bluuebunny/crossref_metadata_2025 huggingface dataset:
New combustion synthesis technique for the production of (InxGa1−x)2O3 powders: Hydrazine/metal nitrate method
Authors: GarcÍa R. , Hirata G. A. , McKittrick J.
Published: March 2008

A new low-temperature method to produce (InxGa1−x)2O3 (x = 0.1, 0.2, and 0.3) powders with high purity, high chemical homogeneity and improved crystallinity in the as-synthesized state has been developed. This procedure produced finely divided powders through an exothermic reaction between the precursors. The process starts with aqueous solutions of In(NO3)3 and Ga(NO3)3 as the precursors and hydrazine as the (noncarbonaceous) fuel. The combustion reaction occurred when heating the precursors between 150 and 200 °C in a closed vessel filled with an inert gas (Ar), which yields (InxGa1−x)2O3 directly. These materials were compared with powders prepared by a more typical combustion synthesis reaction between nitrates and a carbonaceous fuel at a higher ignition temperature of 500 °C.
Solid-phase synthesis of cupric tungstate
Authors: Dorfman Leonid P. , Houck David L. , Scheithauer Michael J. , Dann Jeffrey N. , Fassett Harry O.
Published: March 2008

The high degree of mixing of W and Cu phases in copper tungstates makes them an attractive source for manufacturing W–Cu composite powders. Hydrogen reduction of copper tungstates provides composite W–Cu powder products with a uniform, homogeneous dispersion of the metal phases. This paper presents test results for a variety of solid-phase reactions to synthesize cupric tungstate (CuWO4). Hydrated, dehydrated, and complex oxides of tungsten and copper have been used as solid reactants. With stoichiometric ratios of reactants, synthesis in air at 800 °C produced 96% to 100% conversion to CuWO4. Heterogeneous synthesis of CuWO4 with the participation of three solid phases (S1 + S2 →S3) required the simplest, most inexpensive equipment. The end product properties of synthesized CuWO4 could be controlled by the proper choice of reactants.
Directional solidification and microstructural studies of the peritectic Y2BaCuO5 phase
Authors: Reddy E. Sudhakar , Noudem J. G. , Tarka M. , Schmitz G. J.
Published: March 2008

Directional solidification using a Bridgman furnace was performed to produce textured Y2BaCuO5 (211) rods of both stoichiometric and off-stoichiometric compositions and to investigate microstructure formation at various solidification rates. The solidification morphology of the samples changed from planar to cellular and eventually to equiaxed blocky grains with increasing solidification rate. The microstructure of the stoichiometric 211 sample revealed elongated, aligned YBa2Cu3Oy (123) phase residual in the 211 matrix. The 211 samples rich in Y2O3 phase showed no trace of residual 123 but did show trapped Y2O3 particles. The morphology of the Y2O3 particles varied from spherical to a rodlike morphology as well along the length of a specific sample as also with decreasing growth rates in different samples. The Y2O3 particles in samples exposed for longer time to the liquid phase at high temperatures exhibited coarsening and unidirectional coalescence into a rodlike morphology and retained their morphology even in the 211 matrix after solidification.
Processing of highly oriented lithium niobate films through chemical solution deposition
Authors: Ono Satomi , Hirano Shin-Ichi
Published: March 2008

A precursor solution for processing lithium niobate (LiNbO3) films was prepared from lithium niobium ethoxides through modification with acetic acid in hydrolysis. Homogeneous gel films were spin-coated on various substrates. Highly oriented LiNbO3 films were crystallized on sapphire and Pt-coated substrates by heat treatment at 500 °C. Crystallization behavior of the LiNbO3 films depended on the orientation of platinum under-layer films. LiNbO3 films crystallized with preferred (001) orientation on Pt(111) layers, while LiNbO3 films crystallized with preferred (113) orientation on Pt(100) layers. LiNbO3 films prepared on Si(111), SiO2, and MgO(100) substrates showed polycrystalline characteristics with less orientation by heat treatment at 500 °C.
Orientation dependence of Portevin–Le Châtelier plastic instabilities in depth-sensing microindentation
Authors: Kovács Zs. , Chinh N. Q. , Lendvai J.
Published: March 2008

Plastic instabilities were investigated in an Al–Zn–Mg–Cu alloy by depth-sensing microhardness testing in Vickers geometry. The alloy investigated showed strong age hardening as a consequence of Guiner–Preston zone formation at room temperature. The orientation dependence of the Portevin–Le Chátelier (PLC) effect was investigated by microindentation tests in differently oriented grains. If the direction of the indentation was close to the 〈100〉 crystal axis and the diagonal of the Vickers indenter coincides with the 〈110〉 crystal direction, the PLC effect was more pronounced. Under these conditions the instabilities could be observed even after 5 h of natural aging, while the PLC effect disappeared in grains with other orientations after 2 h of aging. The orientation dependence of the indentation curves was observed up to the maximal measured imprint size (d ≈ 80 μm). It is suggested that the initialization of the PLC bands takes place in the close vicinity of indenter/sample contact surface. Considering only a uniaxial compressive stress component in the sample/indenter contact planes, in the vicinity of the indenter single sliplike and multiple sliplike conditions are attained depending on the orientation of the indenter relative to the sample. Changes of the slip conditions correlate with changes in the observation regime of instability which explains the orientation dependence.
Structure and phase characteristics of amorphous boron–carbon–nitrogen under high pressure and high temperature
Authors: Huang Jianyu , Zhu Yuntian T. , Mori Hirotaro
Published: March 2008

An amorphous boron–carbon–nitrogen (a-BCN) phase was synthesized by ball milling of a mixture of hexagonal BN (h-BN) and graphite with a nominal composition of (BN)0.5C0.5 in atomic ratio. Electron energy-loss spectroscopy studies indicated that the bonding of the a-BCN is in an sp2 configuration and the mixing between the BN and the C species was achieved at a nanometer scale, but the a-BCN phase was more likely a mechanical mixture rather than a chemical mixture. High-pressure and high-temperature (HPHT) treatment at 7.7 GPa and 2300 °C of the a-BCN phase resulted in complete segregation of the carbon and BN species, forming a nanocrystalline composite material comprising cubic BN (c-BN), amorphous carbon, and turbostratic graphite. The grain size of the c-BN phase was about 70 nm. No mutual solubilities between c-BN and carbon were found, and the two different species (C and BN) were well separated. An epitaxial relationship, i.e., the (0002) planes of graphite being parallel to the (111) planes of c-BN, was also found. The formation of ternary BCN phases was never found in the present experiment. Our experimental results also suggest the possibility of synthesizing c-BN grains encapsulated with graphite under controlled HPHT conditions.
Synthesis of Ba2Ti9O20via ethylenediaminetetraacetic acid precursor
Authors: Xu Yebin , He Yanyan , Wang Liangbin
Published: March 2008

The modified Pechini method using ethylenediaminetetraacetic acid as a chelating agent to prepare Ba2Ti9O20is reported. The resin precursors were prepared and heated at 700 to 1200 °C in air, and x-ray diffraction was used to determine the phase transformations as a function of temperature. Single-phase Ba2Ti9O20was obtained at 1200 °C for 2–6 h, without the need of prolonged heat treatment time. The process was simple and easy to control: low-temperature conditions or a protective atmosphere was not needed. Differential thermal analysis, thermogravimetric analysis, and Raman spectroscopy were used to characterize the precursors and derived oxide powders. Details of the synthesis and characterization of the resultant products were given.
Processing effects on the composition and dielectric properties of hydrothermally derived BaxSr(1−x)TiO3 thin films
Authors: McCormick Mark A. , Roeder Ryan K. , Slamovich Elliott B.
Published: March 2008

Polycrystalline BaxSr(1−x)TiO3 (BST) thin films were processed on Pt-coated glass substrates at temperatures below 100 °C by reacting TiO2 films in alkaline solutions containing Ba2+ and/or Sr2+. The TiO2 was deposited by spin-casting a titanium metalorganic precursor onto Pt-coated glass substrates, followed by pyrolysis in air at 400 °C. Film stoichiometry deviated from the initial solution composition, with a preferred incorporation of Sr2+ into the perovskite lattice. The BST thin films had dielectric constants ranging from 100 to 185 and dielectric loss values below 0.25. Capacitance–voltage and current–voltage relationships were examined to determine the effect of phase stoichiometry and processing route on dielectric properties.
Mechanochemical-hydrothermal preparation of crystalline hydroxyapatite powders at room temperature
Authors: Shuk Pavel , Suchanek Wojciech L. , Hao Tian , Gulliver Eric , Riman Richard E. , Senna Mamoru , TenHuisen Kevor S. , Janas Victor F.
Published: March 2008

Crystalline hydroxyapatite (HAp) powders were prepared at room temperature from heterogeneous reaction between Ca(OH)2powders and (NH4)2HPO4 solutions via the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, thermogravimetric characterization, and chemical analysis were performed, and it was determined that the room temperature products were phase-pure, thermally stable HAp with a nearly stoichiometric composition. Dynamic light scattering revealed that the dispersed particle size distribution of the room temperature HAp powders was in the range of 0.15–3.0 μm with a specific surface area of ≈90 m2/g. Both specific surface area measurements and scanning electron microscopy confirmed that the HAp powders consisted of agglomerates containing hundreds of ≈20 nm HAp crystals.
Preliminary study on alternating thienylene/phenylene copolymers functionalized with an electron-donating or -withdrawing group
Authors: Xu J. M. , Ng S. C. , Chan H. S. O.
Published: March 2008

Three novel regioregular polymers substituted with electron-donating or -withdrawing groups, poly[1,4-bis(3-X-2,5-thienylene)phenylene-alt-2,5-dioctyl-1,4-phenylene] [PBT(X), X = OMe, H, CN], were synthesized and characterized. They are highly fluorescent, but the absorption wavelength of PBT(CN) and PBT(OMe) are shifted toward the blue and red regions, respectively, with reference to PBT(H). The onset reduction potential of PBT(CN) is –1.11 V versus SCE (saturated calomel electrode), which is higher than that of the cyano derivative of poly(phenylene vinylene), indicating it be a good candidate as electron transport layer. The onset oxidation and reduction potentials of PBT(OMe) (0.96 and –1.28 V versus SCE respectively) suggest it would perform well as emissive layer in light-emitting display applications.
Small correction required when applying the Hertzian contact model to instrumented indentation data
Authors: Hay J. L. , Wolff P. J.
Published: March 2008

Instrumented indentation testing (IIT) is a relatively new form of mechanical testing which significantly expands on the capabilities of traditional hardness testing. In an IIT experiment, an indenter of known mechanical properties is pressed into contact and then withdrawn from a test material. The fundamental measurements during an IIT experiment are the applied load and the resulting penetration of the indenter into the test surface. The Hertzian contact model, or a derivative thereof, is often employed to relate these measurements to interesting mechanical properties of the test material. This article argues for a small correction to the Hertzian contact model when applied to instrumented indentation data. The magnitude of the correction primarily depends on Poisson's ratio of the test material and the contact radius normalized by the radius of the indenter tip. Neglecting this correction can cause significant errors in the calculation of elastic modulus and hardness from instrumented indentation data.
Precipitation of icosahedral phase from amorphous Zr65Cu17.5−xAl7.5Ni10Agx (x = 0, 5) alloys
Authors: Lee J. K. , Choi G. , Kim W. T. , Kim D. H.
Published: March 2008

Crystallization behavior of amorphous Zr65Cu17.5−xAl7.5Ni10Agx (x = 0, 5) alloys prepared by melt spinning and injection casting techniques has been studied using differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Ag addition changes crystallization sequence of the amorphous phase. The amorphous Zr65Cu17.5Al7.5Ni10 alloy crystallizes via simultaneous precipitation of icosahedral phase and NiZr2 phase in the first crystallization step whereas that in Zr65Cu12.5Al7.5Ni10Ag5 alloy crystallizes via precipitation of only icosahedral the phase. Partial replacement of Cu by Ag in Zr65Cu17.5Al7.5Ni10 alloy stabilized the icosahedral phase relative to competing intermetallic phases resulting in suppression of the precipitation of the NiZr2 phase, enhancement of the precipitation of icosahedral phase, and reduction of undercooled liquid range. Crystallization behavior of the amorphous Zr65Cu12.5Al7.5Ni10Ag5 alloy is not affected by cooling rate during solidification. Johnson–Mehl–Avrami analysis of isothermal transformation data suggests that the formation of the quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of the solute at later state.
Creep and toughness of cryomilled NiAl containing Cr
Authors: Whittenberger J. Daniel , Aikin Beverly , Salem Jon
Published: March 2008

NiAl–AlN + Cr composites were produced by blending cryomilled NiAl powder with approximately 10 vol% Cr flakes. In comparison to the as-consolidated matrices, hot isostatically pressed Cr-modified materials did not demonstrate any significant improvement in toughness. Hot extruded NiAl–AlN + 10.5Cr, however, possessed a toughness twice that determined for the base NiAl–AlN alloy. Measurement of the 1200 to 1400 K plastic flow properties revealed that the strength of the composites was completely controlled by the properties of the NiAl–AlN matrices. This behavior could be successfully modeled by the Rule-of-Mixtures, where load is shed from the weak Cr to the strong matrix.
CsCl-modified Ga2S3–La2S3 glasses: Structural approach by x-ray absorption spectroscopy
Authors: Ramos A. Y. , Cardona M. Grisolía , Tolentino H. C. N. , Alves M. C. M. , Watanabe N. , Alves O. L. , Barbosa L. C.
Published: March 2008

Gallium–lanthanum sulfide glasses are potential hosts for 1.3-μm optical fiber amplifiers and for fiber lasers in the near and middle infrared. In these glasses the addition of CsCl increases the thermal stability region making possible to draw optical fibers, without altering the optical properties of the glass. Ga2S3–La2S3 glasses modified by 10 to 40% CsCl have been studied by x-ray absorption spectroscopy, to investigate the structural role of CsCl. The chlorine environment is found similar to that in CsCl. The gallium-based network is composed from almost regular tetrahedra weakly connected by corners and is not altered by the addition of CsCl.
Biomimetic model of a sponge-spicular optical fiber—mechanical properties and structure
Authors: Sarikaya M. , Fong H. , Sunderland N. , Flinn B. D. , Mayer G. , Mescher A. , Gaino E.
Published: March 2008

Nanomechanical properties, nanohardness and elastic modulus, of an Antarctic spongeRosella racovitzeawere determined by using a vertical indentation system attached to an atomic force microscope. The Rosella spicules, known to have optical waveguide properties, are 10–20 cm long with a circular cross section of diameter 200–600 μm. The spicules are composed of 2–10-μm-thick layers of siliceous material that has no detectable crystallinity. Measurements through the thickness of the spicules indicated uniform properties regardless of layering. Both the elastic modulus and nanohardness values of the spicules are about half of that of either fused silica or commercial glass optical fibers. The fracture strength and fracture energy of the spicules, determined by 3-point bend tests, are several times those of silica rods of similar diameter. These sponge spicules are highly flexible and tough possibly because of their layered structure and hydrated nature of the silica. The spicules offer bioinspired lessons for potential biomimetic design of optical fibers with long-term durability that could potentially be fabricated at room temperature in aqueous solutions.
Texture in Ti/Al and Nb/Al multilayer thin films: Role of Cu
Authors: Lucadamo G. , Barmak K. , Rodbell K. P.
Published: March 2008

Fiber texture in Ti/Al and Nb/Al polycrystalline multilayer thin films, with bilayer thicknesses (Λ) ranging from 20–333 nm and having a fixed stoichiometry of 1/3, has been investigated by using x-ray pole figures and transmission electron microscopy. Two sets of films were deposited; one set contained pure Al and the other Al–1.0 wt% Cu. The results indicated that texture was strengthened by the formation of a coherent superlattice for the Nb/pure-Al film with the smallest bilayer thickness. By contrast, the texture in Ti/pure-Al films with a similar period was not as strong. The texture also decreased with increasing Λ for both the Ti/pure-Al and Nb/pure-Al films. An increase in the width of the Al (111) peak and an offset of the fiber axis from the substrate normal of 5–8° was observed in the Λ = 333 nm films prepared by using Al–1.0 wt% Cu. The decrease in texture on addition of Cu to Al was attributed primarily to an increase in interlayer roughness as a consequence of reduction in the Al(Cu) grain size. These observations were interpreted in the context of structure zone and dynamic roughness models of film growth.
Direct measurement of plowing friction and wear of a polymer thin film using the atomic force microscope
Authors: Du Binyang , VanLandingham Mark R. , Zhang Qingling , He Tianbai
Published: March 2008

Nanometer-scale plowing friction and wear of a polycarbonate thin film were directly measured using an atomic force microscope (AFM) with nanoscratching capabilities. During the nanoscratch tests, lateral forces caused discrepancies between the maximum forces for the initial loading prior to the scratch and the unloading after the scratch. In the case of a nanoscratch test performed parallel to the cantilever probe axis, the plowing friction added another component to the moment acting at the cantilevered end compared to the case of nanoindentation, resulting in an increased deflection of the cantilever. Using free-body diagrams for the cases of nanoindentation and nanoscratch testing, the AFM force curves were analyzed to determine the plowing friction during nanoscratch testing. From the results of this analysis, the plowing friction was found to be proportional to the applied contact force, and the coefficient of plowing friction was measured to be 0.56 ± 0.02. Also, by the combination of nanoscratch and nanoindentation testing, the energetic wear rate of the polycarbonate thin film was measured to be 0.94 ± 0.05 mm3/(N m).
Polarization reversal and domain anisotropy in flux-grown KTiOPO4 and isomorphic crystals
Authors: Urenski P. , Rosenman G. , Molotskii M.
Published: March 2008

Spontaneous polarization reversal and domain structures of flux-grown ferroelectric KTiOPO4 and isomorphic crystals were studied. Two temperature regions with dominant either ionic or electronic conductivity were found. It was shown that in the high-temperature region mobile cations contributed sufficiently to internal screening process. The ionic leakage current was suppressed at a specific temperature point for each studied crystal. High crystallographic asymmetry of domain wall velocity was observed. This shows that the electrode pattern should be properly oriented relative to the crystal axes of KTiOPO4 and its isomorphs for fabrication of periodically poled domain configurations used in nonlinear optical conversions.
High critical current density YBa2Cu3O7δ thick films using ion beam assisted deposition MgO bi-axially oriented template layers on nickel-based superalloy substrates
Authors: Groves J. R. , Arendt P. N. , Foltyn S. R. , Jia Q. X. , Holesinger T. G. , Kung H. , Peterson E. J. , DePaula R. F. , Dowden P. C. , Stan L. , Emmert L. A.
Published: March 2008

Nickel-based superalloys have been coated with magnesium oxide (MgO) using ion-beam-assisted deposition (IBAD). This technique produced a well-oriented bi-axially textured MgO template layer with a Ф scan full width half maximum of 6.4°. The layer architecture for these samples was as follows: polished hastelloy C276/amorphous Si3N4/IBAD MgO/ pulsed laser deposited (PLD) Y2O3–ZrO2/PLD CeO2/PLD YBa2Cu3O7?δ. The subsequent heteroepitaxial PLD of 1.5-mm-thick YBCO showed a nominal critical current density of over 1 MA/cm2 (75 K, self-field) along a microbridge and had an in-plane mosaic spread of 4.8° and an out-of-plane spread of 1.3°. These results compare well with our earlier work using IBAD yttria-stabilized zirconia (YSZ) as a template layer and indicate that IBAD MgO is a suitable substitute. Furthermore, these results suggest that IBAD MgO could be adapted to and increase the feasibility of a continuous process to fabricate longer lengths of coated conductors at speeds 100 times faster than that previously realized with IBAD YSZ.
Improved creep resistance in anisotropic silicon nitride
Authors: Kondo Naoki , Suzuki Yoshikazu , Brito Manuel E. , Ohji Tatsuki
Published: March 2008

Tensile creep behavior of silicon nitride with aligned rodlike grains (anisotropic silicon nitride), fabricated by superplastic forging, was investigated at elevated temperatures. Creep rate of the anisotropic silicon nitride was about 1 order of magnitude lower than that of the isotropic one (without forging). The stress sensitivities for the isotropic and anisotropic specimens at 1200 °C were 2.1 and 2.6, respectively, and that for the anisotropic specimen at 1250 °C was 3.6. The grain alignment should cause a remarkable improvement in the creep resistance when a tensile stress is applied along the alignment direction.
Temperature dependence of the optical properties in p-Cd0.96Zn0.04Te single crystals
Authors: Lee H. Y. , Kang T. W. , Kim T. W.
Published: March 2008

Photoluminescence (PL) measurements were performed on p-Cd0.96Zn0.04Te single crystals to investigate the dependence of the excitons on temperature. The activation energies and the longitudinal acoustic parameters of the excitons were determined from the temperature dependence of the PL spectra and were in reasonable agreement with the theoretical calculations. These results can help improve understanding for the application of p-CdxZn1–xTe single crystals in optoelectronic devices.
Thermal and structural characterization of the ZrO2−x(OH)2xto ZrO2 transition
Authors: Torres-GarciÁa E , Peláiz-Barranco A. , Vázquez-Ramos C. , Fuentes G. A.
Published: March 2008

The exothermic process that occurs around 700 K during calcination of ZrO2−x(OH)2x, associated with the crystallization of the low-temperature tetragonal metastable phase of ZrO2, was analyzed using x-ray diffraction, high-resolution thermogravimetric analysis (TGA), nitrogen adsorption, and modulated differential scanning calorimetry (MDSC). High-resolution TGA allowed us to determine the water loss, resulting from condensation of OH− groups. The amount was 0.137 wt% in our case, equivalent to 1.7 × 10−2 mol of H2O/mol of ZrO2. That corresponds to about one −OH group per nm2 being lost in that process. By using MDSC we determined that the change in enthalpy (∆Hglobal = −15.49 kJ/mol of ZrO2) was the result of two parallel contributions. One of them was reversible and endothermic (∆Hrev = 0.11 kJ/mol of ZrO2), whereas the other was irreversible and exothermic (∆Hirrev = −15.60 kJ/mol of ZrO2). The variability and magnitude of the exotherm, as well as the fact that the accompanying weight loss is so small, are consistent with a mechanism involving the formation of tetragonal nuclei, rather than global crystallization, and hence depend on the number of nuclei so formed.
Size effect on the mechanical properties of microfabricated polysilicon thin films
Authors: Ding J. N. , Meng Y. G. , Wen S. Z.
Published: March 2008

A new microtensile test device using a magnetic-solenoid force actuator was developed to evaluate the mechanical properties of microfabricated polysilicon thin films that were 100–660 mm long, 20–200 μm wide, and 2.4-μm thick. It was found that the measured average value of Young's modulus, 164 GPa ± 1.2 GPa, falls within the theoretical bounds. The average fracture strength is 1.36 GPa with a standard deviation of 0.14 GPa, and the Weibull modulus is 10.4–11.7. Statistical analysis of the specimen size effects on the tensile strength predicated the size effects on the length, the surface area, and the volume of the specimens. The fracture strength increases with an increase of the ratio of surface area to volume. In such cases, the size effect can be corrected to the ratio of the surface area to volume as the governing parameter. The test data accounts for the uncertainties in mechanical properties and may be used to enhance the reliability and design of polysilicon microelectromechanical systems devices.
Role of the primary phase particles during the peritectic solidification of Y-123 superconducting oxides
Authors: Kambara M. , Yoshizumi M. , Umeda T. , Miyake K. , Murata K. , Izumi T. , Shiohara Y.
Published: March 2008

Non-steady-state solidification of YBa2Cu3O6+δ(Y-123) superconducting oxides was observed by the isothermal undercooling experiment. A sudden decrease in crystal growth rate was found for all the Y-123 samples processed at the different temperatures and from the different Y2BaCuO5(Y-211) contents in the initial composition. Quantitative analysis revealed that the Y-211 particles are pushed by the Y-123 crystal and accumulate in the liquid during solidification. It is also found that the particle volume fraction increased and reached a constant value of about 0.6, when the growth rate decreased abruptly, regardless of a variety of growth conditions. A simple solidification model is developed to interpret the experimental observation. This model shows that particle accumulation, as a result of the particle-pushing behavior, causes less connectivity of the liquid and thereby decreases the liquid diffusion flux, which is responsible for the non-steady-state solidification of Y-123.
Crystallography and structural evolution of LiNbO3 and LiNb1−xTaxO3 films on sapphire prepared by high-rate thermal plasma spray chemical vapor deposition
Authors: Shtansky D. V. , Kulinich S. A. , Terashima K. , Yoshida T. , Ikuhara Y.
Published: March 2008

The structure and the crystallography of lithium niobate and lithium niobate–tantalate thin films (0.2–1.0 μm in thickness) with the tantalum composition range of 0 ≤ x ≤ 0.5 grown on (0001) sapphire substrate by thermal plasma spray chemical vapor deposition have been studied by means of cross-sectional high-resolution transmission electron microscopy and x-ray diffraction. The tantalum composition in the films shows a minor effect on the rocking curve full width at half maximum values. The narrowest rocking curve width was obtained for the LiNb0.5Ta0.5O3 film to be as low as 0.25° θ. The films are under compressive strain along the c direction; c- and a-axis lattice parameters are correspondingly smaller and higher than those of the bulk single crystal. Under optimized growth conditions, the LiNbO3 and LiNb1−xTaxO3 films are 97% c-axis oriented. The film out-of-plane orientation changes from the [0001] to the [0112] direction by either decreasing the growth rate or increasing the substrate temperature. Particular attention has been paid to the orientation of individual grains in the partly c-axis-oriented films. The results demonstrate that their orientations are not random and specific orientation relationships are preferred for the film nucleation. The surface of as-received sapphire substrate reveals polishing defects with the well-defined surface ledges of 1–2 nm in height with smooth terraces of 25 nm in width. In the case of columnar growth, the terrace width becomes a limiting factor controlling the lateral crystallite size in the film. Finally, the film growth mechanism is discussed.
Identification of the constitutive equation by the indentation technique using plural indenters with different apex angles
Authors: Futakawa Masatoshi , Wakui Takashi , Tanabe Yuji , Ioka Ikuo
Published: March 2008

This paper describes a novel technique for determining the constitutive equation of elastic–plastic materials by the indentation technique using plural indenters with different apex angles. Finite element method (FEM) analyses were carried out to evaluate the effects of yield stress, work hardening coefficient, work hardening exponent, and the apex angle of indenter on the load–depth curve obtained from the indentation test. As a result, the characterized curves describing the relationship among the yield stress, work hardening coefficient, and the work hardening exponent were established. Identification of the constants of a constitutive equation was made on the basis of the relationship between the characterized curves and the hardness given by the load–depth curve. This technique was validated through experiments on Inconel 600 and aluminum alloy. The determined constitutive equation was applied to the FEM analyses to simulate the deformation including necking behavior under uniaxial tension. The analytical results are in good agreement with experimental results.
Elastic constants of polycrystalline Al and TiN calculated by an ab initiomethod within the local-density approximation
Authors: Zhang Ming , Shen Jiang , He Jiawen
Published: March 2008

The three single-crystal elastic constants of the cubic materials Al and TiN were calculated by an ab initio method within the local-density approximation of density-functional theory. The values were compared with experiment and averaged by the Kroner method to give polycrystalline results. The results agree well with experiment.
Microstructure and growth of joins in melt-textured YBa2Cu3O7−δ
Authors: Bradley A. D. , Lo W. , Mironova M. , Babu N. H. , Cardwell D. A. , Campbell A. M. , Salama K.
Published: March 2008

Joining of melt-textured YBa2Cu3O7-δ (Y123) grains has been achieved without use of an external agent. The technique uses barium-cuprate liquid phase released from platelet boundaries to mediate the growth of Y123 at the interface between two grains. The epitaxial nature and high quality of the growth was determined by optical and transmission electron microscopy. The composition of Ba–Cu–O phases found in some parts of the joins was determined by electron probe microanalysis. A clean low-angle join was found to consist of a grain boundary with dislocation networks and facets. Transport critical current measurements on this type of join revealed strongly coupled behavior. The technique shows promise for the joining of melt-textured material for power engineering applications.
Modeling of electric field induced texture in lead zirconate titanate ceramics
Authors: Wan Shan , Bowman Keith
Published: March 2008

Preferred domain orientation of a piezoelectric ceramic develops through domain switching under electric poling. In previous investigations the critical free energy required for domain switching has been assumed as a constant. This assumption leads to overestimation of the poling-induced texture and provides no explanation for the switching reversal in ferroelectric ceramics after the poling field is removed. In this paper, the contribution of intergranular stress to critical energy for 90° domain switching is investigated. A criterion including intrinsic threshold energy and an interaction energy, which is related to the intergranular stress and the intergranular depolarization field, is proposed. The texture evolution during poling process is simulated using a computational model starting from an initial random domain orientation distribution. The resulted domain orientation distributions under and after poling are predicted. The remanent domain switching after poling is the result of the balance between the interaction energy and intrinsic threshold energy. The final texture is much weaker than that under the electric field. Pole figures of poled Navy VI lead zirconate titanate measured by x-ray diffraction are consistent with the predicted textures.
Electrolyte electroreflectance study of TiO2 films modified with metal nanoparticles
Authors: Kulak A. I. , Kokorin A. I. , Sviridov D. V.
Published: March 2008

Electrolyte electroreflectance (EER) has been used as an in situ probe for determining the distribution of energy states at the surface of naked and metal-modified TiO2 film in contact with aqueous solution. The surface modification of polycrystalline TiO2films by electrodeposition of fine (a few nanometers in size) metal particles has been shown to result in the appearance of surface states with an energy of approximately 2.15 eV for Cu, 2.40 eV for Pd, 2.50 and 2.30 eV (two peaks in the EER spectrum) for Pt, and 2.65 eV for Ag (the energy values are measured versus valence band edge of TiO2). The important role of metal-induced surface states in the enhancement of charge exchange between conduction band of semiconductor oxide and metal islets has been demonstrated using the electrocatalytic oxidation of boron hydride as a model reaction.
Glass transformation in vitreous As2Se3 studied by conventional and temperature-modulated differential scanning calorimetry
Authors: Kasap S. O. , Tonchev D.
Published: March 2008

We have studied the glass transition behavior of vitreous As2Se3 by carrying out temperature-modulated differential scanning calorimetry (TMDSC) and conventional differential scanning calorimetry (DSC) experiments to measure the glass transition temperature Tg. In TMDSC experiments we have examined the reversing heat flow (RHF), that is the complex heat capacity CP in the glass transition region as the glass is cooled from a temperature above the glass transition temperature (from a liquidlike state) and also as the glass is heated starting from room temperature (from a solidlike state). The RHF, or CP versus T, in TMDSC changes sigmoidally through the glass transition region without evincing an enthalpic peak which is one of its distinct advantages for studying the glass transformations. The Tg measurements by TMDSC were unaffected by the amplitude of the temperature modulation. We have determined apparent activation energies by using Tg-shift methods based on the Tg-shift with the frequency (ω) of temperature modulation in the TMDSC mode and Tg-shift with heating and cooling rates, r and q, respectively, in the DSC mode. It is shown that the apparent activation energies ∆h* obtained from ln ω versus 1/Tg and ln q versus 1/Tg plots are not the same, but nonetheless, they are approximately the same as the apparent activation energy ∆hn of the viscosity over the same temperature range where the empirical Vogel expression of Henderson and Ast, η = 12.9 exp[2940/(T - 335)], was used for the viscosity. The latter observation is in agreement with the assertion that the structural relaxation time Ʈ is proportional to the viscosity h. The apparent activation energy ∆hr obtained from the ln r versus 1/Tg plot during heating DSC scans is lower than ∆h* observed during cooling scans. The results are discussed in terms of a phenomenological Narayanaswamy type relaxation time. It was observed that Tg obtained from TMDSC cooling experiments did not depend on the underlying cooling rate for q ≤ 1 °C min-1; and for temperature amplitudes 0.5–5 °C. The transition due to the temperature modulation was well separated from the transition due to the underlying cooling rate. Further, the apparent activation energies obtained from ln ω versus 1/Tg during cooling and heating scans for q and r ≤ 1 °C min−1 are approximately the same as expected from Hutchison's calculations using a single relaxation time model of TMDSC experiments.
Epitaxial growth of skutterudite (CoSb3) thin films on (001) InSb by pulsed laser deposition
Authors: Caylor J. C. , Sander M. S. , Stacy A. M. , Harper J. S. , Gronsky R. , Sands T.
Published: March 2008

Heteroepitaxial growth of the cubic skutterudite phase CoSb3 on (001) InSb substrates was achieved by pulsed laser deposition using a substrate temperature of 270 °C and a bulk CoSb3 target with 0.75 at.% excess Sb. An InSb (a0 = 4 0.6478 nm) substrate was chosen for its lattice registry with the antimonide skutterudites (e.g., CoSb3 with a = 0 4 0.9034 nm) on the basis of a presumed 45° rotated relationship with the InSb zinc blende structure. X-ray diffraction and transmission electron microscopy confirmed both the structure of the films and their epitaxial relationship: (001)CoSb3 ∥ (001)InSb; [100]CoSb3 ∥ [110]InSb.
Deformation mechanisms in nacre
Authors: Wang R. Z. , Suo Z. , Evans A. G. , Yao N. , Aksay I. A.
Published: March 2008

Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamellar ceramic. The inelastic deformation of this material has been experimentally examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in compression with the boundaries oriented at 45° to the loading axis. The steady-state shear resistance τss has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress, σsss ≈ 110 MPa. The strain was associated with the formation of multiple dilatation bands at the intertablet boundaries accompanied by interlamellae sliding. Nano-asperities on the aragonite tablets and their interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. Detailed mechanisms and their significance for the design of robust ceramics are discussed.
Mechanical stress of the electrical performance of polycrystalline-silicon resistors
Authors: Nakabayashi N. , Ohyama H. , Simoen E. , Ikegami M. , Claeys C. , Kobayashi K. , Yoneoka M. , Miyahara K.
Published: March 2008

Results are presented of a study on the mechanical stress dependence of the resistance of polycrystalline silicon (Poly-Si) films doped with different atomic species. Two types of Poly-Si film implanted with boron and phosphorus ions were studied, namely, B-doped films of 400 nm and P-doped films of 250 nm thickness, which were deposited by low-pressure chemical vapor deposition at 620 °C on thermally oxidized silicon wafers. The film doping was done by ion implantation at 50 keV, with a dose of boron and phosphorus of 2 × 1014 and 5.3 × 1014 cm−2, respectively. The Poly-Si films were annealed in a N2 ambient at 1000 °C for 20 min to activate the implanted atoms. A controlled amount of external stress was applied to the silicon wafers to study the impact on the electrical performance of the implanted Poly-Si resistors. The resistance of the B-doped Poly-Si films is shown to increase by the mechanical stress, while the resistance of the P-implanted Poly-Si films remained unchanged. It is concluded that this difference is related to the structural differences between Poly-Si films implanted with boron and phosphorus, respectively.
Comparison of crystal structure parameters of natural and synthetic apatites from neutron powder diffraction
Authors: Leventouri Th. , Chakoumakos B. C. , Papanearchou N. , Perdikatsis V.
Published: March 2008

A systematic behavior in the crystal structure parameters of natural, synthetic, carbonate, and non-carbonate apatite is revealed from Rietveld refinements of neutron powder diffraction experiments. The results of this work on synthetic carbonate hydroxyapatites (CHAps) are consistent with the mechanism of carbonate substitution on the mirror plane of the phosphate tetrahedron, as it was introduced for the natural carbonate fluorapatite (CFAp). The present comparison shows that the tetrahedral bond lengths P–O1 and P–O2 decrease by 3–4% in all carbonate apatites. The atomic displacement parameters (ADPs) of the tetrahedral (T) and the O3 sites are greater in the carbonate than in the non-carbonate apatites. The atomic positional disorder of the T site (P/C site) is greater in the CFAp than in the CHAps, while the opposite happens at the O3 sites. Finally, the room-temperature ADPs of all of the atoms in the CFAp and CHAps show the same behavior as in the corresponding non-carbonate materials.
Freeform fabrication of aluminum metal-matrix composites
Authors: Souvignier C. W. , Sercombe T. B. , Huo S. H. , Calvert P. , Schaffer G. B.
Published: March 2008

A series of metal-matrix composites were formed by extrusion freeform fabrication of a sinterable aluminum alloy in combination with silicon carbide particles and whiskers, carbon fibers, alumina particles, and hollow flyash cenospheres. Silicon carbide particles were most successful in that the composites retained high density with up to 20 vol% of reinforcement and the strength approximately doubles over the strength of the metal matrix alone. Comparison with simple models suggests that this unexpectedly high degree of reinforcement can be attributed to the concentration of small silicon carbide particles around the larger metal powder. This fabrication method also allows composites to be formed with hollow spheres that cannot be formed by other powder or melt methods.
Growth and characterization of conductive SrRuO3 and LaNiO3 multilayers on textured Ni tapes for high-Jc Yba2Cu3O7–delta; coated conductors
Authors: Aytug T. , Kang B. W. , Cantoni C. , Specht E. D. , Paranthaman M. , Goyal A. , Christen D. K. , Verebelyi D. T. , Wu J. Z. , Ericson R. E. , Thomas C. L. , Yang C-Y. , Babcock S. E.
Published: March 2008

Power applications of high-temperature superconducting (HTS) coated conductors will require stabilization against thermal runaway. We have developed conductive buffer layers to electrically couple the HTS layer to the underlying metal substrate. The structure comprises the layer sequence of SrRuO3 (SRO) on LaNiO3 (LNO) on biaxially textured Ni substrates. We report baseline investigations of compatibility of SRO/LNO multilayer structure with processing of Yba2Cu3O7−δ (YBCO) and demonstrate biaxially textured YBCO films on conductively buffered Ni tapes. These YBCO coatings exhibit self-field Jc values as high as 1.3 × 106 A/cm2 at 77 K, and the entire structure (HTS + conductive buffers + metal substrate) shows good electrical connectivity. These results demonstrate that SRO/LNO buffer layers may provide a basis for stabilized coated conductors.
Electric properties of barium–strontium titanate thin films deposited by two-step radio-frequency sputtering
Authors: Fang J. S. , Chang C. T. , Chin T. S.
Published: March 2008

Barium-strontium titanate (BST) thin films were prepared by a two-step deposition using radio-frequency magnetron sputtering on Pt/Ti/SiO2-buffered Si(100) substrate. The initial BST layer thickness and intermediate annealing strongly affect the resultant electric properties of the two-step BST thin films. The optimal two-step BST films, with a first-layer thickness of 30 nm intermediate annealed at 610 °C under 1 torr oxygen. The dielectric breakdown and leakage current density of the two-step film are above 625 kV/cm and 9.5 nA/cm2 at 100 kV/cm, respectively, compared with 400 kV/cm and 17 nA/cm2 for the one-step films. We conclude that the two-step deposition dramatically improves dielectric breakdown and enhances leakage current density while keeping the dielectric constant uninfluenced.
Optical and electrochromic properties of heated and annealed MoO3 thin films
Authors: Hussain Zahid
Published: March 2008

Heating and annealing effects on the optical properties of slightly blue substoichiometric molybdenum trioxide thin films are reported partially. During heating and annealing, different levels of coloration seem to be generated by simultaneous reduction and proton injection into thin films, which cause the formation of hydrogen molybdenum bronzes of different concentrations. The optical band gap, Eo, of MoO3 thin film when annealed in between 313 and 473 K is decreased to 2.82 eV, and this reduction in Eo has been explained with a view to phonon and polaron species. Moreover, temperature-dependent change in the optical band gap has also been interpreted in terms of band gap slope, B, and the real part of the refractive index, n. Urbach slope, σ, also goes down to 0.67 eV−1 due to annealing treatment. Using the oscillator model, a phonon energy, hνo, of about 0.08 eV was found for the reported MoO3 thin film which is very close to the characteristic phonon energy of MoO3. Over and above, the intensity for the blue absorption band, over the photon energy range 0.4–3.0 eV, also reaches a maximum as MoO3 thin film is annealed at 473 K for 1 h and then decreases by 32% after annealing at the same temperature for 2 h. This phenomenon is due to polaronic band intensity which rises and falls during annealing. Half-width of the blue band, as found by fitting polaron model, is changed only by 3% on annealing the MoO3 thin film at 473 K as compared to its value at room temperature.
Mechanical properties of nanocrystalline and epitaxial TiN films on (100) silicon
Authors: Wang H. , Sharma A. , Kvit A. , Wei Q. , Zhang X. , Koch C. C. , Narayan J.
Published: March 2008

We investigated mechanical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25 to 700 °C during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having a uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using x-ray diffraction and high-resolution transmission electron microscopy. Hardness measurements were made using nanoindentation techniques. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant at less than 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size. This behavior was modeled recently involving grain boundary sliding, which is particularly relevant in the case of hard materials such as TiN.
Space-charge concepts on grain boundary impedance of a high-purity yttria-stabilized tetragonal zirconia polycrystal
Authors: Lee Jong-Sook , Kim Doh-Yeon
Published: March 2008

A detailed impedance analysis using the brick-layer model is performed on a high-purity yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). Space-charge impedance is generally formulated and expressions for the respective space-charge models are therefrom derived depending on whether dopant ions are mobile or immobile. Pronounced yttrium segregation in Y-TZP is also considered in the analysis in that the dopant profile is assumed to be frozen from a high-temperature equilibrium distribution. Comparison with experimental observations shows that the electrically measured grain-boundary thickness corresponds to the Schottky-barrier width, slightly modified by the dopant segregation. The grain-boundary resistance is not consistent with any space-charge models and the strong defect interaction due to the yttrium enrichment is suggested to be mainly responsible.