bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial Growth of Anisotropically Shaped, Single-crystal Particles of Cubic SrTiO3
Authors: Watari Koji , Brahmaroutu Bhaskar , Messing Gary L. , Trolier-McKinstry Susan , Cheng Shang-Cong
Published: March 2008

A novel method for synthesizing anisotropically shaped particles of materials having cubic symmetry is reported. Anisotropically shaped single-crystal particles of cubic SrTiO3 were obtained by epitaxial growth on tabular tetragonal Sr3Ti2O7. Transmission electron microscopy revealed that both the shape and the size of the single-crystal particles was regulated by selecting a precursor material that can act as a reaction site in molten KCl and has an epitaxial relation with SrTiO3. The [001] and [110] directions of tabular SrTiO3 are parallel to the [001] and [110] directions of the Sr3Ti2O7 host particle, respectively. Tabular SrTiO3 particles with rectangular faces having an edge length of 10–20 μm and a thickness of ˜2 μm were obtained by reacting TiO2 and tabular Sr3Ti2O7 particles of the same edge length in molten KCl.
Materials Aspects of the High-temperature Superconductors in the System Bi2O3–SrO–CaO–CuO
Authors: Majewski Peter
Published: March 2008

Ten years after the discovery of high-Tc superconductivity in the system Bi–Sr–Ca–Cu–O, the superconducting compounds have been identified, and their structures, crystal chemistry, phase equilibria, and properties have been extensively investigated. In this review, the results of studies of crystal chemistry and phase equilibria are presented to give materials scientists a comprehensive insight into the phase equilibria and crystal chemistry of these challenging materials.
Stability and Phase Transformations of Icosahedral Phase in a 41.5Zr41.5Ti17Ni Alloy
Authors: Yi S. , Kim D. H.
Published: March 2008

Phase stability and transformations of the icosahedral phase (I-phase) in a 41.5Zr41.5Ti17Ni alloy were investigated using melt-spun ribbons and arc-melted bulk samples. A perfect I-phase can be formed directly from liquid through the melt-spinning technique. The I-phase formed in the ribbon is thermodynamically stable and transforms to W-phase, a 1/1 rational approximant above 565 °C. Formation of the perfect I-phase during annealing treatment of the arc-melted sample is very sluggish. Various types of approximants exist as intermediate states for the transformation of crystalline phases to a perfect I-phase.
Nano-scratch Behavior of a Bulk Zr–10Al–5Ti–17.9Cu–14.6Ni Amorphous Alloy
Authors: Wang J. G. , Choi B. W. , Nieh T. G. , Liu C. T.
Published: March 2008

The tribological behavior of a Zr–10Al–5Ti–17.9Cu–14.6Ni (at.%) bulk amorphous alloy, in both the as-cast and annealed states, was investigated using nano-scratch tests, including ramping load scratch and multiple sliding wear techniques. The crystallization sequence of the alloy was also characterized. Mechanical properties, such as Young's modulus, hardness, friction coefficient, and tribological wear were measured. These properties were found to vary with microstructure. In general, an increase in annealing temperature results in an increase in hardness, which in turn produces a decrease in friction coefficient but an increase in wear resistance. Samples having a structure consisting of supercooled liquid matrix with dispersed nanocrystalline particles exhibit the best wear performance.
Reaction Pathways at the Iron–microspherical Silica Interface: Mechanistic Aspects of the Formation of Target Iron Oxide Phases
Authors: Ramesh Sivarajan , Felner Israel , Koltypin Yuri , Gedanken Aharon
Published: March 2008

Oxidative hydrolysis of elemental iron nanoclusters on hydroxylated surfaces such as silica or alumina is known to be influenced by the degree of hydration of the surface. The understanding and control of this process is crucial in the synthesis of iron oxide coated silica microspheres with a desired magnetic property. The hydrolysis of iron nanoparticles followed by heat treatment in the case of a hydrated microspherical silica surface results in the formation of maghemite (γ–Fe2O3), whereas a dehydrated surface yielded hematite (α–Fe2O3) nanoparticles. The influence of adsorbed water on the formation of intermediate iron oxides/oxidehydroxides and the mechanistic aspects of their subsequent thermal dehydration iron oxide phases were investigated by thermogravimetric analysis, Fourier transform infrared, and Mössbauer spectroscopies. The reactions on both the hydrated and the dehydrated surfaces were found to proceed through the formation of an x-ray amorphous lepidocrocite [γ–FeO(OH)] intermediate and its subsequent dehydration to maghemite (γ–Fe2O3). Maghemite to hematite transformation was readily facilitated only on a dry silica surface. The retardation of the lepidocrocite →maghemite →hematite transformation in the case of a hydrated silica surface is suggested to arise from strong hydrogen-bonded interactions between the substrate silica and the adsorbed nanoparticles.
Oxygen Stoichiometry in PdOxand PdOx/Pt Electrode Layers During Processing of Ferroelectric and High-epsilon Perovskites
Authors: Saenger K. L. , Cabral C. , Duncombe P. R. , Grill A. , Neumayer D. A.
Published: March 2008

High-epsilon (HE) and ferroelectric (FE) perovskites such as (Ba, Sr)TiO3 and SrBi2Ta2O9 are attracting substantial interest for use in dynamic random-access memory and nonvolatile memory. In this paper, we describe how an easily decomposable PdO bottom electrode layer may be used as a marker for possible HE/FE damage induced by exposure to reducing environments. Oxygen loss from PdO films with and without a HE/FE overlayer was monitored by in situ x-ray diffraction during heating in an inert ambient. Additional measurements were performed on PdO films in contact with Pt underlayers. A Pt underlayer was found to reduce the temperature of oxygen release from PdO, suggesting that it may be possible to custom-design PdO-based oxygen sources with specific oxygen release characteristics to resupply the HE/FE with oxygen lost during processing.
Novel Synthesis of Nitride Powders by Microwave-assisted Combustion
Authors: Vaidhyanathan B. , Agrawal D. K. , Roy R.
Published: March 2008

A novel and simple microwave-assisted combustion procedure for the synthesis of a number of technologically important metal nitrides was demonstrated. The method involves the combustion reaction of a porous metal powder compact with N2 gas in the microwave field and provides phase-pure metal nitride products (consisting of fine particles, fibers, and whiskers) within minutes. The ignition and combustion temperatures of the reaction were found to vary as a function of compaction pressure. The microwave-prepared nitrides were characterized using x-ray diffraction, scanning electron microscopy energy dispersive spectroscopy, thermogravimetric analysis, and infrared spectroscopy. The present microwave-assisted hybrid-heating procedure allows the preparation of nitrides with good crystallinity, structural uniformity, and phase purity, and appears to have general applicability for the preparation of metal nitrides (using the respective metals or even their oxides).
A Method for Determining Crystallization Kinetic Parameters from one Nonisothermal Calorimetric Experiment
Authors: Zhang Haoyue , Mitchell Brian S.
Published: March 2008

A new equation was developed for evaluating kinetic parameters in the isokinetic range of a phase transformation using nonisothermal calorimetric techniques. The Johnson–Mehl–Avrami equation was extended by considering that the transformation rate in an isothermal process can be translated into the nonisothermal transformation in an isokinetic range. The Avrami exponent, n, activation energy, E, and frequency factor, K0, were calculated from only one nonisothermal experiment by using the new kinetic equation for amorphous Se (a-Se), polysilane/polycarbosilane (PS/PCS), and lithium disilicate (LiO2 · 2SiO2 or LS2) samples with nucleation site saturation. The values of E and K0 calculated using the new kinetic equation agree well with those obtained by the Kissinger equation for the prenucleated a-Se, PS/PCS, and LS2 samples. The values of n indicate that volume crystallization is dominant in the bulk a-Se and LS2 samples, whereas surface crystallization is dominant in the powdered PS/PCS sample. These results for a-Se were confirmed by scanning and transmission electronic microscopy.
Role of Adhesive Interlayer in Transverse Fracture of Brittle Layer Structures
Authors: Chai Herzl , Lawn Brian
Published: March 2008

The role of a soft adhesive interlayer in determining critical conditions for fracture in brittle layer structures from indentation with hard spheres is investigated. A model transparent trilayer system consisting of a glass plate overlayer (thickness range 80 μm to 2 mm) joined to a glass plate underlayer (thickness 5.6 mm) by an epoxy adhesive (thickness range 5 μm to 8 mm), loaded at its top surface with a hard tungsten carbide sphere (radius 3.96 mm), facilitatesin situobservations of the crack initiation and propagation. Whereas in bulk glass fracture occurs by inner Hertzian cone cracking immediately outside the contact circle, the soft adhesive allows the overlayer glass plate to flex, initiating additional transverse fracture modes within the overlayer: downward-extending outer ring cracks at the top glass surface well outside the contact, and upward-extending radial cracks at the bottom glass surface (i.e., at the glass/adhesive interface) on median planes containing the contact axis. The top and bottom surfaces of the glass overlayers are given selective prebonding abrasion treatments to ensure uniform flaw states, so as to enable accurate comparisons between crack initiation conditions. The adhesive bonding is strong enough to preclude delamination in our layer system. Of the three transverse crack systems, the subsurface radials generates most easily in systems with large adhesive thicknesses (and smaller overlayer thicknesses). Semi-empirical relations are specified for the dependence of the critical loads for radial and ring cracking on adhesive as well as overlayer thickness, based on the assumption that crack initiation occurs when the maximum tensile stresses in the flexing glass plate exceed the bulk strength of the (abraded) glass. Coupled with the traditional “Auerbach's law” for cone crack initiation, these relations afford a basis for the construction of simple design diagrams for brittle layer systems joined by adhesives.
Critical concentration of Mg addition for plastic instabilities in Al–Mg alloys
Authors: Chinh N. Q. , Csikor F. , Kovács Zs. , Lendvai J.
Published: March 2008

Plastic instabilities were investigated by the depth-sensing microhardness test in binary high-purity Al–Mg alloys with different Mg contents. During the tests the applied load was increased from 0 to 2000 mN at constant loading rate. The instabilities appeared as characteristic steps in the load–depth curves during indentation. It was shown that the occurrence and development of the plastic instabilities depend strongly on the solute content. Furthermore, the plastic instabilities occurred only when the solute concentration was larger than a critical value, C0. From room-temperature tests on Al–Mg alloys, C0 was found to be 0.86 wt% Mg. The critical concentration, which is necessary to get plastic instabilities, was also interpreted theoretically.
Study of electrolytic laminated ferroelectric thin films from electroded substrates
Authors: Jimeénez R. , Gonzaález A. , Calzada M. L. , Mendiola J.
Published: March 2008

An electrolytic process is described to peel off ferroelectric thin films from electroded substrates. This procedure was used to study the evolution of stress in ferroelectric calcium-modified lead titanate thin films. Stresses developed during the different steps of the preparation of the film on the substrate were calculated from curvature radii of the deposited films after each step. During the film preparation, the substrate was permanently deformed by the generated stresses. This was shown by curvature of the substrate after the electrolytic separation of the film. The laminated film liberated a large amount of stresses, as deduced from the lattice parameters of the deposited and laminated film, obtained by x-ray diffraction. The moderate residual stress that the laminated film maintained could be associated with intrinsic defects of the film.
Formation of bulk β–FeSi2by annealing rapidly solidified α–FeSi2ribbons
Authors: Zhou Zhenhua , Zhao Jianhua , Wang Wenkui , Sun Liling
Published: March 2008

Solidification of FeSi2alloy by single-roller rapid solidification technology was studied, and monophase α–FeSi2ribbons were obtained. Phase evolution of the monophase and metastable α–FeSi2ribbons during subsequent annealing was studied within situelectric resistance measurements. The results show that the metastable α–FeSi2phase transforms into the β–FeSi2phase at about 620 °C and then transforms into the α–FeSi2phase again at a higher temperature when heated. A new relatively simple method to prepare bulk β–FeSi2alloy, that is, formation of bulk β–FeSi2alloy by annealing monophase α–FeSi2alloy, is presented.
Abnormal grain growth of sputtered CuNi(Mn) thin films
Authors: Brückner W. , Weihnacht V. , Pitschke W. , Thomas J. , Baunack S.
Published: March 2008

The evolution in both stress and microstructure was investigated on sputtered Cu0.57Ni0.42Mn0.01thin films of 400 nm thickness during the first temperature cycle up to 550 °C. Samples from stress–temperature measurements up to various maximum temperatures were analyzed by x-ray diffraction, scanning and transmission electron microscopy, and Auger electron spectroscopy. The columnar grains with lateral diameters of about 20 nm in the as-deposited state coarsen to about 400 nm above 300 °C. Probably due to the impurity (Mn) drag effect, the coarsening occurs by abnormal grain growth rather than by normal grain growth, starting near the film–substrate interface. The stress development results from a combination of densification due to grain growth and plastic stress relaxation.
Effect of Cr doping on the electrical conductivity and Seebeck coefficient in the superconductors obtained from the Bi–Pb–Sr–Ca–Cu–Cr–O-type glassy precursors by annealing
Authors: Barik H. K. , Ghorai S. K. , Bhattacharya S. , Kilian D. , Chaudhuri B. K.
Published: March 2008

Homogenous (Bi3Pb)Sr3Ca3 (Cu4−nCrn)Ox (n 4 0 to 0.20) type glassy precursors become high-Tc superconductors by annealing at 840 °C. The suppression of Tc with increase of Cr concentration supports the pair-breaking mechanism. The feeble semiconducting behavior shown by the doped samples above their respective Tc values followed Mott's variable range hopping conduction mechanism. Like Ti- and Fe-doped samples, studied earlier, the thermoelectric power (TEP) of the present Cr-containing sample showed small positive peak above Tc, which was considered to be associated with the phonon-drag effect. The linear part of the temperature-dependent TEP (above Tc) well fitted the two-band model.
Influence of matrix characteristics on fracture toughness of high volume fraction Al2O3/Al–AlN composites
Authors: Nagendra N. , Jayaram V.
Published: March 2008

The role of matrix microstructure on the fracture of Al-alloy composites with 60 vol% alumina particulates was studied. The matrix composition and microstructure were systematically varied by changing the infiltration temperature and heat treatment. Characterization was carried out by a combination of metallography, hardness measurements, and fracture studies conducted on compact tension specimens to study the fracture toughness and crack growth in the composites. The composites showed a rise in crack resistance with crack extension (R curves) due to bridges of intact matrix ligaments formed in the crack wake. The steady-state or plateau toughness reached upon stable crack growth was observed to be more sensitive to the process temperature rather than to the heat treatment. Fracture in the composites was predominantly by particle fracture, extensive deformation, and void nucleation in the matrix. Void nucleation occurred in the matrix in the as-solutionized and peak-aged conditions and preferentially near the interface in the underaged and overaged conditions. Micromechanical models based on crack bridging by intact ductile ligaments were modified by a plastic constraint factor from estimates of the plastic zone formed under indentations, and are shown to be adequate in predicting the steady-state toughness of the composite.
Influence of Mn–O bond length on carrier localization in La1−x (Ca,Sr)x MnO3, where x = 0.28 to 0.375
Authors: MacManus-Driscoll J. L. , Tan G. T. , Hung W. Y. , Berenov A. V. , Alonso J. A. , Blamire M. G. , Evetts J. E. , Damay F. , Cohen L. F.
Published: March 2008

A series of rhombohedral alkaline-earth-doped manganites, La1−x (Ca,Sr)x MnO3, were studied, with x = 0.28 to 0.375, a constant tolerance factor of 0.927 ± 0.002, a very small variation of the Mn–O bond angle (<0.3°), and constant ion size variance (ς2) of 0.0020 ± 0.0010. Compositional uniformity and crystallinity were excellent, and porosity low. The temperature of the maximum in the resistivity, Tm, for x 4 0.28 was higher (by more than 20 K) than previously reported. With increasing x (and at the same time increasing Ca for Sr substitution), the Mn–O bond length shortened, Tm decreased, and the polaron hopping activation energy increased, indicative of increased carrier localization. The behavior is opposite to the La1−xSrxMnO3 series and can be explained by a strong dependence of the electron–phonon interaction on Mn–O bond length. In order to maximize Tm, Mn–O bond length must be controlled to a precise degree.
Spectral hole burning in sol-gel-derived Eu3+-doped film
Authors: Nogami Masayuki , Ishikawa Tomotaka , Hayakawa Tomokatsu , Hayakawa Tomokatsu
Published: March 2008

The sol-gel technique was applied to the preparation of Eu3+ ion–doped films, which showed persistent spectral hole burning. A gel film of ∼3500-nm thickness was prepared by dip-coating of the solution synthesized from Si(OC2H5)4, CH3Si(OC2H5)3, Eu(NO3)3 · 6H2O, and hydropropyl-cellulose. The spectral hole was burned in the 7F0 → 5D0 transition band of the Eu3+ ions at 7 K, the depth of which was 24% of the total fluorescence intensity and decreased as the heat-treatment temperature of film increased. It was found that the hole was thermally filled and erased above ∼170 K; the temperature at which the hole was erased was lower for the film heated at high temperature.
Synthesis of Co3O4 Spinel at Ambient Conditions
Authors: Zeng H. C. , Lim Y. Y.
Published: March 2008

Co3O4 was prepared in aqueous solutions through a staged oxidation process. When the mole ratio of starting chemicals Co2+:OH− is ≤1:2 (Co2+ as a limiting reagent), the formation reaction follows the brucitelike phase to cobalt oxide-hydroxide, and then to cubic spinel. However, when the ratio of Co2+:OH− is > 1:2 (OH− as a limiting reagent), the reaction path changes to the brucite-like to hydrotalcite-like phase, and then to the spinel. Using the present method, Co3O4 can be formed at a temperature as low as 40 °C, and single-phase spinel Co3O4 can be prepared at 50 °C within hours under normal atmospheric pressure.
Scanning Tunneling Spectroscopy Investigation of the Strained Si1−xGex Band Structure
Authors: Chen Xiangdong , Wang Xiang-Dong , Liu Kou-Chen , Kim Dong-Won , Banerjee Sanjay
Published: March 2008

The band offsets and band gap are the most important parameters that determine the electrical and optical behavior of a heterojunction. In situ scanning tunneling spectroscopy was employed to measure the valence-band offset of strained Si1−xGex-on-Si (100) for the first time. The valence-band offsets of the strained Si0.77Ge0.23 and Si0.59Ge0.41 on Si(100) were found to be 0.21 and 0.36 eV, respectively. The results were in good agreement with theory and with results from other experimental methods. Due to band bending and surface states, it was difficult to determine the conduction band edge at the interface of the Si1−xGex/Si exactly but we found that the conduction band offset is much smaller than the valence-band offset.
Microstructure and Physical Properties of CaF2–MgO Eutectics Produced by the Bridgman Method
Authors: Larrea A. , Contreras L. , Merino R. I. , Llorca J. , Orera V. M.
Published: March 2008

The microstructure and crystallographic orientation relationship of CaF2–MgO eutectics produced for the first time were characterized by electron microscopy. The eutectic contains single-crystal MgO rods (∼0.7 μm in size, spaced ∼8 μm) oriented parallel to the cubic axis of a CaF2 matrix. The rods present low-energy {100}CaF2 //{111}MgO interfaces. Light guiding was experimentally proved and considered for possible optical applications. Crack propagation was also studied to show the potential improvement in fracture toughness through crack deflection at the interfaces.
Unit Cell Indexing of Luminescent Tantalum Zinc Oxide
Authors: Kurinec Santosh K. , Rack Philip D. , Potter Michael D. , Blanton Thomas N.
Published: March 2008

Tantalum zinc oxide (TZO) with the chemical formula Ta2Zn3O8 can be generated from the reaction of 3 mol ZnO and 1 mol Ta2O5 at elevated temperatures. This phase has been shown to exhibit blue cathodoluminescence at low electron beam voltages. It has also been realized in thin film form on silicon substrate, making TZO an important material for monolithic field emission display devices. The structure type of TZO has been investigated using powder x-ray diffraction techniques. The unit cell of this phase has been determined and found to be monoclinic. These results allow for indexing of the powder pattern first reported by Kasper in 1967 and correct for a discrepancy in the single-crystal structure lattice constants reported by Waburg and Muller-Buschbaum in 1984.
Dielectric Properties of Nanocomposites of Silver in a Glass-ceramic Containing the Lithium Niobate Phase
Authors: Dan A. , Chakravorty D.
Published: March 2008

Glass-ceramics containing the LiNbO3 phase were used to grow nanometer-sized silver metal particles with median diameters in the range 10.5–17.3 nm. These nanocomposites showed large values of dielectric constant of the order of 103–104. Bergman's space charge model of a two-component composite gave results that differed from the experimental data. The polarization mechanism was concluded to be electronic in origin. An interrupted metallic strand model developed earlier by Rice and Bernasconi was used to explain the results obtained in the present specimen system.
Preparation and Characterization of Pb(Zr0.52Ti0.48)O3 Powders and Thin Films by a Sol-gel Route
Authors: Liu Dage , Zhang Hongxi , Wang Zhong , Zhao Liancheng
Published: March 2008

Lead zirconate titanate [Pb(ZrxTi1−x)O3 (PZT)] powders and ferroelectric thin films with a composition near the morphotropic phase boundary [Pb(Zr0.52Ti0.48)O3] were prepared by a modified sol-gel process using zirconium oxynitrate-2-hydrate as the zirconium source and ethylene glycol as solvent. The precursor solution was prepared from lead acetate-3-hydrate, tetrabutyl titanate, and zirconium oxynitrate-2-hydrate. Perovskite PZT powders were obtained after sintering at 450 °C for 2 h. Films rapid-thermally annealed at 650 °C for 1 min formed well-crystallized perovskite.Microstructures of these films indicated the presence of nano-sized grains (∼50 nm). The remnant polarization was 28.5 μC/cm2, and the coercive field was 39.8 kV/cm. Ferroelectric polarization fatigue test of In/PZT/Pt/Ti/SiO2/Si showed a high fatigue resistance up to 3 × 1010 cycles before Pr decreased by 50%.
Anisotropic Thermal Expansion of Barium Hexaferrite Using Dynamic High-temperature X-ray Diffraction
Authors: Sriram D. , Snyder R. L. , Amarakoon V. R. W.
Published: March 2008

Barium hexaferrite is a well-known ceramic permanent magnet and due to its high coercivity, remanence, and large uniaxial magnetic anisotropy, finds applications that compete with metallic magnets. Even though a number of the high-temperature properties of barium hexaferrite have been studied extensively, its anisotropic thermal expansion has not been reported so far. Dynamic high-temperature x-ray diffraction (HT-XRD) is one powerful method to obtain thermal expansion data for anisotropic polycrystalline materials in a very short period of time. In this paper the anisotropic nature of the thermal expansion coefficient of the barium hexaferrite phase is reported with the use of a dynamic HT-XRD setup. The thermal expansion coefficient (linear fit) was determined to be 8.36 × 10−6 K−1 along the a–b plane to 1.4 × 10−5 K−1 along the c axis between the temperature range of 293 to 1343 K.
Phase Evolution During Sintering of Mullite/zirconia Composites Using Silica-coated Alumina Powders
Authors: Yaroshenko V. , Wilkinson D. S.
Published: March 2008

Mullite-based composites can be made by an in situ reaction process using silica-coated alumina (SCA) powder as a mullite precursor. In this paper we present the combined effects of zirconia and premullite seeds on the crystallization process and microstructure development. When zirconia is added without seeding, mullite formation proceeds through the formation of transient zircon. This phase provides a lower energy barrier for mullite nucleation and thus lowers the mullitization temperature. The presence of yttria as a stabilizer in zirconia reduces the activation energy for zircon formation and thus promotes the transient reaction. The addition of premullite seeds results in the nucleation of mullite from alumina and silica, and zircon does not form. At low seeding levels mullitization remains nucleation-controlled; however, once the seeding level exceeds 1–2%, this is no longer the case.
Crystalline Structure Determination of Anisotropic Dimethyl Terephthalate Crystallites by Micro-Raman Spectroscopy
Authors: Rodrĺguez R. , Pacheco S. , Vargas S. , Jiménez S. , Castaño V. M.
Published: March 2008

A novel approach to determine the molecular orientation of dimethyl terephthalate molecules with respect to the direction of the crystal axis is reported. This determination was achieved by changing the crystal orientation with respect to the incident laser light of a micro-Raman spectrometer. Raman spectra were obtained at different incidence angles of the laser beam with respect to the crystal symmetry axis. The intensities of some specific bands were analyzed as a function of the tilting angle. With this information the molecular orientation with respect to the crystal axis was determined making use of a simple mechanical model.
Preparation and Characterization of Fine Indium Tin Oxide Powders by a Hydrothermal Treatment and Postannealing Method
Authors: Yanagisawa K. , Udawatte C. P. , Nasu S.
Published: March 2008

Indium tin oxide powder with an In to Sn mole ratio of 95:5 was successfully prepared from a coprecipitated In–Sn hydroxide gel by hydrothermal processing followed by calcination at relatively low temperatures (∼500 °C). Hydrothermal treatment of the In–Sn coprecipitated gel at 300 °C for 24 h led to the formation of a single phase of tin-doped indium oxyhydroxide (InOOH:Sn). Under hydrothermal conditions the oxyhydroxide phase appeared well crystallized with particles ∼80 nm in size. Calcination of the oxyhydroxide phase above 450 °C in air yielded a substitutional-vacancy-type solid solution of In2Sn1−xO5−y.
Microstructure and Chemistry of Nonstoichiometric (Ba,Sr)TiO3 Thin Films Deposited by Metalorganic Chemical Vapor Deposition
Authors: Levin Igor , Leapman Richard D. , Kaiser Debra L.
Published: March 2008

The microstructure and chemistry of (Ba,Sr)TiO3 thin films deposited on Pt/SiO2/Si substrates by metalorganic chemical vapor deposition were studied using highresolution transmission electron microscopy and quantitative spectrum imaging in electron energy loss spectroscopy. The grain boundaries in all films with overall Ti content ranging from 50.7% to 53.4% exhibit a significant increase in Ti/Ba ratio as compared to the grain interiors. The results suggest that the deviations of Ti/(Ba + Sr) ratio from the stoichiometric value of unity are accommodated by the creation of Ba/Sr vacancies, which segregate to the grain boundary regions. The films with Ti contents equal to or greater than 52% additionally contained an amorphous Ti-rich phase at some grain boundaries and multiple grain junctions; the amount of this phase increases with increasing overall Ti content. The analysis indicates that the amorphous phase can only partially account for the significant drop in dielectric permittivity accompanying increases in the Ti/(Ba + Sr) ratio.
Microporous Semicrystalline Silica Materials
Authors: Park Man , Komarneni Sridhar , Lim W. T. , Heo N. H. , Choi J.
Published: March 2008

A new family of microporous semicrystalline silica materials (MSSMs) were developed at room temperature from acidic mixtures of alkyl-substituted silane and tetramethylalkoxysilane. Hydrolyzed alkyl-substituted silica precursors, having hydrophilic silanol groups and hydrophobic alkyl groups, presumably act not only as templates but also as sol stabilizers for continuous pore engineering of silica materials in the micropore region. Depending on the substituted alkyl (SUA) groups in initial sols, MSSMs have distinct broad x-ray diffraction peaks in low 2θ range of 2° to 12°, distinguishable thermal behavior of SUA groups, highly flexible processability, and discrete micropore size with good thermal stability of micropores after the removal of SUA groups. These designer microporous silicas are expected to be useful for molecular sieving applications.
Hydrothermal Synthesis of Submicron SnO Crystallites
Authors: Wu Dien-Shi , Wu Nae-Lih
Published: March 2008

SnO crystallites having a size ranging 0.1–0.2 μm were synthesized by a hydrothermal process, which consisted of prolonged solution aging under pH = 1.0, followed by hydrothermal treatment under pH = 9 to 10 at 75–95 °C. Oxidation of Sn+2 to Sn+4 during the hydrothermal stage was effectively inhibited by increasing the solution-aging time. This was attributed to the formation, upon aging, of polymeric hydrous SnO colloids, which are more oxidation resistant than aquo-hydroxo tin complex monomers. For solutions with a sufficiently long (≥240 h) aging time, the SnO yield increased with increasing pH and temperature during the hydrothermal treatment.
Voids in Silicon by He Implantation: From Basic to Applications
Authors: Raineri V. , Saggio M. , Rimini E.
Published: March 2008

The mechanism of bubble formation when He is implanted into silicon is described. Many experiments are reviewed and several techniques are considered. During implantation and subsequent annealing, complex Hen–Vm clusters are formed, trapping vacancies, while Si self-interstitials recombine directly at the surface. By increasing temperature He atoms out-diffuse, and the entire process produces a supersaturation of vacancies (void formation). Their evolution is studied during isothermal and isochronal annealing, describing the mechanisms involved; that is, direct coalescence or Ostwald ripening. The internal surface is an efficient trap for self-interstitials and for metals. The gettering mechanism is governed by a surface adsorption at low impurity concentration while at high value a silicide phase is observed. The high getter capability is ensured by the large number of traps introduced (1017–1019 cm−3). Finally, voids introduce mid gap energy levels that act as minority carrier recombination centers, providing a powerful method to control lifetime locally in silicon devices. The reviewed results demonstrate that the trap levels are due to the dangling bonds present on the void surface. This property can be used in many applications.
Oxidation Behavior and Effect of Oxidation on Strength of Si3N4/SiC Nanocomposites
Authors: Kim Hae-Won , Koh Young-Hag , Kim Hyoun-Ee
Published: March 2008

The oxidation behavior and the effect of oxidation on the flexural strength of Si3N4/SiC nanocomposites were investigated. Parabolic weight gains, with respect to the oxidation time, were observed for all the specimens containing different amounts of SiC. However, the parabolic rate constant decreased with increasing SiC content. The main oxidation product, being in equilibrium with SiO2, was Y2Si2O7. The oxidation product became denser and retained more crystalline phase as the amount of SiC increased. The flexural strength of the nanocomposites increased by up to 40%, while that of pure Si3N4 decreased after oxidation at 1300 or 1400 %C for 100 h. This excellent oxidation resistance of Si3N4 nanocomposite was attributed to the enhancement of the crystallization of the oxidation product and the grain boundary phase by the SiC nanoparticles.
Phase Transformations in Rapidly Quenched Ni–Mn–Ga Alloys
Authors: Chernenko V. A. , Cesari E. , Pons J. , Seguí C.
Published: March 2008

Structural and ferromagnetic transitions in shape memory Ni–Mn–Ga alloys and their martensitic structure and microstructure were found to be strongly influenced by rapid quenching from the liquid state and by subsequent aging. Detailed calorimetric and magnetic measurements, dynamic mechanical analysis, and transmission electron microscopy observations were performed to characterize the transformation behavior of thin ribbons compared to the bulk materials. The rapid quenching caused the decrease of the ferromagnetic, martensitic, and premartensitic transformation temperatures, as well as of the saturation magnetization, while the subsequent annealing brought about an increase of the depressed values. This influence was attributed to quenched-in short-range chemical disorder within sublattices, the ordering being improved by a vacancy migration mechanism upon subsequent annealing.
Microstructure and Mechanical Properties of Sm1-xSrxCo0.2Fe0.8O3
Authors: Chou Y-S. , Stevenson J. W. , Armstrong T. R. , Hardy J. S. , Hasinska K. , Pederson L. R.
Published: March 2008

The room temperature mechanical properties of a mixed conducting perovskite Sm1?xSrxCo0.2Fe0.8O3 (x = 0.2 to 0.8) were examined. Density, crystal phase, and microstructure were characterized. It was found that the grain size increased abruptly with increasing Sr content. Mechanical properties of elastic modulus, microhardness, indentation fracture toughness, and biaxial flexure strength were measured. Young's modulus of 180–193 GPa and shear modulus of 70–75 GPa were determined. The biaxial flexure strength was found to decrease with increasing Sr content from ∼70 to ∼20 MPa. The drop in strength was due to the occurrence of extensive cracking. Indentation toughness showed a similar trend to the strength in that it decreased with increasing Sr content from ∼1.1 to ∼0.7 MPa m1/2. In addition, fractography was used to characterize the fracture behavior in these materials.
Intracrystalline Microstructure of Synthetic Merwinite
Authors: Fukuda Koichiro
Published: March 2008

Crystals of merwinite were prepared at 1550 °C from chemical reagents, and their intracrystalline microstructures were examined by the combined use of x-ray diffraction and optical microscopy. The crystals were composed of pseudomerohedral twins. The adjacent twin domains were related by the pseudosymmetry two-fold axis parallel to ⟨011⟩with the composition surface {811} The overall twin structure was constructed by introducing the pseudo-symmetry three-fold axis normal to (100), which must originally be a symmetry element of the former high-symmetry phase. The transition from the primitive trigonal (point group3m) to the primitive monoclinic (space groupP21/a) was accompanied by the combination of reducing the order of the point group and the change in the size of the unit cell. The order of the point group was reduced from 12 to 4, resulting in three twin domains with six different interfaces. This accounted for the experimentally observed microstructure consisting of repeated lamella twins in several orientations. Because the unit lattice translation would be lost during the transition, the formation of antiphase domains was expected. The lost translation vectors were 1/2[011], 1/2[100], and 1/2[111] resulting in four antiphase domains. As a result, the total number of domains possible in the transition was 3 × 4 = 12.
Oxygen Potential in Molten Tin and Gibbs Energy of Formation of SnO2 Employing an Oxygen Sensor
Authors: Kurchania Rajnish , Kale Girish M.
Published: March 2008

On-line monitoring of the dissolved impurities in molten metals is important for better process control during alloying and metal refining operations. Disposable-type oxygen sensors are commercially available and are used in the iron and steel industry worldwide. However, there is a need for developing low-cost, reliable, long-life oxygen sensors for continuous monitoring of dissolved oxygen in molten metals. In this paper we present the results of the physical and electrical characterization of the solid electrolyte material ZrO2 (8 mol%Y2O3). The experimental results of the application of long-life solid-state electrochemical sensors designed using yttria-stabilized zirconia solid electrolyte for the measurement of oxygen potential in molten tin between 823 to 1273 K and standard Gibbs energy of formation of SnO2 from its elements are also reported.
Ferroelectric and Dielectric Properties of Strontium Bismuth Niobate Vanadates
Authors: Wu Yun , Cao Guozhong
Published: March 2008

Strontium bismuth niobate vanadates, SrBi2 (VxNb1-x)2O9 (with 0 ≤ x ≤ 0.1), were prepared by reaction sintering of powder mixtures of constituent oxides. With partial substitution of niobium by vanadium cations (up to 10 at.%), the single-phase layered perovskite structure was preserved, and the sintering temperature of the system was significantly lowered (∼200 °C). The incorporation of vanadium into the layered perovskite structure resulted in a shift of the Curie point to higher temperatures from 435 to 457 °C, with 10 at.% vanadium doping, and an increase in dielectric constant from ∼700 to ∼1100, with 10 at.% vanadium doping, at their respective Curie points. The remanent polarization increased from ∼2.4 to ∼8 µC/cm2, while the coercive field decreased from ∼63 to ∼45 kV/cm with 10 at.% V5+ doping.
Formation of Bulk Nanostructured Materials by Rapid Solidification
Authors: Guo W. H. , Chua L. F. , Leung C. C. , Kui H. W.
Published: March 2008

When a eutectic melt is undercooled below its liquidus T1 by a critical amount, it undergoes metastable liquid-state spinodal decomposition. The resulting morphologies can be described as intermixing undercooled liquid networks of characteristic wavelength λ. At a temperature substantially below T1, λ can be <100 nm. When λ ≤ 100 nm, the undercooled liquid networks break up into nanometer-size droplets/strips driven apparently by surface tension. The morphologies of the tiny droplets/strips can be frozen by subsequent crystallization. The as-crystallized specimen is a nanostructured material. It is microvoid free and the size of the constituent grains is rather uniform. Two systems, Pd40.5Ni40.5P19 and Pd82Si18, were chosen to illustrate the synthesis process.
Photo- and Cathodoluminescence of the Combustion-synthesized Al2O3–TiB2 Composites
Authors: Xia Tian D. , Liu Tian Z. , Zhao Wen J. , Munir Zuhair A. , Wang Tian M.
Published: March 2008

Al2O3–TiB2 composites were synthesized by the combustion reaction 3TiO2 + 3B2O3 – (10 + x)Al, with x ranging from 0 to 4.71. The products consisted of corundum, TiB2, and a trace of Ti2O3 for the reactions with x = 0 and x = 1.4. However, the products of the reaction with x = 2.96 contained corundum and TiB2 only. For products of samples with x = 0, 1.4, and 2.96, similar room-temperature absorption spectra were observed in the ultraviolet and visible range at wavelengths of 265, 706, and 844 nm. Room-temperature photoluminescence spectra of the composites showed one visible band at about 720 nm. Room-temperature cathodoluminescence (CL) spectra of the composites synthesized by reactions with x = 0 and 1.4 exhibited two visible bands centered at 400 and 710 nm, respectively. From samples synthesized with x = 2.96, another visible band centered at 570 nm was observed in the CL spectrum. Comparing secondary electron images to panchromatic and monochromatic CL images of the composites, it was found that the light-emitting phase is TiB2-containing corundum. The 710-nm band is attributed to the transition between 1T1 (et) and 3T2 (et) excited states, and the 570- and 400-nm bands to the transitions between 3T1 (et) or 3A2 (e2) and 1T1 (et) excited states and 3T1 (t2) ground state of Ti2+ in corundum, respectively.
Synthesis and Characterization of Sr1−xBaxBi2Ta2O9 Materials
Authors: Melgarejo R. E. , Tomar M. S. , Dobal P. S. , Katiyar R. S.
Published: March 2008

Due to its endurance to ferroelectric fatigue, SrBi2Ta2O9 (SBT) has been extensively investigated. We report here the synthesis of Sr1−xBaxBi2Ta2O9 (x = 0.0, 0.1, 0.5, 1.0) using a solution-based route. The precursors used in this work were the salts of strontium, barium, bismuth, and tantalum ethoxide. X-ray diffraction and Raman spectroscopic studies indicated the formation of complete solid solution system for Sr1−xBaxBi2Ta2O9. This material system may provide interesting properties relevant to microwave tuning and ferroelectric memory applications, which are under investigation.
Brittle to Ductile Transition Dependence upon the Transition Pressure Value of Semiconductors in Micromachining
Authors: Jasinevicius Renato G. , Pizani Paulo S. , Duduch Jaime G.
Published: March 2008

Single-point diamond turning tests were carried out in two different [001]-oriented semiconductors, InSb and Si single crystals. The analysis of the conditions in which the machining is in ductile or brittle mode indicates that the plasticity presented by semiconductor crystals during micromachining can be correlated to the value of the transition pressure. It is shown that the ductility presented by different semiconductor single crystals is inversely related to the transition pressure value of the material.
Defect-dependent Elasticity: Nanoindentation as a Probe of Stress State
Authors: Jarausch K. F. , Kiely J. D. , Houston J. E. , Russell P. E.
Published: March 2008

Using an interfacial force microscope, the measured elastic response of 100-nm-thick Au films was found to be strongly correlated with the films' stress state and thermal history. Large, reversible variations (2×) of indentation modulus were recorded as a function of applied stress. Low-temperature annealing caused permanent changes in the films' measured elastic properties. The measured elastic response was also found to vary in close proximity to grain boundaries in thin films and near surface steps on single-crystal surfaces. These results demonstrate a complex interdependence of stress state, defect structure, and elastic properties in thin metallic films.
Creep-controlled Diffusional Hillock Formation in Blanket Aluminum Thin Films as a Mechanism of Stress Relaxation
Authors: Kim Deok-Kee , Nix William D. , Deal Michael D. , Plummer James D.
Published: March 2008

Hillock formation, a stress-induced diffusional relaxation process, was studied in sputter-deposited Al films. The grain sizes in these films were small compared to those in other sputter-deposited Al films, and impurities (O, Ti, W) were incorporated during the preparation of the films. Stress and hardness measurements both indicate that the Al films were strengthened by the small grain size and incorporated impurities. We observed a new type of hillock in these Al thin films after annealing for 2 h at 450 °C in a forming gas ambient. The hillocks were composed of large Al grains created between the substrate and the original Al film with its columnar grain structure, apparently by diffusion from the surrounding area. By modifying the boundary conditions of Chaudhari's hillock formation model [P. Chaudhari, J. Appl. Phy. 45, 4339 (1974)], we have created a new model that can describe the experimentally observed hillocks. Our model seems to explain the experimentally observed abnormal hillock formation and may be applied to other types of hillock formation using different creep laws.
Thermal Expansions of the Beta and Gamma Phases in a Co–Ni–Fe Superalloy Determined by X-ray Diffraction
Authors: Seehra M. S. , Cionca C. , Manivannan A.
Published: March 2008

Commercially useful multiphase alloy Inconel 783 is made up of Ni(28%), Fe(25%), and Co(35%) with smaller amounts of Cr, Al, Nb, Mo, Ti, C, and Si. In this work, relative temperature variations of the lattice constants a(T)/a0 of the gamma (face-centered-cubic) and beta (body-centered-cubic) phases of this alloy are determined from 97 to 773 K using analyses of their x-ray diffraction (XRD) patterns. Plots of a(T)/a0 for the two phases vary from 1.0 at 97 K to 1.012 at 773 K and show that (i) for T = 500 K, thermal expansion of the β phase is larger than that of the = phase; and (ii) an abrupt jump is observed near 300 K. The appearance of new lines above 700 K in XRD representing Co2CrO4 and CoCr2O4 is interpreted in terms of the oxidation of the γ phase, whereas the β phase is oxidation resistant. The anomalous change in a(T)/a0, observed near 300 K and accompanied by a similar change in the temperature variation of the initial magnetic susceptibility, is not well understood. A brief discussion on the implications of these results is presented.
Effects of Nd123/MgO Thin Film and MgO Single-crystal Seeds in Isothermal Solidification of YBaCuO/Ag
Authors: Cai Chuanbing , Fujimoto Hiroyuki
Published: March 2008

The seeding effects of (001) Nd123/MgO thin films and MgO single crystals were studied in isothermal solidification of YBa2Cu3Oy composite with the additions of 40 mol% Y2BaCuO5, 10 wt% Ag, and 0.5 wt% Pt. Seeding with the Nd123/MgO thin film resulted in single-domain growth of Y123 crystal with a stable growth along the “100”?direction, while seeding with MgO single crystal produced multidomain growth in which the dominant growth facet is rotated 45° about (100) plane of MgO. Multidomain growth in MgO seeded sample was suppressed by decreasing undercooling degree. The effects of undercooling degree and seed size on multidomain growth are discussed in view of classical nucleation and growth theory.
Sintering of Cordierite–borosilicate Glass Composites
Authors: Shyu Jiin-Jyh , Wang Jui-Kai
Published: March 2008

The sintering and properties of cordierite–borosilicate glass composites were investigated. For the composites with ≥35% low-viscosity glass, the sintered densities decreased with the increasing sintering temperature above 850 °C. No crystallization of the glass was found. For the composites with 50–90 wt% high-viscosity glass, the sintered densities remained nearly constant (>95%) in a wide sintering temperature range. However, cristobalite crystallized from the glass phase, resulting in an undesirably high coefficient of thermal expansion. Presintering processing and a lower heating rate improved the densification of the composites with low-viscosity glass while limiting that of the composites with high-viscosity glass. This result is explained by the difference in crystallizability between these two glasses. As low- and high-viscosity glass powders were simultaneously added, the density reduction was reduced and the coefficient of thermal expansion was closer to that of Si because of the absence of cristobalite phase. The dielectric constant of all the composites was in the typical range of 4.9–5.7 at 1 MHz.
Thermal Expansion of Ti5Si3 with Ge, B, C, N, or O Additions
Authors: Williams J. J. , Kramer M. J. , Akinc M.
Published: March 2008

The crystallographic thermal expansion coefficients of Ti5Si3 from 20 to 1000 °C as a function of B, C, N, O, or Ge content were measured by high-temperature x-ray diffraction using synchrotron sources at Cornell University (Cornell High Energy Synchrotron Source; CHESS) and Argonne National Laboratory (Advanced Photon Source; APS). Whereas the ratio of the thermal expansion coefficients along the c and a axes was approximately 3 for pure Ti5Si3, this ratio decreased to about 2 when B, C, or N atoms were added. Additions of O and Ge were less efficient at reducing this thermal expansion anisotropy. The extent by which the thermal expansion was changed when B, C, N, or O atoms were added to Ti5Si3 correlated with their expected effect on bonding in Ti5Si3.