bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of CeO2–Al2O3–SiO2 glasses by infrared and x-ray absorption near edge structure spectroscopies
Authors: Lin Sin-Lung , Hwang Chii-Shyang , Lee Jyh-Fu
Published: March 2008

Structural characteristics of CeO2–Al2O3–SiO2 glasses have been studied by infrared and x-ray absorption near edge structure (XANES) spectroscopies, and the Kramers-Kronig analysis of IR reflection data was performed. Results of IR spectra show that ceria is the network modifier and favors the formation of [SiO4] tetrahedron with nonbridging oxygens. The high frequency Si–O–Si stretching vibrational peak near 1100 cm−1 shifts toward the lower frequency as ceria content increases and alumina content is constant. XANES data of the cerium LIII edge show that the majority of cerium ions in cerium aluminosilicate glasses are Ce3+ ions. The ratio of Ce4+/Ce3+ increases with increasing the ratio of Ce/(Al + Si). However, the ratio of Ce4+/Ce3+ decreases with increasing the ratio of Al/(Al + Si).
The relationship between glass structure and poling-induced optical second harmonic intensity for ZnO–TeO2 glasses
Authors: Shimizugawa Y. , Hirao K.
Published: March 2008

Local ordering around Te and Zn atoms of ZnO–TeO2 glass systems is investigated by Te K and Zn K EXAFS using synchrotron radiation. Tellurium K EXAFS results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO311 polyhedra or TeO3 trigonal pyramids with increasing of ZnO. Zinc K EXAFS results indicate that the Zn atom has the second oxygen shell which locates at the distance of 0.222–0.228 nm. The second harmonic intensity of the poled glass samples was also measured. The compositional dependence of the second harmonic intensity is explained in terms of the structural change of ZnO–TeO2 glass with the addition of ZnO.
Study of electrical and optical properties of ion-implanted polymers in relation to carbon structure
Authors: Sakamoto Kazuo , Iwaki Masaya , Takahashi Katsuo
Published: March 2008

The relationship among electrical conductivity, optical properties, and carbon structure of ion-implanted polymers has been studied by optical transmission and Raman spectroscopy. The electrical conductivity, which depends not only on the ion dose but also on the dose rate in a complicated manner, was found to have a simple relation to the optical absorbance. By Raman spectroscopic analyses, the difference in the electrical conductivity was explained in terms of the difference in carbon structure.
Effects of sequential He+ and Ar+ implantation on surface properties of polymers
Authors: Rao Gopal R. , Lee Eal H.
Published: March 2008

Three important polymers: polystyrene (PS), poly ether ether ketone (PEEK), and polyimide Kapton, were irradiated separately with 1 MeV He+, 1 MeV Ar+, and 1 MeV He+ followed by 1 MeV Ar+ sequentially, to a fluence of 3 × 1019 ions/m2 for each ion. The specimens were characterized for changes in surface hardness using a nanoindentation technique, and wear resistance using a reciprocating sliding wear apparatus with a steel ball counterface. Results indicated that while all polymers showed higher hardness values after ion irradiation, the dual irradiation resulted in the largest hardness increase, greater than for the single ion-irradiated specimens. Wear test results also indicated that the dual He+ + Ar+ irradiation resulted in the best improvement in wear resistance of the polymers. These improvements in properties are a consequence of cross-linking of the polymer material caused by the ion irradiation. Linear energy transfer considerations showed that the dual He+ + Ar+ implantation was better because it combined a deeper implant, in the form of He, along with Ar irradiation which resulted in a shallower but more highly cross-linked layer at the near surface. Thus a deeper and graded cross-linked surface region was formed. The study shows that there is greater flexibility for tailoring surface properties of polymers by using a judicious combination of ion species, ion energies, and fluences.
Processing of submicron grain 304 stainless steel
Authors: Jain M. , Christman T.
Published: March 2008

A novel thermomechanical processing technique for the synthesis of bulk submicron grain (grain size ≈200 nm) 304 stainless steel is reported. This ingot-metallurgical technique requires a total deformation of only 95%, and the key steps to this processing technique involve (i) formation of ultrafine dislocation cell structure, and (ii) the conversion of dislocation cells into grains with medium to high misorientation by grain boundary sliding.
Microstructures and electrical resistivities of the RuO2 electrode on SiO2/Si annealed in the oxygen ambient
Authors: Lee Jeong Soo , Kwon Hyun Ja , Jeong Young Woo , Kim Hyun Ha , Kim Cha Yeon
Published: March 2008

The electrical resistivity property of RuO2 thin films grown on the SiO2/Si substrate by reactive dc sputtering was examined in terms of microstructure using x-ray diffraction and cross-sectional transmission electron microscopy. As the samples were annealed in the oxygen ambient over the temperature range 300–700 °C, the resistivity decreased from 270 to 90 μΩcm with increasing annealing temperature. When heat treatment was performed below 500 °C, the strain which accumulated in the RuO2 layer during deposition was released without significant increase in grain size. It is thought that below 500 °C improvement in the crystallinity plays an important role in the variation of the resistivity. Although a considerable amount of growth of RuO2 grains was achieved, the columnar structure of the RuO2 layer in the as-deposited sample remained unchanged even after annealing at 700 °C. The resistivity improvement above 500 °C was driven mainly by the grain boundary annihilation.
Synthesis of bulk nanocrystalline Ti–Cu alloy by pressure-quenching method
Authors: Li Dongjian , Wang Aiming , Yao Bing , Ding Bingzhe , Hu Zhuangqi
Published: March 2008

A new method is proposed to prepare bulk nanocrystalline alloys by quenching alloy melts under high pressure. Due to application of pressure to solidification processes, the nucleation rate is increased whereas the growth rate of nuclei decreased with increase of pressure, which makes it possible to obtain bulk ingots with nanometer-sized crystalline grains if appropriate pressure, temperature, and cooling rate are selected. The as-pressure-quenched products are cylinder-like with diameter about 4 mm and height several millimeters. This method can produce dense, free-porosity bulk nanocrystalline alloys with clean crystalline interfaces, promising use for experimental research and technological applications.
The oxidation behavior and magnetic properties of iron carbonitride ultrafine particles
Authors: Zhao X. Q. , Liang Y. , Hu Z. Q. , Liu B. X.
Published: March 2008

Iron nitride and iron carbonitride (ICN) ultrafine particles (20–80 nm in size) have been synthesized by laser-induced pyrolysis of the Fe(CO)5–NH3–C2H4 system. The oxidation behavior, surface morphologies, and structural characteristics as well as magnetic properties of these particles are reported and discussed. It is found that the presence of very thin carbon coating (1–2 nm) on the ICN particles plays an important role in preventing the oxidation of the particles. Accordingly, the ICN ultrafine particles exhibit higher saturation magnetization (142 emu/g) than the iron nitride ones (124 emu/g).
Preparation of YBa2Cu3O7−δ thin film by laser-assisted metal-organic chemical vapor deposition using highly volatile fluorocarbon-based Ba source
Authors: Mizushima Yasuyuki , Hirabayashi Izumi
Published: March 2008

Superconducting oxide films of YBa2Cu3O7−δ (YBCO) were produced on magnesia (MgO) single crystalline substrates (100) by laser-assisted metal-organic chemical vapor deposition. The highly volatile Ba(hfa)2 · tetraglyme was used as a Ba source metal-organic material. Smoother surface YBCO film was obtained with KrF laser irradiation than without. However, KrF laser irradiation does not lower the temperature for formation of YBCO(123) phase. YBCO film prepared at 750 °C on the MgO substrate showed a Tc(R = 0) of 69 K, and that prepared with KrF laser irradiation was 85 K. When water was added to the reaction chamber, barium fluoride was reduced and the YBCO formation was detected at a temperature of 650 °C and higher. YBCO film prepared at the temperature of 700 °C for 40 min without KrF laser irradiation behaves as a semiconductor, and one prepared with laser irradiation showed a Tc(R = 0) of 78 K.
Growth mechanism and morphology of melt-texture-growth-processed YBa2Cu3O7−x with different presintered microstructures
Authors: Wang J. , Monot I. , Desgardin G.
Published: March 2008

This work deals with the influence of the starting Y-123 grain size on the growth mechanism and final microstructure of the melt-textured YBa2Cu3O7−x ceramics. Observations of the growth front morphology and stability for the different precursors using several decomposition temperatures are correlated with the theoretical equations. It is found that the final 211 inclusion size increases as the starting 123 grain size increases. However, using a small-grained 123 precursor disrupts the growth front and makes the control of grain alignment difficult. An appropriate morphology of the 123 precursor should be chosen prior to the MTG process in order to obtain the best properties.
Thermal decomposition of mechanically alloyed nanocrystalline fcc Fe60Cu40
Authors: Huang J. Y. , Yu Y. D. , Wu Y. K. , Ye H. Q. , Dong Z. F.
Published: March 2008

A ferromagnetic and supersaturated fcc Fe60Cu40 solid solution was prepared by mechanical alloying (MA). The phase transformations of the as-milled Fe60Cu40 powder upon heating to 1400 °C and subsequently cooling to room temperature were characterized by differential thermal analysis (DTA) and thermal magnetic measurement. The fcc Fe60Cu40 solid solution decomposes into α–Fe(Cu) + γ–Fe(Cu) + Cu(Fe) upon heating from 300 to 460 °C, and on further heating, α–Fe(Cu) transforms to γ–Fe(Cu) at 640 → 760 °C; during cooling, the reverse transformation occurs from 800 → 640 °C (obtained from thermomagnetic measurement) or from 700 → 622 °C (obtained from DTA). The γ ⇆ α transformation in mechanically alloyed Fe60Cu40 nanocrystalline occurs in a wide temperature range; the transformation temperature is higher than that of the martensite transformation in as-cast Fe–Cu alloys, but is much lower than that of the allotropic transformation of pure Fe. These differences may be caused by the different fabrication process, the nonequilibrium microstructure of MA, as well as the inhomogeneous grain size in α–Fe(Cu). High resolution transmission electron microscope (HRTEM) observations carried out in the specimen after the DTA run show that N-W or K-S orientation relationships exist between α–Fe(Cu) and Cu(Fe), which also represent the orientation relationship between α–Fe(Cu) and γ–Fe(Cu) due to excellent coherency between γ–Fe(Cu) and Cu(Fe). The grain size of the α–Fe(Cu) is inhomogeneous and varies from 50–600 mm. Energy dispersive x-ray spectroscopy (EDXS) result shows that the Cu content in these α–Fe(Cu) grains reaches as high as 9.5 at. % even after DTA heating to 1400 °C, which is even higher than the maximum solubility of Cu in γ–Fe above 1094 °C. This may be caused by the small grain size of α–Fe(Cu).
Anelastic and plastic relaxation in polycrystalline alumina and single-crystal sapphire
Authors: Ota Ken'ichi , Pezzotti Giuseppe
Published: March 2008

Internal friction and torsional creep behaviors of high-purity single-crystal sapphire and three polycrystalline aluminas with different grain sizes have been measured up to very high temperature. The hexagonal c -axis-oriented sapphire specimen was tested at frequencies of 10–13 Hz, up to melting point (i.e., ∼2323 K). No relaxation peak was found and the exponential background curve was discussed in analogy to that of the hexagonal single-crystal ice reported in previous literature. The internal friction curves of the polycrystalline specimens were constituted by the superposition of a background component, of plastic nature, and a broad anelastic grain-boundary peak. These curves were markedly shifted to lower temperatures as compared to that of sapphire: the higher the shift, the smaller the average grain size. Also, the intensity of the grain-boundary peak decreased with increase in grain size. In the polycrystalline specimens, both creep and internal-friction background data fit the same Arrhenius plot, the slope corresponding to an activation energy of 200 kJ/mol. These data provide evidence for the occurrence of anelastic relaxation at the grain boundary and for the plastic nature of the internal-friction background in Al2O3 ceramics.
Rare-earth-doped α′-Sialon ceramics with novel optical properties
Authors: Karunaratne B. S. B. , Lumby R. J. , Lewis M. H.
Published: March 2008

A new phenomenon in the field of Sialon ceramics is reported which may lead to applications based on their optical or electronic properties in combination with their mechanical and thermal properties. For the first time a colored α′-Sialon ceramic has been synthesized, with relatively high optical transparency by careful control of the sintering atmosphere, and adding suitable rare earths as stabilizing cations. This compares with normal Sialons and silicon nitrides which are grey-black in color and are opaque. Oxidation/reduction mechanisms have been identified as an influence on the valence of the stabilizing cation, which is responsible for the unusual optical properties.
Residual stress in ceramics with large thermal expansion anisotropy
Authors: Paulik S. W. , Zimmerman M. H. , Faber K. T. , Fuller E. R.
Published: March 2008

Residual stress was measured in sintered and heat-treated Fe2TiO5 samples with various grain sizes. The influence of texturing was assessed by comparing the residual stress states of samples having randomly oriented grains and highly oriented grains produced through magnetically assisted processing. The residual stress was measured with x-ray diffraction using Cr Kα radiation. Due to the significant texture and the consequential oscillations in the dφψ vs sin2ψ data, the residual stress was calculated using the Marion–Cohen method. Textured samples showed significantly lower residual stresses except when spontaneous microcracking accompanied grain growth in the randomly oriented systems. Elastic modulus measurements showed a direct correlation between the decrease in residual stress and the microcrack density.
Ternary packing of SiC and diamond particles in ethanol
Authors: Lee Jong-Heon , Lackey W. Jack , Benzel James F.
Published: March 2008

Particle packing techniques employing a liquid phase were used for preparation of dense disks of SiC and diamond particulates. Forty-one SiC and fifteen diamond compositions in the ternary-component particle systems were used to determine the optimum percentages of coarse, medium, and fine particles for achieving high packing densities: over 80% for SiC and over 62% for diamond. High packing densities were achieved without vibration by simply mixing the three size fractions in ethanol followed by stirring during the initial evaporation stage. The packing density results for SiC were successfully correlated with the percentages of the coarse and fine particles using multiple regression analysis; however, the data for diamond could not be similarly correlated with particle composition because the experimental work was done in a narrow range of compositions and the range of packing densities was small.
Optical emission spectroscopy during the bias-enhanced nucleation of diamond microcrystals by microwave plasma chemical vapor deposition process
Authors: Barshilia H. C. , Mehta B. R. , Vankar V. D.
Published: March 2008

Microwave plasma chemical vapor deposition (MWPCVD) process has been used to grow diamond thin films on silicon substrates from CH4–H2 gas mixture. Bias-enhanced nucleation (BEN) pretreatment has been used to increase the density of diamond nuclei. Various species in the CH4–H2 plasma have been identified using optical emission spectroscopy (OES), and their effect on the film microstructure has been studied. During the pretreatment process the emission intensities of CH, CH+, C2, H, and H2* species have been found to increase significantly for a negative dc bias voltage |VB| > 60 V. The higher concentration of excited species and the associated effects play a significant role in the growth process. A very thin layer of a-C containing predominant sp3 bonded carbon species in the initial stages of the growth is found to be present in these films. The microstructure of the films has been found to be very sensitive to the biasing conditions.
Energy losses of ions implanted in matter
Authors: Liang J. H. , Liao K. Y.
Published: March 2008

A set of simple and accurate formulae for the first four moments of nuclear and electronic energy losses is proposed. A new variable is introduced to include the finite maximum-impact-parameter effect in the nuclear stopping process, which is assumed to be infinite in most studies. A critical energy at which the electronic energy loss is equal to the nuclear energy loss is also defined. It determines whether the nuclear or the electronic stopping process is the dominant mechanism in terms of incident-ion energy. The critical energy increases for heavy ions implanted in heavy target materials during the first moment of energy loss. The second moment of electronic energy loss is important only for light ions implanted at high ion energies. The third and fourth moments of nuclear energy loss are much larger than those of the electronic energy loss for all ion-target combinations. Theoretical predications of the projected ranges and range stragglings for gold ions implanted in carbon films are close to the experimental data when these proposed four moments of nuclear and electronic energy losses are considered.
Reaction sintering of alumina-aluminide alloys (3A)
Authors: Claussen N. , Garcia D. E. , Janssen R.
Published: March 2008

A novel pressureless reaction sintering process is presented for the fabrication of Al2O3-aluminide alloys (3A). Compacts of intensively milled metal oxide-aluminum mixtures are heat-treated in vacuum or inert atmosphere such that the exothermic reactions take place in a controlled manner essentially at temperatures below the melting point of Al. Dense, homogeneous microstructures were obtained with a variety of Al2O3-matrix systems with interpenetrating networks of aluminides of Ti, Fe, Nb, Mo, Zr, Ni, etc. By adding modifiers in the form of oxides or metals, volume and phase composition as well as properties can be tailored in a wide range.
Electrical properties of polyethylene highly filled with carbon
Authors: Modine F. A. , Duggal A. R. , Robinson D. N. , Churnetski E. L. , Bartkowiak M. , Mahan G. D. , Levinson L. M.
Published: March 2008

Carbon-filled polyethylene composites were fabricated and tested to establish the practical lower limit of their electrical resistivity at room temperature and to investigate the trade-offs between low resistivity and the magnitude of the resistance anomaly (i.e., a large positive temperature coefficient of resistivity) that appears when such composites are heated through the polyethylene crystalline melting transition. Carbon blacks with large particle size and low surface area provided low-resistivity composites having large resistance anomalies. The largest resistance anomalies were found in composites that were well mixed, but the room-temperature resistivity also increased in composites that were cycled repetitively through the crystalline-melting transition. A mixture of carbon blacks of two different sizes provided a lower resistance than was found in a material with the same fill of only the coarser black. By controlling the composition and the processing, composites were made with room-temperature resistivities lower than 0.2 ohm cm and resistance changes of at least 2 orders of magnitude. A resistance change of as much as 5 orders of magnitude was obtained for composites with room-temperature resistivities of only 1 ohm cm.
Study of the growth mechanism of highly in-plane aligned α-axis YBa2Cu3O7−x thin films on LaSrGaO4 substrate by high resolution electron microscopy
Authors: Wen J. G. , Mahajan S. , Ohtsuka H. , Morishita T. , Koshizuka N.
Published: March 2008

Highly in-plane aligned α-axis YBa2Cu3O7−x thin films deposited on (100) LaSrGaO4 substrates by a self-template method were studied by high-resolution electron microscopy along three orthogonal 〈100〉 axes of the substrate. Plan-view images confirm that the majority of the film preferentially aligns across the entire substrate except for very few misaligned domains with average size 10 nm2. Cross-sectional images along the [100] orientation of YBa2Cu3O7−x reveal that in-plane aligned α-axis YBa2Cu3O7−x is grown on a template layer dominated by c-axis oriented film. This strongly suggests that the in-plane alignment of α-axis YBa2Cu3O7−x thin films on (100) LaSrGaO4 substrates is governed by the different stresses along the b and c axes of the substrate. Cross-sectional images along [001] of the YBa2Cu3O7—x thin film reveal that the 90° domains easily nucleate in the region between α-axis YBa2Cu3O7—x and the YBa4Cu3Ox phase. Cracks along the (001) plane of YBa2Cu3O7−x are found to be due to the large mismatch between the c parameters of the thin film and substrate.
Growth of highly (111)-oriented, highly coalesced diamond films on platinum (111) surface: A possibility of heteroepitaxy
Authors: Shintani Yoshihiro
Published: March 2008

A highly (111)-oriented, highly coalesced diamond film was grown on platinum (111) surface by microwave plasma chemical vapor deposition (MPCVD). Scanning electron microscopy and x-ray diffraction analyses revealed that the (111) diamond facets were azimuthally oriented epitaxially with respect to the orientation of the Pt(111) domain underneath, with the neighboring facets of diamond being coalesced with each other. The film was confirmed as diamond using Raman spectroscopy.
Combustion co-synthesis of Si3N4-based in situ composites
Authors: Li J. T. , Liu W. S. , Xia Y. L. , Ge C. C.
Published: March 2008

The feasibility of synthesizing silicon nitride-silicon carbide-titanium carbonitride composites by combustion reactions is demonstrated. With titanium carbonitride taken to be an ideal solid solution, its composition is determined as TiC0.36N0.64. Thermodynamic analysis supports the experimental results.
Microstructural study of growth of a YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x trilayered film by pulsed laser deposition
Authors: Li Y. H. , Staton-Bevan A. , Kilner J. A. , Trajanovic Z. , Venkatesan T.
Published: March 2008

The growth process of a YBCO/LaAlO3/YBCO trilayered film made by pulsed laser deposition has been studied by high resolution transmission electron microscopy (HRTEM). The high resolution images of the cross-section samples have shown that a 7 nm layer of LaAlO3 has been grown epitaxially between c-axis oriented YBCO layers having the nominal thickness of 250 nm. A stacking fault in the LaAlO3 layer may introduce a stacking fault into the YBCO layer, which may form nucleation sites for α-axis oriented grains. A second phase had been formed at the interface between the LaAlO3 layer and the lower YBCO layer, which has been identified by image simulation and energy dispersive x-ray (EDX) analysis as a new tetragonal La–Al–Cu–O phase based on LaAlO3 in which some of Al atoms have been replaced by Cu. The approximate lattice parameters of the new phase are a = 0.38 nm and c = 0.76 nm. However, no second phase was found at the interface between the lower YBCO layer and the LaAlO3 substrate.
Microstructure and phase stability of single crystal NiAl alloyed with Hf and Zr
Authors: Locci I. E. , Dickerson R.M. , Garg A. , Noebe R. D. , Whittenberger J.D. , Nathal M. V. , Darolia R.
Published: March 2008

Six near stoichiometric, NiAl single-crystal alloys, with 0.05−1.5 at.% of Hf and Zr additions plus Si impurities, were microstructurally analyzed in the as-cast, homogenized, and aged conditions. Hafnium-rich interdendritic regions, containing the Heusler phase (Ni2AlHf), were found in all the as-cast alloys containing Hf. Homogenization heat treatments partially reduced these interdendritic segregated regions. Transmission electron microscopy (TEM) observations of the as-cast and homogenized microstructures revealed the presence of a high density of fine Hf (or Zr) and Si-rich precipitates. These were identified as G-phase, Ni16X6Si7, or as an orthorhombic NiXSi phase, where X is Hf or Zr. Under these conditions the expected Heusler phase (β′) was almost completely absent. The Si responsible for the formation of the G and NiHfSi phases is the result of molten metal reacting with the Si-containing crucible used during the casting process. Varying the cooling rates after homogenization resulted in the refinement or complete suppression of the G and NiHfSi phases. In some of the alloys studied, long-term aging heat treatments resulted in the formation of Heusler precipitates, which were more stable at the aging temperature and coarsened at the expense of the G-phase. In other alloys, long-term aging resulted in the formation of the NiXSi phase. The stability of the Heusler or NiXSi phases can be traced to the reactive element (Hf or Zr) to silicon ratio. If the ratio is high, then the Heusler phase appears stable after long time aging. If the ratio is low, then the NiHfSi phase appears to be the stable phase.
Synthesis and solid solution in ceramic (Ca1−xSrx)2PbO4
Authors: Xu Ming , Finnemore D. K. , Gao Wei
Published: March 2008

Ceramic (Ca1−xSrx)2PbO4 samples have been prepared with x = 0.00, 0.25, 0.50, 0.75, and 1.00 in order to study the change in lattice constants with the ratio of Ca/Sr. This phase is frequently an intermediate phase in the fabrication of Bi–Sr–Ca–Cu–O superconductors, and it is important to connect the lattice constants with stoichiometry. The behavior of the lattice constants closely follows Vegard's law.
Description and classification of uranium oxide hydrate sheet anion topologies
Authors: Miller Mark L. , Finch Robert J. , Burns Peter C. , Ewing Rodney C.
Published: March 2008

The sheets of uranyl ions (U6+O2)2+in the structures of all uranyl oxide hydrates (UOH) (and the structurally related α- and β-forms of U3O8) are based on only four structural unit chains. Each sheet type may be reduced to its underlying sheet anion topology to determine the chains present within each topology and to describe the structural relationships among these phases. Each sheet type is described by a chain stacking sequence. The four chain types required to construct the UOH sheet anion topologies are theH-chain, theR-chain, theP-chain, and the directional “arrowhead” chains denoted byUandD. TheH-chain is found only in the sheet anion topology of α-UO2(OH)2and consists of hexagonal sites sharing opposing edges. In α–UO2(OH)2, all hexagons are populated with uranyl ions. The “arrowhead” chain is composed of pentagonal sites populated with uranyl ions and sharing edges and alternating with vacant triangular sites. Arrowhead chains are present in the sheet anion topologies of all other UOH sheets. Arrowhead chains are directional and can occur in bothUandD“senses” within a single anion topology. The P-chain consists of edge-sharing pentagonal sites populated with uranyl ions forming a zigzag chain. TheP-chain is flanked on both sides by arrowhead chains of the same “sense”. The remaining structural unit is a discontinuous “chain” of rhombic sites. This “R-chain” is produced when nested; adjacentUandD“arrowhead” chains are translated diagonally. TheR-chain occurs in the sheet anion topologies of sheets which contain only 4-coordinate uranyl ions and those containing both 4- and 5-coordinate uranyl ions. The rhombic sites may be populated with a uranyl ion, a U4+or other cation and two apical oxygens, or they may be vacant.
Toughness determination of zirconia toughened alumina ceramics from growth of indentation-induced cracks
Authors: Basu D. , Sarkar B. K.
Published: March 2008

Short surface cracks were generated by Vickers indentation on the polished surface of alumina and different zirconia toughened alumina (ZTA) specimens, and their morphology was studied by serial sectioning. These cracks were grown in three-point bend tests under stepwise loading, and variation of toughness with crack extension was plotted to graphically separate the contributions from residual stress intensity and applied stress intensity factors. The plateau toughness determined from the intercept height of the crack extension plots exhibited an upward trend with zirconia content up to 15 vol % ZrO2 addition in the composition, which was proportional to the fraction of transformable tetragonal grains contributing to transformation toughening.
Structure of nanocrystalline palladium and copper studied by small angle neutron scattering
Authors: Sanders P. G. , Weertman J. R. , Barker J. G.
Published: March 2008

The structure of nanocrystalline palladium and copper, made by inert gas condensation and compaction, was studied using small angle neutron scattering (SANS), optical microscopy, and scanning electron microscopy. The effects of annealing and warm compaction were also examined with these techniques. The SANS results were interpreted using a maximum entropy routine, combined with knowledge of the Archimedes density and hydrogen concentration determined by prompt gamma activation analysis (PGAA). Similar hydrogen concentrations were detected by SANS and PGAA. This hydrogen content, which was approximately 5 at. % in samples compacted at room temperature, was reduced by both annealing and warm compaction. Defects in several size classes were observed, including missing grain pores (≈1−50 nm diameter) and defects of micrometer size. Warm compaction produced a lower number density of pores in nanocrystalline palladium, which led to increased density. The observed structure was correlated with Vickers microhardness and fracture surface morphology.
Continuous microscratch measurements of the practical and true works of adhesion for metal/ceramic systems
Authors: Venkataraman S. , Kohlstedt D. L. , Gerberich W. W.
Published: March 2008

Using a continuous microscratch technique, the adhesion strengths of Pt, Cr, Ti, and Ta2N metallizations to NiO and Al2O3 substrates have been characterized. The practical work of adhesion was determined as a function of both thickness and annealing conditions. For all except the Ta2N films, the practical work of adhesion increases nonlinearly from a few tenths of a J/m2 to several J/m2 as the thickness of the thin film is increased, indicating that a greater amount of plastic work is expended in delaminating thicker films. Further, the practical work of adhesion also increases with increasing annealing temperature, indicating stronger bonding at the interface. In the limit that the film thickness tends to zero, the plastic energy dissipation in the film tends to zero. As a result, the extrapolation to zero thickness yields the true work of adhesion for that system.
[NZP], NaZr2P3O12-type materials for protection of carbon-carbon composites
Authors: Agrawal Dinesh K. , Harshé Girish , Breval Else , Roy Rustum
Published: March 2008

Carbon-carbon composites, if not suitably protected, suffer from the problem of oxidation of the surface in normal atmospheres at temperatures above 350 °C. For this reason they need to be protected from oxidizing environments by either using an impermeable coating, or using a sacrificial protective coating of a suitable material, and/or doping of an oxidation inhibitor in the carbon. In this study we have used a new family of materials with tailorable thermal expansion characteristics, namely, the [NZP] family as the materials for developing a suitable coating material for C-C composites. The candidates selected for matching thermal expansion with that of carbon are Ca0.5Sr0.5Zr4P6O24, SrZr4P6O24, and Ba1.175Zr4P5.65Si0.35O24. They can be sintered in inert atmosphere without decomposition of the phases, and can be hot-pressed in inert atmosphere with C-C composites at 1250 °C without decomposition or chemical interaction. They are stable in the presence of carbon up to 1200 °C for at least a period of 4 h. They also do not show any weight loss after exposure to various temperatures up to 1200 °C for 4 h.
Microporous SiO2/Vycor membranes for gas separation
Authors: Levy R. A. , Ramos E. S. , Krasnoperov L. N. , Datta A. , Grow J. M.
Published: March 2008

In this study, porous Vycor tubes with 40 Å initial pore diameter were modified using low pressure chemical vapor deposition (LPCVD) of SiO2. Diethylsilane (DES) in conjunction with O2 or N2O were used as precursors to synthesize the SiO2 films. Both “single side” (reactants flowing on the same side of porous membrane) and “counterflow” (reactants flowing on both sides of porous membrane) reactant geometries have been investigated. The flow of H2, He, N2, Ar, and toluene (C7H8) was monitored in situ after each deposition period. Membranes modified by the “single side” reactants geometry exhibited good selectivities between small and large molecules. However, cracking in these membranes after prolonged deposition limited the maximum achievable selectivity values. Higher selectivities and better mechanical stability were achieved with membranes produced using the “counterflow” reactants geometry. Pore narrowing rate was observed to increase with oxidant flow (O2 or N2O). For membranes prepared using both oxidants, selectivities on the order of 1000: 1 were readily attained for H2 and He over N2, Ar, and C7H8. As compared to O2, the use of N2O caused improvements in both the pore narrowing rate and N2: C7H8 selectivity. Membranes prepared using the “counterflow” geometry showed no signs of degradation or cracking after thermal cycling.
Status of and prospects for organic electroluminescence
Authors: Rothberg Lewis J. , Lovinger Andrew J.
Published: March 2008

We review the device and materials science behind organic electroluminescent diodes made both using discrete evaporable molecules and spin-cast organic polymers. A great deal of progress has been made in improving the efficiencies and spectral properties of organic light-emitting diodes, and these are now adequate for many applications. More work is necessary to understand the stability and degradation of emissive and charge-transporting organics, but some systems have been shown to be stable for 104 hours at display brightness. Major challenges still face the community in terms of developing satisfactory systems design and processing techniques if organic electroluminescence is to realize either performance or economic advantages over technologies and significantly penetrate the display market. We present an analysis of the suitability of organic light-emitting diodes for various applications, and consider the materials and manufacturing obstacles that must be overcome.
Martensite transition in rapidly solidified Ti3Al−2Nb alloy
Authors: Xu R. , Cui Y. Y. , Xu D. M. , Li D. , Li Q. C. , Hu Z. Q.
Published: March 2008

The microstructure of rapidly solidified Ti3Al−2Nb alloy consists of an ordered orthorhombic α″0 phase. In the foil samples for transmission electron microscopy prepared by chemical thinning, the α″0 → β0 transformation took place due to the charging of hydrogen during thinning. The β0 → α″0 transition in the rapidly solidified alloy can be explained by a shape deformation mechanism, and the β0/α″0 interface (habit) plane is near to {334}β0. The orientation relationships between the β0 and α″0 phases are , and .
The crossover of preferred orientation in TiN film growth: A real time x-ray scattering study
Authors: Je J. H. , Noh D. Y. , Kim H. K. , Liang K. S.
Published: March 2008

The orientational crossover phenomena in a radio-frequency (rf) sputtering growth of TiN films were studied in a real-time synchrotron x-ray scattering experiment. Following the initial random nucleation and growth stage, the growth was dominated by the grains with the (002) planes aligned with the substrate surface. Surprisingly, at later stages, the grains with the (002) growth front tilted away from the surface by about 60° became dominant. The tilting of the growth front resulted in a faceted surface topology that was confirmed by an ex situ AFM study. Our x-ray results suggest that the crossover was driven by the competition between the surface and the strain energy
Electroluminescence from amorphous-silicon-based switching devices
Authors: Kuznetsov V. A. , Haneman D.
Published: March 2008

Information about the nature of formed switching structures in amorphous hydrogenated silicon has been found from features of the electroluminescence (EL) spectrum. Several small peaks have been detected in the region of 1.8 to 2.4 eV, on the shoulder of the usual a-Si : H peak at 1.32 eV. The intensity of the latter is found to depend on the voltage across the film rather than the current. The EL fine structure can be explained in terms of a model of the switching where there are small metal-rich inclusions in the film. The apparent dependence of EL intensity on voltage is explained in terms of this model with parallel current paths in the structure.
Low-load indentation behavior of HfN thin films deposited by reactive rf sputtering
Authors: Nowak R. , Li C. L. , Maruno S.
Published: March 2008

Deformation of HfN thin films deposited by the reactive sputtering method on silicon and alumina substrates has been investigated using depth-sensing indentation. The experiments performed in a low load range (2−50 mN) revealed that even extremely shallow indentations were affected by the elastic/plastic response of the substrate. The analysis of the shape of the indentation load-depth hysteresis loops and of conventional hardness data was supplemented by considerations based on the recently proposed energy principle of indentation.
Short-range ordering of Cu3Au above Tc in the topmost 80 A of a (001) face
Authors: Kimura M. , Cohen J. B. , Chandavarkar S. , Liang K.
Published: March 2008

The short-range order in the near surface region of the Cu3Au(001) face was investigated above the critical temperature by glancing-incidence x-ray diffraction, measuring the diffuse intensity throughout a two-dimensional region of reciprocal space. This intensity was analyzed quantitatively to obtain the two-dimensional Cowley–Warren short-range-order parameters and atomic displacements. Monte-Carlo simulation based on these values has revealed that the atomic configurations in the surface consist of ordered domains and clusters in a disordered matrix. There is a large number of {10} antiphase domain boundaries (APDB).
X-ray photoelectron spectroscopy studies of silicon suboxides obtained by the sol-gel method
Authors: Santucci S. , Cordeschi E. , Lozzi L. , Passacantando M. , Picozzi P. , Esposti L. Mancinelli degli
Published: March 2008

Silicon suboxides thin films obtained by sol-gel and dip-coating methods, starting from a sol containing different percentages of TEOS (tetraethoxysilane) and MTEOS (methyltriethoxysilane), were grown onto silicon substrates. The samples were annealed at 100, 300, and 500 °C, and the electronic and compositional properties of the surface were studied by x-ray photoelectron spectroscopy (XPS) detecting the Si “Auger parameter” and the valence band. The effects produced by an ion-sputtering treatment of the samples were also studied.
Copper-boron nitride interaction in hot-pressed ceramics
Authors: Hubáček Milan , Sato Tadao , Ueki Masanori
Published: March 2008

Ceramics were prepared by hot pressing of chemical mixtures of turbostratic boron nitride with copper. A positive effect of copper on boron nitride crystallization and densification has been found. Preferred orientation of boron nitride grains has been revealed in such ceramics, being opposite to general experience: the c-axis of boron nitride crystallites was arranged preferably within a plane perpendicular to the direction of uniaxial pressure. Such an arrangement is interpreted as a result of the uniaxial compression of the boron nitride grains extensively growing within the c crystallographic axis.
Finite size corrections for the Johnson–Mehl–Avrami–Kolmogorov equation
Authors: Levine L. E. , Narayan K. Lakshmi , Kelton K. F.
Published: March 2008

The Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation is frequently used to describe phase transformations involving nucleation and growth. The assumptions used in the derivation of this equation, however, are frequently violated when making experimental measurements; use of the JMAK equation for analyzing such data can often produce invalid results. Finite-size effects are among the most serious of these problems. We present modified analytic JMAK equations that correct for the finite-size effects and are roughly independent of both the sample shape and the shape of the growing nuclei. A comparison with computer simulations shows that these modified JMAK equations accurately reproduce the growth behavior over a wide range of conditions.
Reactive phase formation in sputter-deposited Ni/Al multilayer thin films
Authors: Barmak K. , Michaelsen C. , Lucadamo G.
Published: March 2008

We have investigated reactive phase formation in magnetron sputter-deposited NiyAl multilayer films with a 1 : 3 molar ratio and various periodicities, L, ranging from 320 nm down to a codeposited film with zero effective periodicity. The films were studied by x-ray diffraction, differential scanning calorimetry, electrical resistance measurements, and transmission electron microscopy. We find that Ni and Al have reacted during deposition to form the B2 NiAl phase and an amorphous phase. The formation of these phases substantially reduces the driving force for subsequent reactions and explains why nucleation kinetics become important for these reactions. Depending on the periodicity, these reactions result in the formation of NiAl3 or Ni2Al9 followed by NiAl3. Detailed calorimetric analysis reveals differences in the nucleation and growth behavior of NiAl3 compared with other studies.
Epitaxial growth of aluminum nitride layers on Si(111) at high temperature and for different thicknesses
Authors: Malengreau F. , Vermeersch M. , Hagège S. , Sporken R. , Lange M. D. , Caudano R.
Published: March 2008

We present the epitaxial growth by rf reactive sputtering of aluminum nitride on Si(111) at high temperature. The grain size of the obtained films was sufficient to obtain a good low energy electron diffraction (LEED) pattern from which we determined a lattice parameter of 3.1 Å, indicative of fully relaxed films. The surface of the film was examined in situ by Auger electron spectroscopy (AES); no contamination was detected, with the exception of low levels of oxygen. The film and its interface were studied by high resolution electron energy loss spectroscopy (HREELS), x-ray photoelectron spectroscopy (XPS) depth profiling, and transmission electron microscopy (TEM). Again, a low concentration of oxygen and no carbon contamination were detected by XPS. Three different growth methods were applied to the deposition of aluminum nitride at high temperature. The obtained films were studied in order to determine the influence of the methods on the interface, on the ‘bulk structure’ of the film, and on its surface. Each has been shown to have particular characteristics. The first one, performed at a temperature of 1000 °C, and including a cleaning of the surface by exposure to Al flux, was characterized by an interfacial layer with no long-range order and increasing the interaction between the film and the substrate. The second growth consisting of deposition at the same high temperature has shown a good surface quality for very thin layers (<50 Å ) and the absence of an interfacial layer. The last method, based on a first step of growth at low temperature (700 °C), resulted in good quality thick layers which allowed us to determine the infrared dielectric constants of aluminum nitride by HREELS.
Low temperature synthesis of lead titanate by a hydrothermal method
Authors: Moon Jooho , Li Tuo , Randall Clive A. , Adair James H.
Published: March 2008

Alkoxide-based hydrothermal powder synthesis of lead titanate was investigated. The objective of this work was to lower the synthesis temperature. By modifying titanium isopropoxide with acetylacetone during solution mixing, the phase-pure lead titanate with perovskite structure was synthesized at temperatures as low as 150 °C. It was determined that the pH of the hydrothermal reaction medium and the initial Pb/Ti ratio are critical factors in forming stoichiometric PbTiO3. When the pH of the initial feedstock is above 14 and the Pb/Ti ratio is greater than 1.5, a phase-pure PbTiO3 can be obtained. The modification of titanium alkoxide gave rise to the formation of a stable complex against hydrolysis and eventually reduced the synthesis temperature significantly. A possible formation mechanism for PbTiO3 is the dissolution-recrystallization from an amorphous precursor to a well-crystalline product as originally proposed by Rossetti et al. Hall–Williamson analysis was also performed on the hydrothermally derived PbTiO3 to interpret the systematic peak broadening and asymmetry for {001} reflections, unlike the commercial PbTiO3. It was observed that the strain in the c-axis direction is much higher than that in the a-axis direction while the domain sizes for both directions are similar. This strain anisotropy exerted in the particles may indicate a unique domain structure in the hydrothermally synthesized particles in which either only 180° domains exist or possibly only a single domain.
Sintering of the ultrahigh pressure densified hydroxyapatite monolithic xerogels
Authors: Majling Ján , Znáik Peter , Palová Angela , Svetík Stefan , Kovalík Stefan , Agrawal Dinesh K. , Roy Rustum
Published: March 2008

Dense and translucent ceramics were prepared by sintering of cylindrical preforms of hydroxyapatite extruded from xerogels. Extruded specimens were dried as monoliths and then consolidated by applying cold isostatic pressure, ranging from 500 to 1500 MPa. Upon heating the samples began to densify at 610 °C, and the densification/sintering was completed at 870 °C as was evidenced by the dilatometry plot indicating no further shrinkage. The sintered specimens thus formed were translucent in appearance. Further heating of the samples up to 1200 °C resulted in their “bloating” or creation of pores in the originally dense matrix. Pore creation within the structure is reproducible, it proceeds from the surface to the interior of the sample, and its spreading can be thermally controlled. Pore evolution within the single phase dense polycrystalline material is not related to the frequently occurring phenomenon of microcracking in ceramics during cooling.
Balance of graphite deposition and multishell carbon nanotube growth in the carbon arc discharge
Authors: Ajayan P. M. , Redlich Ph. , Rühle M.
Published: March 2008

Except for atomistic models of individual carbon nanotube growth, there is still no precise understanding of the large scale deposition of carbon during the arc discharge. We study the microstructure of cathode deposits in detail using scanning electron microscopy, focusing on two distinct regimes found in the deposits having different large scale morphology. The shell grown circumferentially consists of extended graphite layers with preferred orientation, and the structure reveals close similarity to pyrolitic graphite. The core region is a porous assembly of nanotubes and nanoparticles. We conclude that closed nanostructures self-assemble from a dense carbon vapor, whereas pyrographitic shell grows by continuous deposition on exposed substrates.