bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of epitaxial Fe3−xO4 films by dipping-pyrolysis process using CO−CO2 gas mixtures
Authors: Yamaguchi I. , Manabe T. , Kumagai T. , Kondo W. , Mizuta S. , Manago T.
Published: March 2008

Epitaxially grown Fe3−xO4 films were prepared on MgO(001) substrates by dipping-pyrolysis process using CO–CO2 gas mixtures. The structure and in-plane alignment of these films were examined by x-ray diffraction θ-2θ scans, β scans (pole figures), and asymmetric ω-2θ scans (reciprocal-space maps). The films heattreated at 500 °C and higher in an atmosphere with pCO/pCO2 = 10−4 had a spinel-type structure and were in an epitaxial (cube on cube) relationship with the substrates.
Synthesis of ZrO2–Y6WO12 solid solution powders by a polymerized complex method
Authors: Ma Junfeng , Yoshimura Masahiro , Kakihana Masato , Yashima Masatomo
Published: March 2008

A series of solid solutions (1 − x) ZrO2 · xY0.857 W0.143 O1.714 (1/7Y6WO12) of metastable cubic phase were synthesized at 800 °C through a polymerized complex method. Lattice parameter a0 of solid solutions varies linearly with Y0.857 W0.143 O1.714 content (x). Crystallization began to occur above 400 °C from amorphous precursor to yield at 800 °C fine powders of 6–10 nm and 19–40 m2/g for crystallite size and surface area, respectively.
Oxidation of MoSi2/SiC nanolayered composite
Authors: Hirvonen J-P. , Torri P. , Lappalainen R. , Likonen J. , Kung H. , Jervis J. R. , Nastasi M.
Published: March 2008

The oxidation behavior of a nanolayered MoSi2/SiC composite material was determined at the temperature range of 400–900 °C in wet oxidation conditions. The samples were produced in the form of thin films using a sputtering technique from two different sources, and a rotating substrate holder, onto silicon single crystals and low carbon steel. For comparison, the oxidations of both constituents, MoSi2 and SiC, produced with the same sputtering technique, were measured separately. The microstructure of the MoSi2/SiC samples was determined with high resolution transmission electron microscopy (HRTEM), and the composition of the sputtered samples was measured using backscattering (BS) of protons. For quantitative determination of oxidation, the nuclear reaction 16O(d, p)17O was utilized. Oxide layers were also analyzed using a secondary ion mass spectrometry (SIMS) and the appearance of the oxidized surface with a scanning electron microscopy (SEM). As expected, the SiC films had both the lowest initial oxidation and steady state oxidation rate. The results show that the oxidation behavior of the MoSi2/SiC nanolayered composite material differs from that of both its constituents and involves a degradation mechanism of its own, resulting in the highest oxidation during the initial phase of the oxidation. A steady-state oxidation rate was observed after the initial transient phase to be the highest for the metastable C40 structure of the single MoSi2 layer. The oxidation rate of the nanolayered structure was retarded by the SiC layers. No signs of pest disintegration were observed on either of the MoSi2 containing coatings during the steady-state phase of the oxidation at 500 °C up to 40 h. Our results show that the oxidation of nanolayered structures can be only in part explained by the oxidation behavior of the constituents and that during the steady-state oxidation of the nanolayered structure the oxidation rate is largely determined by the constituent with the lowest oxidation rate and by the layered structure.
Microstructure of cosputter-deposited metal- and oxide-MoS2 solid lubricant thin films
Authors: Hilton M. R. , Jayaram G. , Marks L. D.
Published: March 2008

The effect of cosputtering small amounts of Ni (3%, 9%) and SbOx (20%) on the final microstructure of MoS2 lubricant thin films has been studied using a combination of scanning and transmission electron microscopy imaging, and electron and x-ray diffraction techniques. The early-growth, near-interface microstructure of both MoS2 and 3% Ni–MoS2 cosputtered films is revealed to be a mixture of (002) basal and elongated, large-size (100) and (110) edge islands. Cosputtering with 9% Ni induces a dramatic change in the microstructure, i.e., primarily basal domains with very small isolated regions of edge islands, while cosputtering with 20% SbOx produces films having no long-range order. The results are compared with and are consistent with previously published x-ray absorption fine structure data. The impact of film morphology on tribological performance is discussed.
Further analysis of indentation loading curves: Effects of tip rounding on mechanical property measurements
Authors: Cheng Yang-Tse , Cheng Che-Min
Published: March 2008

The effects of indenter tip rounding on the shape of indentation loading curves have been analyzed using dimensional and finite element analysis for conical indentation in elastic-perfectly plastic solids. A method for obtaining mechanical properties from indentation loading curves is then proposed. The validity of this method is examined using finite element analysis. Finally, the method is used to determine the yield strength of several materials for which the indentation loading curves are available in the literature.
Occurrence of plastic instabilities in dynamic microhardness testing
Authors: Bérces G. , Chinh N. Q. , Juháasz A. , Lendvai J.
Published: March 2008

Plastic instabilities were observed to appear during dynamic ultramicrohardness testing of a solid solution Al–3.3 wt.% Mg alloy. The tests were carried out at room temperature with a Vickers hardness indenter in a computer-controlled dynamic ultramicrohardness testing machine. During the tests the applied load was increased from 0 to 2000 mN at constant loading rate. The instabilities appear as characteristic steps in the continuously recorded load-indentation depth curves. The physical basis for the occurrence of the instabilities is the interaction between moving dislocations and solute atoms, a phenomenon termed in the literature as serrated yielding, jerky flow, or Portevin-Le Châtelier effect. The instabilities start at a critical load, Fc, in the depth-load curve. Varying the loading rate, μ, by two orders of magnitude Fc was found to increase linearly with the loading rate.
Preparation of wurtzitic AlN thin films with a novel crystallographic alignment on MgO substrates by molecular-beam epitaxy
Authors: Heffelfinger J. R. , Medlin D. L. , McCarty K. F.
Published: March 2008

Thin films of wurtzitic AlN have been deposited by molecular-beam epitaxy onto (001) oriented MgO substrates. The films are epitactic and align with the and the , as evidenced by transmission electron microscopy. This configuration, which matches a close-packed direction of the film and substrate, allows for growth of two symmetrically equivalent orientation variants of the AlN film. These variants are distinguished by a 90° rotation about the direction that is normal to the substrate surface. Each variant also aligns the and the to within 5° of being parallel to the (200)MgO. The microstructure of the AlN films and origins of these novel alignments are discussed.
Micron thick epitaxial (100) Ag film growth on MgO
Authors: Carter A. C. , Chang W. , Qadri S. B. , Horwitz J. S. , Leuchtner Robert , Chrisey D. B.
Published: March 2008

Epitaxial films of (100) Ag were deposited onto (100) MgO substrates to a thickness of 4 μm with no evidence of (111) nucleation. Deposited films were smooth and had large areas, 50 × 50 microns square, free of morphological defects. Films were deposited using a two-step process. First, pulsed laser deposition was used to grow a 1000 Å Ag (100) seed layer on the MgO substrate. Second, e−beam evaporation was used to grow the film to the desired thickness. The high quality of the resulting films will allow them to be used as templates for further epitaxial deposition of other applied materials.
Secondary ionic forces in lead molybdate melt solidification
Authors: Zeng H. C. , Lim L. C.
Published: March 2008

We report a dendritic crystallization of ionic melt of lead molybdate (PbMoO4) under a concentric thermal field. The solidified melt is a PbMoO4 single crystal with [001] axis normal to surface. The dendrite arms propagate and branch along 〈310〉 and 〈130〉, forming a well-organized surface structure. It is evident that the interaction between a cation to its second-nearest anions determines the dendrite development and meltsolidification.
Formation of ultrafine powders of binary alloy systems by plasma jet
Authors: Umemoto M. , Udaka M. , Kawasaki K. , Liu X. D.
Published: March 2008

Recently, a new method, i.e., a plasma jet method, was developed in our lab for the production of ultrafine powders. In the present work, we investigated the formation of binary Al–Fe, Al–Si, Fe–Si, Al–Cu, Al–Ni, Ni–Ti, Fe–Cu, and Fe–Ti ultrafine powders using this method. Premixed pure elemental powders of various compositions of Al–Fe, Al–Si, Fe–Si, Al–Cu, Al–Ni, Ni–Ti, Fe–Cu, and Fe–Ti were used as starting materials. These premixed powders were injected into the plasma jet of Ar–N2 working gas to form ultrafine powders. The obtained ultrafine powders were characterized by x-ray diffraction and transmission electron microscope to check the microstructures of ultrafine particles.
The use of reliability factors in analyzing powder patterns in Pt–Si sputtering targets and subsequent films
Authors: Rahman Abdul , Lowe Walter P. , Bates Clayton W.
Published: March 2008

X-ray powder diffraction was used to characterize a Pt–Si sputtering target and subsequent films. The powder patterns of each sample indicated lines due to diffraction from different phases. We have initiated a preliminary study through which we have analyzed and characterized these films. The results presented for these samples corroborate with results observed for this system in the planar configuration.
Structural characterization of combustion synthesized MoSi2–Si3N4 composite powders and plasma sprayed MoSi2–Si3N4 composites
Authors: Kung H. , Lu Y. C. , Bartlett A. H. , Castro R. G. , Petrovic J. J. , Shtessel E.
Published: March 2008

A systematic structural characterization has been conducted on combustion synthesized MoSi2–Si3N4 powders and plasma sprayed composites by transmission electron microscopy (TEM). The powders are cleaner and with little surface oxide contamination than most commercial powders. The distribution of the two phases can be tailored by modifying the synthesis conditions, which has resulted in improved retention of Si3N4 after plasma spraying. TEM studies performed on deformed composites indicate a strong link between even dispersion of second phases and enhanced dislocation plasticity in the plasma sprayed composites.
Epitaxial films of Li12xNb1–xWxO3 prepared by chemical solution deposition
Authors: Lakeman Charles D. E. , Xia Yin , Kim Jin-Hyeok , Wu Xuehua , Eckert Hellmut G. , Lange Fred F.
Published: March 2008

The growth of epitaxial thin films of Li1–xNb1–xWxO3 from solution precursors on single-crystal LiNbO3 substrates is reported. An all-alkoxide solution readily gave single phase powders after simply mixing the constituent components, whereas an acetate-alkoxide system required additional solution processing stages to give phase pure powders. Heat treatment of films on single-crystal, basal plane LiNbO3 substrates at 600 °C formed a nanocrystalline, porous film which was converted to an epitaxial film after heating to 800 °C. Measurements of second harmonic generation in powders indicate an increase in SHG efficiency with increasing tungsten content. Optical absorption data for films were calculated using reflectance and transmittance spectroscopy data, and indicate a decrease in bandgap with increasing tungsten.
Heterogeneous junction of yttria partially stabilized zirconia by superplastic flow
Authors: Domínguez-Rodríguez Arturo , Guiberteau Fernando , Jimenez-Melendo Manuel
Published: March 2008

Layers of different composition and/or grain size of yttria partially stabilized zirconia (YPSZ) have been compressed, with the stress perpendicular to the interface of the layers and temperature of 1400 °C, in order to produce a joint using the microstructural feature of superplasticity found in fine-grained ceramics. The pieces joined have been characterized by scanning electron microscopy (SEM), showing a clean interface with no cavitation. The stiffness of the junction was checked using Vickers indentation at room temperature at the interface and compression tests at the same conditions (T = 1400 °C in air) used for the joining and the stress parallel to the interface. The observation and comparison between the cracks developed around the indents at the interface and in the bulk of the pieces joined as well as the absence of cavities along the interface in the samples compressed parallel to the interface shows that this technique is useful to produce a joint with a clean and strong interface.
Niobium-titanium oxide powders obtained by laser-induced synthesis: Microstructure and structure evolution from diffraction data
Authors: Depero Laura E. , Sangaletti Luigi , Allieri Brigida , Bontempi Elza , Salari Roberto , Zocchi Marcello , Casale Cristina , Notaro Maurizio
Published: March 2008

The influence of the niobium content on the anatase-to-rutile phase transition in nanopowders of Nb–Ti oxides was studied and the changes in the particle size and microstrain distribution obtained at different temperatures were analyzed. A correlation is found between the initial microstructure in the Ti1 –xNbxO2(x= 0.03, 0.2) powder and the niobium content. The presence of Nb was found to inhibit the growth of both the anatase and the rutile phases.
Influence of surface hardening by laser irradiation on the loss factor of cast iron
Authors: Adachi Hiromasa , Masuo Yoshihiko , Hasegawa Teruo
Published: March 2008

Surface hardening by laser irradiation was examined regarding the loss factor, which is the parameter of the vibration-damping characteristics, for flake graphite cast irons and spherical graphite cast irons. The surface of the samples was quenched by changing speed of beam, gas pressure, and beam frequency. It was found that the depth of the hardening region was from 0.12 mm to 1.11 mm, and the hardness of the boundary between the hardening and the nonhardening regions changed suddenly. It was confirmed that the loss factor of the laser hardened specimens increased considerably as compared with that of the as-cast specimens. The internal friction at the vicinity of the boundary between the hardening and the nonhardening regions may be responsible for this result.
Shrinkage anisotropy of glass powder compacts sintered in dilatometers
Authors: Boccaccini Aldo R.
Published: March 2008

Dilatometer push rods exert uniaxial compressive stresses on powder compacts undergoing sintering. In this study the effect of such stresses on the shrinkage anisotropy behavior of glass powder compacts is considered. A shrinkage anisotropy factor (k), defined by the ratio between axial and radial strain, is used to quantify the anisotropy in cylindrical compacts (k = 1 represents isotropic shrinkage). The available experimental data in the literature indicate that the effect of the applied dilatometer stress is to increase the value of k over that of free sintering conditions. For the small stresses exerted by the dilatometer push rods, it is shown that k is always. 1. The common practice of calculating the sintered density from uniaxial dilatometer data, ignoring the existence of shrinkage anisotropy, is shown to lead to significant errors, even for values of k only slightly different from k = 1.
A study on the migration of Co(II) and Fe(III) ions in the process of thermal phase separation of an alkali-borosilicate glass containing cobalt and ubiquitous trace iron
Authors: Debnath Radhaballabh
Published: March 2008

Absorption spectra of added Co(II) ions and EPR spectra of both Co(II) and ubiquitous Fe(III) ions in an alkali-borosilicate glass of vycor-type composition are studied both before and after thermal phase separation of the glass as well as in a silica glass derived from the phase-separated glass through vycorization. The results show that although almost all Co(II) ions migrate to the separated alkali-borate phase at the time of phase separation, only the interstitial ions in the case of Fe(III) take part in similar migration. The Fe(III) ions in the substitutional silicon sites, however, remain unaffected. It is also revealed that as a consequence of the process of phase separation a small fraction of the interstitial Fe(III) ions gets converted into substitutional ions leading to a net increase in the concentration of substitutional Fe(III) ions in the glass. Analysis of both absorption and EPR spectra of the Co(II) ions suggests that a change of host of the ion due its migration does not bring about any significant change in its coordination structure, which is typically a distorted tetrahedron both in the parent glass as well as in the phase-separated borate glass.
Generation of microwave plasma under high pressure and fabrication of ultrafine carbon particles
Authors: Yagi H. , Ide T. , Toyota H. , Mori Y.
Published: March 2008

A microwave plasma generator, which functions under high pressure, has been developed and used in the fabrication of fine carbon particles. The plasma generator is a two-stage-type resonator, which consists of rectangular and semi-cylindrical-type resonators which are coupled in series for torching plasma and keeping it stable under high pressure. The plasma can be torched in helium gas at 3 × 106 Pa by tuning the dimensions of apparatus elements. Fine carbon particles of ~50 nm are obtained using a mixture of helium and methane gas. The particles are found to be crystalline from the results of transparent electron microscopy and diffraction analysis.
Novel in situ production of smooth diamond films
Authors: Gilbert Donald R. , Lee Dong-Gu , Singh Rajiv K.
Published: March 2008

We have developed a unique method to produce smooth diamond films using a modified microwave plasma process system. This method consists of sequential in situ deposition and planarization in an electron cyclotron resonance plasma system. Diamond films were deposited to a thickness of 3.0 μm in this system at a pressure of 1.000 Torr from gas mixtures of methanol and hydrogen. Deposition was followed by planarization using a two-grid ion beam extraction process with a pure oxygen plasma at 10 mTorr. The average roughness of the diamond films so produced was as low as 30 nm, which was a factor of two lower than that of the as-deposited diamond films.
Atomistic computer study on Mg segregation in the Ni3Al grain boundary
Authors: Jiang Bingyao , Liu Xianghuai , Zou Shichang , Sun Jian , Wang Jian
Published: March 2008

The embedded atom method (EAM) was applied to calculate the energy on Mg doping in polycrystalline Ni3Al. The EAM predicted the energy of Mg in Al site in grain boundary is lower than that of Mg in Ni site and much lower than that of Mg in Al or Ni site in bulk and in free surface. It means that Mg would segregate to grain boundary rather than bulk and free surface and Mg will favor to be the substitute of Al rather than of Ni in grain boundary. These results were consistent with the experiments that Mg segregated to grain boundaries with Al depletion and Ni enrichment.
Determination of x-ray elastic constants using an in situ pressing device
Authors: Teeuw D. H. J. , Hosson J. Th. M. De
Published: March 2008

The experimental determination of x-ray elastic constants are performed by in situ measurements of the dependence of the strain state in selected crystallites for different applied external compressive stresses. The use of compressive applied stresses instead of tensile applied stresses is of interest for x-ray elastic constant determinations for materials which exhibit brittle crack-like behavior, which cannot be loaded to high tensile stresses in, for example, four-point bending devices. The x-ray elastic constants for {146} α–Al2O3 are determined with the pressing device and compared to calculated as well as experimentally determined values which were tested in tensile loading devices.
The coexistence of silicon borides with boron-saturated silicon: Metastability of SiB3
Authors: Aselage T. L.
Published: March 2008

The silicon-rich end of the Si-B phase diagram, defining the silicon boride(s) that coexist in equilibrium with boron-saturated silicon, is poorly known. Understanding this equilibrium has implications for the processing of p+ silicon wafers, whose boron concentrations are near the solubility limit. Additionally, silicon boride precipitates produced by boron-ion-implantation and annealing of crystalline silicon have recently been shown to be efficient internal getters of transition metal ions. The experiments described in this paper probe the stability of these silicon borides. A phase with a boron-carbide-like structure, SiB3, grows from boron-saturated silicon in both the solid and the liquid state. However, SiB3 is not found to be stable in either circumstance. Rather, SiB3 is a metastable phase whose formation is driven by the relative ease of its nucleation and growth. The silicon boride that exists in stable equilibrium with boron-saturated silicon is SiB6. A qualitative understanding of the metastability of SiB3 comes from recognizing the conflict between the bonding requirements of icosahedral borides such as SiB3 and the size mismatch between silicon and boron atoms.
Structural changes in GaAs induced by ultrafast (fs) laser pulses
Authors: Nánai L. , Vajtai R. , Beleznai Cs. , Remes J. , Leppävuori S. , George Thomas F.
Published: March 2008

Ultrafast changes in the crystal structure of GaAs induced by intense femtosecond laser pulses are detected and investigated. Atomic force microscopy and Raman microprobe analysis of the laser-treated area show centrosymmetric (disordered) features which are different from the original zinc-blend structure of the GaAs lattice. The frozen-in structure shows evidence for a special heat transfer from the laser-induced crater to the boundary, namely the heat has been transferred ballistically by a high-density electron-hole plasma.
Inner surface reaction and modification of titanium alloy by a new plasma source ion implantation method
Authors: Sun Mu , Xie Kan , Yang Si-ze
Published: March 2008

The inner surface of a cylindrical titanium alloy target was successfully implanted with nitrogen ion using a new plasma source ion implantation method. By means of x-ray photoelectron spectroscopy and x-ray diffraction, the reactive phases and their chemical state in the implanted layer were investigated. In order to characterize the modification effect and its uniformity, the retained dose and the microhardness at seven different positions along the axis on the inner surface of the cylindrical target were measured, respectively. The experimental results show that a TiN reactive phase was formed in the implanted layer, which contributed to the improvement of inner surface microhardness. The root-mean-square deviations of retained dose and microhardness measured along the axis of the target are less than 9% and 4%, respectively, which are well within an acceptable tolerance range for metallic applications of ion implantation.
Microstructural evolution of the η-phase in the Cu–Sn system
Authors: Sudhakar Reddy E. , Rajasekharan T.
Published: March 2008

The formation of η-phase by a peritectic reaction in the Cu–Sn metallic system has been cited in the literature while discussing the solidification of the high temperature superconductor Yba2Cu3O7 through the peritectic temperature, from Y2BaCuO5 and liquid phases. Similar schematic phase diagrams and driving forces have been invoked to discuss the reactions in both cases. In this paper, we have studied the microstructural evolution of the η-phase from є + liquid in the Cu–Sn system, by observing quenched microstructures at various stages of processing, when subjected to a thermal schedule similar to the one used for the melt-processing of YBa2Cu3O7. A comprehensive picture of the mechanism by which the η phase nucleates and grows has evolved.
Photoluminescence in PbMg1/3Nb2/3O3–PbIn1/2Nb1/2O3 systems
Authors: Meng J. F. , Cheng Z-Y. , Rai Brajesh K. , Katiyar R. S. , Alberta E. , Guo R. , Bhalla A. S.
Published: March 2008

Photoluminescence for PbMg1/3Nb2/3O3 (PMN)– PbIn1/2Nb1/2O3 (PIN) solid solutions in the temperature ranging from 35 to 295 K have been obtained for the first time. An abrupt photoluminescence enhancement of the system has been observed to occur at ∼210 K, which can be attributed to the growing and merging of dynamic polar microregions or to the phase transformation of the material at this temperature. The PIN content has been found to affect the photoluminescence of the PMN-PIN system significantly. The photoluminescence mechanism for PMN-PIN has been studied.
Binder surface segregation during spray drying of ceramic slurry
Authors: Zhang Yao , Tang XiaoXia , Uchida Nozomu , Uematsu Keizo
Published: March 2008

Spray-dried granules were observed by a laser microscopy with the immersion liquid technique. The binder distribution in the granules was analyzed from light intensity profiles of the images. The results showed that a surface layer with a large amount of the binder is formed in the spray-dried granule, and the segregation is influenced by initial binder concentration and size of atomized droplet. A computer simulation for soluble binder segregation during spray drying was conducted by considering simultaneously the solvent evaporation, the relative migration between the liquid and the particles, the diffusion, and drying shrinkage. The simulation coincides with the experimental results. To make uniform granules, reducing the amount of binder, liquid content, size of atomized droplet, and drying rate is favorable.
Analytic embedded atom method potentials for face-centered cubic metals
Authors: Pohlong S. S. , Ram P. N.
Published: March 2008

The universal form of embedding function suggested by Banerjea and Smith together with a pair-potential of the Morse form are used to obtain embedded atom method (EAM) potentials for fcc metals: Cu, Ag, Au, Ni, Pd, and Pt. The potential parameters are determined by fitting to the Cauchy pressure (C12 − C44)/2, shear constant GV = (C11 − C12 + 3C44)/5, and C44, the cohesive energy and the vacancy formation energy. The obtained parameters are utilized to calculate the unrelaxed divacancy binding energy and the unrelaxed surface energies of three low-index planes. The calculated quantities are in reasonable agreement with the experimental values except perhaps the divacancy energy in a few cases. In a further application, lattice dynamics of these metals are discussed using the present EAM potentials. On comparison with experimental phonons, the agreement is good for Cu, Ag, and Ni, while in the other three metals, Au, Pd, and Pt, the agreement is not so good. The phonon spectra are in reasonable agreement with the earlier calculations. The frequency spectrum and the mean square displacement of an atom in Cu are in agreement with the experiment and other calculated results.
Stress evolution in passivated thin films of Cu on silica substrates
Authors: Shen Y-L. , Suresh S. , He M. Y. , Bagchi A. , Kienzle O. , Rühle M. , Evans A. G.
Published: March 2008

Stresses supported by thin films of Cu passivated by SiOxhave been measured upon thermal cycling. Very high stresses have been found, approaching 1 GPa in the thinnest (40 nm) films. Strengthening beyond yield occurs upon both cooling and heating, indicative of strongstrain hardening in the Cu. The hardening continues down to at least 77 K. The yielding behavior of the Cu films has been characterized by a kinematic constitutive law, with exceptional strain hardening and a conventional temperature-dependent yield strength. The physical basis for this behavior is ascribed to confined shear bands in the Cu that induce large back stress. Transmission electron microscopy reveals aligned dislocations, which seemingly dictate the inelastic deformations in the shear bands.
Downshift of Raman peak in diamond powders
Authors: Zhao Xing-Zhong , Cherian K. A. , Roy Rustum , White William B.
Published: March 2008

Results are presented on the influence of the size of diamond powders and the laser power on the main Raman line. These results show conclusively that there is a consistent and systematic, reversible, downshift with both decrease of powder size, and increase of power. The shift can be explained by local heating of about 500 °C in the extreme case. Its significance applies to interpretation of the alleged “downshifting” of the 1332 cm−1 line in all diamond research. In the future, the grain size, the thermal contact, and the beam power must be carefully monitored in reporting and interpreting any frequency shifts.
Structural modifications of disordered mesocarbon microbeads with lower temperatures of heat treatment
Authors: Haridoss Prathap , Uribe Francisco A. , Garzon Fernando H. , Zawodzinski Thomas A.
Published: March 2008

We describe the variation of structural and physical properties of mesocarbon microbeads, a potential anode material for rechargeable lithium batteries, as a function of heat-treatment temperature in the range 400–1100 °C. Scanning electron microscopy (SEM) studies indicated changes in the morphology of the mesocarbons with heat treatment. X-ray studies show that average crystallite size varies considerably with heat treatment. The d002 spacing decreases with increasing heat-treatment temperatures. The electronic conductivity of the mesocarbon microbeads also increases substantially with increasing heat-treatment temperature. Based on thermogravimetric analysis (TGA) and other measurements, we find that organic fractions volatilizes out of these carbons in two distinct stages. The observed weight loss correlates with the structural changes observed. We suggest that these observations are consistent with two types of hydrogenated fractions present in the “green” mesocarbons.
Precipitation of carbon nanoparticles encapsulating silicon carbide from molten oxide
Authors: Mitomo Mamoru , Wang Chong-Min , Emoto Hideyuki
Published: March 2008

A kind of fullerenes, carbon nanoparticle encapsulating β–SiC grain, was precipitated during cooling Al2O3–Y2O3 –CaO oxide melt containing SiC and C from 2023 K. The SiC grains with a diameter of 5–20 nm were covered with 2–4 graphitic carbon layers with the spacing of 0.34 nm as revealed by high resolution transmission electron microscopy. The result provides a new preparation method of carbon nanoparticles through a ceramic process, which contrasts with previous physical methods applying electric arc discharge or electron irradiation in vacuum.
Growth morphology of large YBCO grains fabricated by seeded peritectic solidification: (I) The seeding process
Authors: Lo Wai , Cardwell D. A. , Hunneyball P. D.
Published: March 2008

The growth of large grain YBa2Cu3O7−δ (YBCO) by peritectic solidification in the presence of a (Sm,Y)Ba2Cu3O7−δ seed is characterized by the initial seeding process, development of a facet plane around the seed, and finally by continuous nonlocal growth away from the seed. A detailed investigation of the seeding process using electron microscopy, electron probe microanalysis, and thermal analysis techniques is reported here as the first in a series of studies of these key growth features. Results show that the seed partially melts below its nominal melting temperature due to a distribution of yttrium cations across the seed/YBCO interface. The formation of a Sm/YBa2Cu3O7−δ solid solution, which occurs via a reaction between (Sm,Y)2Ba2CuO5 and liquid state Ba3Cu5O8, has been observed across this interface at temperatures below the peritectic temperature Tp of the seed. The temperature window available for melting the YBCO phase while avoiding full peritectic decomposition of the (Sm,Y)Ba2Cu3O7−δ seed is maximized for seeds of high Sm content and thickness in excess of 0.2 mm. Finally, the dwell time at temperatures above Tp should be as short as possible if the integrity of the seed is to be maintained throughout the YBCO growth process.
The effect of molding pressure on the structural and electrical properties of Y1Ba2Cu3O7−δ superconductors
Authors: Kim C. O. , Park J. S. , Kim T. W.
Published: March 2008

Measurements of structural and electrical properties as a function of the molding pressure in Y1Ba2Cu3O7−δ superconductors have been performed to investigate the texturing behavior. The magnitudes of the molding pressure were 0.5 × 103 N/cm2, 1 × 103 N/cm2, 2 × 103 N/cm2, and 4 × 103 N/cm2. As the molding pressure increases, the anisotropy of the crystal structure decreases and the crystal grows preferentially along the c-axis. As the molding pressure increases, since the size of the grain becomes larger due to the decreased porosity, denser textures are formed. This result indicates that the critical current density is improved, resulting in increased thermal stability at higher molding pressure. While the molding pressure does not affect the oxygen mole fraction below 500 °C, increases in the molding pressure have a remarkable effect on the formation of textures and on the onset temperature for the superconducting transition in Y1Ba2Cu3O7−δ. These results indicate that structural and electrical properties in Y1Ba2Cu3O7−δ superconductors are affected by the molding pressure during growth.
Depth-sensing indentation measurements with Vickers and Berkovich indenters
Authors: Rother B. , Steiner A. , Dietrich D. A. , Jehn H. A. , Haupt J. , Gissler W.
Published: March 2008

Depth-sensing indentation measurements are performed with two different Vickers indenters and one Berkovich indenter. The sample materials were mirror polished Ag, Al, Au, Ni, and Ti samples. From the load-indentation depth data, the conventional hardness plots as well as the first derivative are calculated. The latter procedure yields a specific volume related density of deformation energy in the probed material. That specific energy density is shown to be a constant material parameter for extended indentation depths and for different Vickers indenters. Vickers and Berkovch indenters delivered within the error margin the same results.
Metastability of tetragonal ZrO2derived from Zr-n-propoxide-acetylacetone-water-isopropyl alcohol
Authors: Zhan Zhaoqi , Zeng Hua C.
Published: March 2008

ZrO2nanopowders derived from zirconiumn-propoxide [Zr(OC3H7)4]-acetylacetone-water-isopropanol have been investigated with respect to their tetragonal metastability on heating-cooling processes. The transformation temperature of metastable tetragonal to monoclinic (t′ →m) phase is found to be governed by ultimate firing temperature, time, and atmospheres employed. Crystallite growth is fastened with increase in calcination temperatures over 1000–1400 °C, and thet′ →mtransformation temperature is correlated linearly with crystallite size in the studied range of 12–20 nm. Heating in an oxygen environment increases the size of the final crystallites and hence the rate of thet′ →mtransformation. It is revealed that thet′ →mtransformation temperature depends largely on the heating atmosphere, but only weakly on the cooling one. Based on the findings of this work, surface oxygen deficiencies are attributed to be responsible for low-temperature tetragonal metastability. A crystallite growth model to explain the decline oft′-ZrO2phase is proposed. Kinetic and thermodynamic factors are also discussed in connection with the existing theories of tetragonal metastability.
Characterization of aluminosilicate (mullite) precursors prepared by a mechanochemical process
Authors: Temuujin J. , Okada K. , MacKenzie K. J. D.
Published: March 2008

Aluminosilicate precursors were prepared by mechanochemical treatment of gibbsitesilica gel mixtures. The effect of grinding on their structure and thermal behavior has been examined by 27Al and 29Si MAS NMR, x-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), and Fourier transform infrared (FTIR). After 8 h grinding, the hydrated alumina was completely changed to an amorphous phase which showed a new exothermic DTA peak at about 980 °C due to the formation of γ–Al2O3 or spinel phase. This behavior was related to changes in the Al and Si environments, as deduced from the MAS NMR spectra. With increased grinding time, some 4-coordinated Al appears, together with an Al resonance at about 30 ppm. Simultaneously, a new Si resonance appears at about −90 ppm, indicating a greater degree of homogeneity in the ground samples. Mullite crystallizes at 1200 °C from samples ground for 8–20 h, its XRD intensity increasing with increased milling times, in agreement with the NMR, DTA, and FTIR data. Changes in the Al and Si environments during heat treatment, as reflected by the NMR spectra, are also reported.
Conductivity behavior of n-type semiconducting ferrites from hydrothermal powders
Authors: Dias Anderson , Moreira Roberto Luiz
Published: March 2008

The frequency and temperature dependencies of the dielectric permittivity and of the electrical conductivity of excess ferrous ions hydrothermal NiZn ferrites were analyzed before and after sintering. A decreasing tendency with frequency of the dielectric responses was observed, but the high permittivities attained (ε′ ≈ 105) masked any relaxation in these materials. This behavior is characteristic of n-type semiconducting ferrites, where electron hopping between Fe+2 and Fe+3 ions leads to very high conductivity values. The temperature dependence of the dielectric permittivities revealed the existence of broader peaks. The electron hopping mechanism leads to a frequency dispersion of the temperature where the permittivities attain their maxima. The electrical conductivity variations with temperature exhibited Arrhenius-type behaviors, with activation energies ranging from 0.34 eV (hydrothermal powder) to 0.16 eV (for the highest sintering temperature). These results were correlated to the variations in Fe+2 concentration and microstructure.
Epitaxial growth of “infinite layer” thin films and multilayers by rf magnetron sputtering
Authors: Fàbrega L. , Koller E. , Triscone J. M. , Fischer Ø.
Published: March 2008

We report on the preparation and characterization of epitaxial ACuO2 (A = Sr, Ca, Ba) thin films and multilayers with the so- called infinite layer (IL) structure, by rf magnetron sputtering. Films and multilayers without Ba have a remarkable crystal quality, whereas those containing this large ion are often multiphased and unstable. In spite of the excellent crystalline quality of these samples, obtaining thin films having both IL structure and displaying superconducting properties has not succeeded; our pure IL samples display semiconducting behavior, and the different procedures tried in order to dope them—annealings, introduction of disorder or cation vacancies, artificial layering—have failed. These results support that the pure IL structure ACuO2 (A = alkaline earth) cannot superconduct.
In situmonitoring of the sintering behavior of microcomposite particles using a laser scanning micrometer
Authors: Chen Z. , Chen S-F. , Overfelt R. A. , Rose M. F.
Published: March 2008

The densification behavior of silica-coated alumina particles was investigated during sintering using a laser scanning micrometer. Traditional dilatometric techniques require contact between a push-rod and the sample under study and thus place the sample under stress during the test. However, the utilization of a noncontact laser micrometer to measure dimensional changes during sintering enabled the densification behavior to be very accurately characterized under a stress-free condition. Thus higher temperature experiments, where densification rates are particularly temperature sensitive and the samples are especially soft, can be reliably investigated without the disturbing influence of an external force. The present paper describes an application of the technique to evaluate the densification behavior from 900–1300 °C of silica-coated alumina microcomposite particles used for the fabrication of mullite.
Biaxial stretching of superplastic Y -TZP, Y -TZP/Al2O3, and Y -TZP/LAS glass composites in air atmosphere
Authors: Shi J. L. , Zhu G. Q. , Gao J. H. , Li L. , Lu Z. L. , Lai T. R.
Published: March 2008

The biaxial stretching behavior of superplastic Y -TZP (yttria -tetragonal zirconia polycrystals) ceramics and Y -TZP/Al2O3 composites in air atmosphere was investigated. Stretching deformation can be made within a limited range. Larger grain size of Y -TZP led to higher applied load needed to obtain the same amount of deformation. However, if some monoclinic phase was present in the materials, which was caused by the over -large grain sizes, defects would occur and thus make deformation easier. Microstructure study of the deformed specimen showed the occurrence of crack -like defects on the outside surface of the stretched disk specimen. Limited grain growth of single phase Y -TZP was obtained while Y -TZP grains in Y -TZP/Al2O3 composites grew extensively after stretching.
Effect of microstructure on damage tolerance in grinding dental glass-ceramics
Authors: Xu Hockin H. K. , Jahanmir Said
Published: March 2008

This study investigated the modes of grinding-induced subsurface damage in dental glass-ceramics and the influence of microstructure on strength degradation. A series of micaceous glass-ceramics crystallized from the same glass composition were tested. The diameter of the mica platelets in these glass-ceramics was varied via heat treatment. Grinding was performed using three diamond wheels (with diamond particle size of 40, 100, and 180 µm, respectively) at depth of cut ranging from 5 µm to 100 µm. A bonded- interface technique was employed to examine the machining- induced subsurface damage. Relatively large median and lateral cracks were found in the glass-ceramic with the smallest mica platelets. In contrast, no cracks were found in the material containing large mica platelets. The ground specimens were fractured in four-point flexure to measure strength as a function of grinding conditions and mica platelet sizes. The strength of the ground specimens was reduced to approximately 30% of the strength of the polished specimens for the glass- ceramic containing the smallest mica platelets; that of the glass-ceramic with the intermediate mica platelet size was reduced to 60%. In contrast, virtually no strength loss occurred with the glass-ceramic containing large mica platelets. Microstructure was shown to determine the mode and degree of strength-controlling damage in the machining of these dental glass-ceramics. Polishing after grinding removes subsurface damage and recovers strength for the glass-ceramics containing fine mica crystals.
Stabilization of aqueous BaTiO3 suspensions with ammonium salt of poly(acrylic acid) at various pH values
Authors: Jean Jau-Ho , Wang Hong-Ren
Published: March 2008

Ammonium salt of poly(acrylic acid) (PAA-NH4) has been used to stabilize aqueous BaTiO3 suspensions at various pH values. Adsorption of PAA-NH4 causes the zeta potential to become more negative, although this effect becomes less dramatic as the pH increases. The concentration of PAA-NH4 required to stabilize aqueous BaTiO3 suspensions decreases with increasing pH. The critical amount of PAA-NH4 as a function of pH is plotted in a stability map, as determined by adsorption, rheology, and sedimentation studies.
Mass transfer and kinetics of the chemical vapor deposition of SiC onto fibers
Authors: Lackey W. Jack , Vaidyaraman Sundar , Beckloff Bruce N. , III Thomas S. Moss , Lewis John S.
Published: March 2008

An internally consistent set of data was generated for the chemical vapor deposition (CVD) of SiC from methyltrichlorosilane (MTS) and H2 at atmospheric pressure. A moving fiber tow was used as the substrate. Coating rates between 0.3 and 3.7 µm/min and deposition efficiencies between 24 and 48% were obtained for MTS and H2 flow rates in the range 30 to 200 cm3/min and 300 to 2000 cm3/min, respectively. The data were analyzed and found to be best fit under a mass transfer regime. Based on this fit, a value of the constant in the Chilton–Colburn j factor expression for a moving fiber tow was estimated to be 2.74 × 10−6 with a standard deviation of 3.2 × 10−7. The efficiency of the reaction was found to decrease with increases in the total flow rate, indicating that the effect of the decreased residence time of reagents in the reactor was larger than the increase in the mass transfer coefficient. Finally, a comparison between the efficiencies for a stationary and a moving tow revealed that the moving tow had a higher efficiency, possibly due to a disruption of the boundary layer by the tow motion or due to the decrease in the canning of the moving tow.
Growth of diamond and diamond-like films using a low energy ion beam
Authors: Guo Y. P. , Lam K. L. , Lui K. M. , Kwok R. W. M. , Hui K. C.
Published: March 2008

Ion beam deposition provides an additional control of ion beam energy over the chemical vapor deposition methods. We have used a low energy ion beam of hydrogen and carbon to deposit carbon films on Si(100) wafers. We found that graphitic films, amorphous carbon films, and oriented diamond microcrystallites could be obtained separatedly at different ion beam energies. The mechanism of the formation of the oriented diamond microcrystallites was suggested to include three components: strain release after ion bombardment, hydrogen passivation of sp3 carbon, and hydrogen etching. Such a process can be extended to the heteroepitaxial growth of diamond films.
Growth of silicon sheets for photovoltaic applications
Authors: Bell R. O. , Kalejs J. P.
Published: March 2008

Several techniques for the sheet growth of silicon for solar cell substrates are reviewed here. These techniques usually offer an economic advantage over growth in the form of bulk crystals. At least 16 different sheet growth systems have been proposed but only five, that are actively being pursued for commercialization, are discussed here. These include dendritic web, string ribbon, edge-defined film-fed growth (EFG), ribbon growth on a substrate (RGS), and Silicon-Film. The growth systems and the characteristics of the resulting solar cells are briefly described. A discussion of their current status concludes the review.
Cadmium-telluride—Material for thin film solar cells
Authors: Bonnet Dieter , Meyers Peter
Published: March 2008

Due to its basic optical, electronic, and chemical properties, CdTe can become the base material for high-efficiency, low-cost thin film solar cells using robust, high-throughput manufacturing techniques. CdTe films suited for photovoltaic energy conversion have been produced by nine different processes. Usingn-type CdS as a window-partner, solar cells of up to 16% efficiency have been made in the laboratory. Presently five industrial enterprises are striving to master low cost production processes and integrated modules have been delivered in sizes up to 60 × 120 cm2, showing efficiencies up to 9%. Stability, health, and environmental issues will not limit the commercial potential of the final product. The technology shows high promise for achieving cost levels of $0.5/Wpat 15% efficiency. In order to achieve this goal, scientists will have to develop a more detailed understanding of defect chemistry and device operation of cells, and engineers will have to develop methods for high-throughput manufacturing.