bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Y–Ba–Cu–O films with ethylene diamine tetra-acetic acid complexes assisted by excimer laser ablation
Authors: Tanaka Norio , Wakabayashi Hirotaka , Mochizuki Shin-ichi , Ohshio Shigeo , Saitoh Hidetoshi
Published: March 2008

Y–Ba–Cu–O films were prepared on yttria-stabilized zirconia polycrystalline substrate using KrF excimer laser irradiation with ethylene diamine tetra-acetic acid (EDTA) complexes as a target material. The results of the x-ray θ-2θ scan showed that the films grown above 750 °C were preferentially oriented with a c-axis normal to the substrate. The value of full-width at half-maximum of (005) reflection reduced from 4.4° to 2.1° by increasing the laser power density in a range between 0.8 and 3.8 J/cm2. The transcription of the compositional ratio was improved by approaching the target-substrate distance from 45 to 20 mm. The films obtained at 800 °C consisted of many islands showing well-developed spiral growth, suggesting that the droplets of metal-EDTA complexes do not form random oriented crystalline particles on the surface of the substrate.
Formation and catalytic activity of amorphous Ni50Pd40Si10 alloy powder by mechanical alloying
Authors: Zhang H. F. , Li J. , Song Q. H. , Hu Z. Q.
Published: March 2008

Amorphous Ni50Pd40Si10 alloy powder was prepared by mechanical alloying. The surface states and catalytic activities of amorphous and crystalline Ni50Pd40Si10 alloy powder pretreated with hydrofluoric acid (HF) solution were studied. The results show that amorphous Ni-Pd-Si alloy powder was easily prepared by mechanical alloying. After treating with HF solution, the number of Pd atoms on the surface of amorphous Ni–Pd–Si powder was obviously higher than that of the crystalline alloy and catalytic activity of amorphous Ni–Pd–Si powder was higher than that of the crystalline one by three times.
Control of epitaxial growth orientation in YBa2Cu3O7−δ films on vicinal (110) SrTiO3 substrates
Authors: Linehan D. S. , Kvam E. P. , Hou L. , McElfresh M. W.
Published: March 2008

Films of Yba2Cu3O7−δ (YBCO) were grown on (001), exact and vicinal (110), and (111) SrTiO3 single crystal substrates by pulsed laser deposition, and evaluated by x-ray diffraction and scanning force microscopy (AFM). It was observed that the YBCO was always epitaxially aligned to the substrate with the [001] (c-axis) parallel to a substrate cube axis direction. For the exact (001), (110), and (111) surfaces, there were one, two, and three orientations, respectively. For the vicinal (110) surfaces, however, there was usually only one discernible c-axis orientation, corresponding to a single {013} film surface orientation. The reduction of the (110) surface twofold symmetry by use of a vicinal substrate thus allowed controlled growth of a YBCO single crystal with an inclined c-axis orientation.
Relation between internal boundaries and critical current in textured YBa2Cu3O7−δ: Transmission electron microscope observations
Authors: Khalfi A. , Trolliard G. , Soulestin B. , Smith D. S. , Bonnet J. P. , Bourgault D. , Tournier R.
Published: March 2008

The local critical current (Ic) at 77 K measured at the mm scale in a 60 mm long sample of YBa2Cu3O7−δ prepared by a melting zone process is correlated to the microstructure. Lower values of Ic (<20 A) were obtained in a part of the sample which optical microscope examination showed to be generally polycrystalline. In contrast, the rest of the sample, consisting mostly of large textured domains, gave values for Ic of 120 A and above. Transmission electron microscope observations revealed that the textured domains contain internal boundaries. Depending on the scale of observation, the misorientation angles across the boundaries could vary from a few tenths of a degree up to a few degrees. This seems characteristic for boundaries in textured material which allow strong coupling of the superconducting current across themselves.
The effect of excess neodymia on the grain growth of Nd1+xBa2−xCu3Oy solid solutions
Authors: Rogenski Russell B. , Sandhage Kenneth H. , Vasiliev Alexander L. , Kvam Eric P.
Published: March 2008

The grain growth of dense, fine-grained Nd1+xBa2−xCu3Oy (x = 0.1−0.4) specimens has been examined in pure O2(g) at 938 °C and 967 °C. No detectable change in average grain size was observed for Nd1.4Ba1.6Cu3Oy within 72 h at 967 °C; however, a significant increase in average grain size developed between 18 and 24 h at 967 °C for Nd1.3Ba1.7Cu3Oy, and within 8−12 h at ≤967 °C for Nd1.2Ba1.8Cu3Oy and Nd1.1Ba1.9Cu3Oy. Microstructural analyses revealed that sudden changes in average grain size coincided with the formation of relatively large (abnormal) grains. A broadening of the grain size distribution was also observed. TEM analyses revealed that grain boundaries were free of second phases. The possible role of anisotropy in grain boundary energy and/or mobility on grain growth is discussed.
Fabrication of surface barrier layer capacitor on BaTiO3-based composite containing particulate SiC
Authors: Hwang Hae Jin , Niihara Koichi
Published: March 2008

Surface reoxidized-type barrier layer (BL) capacitors were prepared by hot-pressing BaTiO3/SiC powder mixture in argon atmosphere and subsequently oxidizing the semiconducting BaTiO3-based composites with fine SiC particles. Dielectric properties, such as apparent relative dielectric constant, dielectric loss tangent, and Curie temperature, were investigated as a function of SiC content and oxidation procedures. Incorporating SiC particles into BaTiO3 matrix, a thin surface insulating layer was formed, which becomes thinner by increasing the SiC content. BL capacitors showing a higher capacitance than 3 × 102 nF/cm2 could be successfully fabricated. The results were discussed on the basis of high resolution transmission electron microscope (HRTEM) studies. Thin oxidized layer and the resulting high capacitance were associated with the depression of oxygen diffusion due to the presence of intergranular SiC particles. The thickness of the surface layer and some dielectric properties could be controlled by the SiC content as well as oxidation temperature and time.
Melt infiltration casting of bulk metallic-glass matrix composites
Authors: Dandliker R. B. , Conner R. D. , Johnson W. L.
Published: March 2008

The authors describe a technique for melt infiltration casting of composites with a metallic-glass matrix. We made rods 5 cm in length and 7 mm in diameter. The samples were reinforced by continuous metal wires, tungsten powder, or silicon carbide particulate preforms. The most easily processed composites were those reinforced with tungsten and carbon steel continuous wire reinforcement. The Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 matrix was quenched to a glass after infiltrating the reinforcement. We analyzed the microstructure of the composites by x-ray diffraction and scanning electron microscopy. The measured porosity was less than 3% and the matrix was about 97% amorphous material.
A method for crystallographic texture investigations using standard x-ray equipment
Authors: Vaudin Mark D. , Rupich Martin W. , Jowett Martha , Riley G. N. , Bingert John F.
Published: March 2008

A fast and accurate method has been developed for measuring crystalline texture in homogeneous materials. The method uses a conventional powder x-ray diffractometer capable of θ scans. Two scans are recorded from the sample: first, a high resolution θ-2θ scan is obtained of a Bragg peak whose diffracting planes are normal to the preferred orientation direction; second, a θ scan is obtained using this peak. The η scan contains the required texture information, but the intensities must be corrected for defocusing and absorption to obtain the texture profile. The θ-2θ scan of the Bragg peak is used to make the defocusing correction, and first principles calculations are used to correct for absorption. The theory behind these corrections is presented here. The validity of the technique has been verified by making measurements on untextured alumina. Data obtained from Bi2Sr2Ca2Cu3O10 superconducting tape specimens with this technique are compared with texture data obtained with a four-circle diffractometer.
Preparation and characterization of SrBi2Nb2O9 thin films made by polymeric precursors
Authors: Zanetti S. M. , Leite E. R. , Longo E. , Varela J. A.
Published: March 2008

A polymeric precursor solution was employed in preparing SrBi2Nb2O9 (SBN) powder and thin films dip coated onto Si(100) substrate. XRD results show that the SBN perovskite phase forms at temperatures as low as 600 °C through an intermediate fluorite phase. This fluorite phase is observed for samples heat-treated at temperatures of 400 and 500 °C. After heat treatment at temperatures ranging from 300 to 800 °C, thin films were shown to be crack free. Grazing incident angle XRD characterization shows the occurrence of the fluorite intermediate phase for films also. The thickness of films, measured by MEV, was in the order of 80–100 nm.
Monodisperse magnetic nanoparticles: Preparation and dispersion in water and oils
Authors: Lefebure S. , Dubois E. , Cabuil V. , Neveu S. , Massart R.
Published: March 2008

Nanometric maghemite and cobalt ferrite particles are chemically synthesized. The process produces particles polydisperse in size. The positive charges of their surface allow one to disperse them in aqueous acidic solutions and to obtain dispersions stabilized through electrostatic repulsions. Increasing acid concentration (in the range 0.1 to 0.5 mol.L−1), interparticles repulsions are screened and phase transitions are induced. Using this phenomenon, we describe a two-step size sorting process, in order to get significant amounts of nanometric monosized particles (with diameters monitored between typically 6 and 13 nm). As the surface of the latter is not modified by the size sorting process, usual procedures are used to disperse them in several aqueous or oily media.
MoS2 deposited by ion beam assisted deposition: 2H or random layer structure?
Authors: Dunn D. N. , Seitzman L. E. , Singer I. L.
Published: March 2008

The structure of MoS2 films grown by ion beam assisted deposition is investigated using transmission electron microscopy. Films consist of stacks of S–Mo–S planes with a [001] texture; however, three-dimensional crystal symmetry is disrupted by a high density of planar defects. Selected area electron diffraction patterns show (hk0) and (00l) reflections, features similar to a random layer structure, as well as diffuse (103) reflections. It is suggested that these films do not have a true random layer structure, but rather a two-dimensional structure formed by nonrandom in-plane translations.
Enhanced photoluminescent emission of thin phosphor films via pulsed excimer laser melting
Authors: McKittrick J. , Hirata G. A. , Bacalski C. F. , Sze R. , Mourant J. , Hubbard K. M. , Pattilo S. , Salazar K. V. , Trkula M. , Gosnell T. R.
Published: March 2008

Thin films of (Y0.92Eu0.08)2O3 were synthesized through chemical vapor deposition of β-diketonate precursors onto glass and sapphire substrates. The films were weakly luminescent in the as-deposited condition and were composed of spherical particles 3 μm in diameter. A KrF laser was pulsed for 25 ns from 1–3 times on the surface of the films. One pulse was sufficient to melt the film and repeated pulses caused ablation of the material. Melting of the film smoothed the surface, increased the density, and increased the photoluminescent emission intensity.
Sol-gel synthesis and anomalies on magnetic and electric properties of (Ba1−xLax)3Cu3(O, F)yfilms
Authors: Masuda Y. , Jin J-S. , Nakanishi K. , Tanabe K.
Published: March 2008

(Ba1−xLax)3Cu3(O, F)y films were prepared using a sol-gel method. Phases, the c lattice parameters of which are about 13.8, 13.1, and 11.6 Å, respectively, were formed in the films. The compound with the c parameter of ˜13.8 Å is considered to be a Ba2−xLaxCuO2F2+δ which has the La2CuO4-type structure inserted with fluorine. The compound with the c parameter of ˜11.6 Å is thought to have a three-layered structure of the perovskite block which is arisen by ordering between La and Ba elements. The films containing these compounds showed some interesting anomalies in SQUID measurements. However, no film showed a drastic decrease of electrical resistance.
Transformations in undercooled molten Pd40.5Ni40.5P19
Authors: Yuen C. W. , Kui H. W.
Published: March 2008

It was demonstrated that liquid phase separation by nucleation and growth (LNG) occurs in undercooled molten Pd40.5Ni40.5P19 for undercoolings ΔT ≤ 60 K (ΔT = Tl − T where Tl is the liquidus and T is the kinetic crystallization temperature), and liquid state spinodal decomposition (LSD) occurs for ΔT ≥ 100. For 60 ≤ ΔT ≤ 100 K, it is the transition regime from LNG to LSD. A ternary phase diagram is introduced to summarize the reactions occurred in undercooled molten Pd40.5Ni40.5P19. Finally, it is suggested that LSD has an important impact on glass-forming ability of metallic alloys.
Fabrication and characterization of concentric-tubular composite micro- and nanostructures using the template-synthesis method
Authors: Cepak Veronica M. , Hulteen John C. , Che Guangli , Jirage Kshama B. , Lakshmi Brinda B. , Fisher Ellen R. , Martin Charles R.
Published: March 2008

The template-synthetic method is a general approach for preparing tubular micro-and nanostructures. This method has been used to prepare micro- and nanostructures composed of metals, carbons, semiconductors, polymers, and Li+-intercalation materials. This paper describes the use of the template method to prepare composite tubular micro- and nanostructures. These composite structures consist of an outer tubule of one material surrounding inner tubules of different materials. Chemical strategies used to prepare these composite tubular structures include electroless deposition of Au, electropolymerization of conductive and insulating polymers, electrodeposition of metals and semiconductors, carbonization of polymer precursors, chemical vapor deposition synthesis, and sol-gel synthesis.
Helical etch channels in quartz
Authors: Ballato John , Riman Richard E. , Vig John R. , Laffey Sally M.
Published: March 2008

Helical etch channels were found to form in α-quartz when treated with anhydrous HF vapor at 400 °C. Both hydrogen and fluorine species were determined to play an important role in helix formation. Crystal orientation, quartz source, etch channel density, and surface pretreatments had no influence. Helix formation was altogether arrested when water was present in the etch vapor. The genesis of the helices remains unknown.
Size-controlled synthesis of nanocrystalline BaTiO3 by a sol-gel type hydrolysis in microemulsion-provided nanoreactors
Authors: Beck Ch. , Härtl W. , Hempelmann R.
Published: March 2008

Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as is demonstrated by means of x-ray diffractograms and transmission electron micrographs. By variation of the length of the hydrophilic part of the surfactant molecules, the diameter of the water droplets in the microemulsions could be tuned to values between 8 and 55 nm as determined by dynamic light scattering. The size of the resulting nano-BaTiO3 (6 nm ≤ 〈d〉vol ≤ 17 nm) was evaluated from the line broadening of x-ray reflections and correlates to the droplet size. The particle size distribution is very narrow, and in some cases nearly monodisperse.
Effects of electron beam irradiation on time to clear vision of misted dental mirror glass
Authors: Oguri Kazuya , Fujita Katsuhiro , Takahashi Motoi , Omori Yuji , Tonegawa Akira , Honda Naosige , Ochi Masafumi , Takayama Kazuo , Nishi Yoshitake
Published: March 2008

A misting free dental mirror is obtained near the human temperature under the saturated humidity atmosphere by use of the sheet electron beam irradiation treatment. It is shown that electron beam irradiation treatment decreases the time to clear vision in a misted mirror. This effect is due to an enhancement of the interfacial energy between the dental mirror glass and water.
Structural and electrical properties of excess PbO doped Pb(Zr0.52Ti0.48)O3 thin films using rf magnetron sputtering method
Authors: Kim Tae Song , Kim Dong Joo , Leea Jeon Kook , Jung Hyung Jin
Published: March 2008

Well-crystallized Pb(Zr0.52Ti0.48)O3 thin films (4000 Å thickness) can be synthesized on Pt/Ti/SiO2/Si(100) substrate at a temperature as low as 520 °C. The polycrystalline lead zirconate titanate (PZT) perovskite phase formation was confirmed with x-ray diffraction (XRD) analysis, and growth morphologies were studied with a scanning electron microscope (SEM). The electrical properties of PZT thin films were characterized through P-E hysteresis curve, dielectric constant, and loss, fatigue, and leakage current measurements. Remanent polarization (Pr) and coercive field (Ec) of as-grown film were 8–30 μC/cm2 and 24–64 kV/cm with the variation of applied voltage (5–15 V). The post-annealing enhances the electrical properties even at 500 °C, which is below the as-grown temperatures (520 °C). The average polarization loss after applying rectangular pulse (Vp-p = 10 V) up to 1011 cycles was 40.9% for a 300 μm small dot and 22% for a 500 μm large dot, which are relatively improved values for platinum electrode. The values of dielectric constant (ε′) and tan δ measured with small signal sign wave (1 V, 10 kHz) were 1207 and 0.066 in the case of as-grown film.
Synthesis of carbon nitride crystals at high pressures and temperatures
Authors: He D. W. , Zhang F. X. , Zhang X. Y. , Qin Z. C. , Zhang M. , Liu R. P. , Xu Y. F. , Wang W. K.
Published: March 2008

Carbon nitride crystals have been synthesized from C3N4H4 in the presence of a nickel-based alloy or cobalt as a catalyst at high pressure of 7 GPa and temperature of about 1400 °C. Scanning electron microscopy showed rod-like, well-faceted crystals with size of several micrometers, and the N content in these carbon nitride crystals was 47–62%. X-ray diffraction indicated the crystals were composed of α–C3N4 and β–C3N4. The experimental lattice constants of α–C3N4 (a = 6.425 Å, c = 4.715 Å ) and β–C3N4 (a = 6.419 Å, c = 2.425 Å ) agree with ab initio calculations very well.
Absorption length for photon propagation in highly dense colloidal dispersions
Authors: Garg Rajeev , Prud'homme Robert K. , Aksay Ilhan A. , Liu Feng , Alfano Robert R.
Published: March 2008

The absorption length for photon propagation in highly concentrated colloidal dispersions calculated from temporal intensity profiles of 100 femto-second pulses is much longer than the absorption length obtained from the measurements of static light transmission in the pure continuous phase fluid. The difference between these two values is explained on the basis of small interparticle spacing at high particle concentration and hence shorter paths traveled by photons through the absorbing medium relative to the total diffusive path in the dispersion. The two values are in good agreement when the absorption length is rescaled with the interparticle separation.
Weight loss and gas evolution during sintering of silicon nitride powders synthesized by silica reduction and imide decomposition
Authors: Goto Yasuhiro , Ohnuma Yoshiyuki
Published: March 2008

The relationships among weight loss, gas evolution, and other changes during sintering were investigated for silicon nitride powders synthesized by silica reduction and imide decomposition. Small weight losses were detected for all powders at low temperatures (below 1400 °C), and large weight losses were found to occur for the silica-reduction powders at high temperatures (1400–1800 °C). Only CO was detected in the sampled gases during sintering, and CO evolution peaks were seen at around 900–1200 (broad), 1400, and 1600 °C. The main deposited material around the samples was SiO. The weight losses at low temperatures were thought to be caused by evaporation of residual binder or adsorbed substances. The main causes of the large weight losses at high temperatures were thought to be CO and SiO evolutions, and CO evolution at around 1600 °C probably originated from the liquid phase accompanied by α–Si3N4 to β–Si3N4 transformation.
Short-range dislocation interactions using molecular dynamics: Annihilation of screw dislocations
Authors: Swaminarayan S. , LeSar R. , Lomdahl P. , Beazley D.
Published: March 2008

We present results of a large-scale atomistic study of the annihilation of oppositely signed screw dislocations in an fcc metal using molecular dynamics (MD) and an Embedded-Atom-Method (EAM) potential for Cu. The mechanisms of the annihilation process are studied in detail. From the simulation results, we determined the interaction energy between the dislocations as a function of separation. These results are compared with predictions from linear elasticity to examine the onset of non-linear-elastic interactions. The applicability of heuristic models for annihilation of dislocations in large-scale dislocation dynamics simulations is discussed in the light of these results.
Theory of the charged cluster formation in the low pressure synthesis of diamond: Part II. Free energy function and thermodynamic stability
Authors: Jang Hyun M. , Hwang Nong M.
Published: March 2008

To account for the dominant formation of diamond over graphite in the gas-activated chemical vapor deposition (CVD) process we have theoretically examined the free energy function of a small carbon-atom cluster as a function of the cluster size. The scalar potential around a charged spherical cluster was derived using the linearized Poisson–Boltzmann equation. It was shown that the repulsive electrostatic energy associated with the growth of the charged diamond cluster was proportional to the fifth power of the cluster size. This suggests the existence of a deep potential-energy-well for the cluster size larger than the critical size corresponding to the free energy barrier for the nucleation. Thus, the growing diamond cluster will be trapped in this potential well before it transforms to the thermodynamically stable graphite. Considering all the relevant thermodynamic driving forces, we have constructed the free energy function in terms of the cluster size. The numerical computation also supports the existence of the potential-energy-well. Therefore, the present theoretical model clearly explains why the charged diamond cluster does not transform to the neutral graphite cluster when the thermodynamic stability is reversed above a certain critical size during the growth.
Preparation and photoconductivity of PVP-CoPc self-assembled film
Authors: Shi Min-Min , Wang Mang , Chen Hong-Zheng
Published: March 2008

Through the complexation of cobalt phthalocyanine (CoPc) and a film of poly[4-vinyl- pyridine] (PVP) polarized by an electric field, a new type of preferentially oriented self-assembled film (PVP-CoPc) was obtained. The characterization of the film by differential scanning calorimetry (DSC), angle-dependent x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) revealed that the planes of pyridine rings oriented perpendicular to the film surface, while the planes of phthalocyanine rings were oriented parallel with, and coordinated on, the film surface. Photoconductivity study showed that the photoconductivities of the photoreceptors (PR's) made from the PVP-CoPc self-assembled film were much better than those from CoPc alone. These changes were ascribed to the charge transfer and the unique and ordered structure of PVP-CoPc self-assembled film.
Controlled partial melting during isobaric and isothermal processing of dipcoated Bi-2212/Ag tapes
Authors: Crossley A. L. , MacManus-Driscoll J. L.
Published: March 2008

A detailed study has been made of the control and optimization of partial melting of dipcoated Bi2Sr2Ca1Cu2O8+δAg0.1 (Bi-2212) tapes using reduced oxygen partial pressures. A coulometric titration technique has been employed to vary the oxygen partial pressure in a region of the phase diagram corresponding to binary melting, and the amount of partial melting has been quantified. Using this information, tapes have been processed using both isothermal and isobaric techniques. An optimum processing route was determined which combined isothermal and isobaric processes. Highly aligned material at the point of optimum melting was obtained.
Materials in nanopipes of undoped GaN
Authors: Kang Junyong , Ogawa Tomoya
Published: March 2008

The nanopipes in undoped GaN epilayers grown on sapphire substrates were investigated by field emission high-resolution electron microscopy (HREM) and energy-dispersive x-ray spectrometry (EDS). In the HREM images, the cores of the nanopipes appeared disordered in the thin regions and more ordered in the thicker regions, indicating the amorphous layer on the surface has a significant influence on the visible image of the nanopipe in the thin regions. The EDS spectra showed that composition of the materials in nanopipes was mainly oxygen, carbon, and gallium elements. The results suggest that the nanopipes are related to impurities.
Preparation of boron and phosphorus-doped SiC :H films using electron cyclotron resonance chemical vapor deposition: Some effects of microwave power
Authors: Yoon S. F. , Ji R. , Ahn J.
Published: March 2008

Hydrogenated silicon carbide films (SiC :H) were deposited using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique from a mixture of methane, silane, and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the microwave power on the deposition rate and optical band gap were investigated, and variations in the photo- and dark-conductivities and activation energy were studied in conjunction with film analysis using the Raman scattering technique. In the case of boron-doped samples, the conductivity increased rapidly to a maximum, followed by rapid reduction at high microwave powers. The ratio of the photo- to dark-conductivity (σph/σd) peaked at microwave power of ∼600 W. Under conditions of high microwave power, Raman scattering analysis showed evidence of the formation and increase in the silicon microcrystalline and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity. In the case of phosphorus-doped SiC :H samples, it was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the films which occurred in correspondence to a rapid increase in the conductivity and reduction in the activation energy. The conductivity increase stabilized in samples deposited at microwave powers exceeding 500 W probably as a result of dopant saturation. Results from Raman scattering measurements also showed that phosphorus doping has the effect of enhancing the formation of the silicon microcrystals in the film whereas the presence of boron has the effect of preserving the amorphous structure.
Thermal and thermomechanical effects on defect evolution in an Al–Li superplastic alloy
Authors: Padmanabhan K. A. , Balogh A. G. , Puff W.
Published: March 2008

A commercial Al–Li alloy, in which the superplastic microstructure is developed by “strain-assisted continuous recrystallization” in early stages of flow, was studied using positron annihilation lifetime spectroscopy. Results revealed that exposing the material to a temperature of 525 °C (optimal temperature of superplastic deformation for this alloy) led to agglomeration of single vacancies into vacancy clusters of size of approximately four vacancies. Evidence for superplastic strain-induced cavitation was not found at 450 °C up to an elongation of 432% and at 525 °C up to 341%, the initial strain rate of deformation in both cases being 1.0 ×10−3 s−1. These results have practical significance.
Matrix laminate composites: Realizable approximations for the effective moduli of piezoelectric dispersions
Authors: Gibiansky L. V. , Torquato S.
Published: March 2008

This paper is concerned with the effective piezoelectric moduli of a special class of dispersions called matrix laminates composites that are known to possess extremal elastic and dielectric moduli. It is assumed that the matrix material is an isotropic dielectric, and the inclusions and composites are transversely isotropic piezoelectrics that share the same axis of symmetry. The exact expressions for the effective coefficients of such structures are obtained. They can be used to approximate the effective properties of any transversely isotropic dispersion. The advantages of our approximations are that they are (i) realizable, i.e., correspond to specific microstructures; (ii) analytical and easy to compute even in nondegenerate cases; (iii) valid for the entire range of phase volume fractions; and (iv) characterized by two free parameters that allow one to “tune” the approximation and describe a variety of microstructures. The new approximations are compared with known ones.
Abrasion of Al2O3–SiC–(Al, Si) composites made by melt oxidation
Authors: Singh R. Arvind , Jayaram V. , Biswas S. K.
Published: March 2008

We report here the remarkable abrasion wear resistance (normal pressure: 2.92 to 5.42 MPa; sliding speed: 0.25 to 3 m/s) of a soft (relative to other structural ceramics) melt-oxidized ceramic matrix composite Al2O3 –SiC–(Al, Si). In spite of being half as hard and more porous than zirconia toughened alumina (ZTA), a common cutting tool material, this composite fabricated at 1100 °C shows wear resistance comparable to that of ZTA at sliding speeds more than 2 m/s. The ability of this composite to generate a metal-rich tribofilm when rubbed and its high thermal shock resistance are factors which may be responsible for this unique performance.
Effects of Si content on the microstructure and tensile strength of an in situAl/Mg2Si composite
Authors: Zhang Jian , Wang Yu-qing , Yang Bing , Zhou Ben-lian
Published: March 2008

Al/Mg2Si composites were in situ fabricated by the usual die-casting technique, and effects of the Si contents in the composites on microstructures and tensile strengths were investigated. Experimental results show that extra Si contents in Al/Mg2Si composites induce a ductile matrix and a uniform distribution of in situ particles. The refined microstructures lead to an obvious increase in both strength and ductility of the metal matrix composites (MMCs). The effects of extra Si on both the solidification process and fracture characteristics of the Al/Mg2Si composites were analyzed.
Phase transitions of (1−x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions
Authors: Lee Jung-Kun , Youn Hyuk-Joon , Hong Kug Sun
Published: March 2008

Morphotropic phase boundaries and temperature dependent phase transitions of (1 – x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions were investigated by x-ray diffraction, differential scanning calorimetry (DSC), and dielectric property analysis. Two morphotropic phase transitions at room temperature were found at x = 0.1 and 0.13, which were from antiferroelectric orthorhombic (with 4 × 4 × 2 superlattice [orthorhombic (I)]) to antiferroelectric orthorhombic (with 2 × 2 × 2 superlattice [orthorhombic (II)]) and from orthorhombic (II) to ferroelectric rhombohedral, respectively. With increasing temperature, the samples with 0.01 ≤ x < 0.1 showed two phase transitions, i.e., from orthorhombic (I) to orthorhombic (II) and from orthorhombic (II) to cubic. The other samples had only one phase transition with increasing temperature. Phase transition temperatures of all the samples were measured using DSC, and a phase diagram for the solid solutions was constructed. A model illustrating the antiparallel shift of Pb ions in the orthorhombic (II) phase was also proposed.
Microwave dielectric properties and applications of rare-earth aluminates
Authors: Cho Seo-Yong , Kim In-Tae , Hong Kug Sun
Published: March 2008

Rare-earth aluminates, LnAlO3 (Ln = Dy, Er, Gd, La, Nd, Pr, Sm, and Y) were prepared using the mixed oxide method, and their microwave dielectric properties were examined at X-band. Most rare-earth aluminates have suitable permittivities and quality factors for applications as dielectric resonators, but a modification of τf is necessary due to the coefficient's large negative value. When considering dielectric properties and lattice matching, YalO3 rather than LaAlO3, was suggested as a promising substrate material for microstrip antennas utilizing high-temperature superconductor thin films. Rare-earth aluminates with a rhombohedral structure exhibited larger permittivities than those with an orthorhombic structure. This difference was attributed to the difference in ionic size and coordination number. It was demonstrated that a nonzero magnetic susceptibility of rare-earth aluminates has an adverse effect on their quality factor. An abrupt variation in the temperature coefficient of permittivity was discussed in terms of oxygen octrahedra tilting.
Effect of β–Si3N4 seed crystal on the microstructure and mechanical properties of sintered reaction-bonded silicon nitride
Authors: Lee Soo Young , Amoako-Appiagyei K. , Kim Hai Doo
Published: March 2008

β–Si3N4 seed crystal has been synthesized from α–Si3N4 powder. Reaction-bonded Si3N4/SiC composite has been fabricated with β–Si3N4 seed crystals. The nitridation behavior and the changes in mechanical properties resulting from the addition of seed crystals were studied before and after gas pressure sintering. Addition of seeds showed a considerable improvement in the nitridation, resulting in increase in fracture strength of the composite. Highly nitrided reaction-bonded Si3N4 (RBSN) as a result of the addition of seed crystals gave rise to high strength of composite after postsintering. Fracture toughness of the seeded Si3N4 was also improved up to 35% compared to the baseline Si3N4. Micrographs showed that the seeded Si3N4 developed a bimodal microstructure which resulted in an improvement in fracture toughness.
Synthesis of silicon-based polymerized films by excimer laser ablation deposition of hexaphenyldisilane
Authors: Zeng Xiaoyan , Rossignol Fabrice , Konno Shigeru , Nagai Hideaki , Nakata Yoshinori , Okutani Takeshi , Suzuki Masaaki
Published: March 2008

A new method of synthesizing silicon-based polymer films by excimer laser ablation of hexaphenyldisilane (HPDS) has been studied. The polymerized films were formed on a substrate by laser ablation deposition of HPDS at 248 nm. The structure of the polymerized films depended strongly on the laser fluence and repetition rates. The thermal stability and hardness of the deposited films were estimated by thermogravimetry and a Vickers microhardness meter. The films showed good thermal stability, depending on the laser processing parameters.
Morphology of melt-crystallized poly(ethylene 2,6-naphthalate) thin films studied by transmission electron microscopy
Authors: Tsuji Masaki , L Fernando A. Novillo , Fujita Masahiro , Murakami Syozo , Kohjiya Shinzo
Published: March 2008

Thin films of poly(ethylene 2,6-naphthalate) (PEN) were isothermally crystallized at 190 °C after being melted at 300 °C. Morphological observation by transmission electron microscopy (TEM) showed the spherulitic texture in the films. Selected-area electron diffraction (SAED) indicated that the crystals in the films are the a form, as expected from our thermal condition for crystallization. The SAED pattern from the untilted specimen was characterized by the fairly intense reflection ring accompanied by other weak rings, and this intense ring was indexed as 010. A series of SAED patterns, which were obtained from the same specimen area tilted at various angles in the TEM column, suggested that the crystallites are oriented with their (001) planes being preferentially parallel to the film surface. Subsequently, a set of the dark-field images of the two-dimensional spherulite taken by using two different parts of the 010 reflection ring revealed that most of the crystallites in such a spherulite are oriented with their (010) planes being parallel in its radial direction. In addition, the spherulites in small pieces (0.05–0.08 mm thick) of PEN, which had been crystallized under the same thermal condition as above, were determined to be negatively birefringent by polarizing light microscopy.
The influences of reactant composition and substrate material on the combustion synthesis of diamond
Authors: Wolden Colin A. , Draper Charles E. , Sitar Z. , Prater J. T.
Published: March 2008

It has been observed that diamond deposition by flat flame chemical vapor deposition is achieved over a very narrow range of reactant composition. We demonstrate that this diamond deposition window is strongly determined by the nature of the substrate material. Furthermore, once a continuous diamond film is formed, the window appears to be independent of the original material. Substrates examined include silicon, glass, titanium, tungsten, nickel, and molybdenum. The dependence of growth rate, morphology, and quality on reactant composition has been quantified using scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). It was found that the highest quality diamond was grown at conditions where diamond does not nucleate on ultrasonically scratched silicon. Thus, the production of high quality diamond on silicon by combustion synthesis requires different conditions for nucleation and growth.
Superstructure and boundary structure in stage 4 MoCl5–graphite intercalation compounds studied by atomic force microscopy and scanning tunneling microscopy
Authors: Vignal V. , Konno H. , Inagaki M. , Flandrois S. , Roux J. C.
Published: March 2008

Intercalated domains on stage 4 MoCl5–graphite intercalation compounds (MoCl5–GIC’s) were observed by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). On large intercalated domains, a superstructure was found, in relation with a modulation of the electronic properties of the first layer of carbon. From that, the structure of the chloride ions layer was discussed and a model including dimer molecules was proposed. At the boundaries between large intercalated and nonintercalated domains, corrugations were observed along certain crystallographic directions of graphite. Their morphology was studied in detail at atomic scale and formation mechanisms were proposed. Small intercalated domains were also observed. Their shapes were irregular but their boundaries were clear cut.
Thermodynamic characterization of hydrogen interaction with iridium polyhydride complexes
Authors: Zidan Ragaiy A. , Rocheleau Richard E.
Published: March 2008

Hydrogen interaction with solid iridium complexes IrXH2(PPr i3)2 (X = Cl, I) was investigated. Gaseous hydrogen was found to react reversibly with solid chloro-iridium complex IrClH2(PPri3)2, forming IrClH2(PPri3)2H2 The relative partial molal enthalpy and entropy were obtained from equilibrium isotherms at different hydrogen concentrations. The decrease in entropy with increasing hydrogen concentration and the absence of plateaus in the equilibrium isotherms were consistent with a single phase solid solution with two chemical components. Hydrogen release from solid iodo-iridium complex IrIH2(PPri3)2H2 was not observed at temperatures up to 350 K, indicating stronger hydrogen bonding.
Substrate effects on nanoindentation mechanical property measurement of soft films on hard substrates
Authors: Tsui T. Y. , Pharr G. M.
Published: March 2008

Substrate effects on the measurement of thin film mechanical properties by nanoindentation methods have been studied experimentally using a model soft film on hard substrate system: aluminum on glass. The hardness and elastic modulus of aluminum films with thicknesses of 240, 650, and 1700 nm sputter-deposited on glass were systematically characterized as a function of indenter penetration depth using standard nanoindentation methods. Scanning electron and atomic force microscopy of the hardness impressions revealed that indentation pileup in the aluminum is significantly enhanced by the substrate. The substrate also affects the form of the unloading curve in a manner that has important implications for nanoindentation data analysis procedures. Because of these effects, nanoindentation measurement techniques overestimate the film hardness and elastic modulus by as much as 100% and 50%, respectively, depending on the indentation depth. The largest errors occur at depths approximately equal to the film thickness.
Preparation of a nanostructured organoceramic and its reversible interlayer expansion
Authors: Messersmith Phillip B. , Osenar Paul , Stupp Samuel I.
Published: March 2008

We described previously the liquid phase synthesis and characterization of a nanostructured composite from an aqueous solution containing organic polymer and inorganic ions [J. Mater. Res. 7, 2599 (1992)]. The nanocomposite, termed an organoceramic, consisted of poly(vinyl alcohol) chains intercalated between the principal layers of a hydrated calcium aluminate ceramic. A key structural feature of the organoceramic is the polymer-induced expansion of the interlayer spacing by approximately 10 Å compared to the unmodified ceramic. In this paper, we describe the synthetic scheme that favors organoceramic formation and prove the existence of intercalated polymer by observation of reversible interlayer expansion and contraction in response to changes in ambient humidity. This property is unique to the organoceramic and is not observed in the unmodified calcium aluminate ceramic.
Power spectra of roughness caused by grinding of metals
Authors: Venkatesh K. , Bobji M. S. , Biswas S. K.
Published: March 2008

The roughness of metallic surfaces generated by machining depends on the intended intervention by the tool and the inadvertent consequences determined by the response of metals. The roughness generated in four different metals by grinding is studied using the power spectrum method. It was found that the level of power is determined by the intended intervention such as the depth of cut and, to some extent, by hardness because of its possible influence on micropileup geometry. The power gradient is, however, influenced by inadvertent damage which may be related to material properties such as thermal conductivity and adhesion.
Stability of fullerenes under hydrothermal conditions
Authors: Suchanek Wojciech L. , Yoshimura Masahiro , Gogotsi Yury G.
Published: March 2008

Stability of fullerenes C60 under hydrothermal conditions (200–800 °C, 100 MPa, 20 min–168 h) has been investigated. The reaction products have been characterized by Raman spectroscopy and x-ray diffraction. The fullerenes were stable up to 500 °C, but they decomposed immediately at 800 ±C into amorphous carbon. In the transition region between 600 and 750 °C, longer times and higher temperatures of the hydrothermal treatment favored decomposition of C60 with the formation of amorphous carbon. Addition of nickel to the C60–H2OO system neither suppressed hydrothermal decomposition of C60 nor induced formation of other phases, except of the amorphous carbon.
Synthesis and crystal chemistry of the new compounds GdBa4Cu3O8.5+δ and DyBa4Cu3O8.5+δ
Authors: Zhu Y. T. , Peterson E. J. , Baldonado P. S. , Coulter J. Y. , Peterson D. E. , Mueller F. M.
Published: March 2008

Two new compounds, GdBa4Cu3O8.5+δ (Gd143) and DyBa4Cu3O8.5+δ (Dy143), were synthesized from precursors Gd2O3, Dy2O3, BaO2, and CuO at 1000 °C in an oxygen atmosphere. The oxygen stoichiometric value δ was found to be 0.68 for Gd143 and 0.6 for Dy143 by iodometric titration. Rietveld refinement of x-ray powder diffraction data showed that Gd143 belongs to the space group Pm3 while Dy143 belongs to the space group P23. The two space groups, Pm3 and P23, are very similar. Their main difference is that P23 does not have the inversion symmetry of Pm3. Both compounds have a cubic unit cell with a lattice parameter of 8.16528 ± 0.00006 Å for Gd143 and 8.10807 ± 0.00010 Å for Dy143. Superconducting quantum interference device (SQUID) measurement indicated that neither compound was superconductive down to 5 K.
Silicon and zinc telluride nanoparticles synthesized by low energy density pulsed laser ablation into ambient gases
Authors: Lowndes Douglas H. , Rouleau Christopher M. , Thundat T.G. , Duscher G. , Kenik E.A. , Pennycook S.J.
Published: March 2008

The size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure, P, and target-substrate separation, Dts. For both Si and ZnTe, the largest nanoparticles were found closest to the ablation target, and the mean nanoparticle size decreased with increasing Dts. For Si ablation into He, the mean nanoparticle diameter did not increase monotonically with gas pressure but reached a maximum near P = 6 Torr. High resolution Z-contrast transmission electron microscopy and energy loss spectroscopy revealed that ZnTe nanoparticles consist of a crystalline core surrounded by an amorphous ZnO shell; growth defects and surface steps are clearly visible in the crystalline core. A pronounced narrowing of the ZnTe nanocrystal size distribution with increasing Dts also was found. The results demonstrate that the size of laser-ablated nanoparticles can be controlled by varying the molecular weight and pressure of an ambient gas and that nanometer-scale particles can be synthesized. Larger aggregates of both ZnTe and Si having a “flakelike” or “weblike” structure were formed at the higher ambient gas pressures; for ZnTe these appear to be open agglomerates of much smaller (∼10 nm) particles.
Hydrothermal synthesis of ferroelectric perovskites from chemically modified titanium isopropoxide and acetate salts
Authors: Moon Jooho , Kerchner Jeffrey A. , Krarup Henrik , Adair James H.
Published: March 2008

The feasibility of the acetylacetonate-Ti isopropoxide complex as a new precursor for synthesis of Ti-based perovskite particles under hydrothermal conditions has been demonstrated. Perovskite powders including BaTiO3, PbTiO3, PZT, PLZT, and SrTiO3 were prepared by reacting the acetylacetonate-modified Ti precursor in metal acetate aqueous salt solution under hydrothermal conditions. Synthesis parameters including reaction time and temperature, feedstock concentration, nd reaction medium significantly influence particle characteristics of the hydrothermally derived erovskite powders. It is proposed that use of the acetylacetonate-modified Ti precursor promotes ntimate mixing among multicomponent reacting species at the molecular level and promotes article formation through a dissolution/recrystallization mechanism.
Structural characterization of TiO2ultrafine particles
Authors: Zhu Yingchun , Liu Tiao , Ding Chuanxian
Published: March 2008

Four samples of TiO2ultrafine particles (UFP) were obtained through different processes. The structure of TiO2ultrafine particles and the factors influencing the structure were investigated with Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD). Both Raman spectra and x-ray diffractograms show the similar regularity of the phase transformation among the four samples. The observed bimodal lineshape-structure in the Raman spectra is attributed to the intragrain and grain-boundary components of TiO2UFP. The crystal structure of TiO2UFP is found to be distorted by the surface structure such as OH and OCH2CH3groups coordinated on the surface of TiO2UFP.