable, highly concentrated suspensions for electronic and ceramic materials applications
Authors: Sushumna I. , Gupta R.K. , Ruckenstein E.
Published: September 2007

Highly concentrated solid-in-liquid suspensions find applications in a number of areas such as electronics, ceramics, paints, coatings, etc. Highly loaded, stable suspensions which exhibit desirable rheological characteristics (moderate viscosity, shear thinning behavior, thixotropy, and a small yield stress, for example), and which have high thermal or electrical conductivities are frequently sought after. We describe here some techniques which can be used to obtain such highly concentrated suspensions. These involve employing mixed size grades of particles and effective dispersants. For thermal paste applications, for example, compliant pastes of up to 78 vol. % solids with thermal conductivity values as high as 6 W/mK (hence, a few times greater than the values reported previously by others), low electrical conductivity, and moderate viscosity have been prepared by mixing different particle size grades of materials such as Al2O3, SiC, AlN, Al, and diamond. Effective dispersants, both commercial as well as those synthesized in our laboratory as novel variations of previously known molecular architectures, have been used to facilitate the achievement of these very high loading and stable suspensions.
Carbonization and graphitization of polyimide Upilex
Authors: Inagaki Michio , Sakamoto Kou-ichi , Hishiyama Yoshihiro
Published: September 2007

Two-step carbonization was found on a polyimide film, Upilex, similar to that observed on another polyimide, Kapton: large weight loss up to about 22 wt. % and linear shrinkage along the film surface to 30% in a narrow temperature range from 500 to 650 °C, and an additional small weight loss and shrinkage in a wide range between 700 and 1000 °C. The yield of carbonization agreed roughly with that calculated by assuming the release of non-carbon atoms as simple species of CO, O2, and N2. A 25 μm Upilex film yielded a relatively high degree of graphitization after heat treatment at 3000 °C: a layered structure under SEM, high magnetoresistance, and a sharp 002 x-ray diffraction peak at a d-spacing of 0.336 nm. The degree of graphitization was lower than for a similar Kapton film, which is attributed to the lack of flatness in the Upilex molecule. A very much lower degree of graphitization was observed for 50 μm Upilex films. This difference is tentatively attributed to constraints that must have influenced the orientation of the Upilex molecules near the surface of the films as they were formed.
New evidence for a pressure-induced phase transformation during the indentation of silicon
Authors: Pharr G.M. , Oliver W.C. , Harding D.S.
Published: September 2007

Scanning electron micrographs of indents in (111) silicon reveal that a thin layer of material immediately adjacent to the indenter is plastically extruded. The fact that the material can be deformed in this way indicates that it has metallic-like mechanical properties. This is presented as new evidence that a pressure-induced phase transformation to the metallic state occurs during the indentation of silicon.
Superconducting glass-ceramics in BiSrCaCu2Al0.5Ox—Comparison between rod and powder compacted specimens
Authors: Hirata Kazumi , Abe Yoshihiro
Published: September 2007

Superconducting properties are studied for glass-ceramics which were prepared by reheating glass rods and the glass powder compacts in the BiSrCaCu2Al0.5Ox system, respectively. The glass-ceramic rod specimens obtained by reheating rod glass at 800–830 °C for 50 h have a Tc (R = 0) of 85 K, while the disk specimens obtained by reheating the powdered glass compacts in the same way do not exhibit superconductivity above 77 K. This difference in superconductivity between the specimens is discussed in terms of the crystallization process and the amount of oxygen absorption of the specimens during heating.
On a new example of ramified electrodeposits
Authors: Fleury Vincent
Published: September 2007

We have grown extremely flat (2D) electrodeposited copper leaves that exhibit ramified patterns. These patterns are stable and can be withdrawn from the solution. A fractal analysis based on correlation function and branch counting was carried out. Also, x-ray and SEM pictures give insight into the fractal structure of this new type of aggregates and help to find the lower crossover to nonfractal compact substructure.
Bandfilling and structural stability of trialuminides: YAl3, ZrAl3, and NbAl3
Authors: Xu Jian-hua , Freeman A.J.
Published: September 2007

The cohesive properties and electronic structures versus the structural stability of transition-metal trialuminides YAl3, ZrAl3, and NbAl3in their cubic L12, tetragonal DO22, and naturally stable forms (i.e., the DO19structure for YAl3and the DO23structure for ZrAl3) have been investigated using a total energy local-density approach. The variation of structural stability with transition-metal constituent can be simply understood in terms of the bandfilling of the bonding states in the rigid band sense, with the valence electrons gradually filling the bonding states on going from YAl3, ZrAl3to NbAl3. This leads to a phase transition from the cubic L12structure (for YAl3) to the tetragonal DO22structure (for NbAl3). It is argued that this criterion may also apply to explain the variation of the structural stability of other transition-metal compounds (such as transition-metal carbides, nitrides, silicides, etc.) that are dominated by covalent interactions between the transition-metaldand the metalloidpstates.
Fractal fracture of single crystal silicon
Authors: Tsai Y.L. , Mecholsky J.J.
Published: September 2007

The quantitative description of surfaces that are created during the fracture process is one of the fundamental issues in materials science. In this study, single crystal silicon was selected as a model material in which to study the correlation of fracture surface features as characterized by their fractal dimension for two different orientations of fracture with the fracture toughness of the material as measured using the strength-indentation and fracture surface analysis techniques. The fracture toughness on the {110} fracture plane of single crystal silicon was determined to be 1.19 MPa m1/2for the {100} tensile surface and 1.05 MPa m1/2for the {110} tensile surface using the indentation-strength three-point bending method. The fracture surface features of these two orientations are correspondingly different. Within our limitations of measurements (1–100 μm), the fractal dimension appeared different in different regions of the fracture surface. It has a higher value in the branching region and a lower value in the pre-branching and post-branching regions. The fractal dimensions are about the same in the pre-branching regions and post-branching region for these two orientations (D= 1.01 ± 0.01), i.e., nearly Euclidean (smooth); but the fractal dimensions are higher in the branching region for these two orientations. The fractal dimension is 1.10 ±0.4 for the {100} tensile surface and is 1.04 ±0.3 for the {110} tensile surface. If we select the highest dimension on a surface to represent the dimensionality of the surface, then a material with a higher fracture toughness has a higher fractal dimension in the branching region.
Selective and low temperature synthesis of polycrystalline diamond
Authors: Ramesham R. , Roppel T. , Ellis C. , Jaworske D.A. , Baugh W.
Published: September 2007

Polycrystalline diamond thin films have been deposited on single crystal silicon substrates at low temperatures (⋚ 600 °C) using a mixture of hydrogen and methane gases by high pressure microwave plasma-assisted chemical vapor deposition. Low temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 °C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.
Structural study of amorphous WO3 thin films prepared by the ion exchange method
Authors: Nanba Tokuro , Nishiyama Yoshio , Yasui Itaru
Published: September 2007

The structure of amorphous tungsten trioxide films was investigated with IR and Raman spectroscopic analyses and an XRD method. The films were prepared by ion exchange from sodium tungstate as a starting material. Films consisted of microclusters of 10–30 Å diameter, in which the networks are formed with WO6 octahedra sharing their corners and edges. The networks in the as-prepared samples consisted of WO6 units with low symmetry, in which termination by W=O and W—OH2 groups was common. As the post-annealed temperature became higher, the symmetry of WO6 was improved and the edge-sharing octahedra disappeared.
The synthesis of superconducting Tl–Ca–Ba–Cu–oxide films by the reaction of spray deposited Ca–Ba–Cu–oxide precursors with Tl2O vapor in a two-zone reactor
Authors: DeLuca John A. , Garbauskas Mary F. , Bolon Roger B. , McMullen James G. , Balz Winifred E. , Karas Pamela L.
Published: September 2007

Superconducting Tl–Ca–Ba–Cu–oxide films have been prepared on yttria stabilized zirconia substrates via the reaction of Tl2O vapor with precursor Ca–Ba–Cu–oxide films prepared by the spray pyrolysis of a solution of the metal nitrates. The vapor reaction process, evaluated in both air and oxygen ambients, was carried out in a two-zone reactor which permitted the independent control of the temperatures of the sample and of a boat containing thallium oxide. Sample temperatures of 865–905 °C and boat temperatures of 775–870 °C were investigated. X-ray diffraction analysis of the best samples, which were prepared in an oxygen ambient at sample temperatures of 895–900 °C and boat temperatures of 805–810 °C, revealed the presence of a highly oriented Tl2Ca2Ba2Cu3O10+y phase with a trace of the Tl2CaBa2Cu2O8+y phase. FWHM's of ∼2°θ were obtained in x-ray rocking curve analyses of the oriented 2223 phase. Tc (0) values of 95–105 K were measured for the better samples, and a zero field critical current density of 28 800 amps/cm2 was measured at 77 K for the best sample. SEM micrographs taken of the highest Jc samples reveal a highly textured structure consisting of platelike crystals.
Microstructure and superconducting properties of hot-pressed Bi–Pb–Sr–Ca–Cu–O thick film
Authors: Murayama Norimitsu , Kodama Yasuharu , Sakaguchi Shuji , Wakai Fumihiro
Published: September 2007

Superconducting Bi1.84Pb0.34Sr2.03Ca1.9Cu3.06Oy thick films were prepared on MgO substrates by screen printing with the powder consisting almost entirely of the 110 K phase. The thick film sandwiched between the two MgO substrates was then hot-pressed in air under various conditions. The thickness of the film was 20–40 μm. The degree of grain orientation was quantitatively evaluated through the image analysis on the SEM micrographs for the chemically etched cross sections of the samples. The degree of grain orientation and the critical current density (Jc) increased with increasing hot-pressing temperature. When hot-pressed at 855 °C under a constant pressure of 500 kg/cm2 for 270 min, the Jc had a maximum value of 9500 A/cm2 (77 K, 0 Oe), and the critical temperature was 110 K. When the hot-pressing pressure was higher than 200 kg/cm2, the degree of grain orientation was almost independent of hot-pressing pressure. Nevertheless, the Jc increased with increasing hot-pressing pressure. The relationship between the magnetic field dependence of Jc and hot-pressing conditions was examined.
The relationship between thermal history and microstructure in spray-deposited tin-lead alloys
Authors: Bewlay B.P. , Cantor B.
Published: September 2007

Gas-atomized spray deposition involves the creation of a spray of droplets by a gas atomizer and the consolidation and solidification of these droplets on a substrate. The present paper describes an investigation of the fundamental characteristics of heat transfer and solidification during spray deposition. Spray deposition was used to manufacture Sn-15 and 38 wt. % Pb preforms using atomizer-substrate distances of 180 and 360 mm, gas flow rates of 2.5 and 3.4 g/s, and melt flow rates of 61 and 35 g/s. Analytical and numerical models were developed to predict the thermal history of the spray deposit for a range of deposit-substrate heat transfer coefficients. A deposit-substrate heat transfer coefficient of ∼104 W m−2 K−1 was determined by comparing measured and calculated spray-deposit thermal histories both during and after spray deposition. Microstructural analysis of transverse sections of the spray deposits revealed maximum values of spray-deposit density and cell/grain size at specific distances from the deposit-substrate interface. The distance between the density and cell/grain-size maxima and the deposit-substrate interface increased from 0.9 to 10 mm for Sn–15 wt. % Pb and from 2.6 to 11.3 mm for Sn–38 wt. % Pb as the atomizer-substrate distance was increased from 180 to 360 mm and the melt to gas mass flow rate ratio was decreased from 24 to 10. The origin of these microstructural features is described in terms of heat transfer during spray deposition.
Diffraction imaging of polycrystalline materials
Authors: Black David R. , Burdette Harold E. , Kuriyama Masao , Spal Richard D.
Published: September 2007

A new diffraction imaging technique for the characterization of polycrystalline materials is proposed and applied to obtain direct information about individual grains and their size and shape distributions and, in turn, strains in these materials. Unlike traditional powder diffractometry, where divergent and focusing x-ray optics are essential to collect information from an ensemble of grains, the nearly parallel and monochromatic beam available from a synchrotron x-ray source is employed to observe and measure diffraction images from individual grains and component particles in consolidated materials prepared by various processes. Images can be recorded by traditional methods, such as film and pulse counting detectors, but modern image detectors, such as charge coupled device (CCD) detectors and image analyzers, make the proposed imaging technique more practical. Unlike traditional diffractometry, this new technique provides the ability to measure shape, size, and strain without model based analyses. The spatial distribution of strain within individual grains, displayed as a diffraction image (topograph), indicates the presence of defects, such as dislocations, subgrain boundaries, and precipitates, and sheds new light on the origins of residual strains (stresses) in industrial materials. The resolution of the imaging system used is limited to grains ∼10 μm or larger due to diffraction broadening (∼20” from the size effect) and the resolution of the recording medium.
Effect of chromium and phosphorus on the physical properties of iron and titanium-based amorphous metallic alloy films
Authors: DiStefano S. , Ramesham R. , Fitzgerald D.J.
Published: September 2007

Amorphous iron and titanium-based alloys containing various amounts of chromium, phosphorus, and boron exhibit high corrosion resistance. We report some physical properties of Fe and Ti-based metallic alloy films deposited on a glass substrate by a dc-magnetron sputtering technique. The films were characterized using differential scanning calorimetry (DSC), stress analysis, scanning electron microscopy (SEM), x-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), electron microprobe, and potentiodynamic polarization technique.
Energetics of C11b, C40, C54, and C49 structures in transition-metal disilicides
Authors: Carlsson A.E. , Meschter P.J.
Published: September 2007

The relative energies of the related C11b, C40, and C54 crystal structures of group IV–VII transition-metal disilicides are obtained by ab initio self-consistent band-structure calculations using the augmented-spherical-wave (ASW) method. The structural energy differences among these three structures correlate strongly with d-band filling, with C40 being stabilized relative to C54 and C11b relative to C40 as the transition-metal d-electron count increases. The C40/C11b energy difference is <0.05 eV/atom only for CrSi2 and MoSi2. Relative C11b/C40/C54 energies are similar in magnitude to those obtained in previous studies of L12/D022/D023 competition in transition-metal aluminides.1,2 Calculations of the C49/C54 energetic competition are inaccurate; the differences in atomic coordination in these two structures are probably too large for the computational method to handle accurately. The total-energy results are interpreted by a detailed analysis of the electronic density-of-states (DOS) distributions. The stable structures do not correlate as strongly with DOS effects in the vicinity of the Fermi level as in the aluminides.
Low temperature reactions of thin layers of Mn with Si
Authors: Zhang Lin , Ivey Douglas G.
Published: September 2007

Reactions between manganese thin films and silicon substrates, annealed at relatively low temperatures (<430 °C), have been systematically investigated. Three phases, i.e., Mn3Si, Mn5Si3, and MnSi, were formed through a layered growth process. The formation sequence for these silicides was Mn3Si, MnSi, and then Mn5Si3. The unusual phenomena of coexistence of these three phases and simultaneous growth of two phases (MnSi and Mn5Si3) were also observed. A model has been proposed to explain the growth behavior. The formation sequence of Mn3Si, MnSi, and then Mn5Si3, and simultaneous growth of MnSi and Mn5Si3, can be explained by considering both thermodynamic and kinetic effects. Only those reactions that are thermodynamically allowed and kinetically preferred can take place. Kinetic preference is determined by the composition in the reaction region, which is controlled by the diffusion flux of the moving reactant. The proposed model is also compared with existing models.
Atomic theory of fracture of brittle materials: Application to covalent semiconductors
Authors: Masuda-Jindo K. , Tewary V.K. , Thomson Robb
Published: September 2007

Using the lattice Green's function approach and LCAO (linear combination of atomic orbitals) electron theory, we investigate the atomistic configuration and lattice trapping of cracks in Si. The LCAO electron theory coupled to second order perturbation theory (SOP) has been used to derive explicit expressions for the bond breaking nonlinear forces between Si atoms. We calculate the cracked lattice Green's functions for a crack on the (111) plane and lying in the (110) direction. With the nonlinear forces acting in a cohesive region near the crack tips, the crack structure is then calculated. The calculated structure possesses a crack opening at the Griffith load which should allow penetration of typical external molecules to the crack tip at the Griffith loading. Other consequences for chemical reactions at the crack tip are discussed in the light of these results. The lattice trapping is low, only a few percent of the Griffith load.
Low temperature synthesis of ultrafine LiTaO3 powders
Authors: Phulé Pradeep P. , Deis Thomas A. , Dindiger David G.
Published: September 2007

Controlled chemical polymerization of tantalum ethoxide in the presence of glacial acetic acid (HOAc/Alk. = 16) and solubilized lithium acetate (Li/Ta = 1.00, H2O/Alk. = 55.55) was used for the preparation of an amorphous gel precursor to LiTaO3. Although additional investigations are required, the results suggest that successful formation of amorphous gel network, as opposed to that of colloidal tantalum (hydrous) oxide, may be due to the generation of a new organotantalum precursor via a structural modification reaction between the tantalum ethoxide and glacial acetic acid. The evolution of LiTaO3 ceramics from pre-ceramic gels was investigated using thermal analysis, electron microscopy, and x-ray diffraction. The results indicate that after the completion of gel pyrolysis (200–400 °C) and crystallization (Tc = 590 °C), ultrafine (average particle size 100–300 nm), single phase, crystalline (a = 5.243, c = 13.812 Å) LiTaO3 powders can be prepared at low processing temperatures.
Thin film processing for high-Tc superconductors of the Bi-system
Authors: Wasa Kiyotaka , Adachi Hideaki , Hirochi Kumiko , Ichikawa Yo , Matsushima Tomoaki , Setsune Kentaro
Published: September 2007

Basic thin film deposition processes for controlled deposition of the high-Tc superconductors of the Bi-systems are described. The layered structures of Bi-oxide superconductors are fabricated by a multitarget sputtering process. The multitarget sputtering process realizes the controlled deposition of single phase Bi-oxide superconductors, Bi2O2 · 2SrO · (n −1)CaO · nCuO2 for n = 1 to 5. The minimum thickness controlled by the multitarget sputtering is a half crystal unit-cell of around 15 Å, and the superlattices comprising (AkBk) · m, where A and B denote the Bi-oxide superconductors with different numbers of Cu–O layers, could be fabricated for k > 1, although ion mixing takes place during the sputtering deposition due to the bombardment of the highly energetic sputtered adatoms. Multitarget sputtering will be available for the fabrication of the artificially-made layered oxide superconductors (ALOS).
Hardness of ion-implanted Ni3Al and TiAl
Authors: Was Gary S.
Published: September 2007

Experiments were conducted to determine the effect of various implanted species on the hardness of single crystal Ni3Al (Ta, Al, B) and polycrystalline TiAl (Ta, N, B). Implantations were conducted to yield about 7 at. % Ta under the peak and ∼30% Al, N, or B under the peak in the respective targets. Hardness was measured using the Nanoindenter. Results showed that Ta+-implanted Ni3Al softens due to disordering, and subsequent heat treating results in strengthening due to preferential occupation of Al lattice sites. However, B+ and Al+ implantations result in increases in the hardness, while heat treating returns the surface hardness to bulk values. Ta+, N+, and B+ implantations into TiAl all result in hardening with N+ implantation producing the greatest hardening by a factor of ∼1.9. The probable mechanism is solid solution strengthening.
Sol-gel route to high Tc ceramic precursors
Authors: Karis T.E. , Economy J.
Published: September 2007

An aqueous sol-gel procedure to obtain fine Y–Ba–Cu particles with an approximately 1-2-3 stoichiometric ratio is described. This involves precipitating an aqueous solution of the oxides in HC1 by neutralization with Ba(OH)2, and precipitation of BaCO3 from solution with CO2. A novel treatment with H2O2 decreased the weight loss while sintering. The average particle size and shape was characterized by rheology, light scattering, and scanning electron microscope. Particle composition was studied with x-ray diffraction, electron microprobe, and infrared spectroscopy. The suspension was formed into a fiber and sintered, and measurements were made indicating a superconducting transition temperature near 60 K.
Approximants to the icosahedral and decagonal phases in the Al–Cu–Cr system
Authors: Ebalard S. , Spaepen F.
Published: September 2007

A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al65Cu20Cr15 ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.
Fabrication and tensile properties of continuous-fiber reinforced Ni3Al–Al2O3 composites
Authors: Schneibel J.H. , George E.P. , McKamey C.G. , Ohriner E.K. , Santella M.L. , Carmichael C.A.
Published: September 2007

Continuous-fiber reinforced metal-matrix composites consisting of Ni3Al alloys and Saphikon Al2O3 single crystal fibers were fabricated by hot-pressing of fiber-foil lay-ups. Two matrix compositions were employed, namely, IC50 (Ni–22.5Al–0.5Zr–0.1B, at. %) and IC396M (Ni–15.9Al–8.0Cr–0.5Zr–1.7Mo–0.02B, at. %). Etching of the foils in aqueous FeCl3 solution prior to lay-up and hot-pressing tended to improve fiber-matrix bonding and the density-normalized room temperature yield stress. Whereas strength improvements for the IC50 matrix were only moderate, significant improvements were found for an IC396M composite reinforced with 10 vol. % of Saphikon fibers.
Laser induced fractal crystallites in amorphous Te–Se–Br films
Authors: Carrière T. , Ortiz C. , Fuchs G.
Published: September 2007

This work presents the first experimental evidence of the formation of a fractal network of crystalline clusters in the first stage of the amorphous-crystal transformation. Although this transformation has been extensively studied, such an intermediate stage between amorphous and crystalline phases has never been experimentally revealed before. This fractal network was obtained by laser irradiation of an amorphous Te–Se–Br alloy. The irradiation conditions have been determined in order to be in a regime of limited diffusion, which is the basis of fractal formation. Moreover, the fractal dimension has been determined to be 1.55, which corresponds to the theoretical value obtained for fractal growth by a process of cluster-cluster aggregation with some structural readjustment.
Effect of oxygen on the formation of end-of-range disorder in implantation amorphized silicon
Authors: Lorenz E. , Gyulai J. , Frey L. , Ryssel H. , Khanh N.Q.
Published: September 2007

Formation of End-of-Range (EOR) disorder was studied in (100)-oriented silicon, when subjected to amorphization by implantation of Ge+ ions, followed by a 10 s Rapid Thermal Annealing (RTA) at 1050 °C. XTEM, RBS/channeling, and SIMS were used to analyze Czochralski grown (CZ) silicon wafers with oxygen concentrations of 6.5, 7.0, and 8.0 × 1017/cm3 and Float Zone (FZ) silicon, as “low oxygen” wafers. Amorphization on neighboring parts of the 4″ wafers was made either by 60 keV Ge+ implantation or by 110 keV Ge+ implantation and by sequential (60 keV + 110 keV) Ge+ implantation. Parts of each wafer were additionally implanted with 13 keV boron. In FZ silicon, no defects were found for 60 keV Ge+ implantation and RTA at 1050 °C. For 110 keV Ge+ and sequential (60 keV + 110 keV) Ge+ implantation in FZ-silicon the majority of the samples showed perfect annealing. Two wafers, however, subjected to sequential implantation still contained defects but with a defect density that was one order of magnitude lower than for CZ wafers. For one of them, not even a continuous layer of defects was formed. In contrast, CZ wafers contained defect bands, except for the 60 keV Ge+ implantation [in accord with the findings of Ozturk et al., IEEE Trans. on Electronic Dev. 35, 659 (1988)]. The presence of boron had no visible effect on the defect structure.
Characteristics of oxide thin films from carboxylate precursors
Authors: Chu Peir-Yung , Buchanan Relva C.
Published: September 2007

Oxide thin films on Si substrates were prepared from carboxylate precursors by the reaction of the metal nitrates and ammonium trimethylacetate. Precursor salts were characterized with respect to purity, structure, thermal pyrolysis, and phase development during calcination. A solvent system, based on carboxylic acid/amine mixture, was developed to dissolve the synthesized precursors, resulting in increased solubility, viscosity, and stability. Smooth, fine-grained ZrO2, Y2O3, and YSZ films were obtained on Si wafers by spin-coating and subsequent heat treatment above 500 °C. Films heat treated below 700 °C were generally adherent, amorphous, or microcrystalline, while YSZ and ZrO2 showed (111) preferred orientation above 700 °C. These oxide films show promise as protective or buffer layers on Si wafers.