bluuebunny/crossref_metadata_2025 huggingface dataset:
Precipitation from a reactive silicate on MgO
Authors: Yanina S. V. , Carter C. Barry
Published: March 2008

For this paper, high-temperature interactions between a reactive silicate liquid and the (001) surface of a MgO single crystal were studied. The paper discusses the influence of the morphology of the MgO surface on both the dewetting of a silicate liquid and the mechanism of precipitation of excess MgO out of this silicate liquid. Alternative pathways were considered for MgO precipitation; it may occur by nucleation and growth of plateaus on the MgO surface or by MgO absorption at surface steps. On flat MgO(001) surfaces, precipitation of MgO from the continuous layer of silicate liquid led to the formation of plateaulike precipitates. Precipitation from disconnected silicate droplets onto stepped MgO(001) surfaces resulted in the growth of ridges at steps on the surface.
Influence of hole carrier density and sintering temperature on the electronic properties of magnetoresistive La0.7Pb0.3Mn1⊟xRuxO3 (0.0 ≤ x ≤x 0.4)
Authors: Sahu Ranjan Kumar , Rao Manju Lata , Manoharan Solomon Sundar , Elefant Dieter , Verges Peter , Schneider Claus M.
Published: March 2008

A novel magnetic pair-making interaction between Mn and Ru shows a strong correlation between the magnetic ordering and electronic transport, which was well exemplified in the investigation of bulk polycrystalline samples of La0.7Pb0.3Mn1⊟xRuxO3 and La0.6Pb0.4Mn1⊟xRuxO3, where 0.0 ≤ x ≤ 0.4. The metal-insulator transition (Tρ) complementing the Curie temperature (Tc) was observed up to 30% of Ru in La0.7Pb0.3Mn1⊟xRuxO3, and extended up to 40% of Ru in La0.6Pb0.4Mn1⊟xRuxO3, showing a unique double-exchange ferromagnetic exchange interaction between Mn and Ru ions. An upturn in resistance due to charge carrier localization at low temperatures (T<0.5 Tc) for more than 20% Ru doping was due to a dominant hole carrier density contribution rather than to grain boundary effects as inferred from the scanning electron microscopy and energy dispersive x-ray studies of the samples sintered at 1200 and 1400 °C. The charge localization effect of the eg electrons was removed by tuning the hole carrier density as demonstrated in the La0.6Pb0.4Mn1⊟xRuxO3 samples. Long range correlations between magnetism and transport in this series was attributed to the presence of mixed valence Ru(IV/V) and Mn(III)/(IV) pair, which shows a unique double exchange mediated interaction.
Polymer matrix templated synthesis: Cobalt ferrite nanoparticles preparation
Authors: Hoh J. C. , Yaacob Iskandar I.
Published: March 2008

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by polymer matrix templated synthesis. Synthetic ion-exchange resins were used as hosts for the coprecipitation of cobalt ferrite where the nanopores of the resin acted as the constrained environment. The weight fraction of the particles within the resin was roughly 16%. X-ray diffraction analysis indicated that cobalt ferrite crystallites were about 1–7 nm in diameter. Magnetic properties measured using an alternating gradient magnetometer showed the particles (prepared using initial salt solution ratio of Fe3+:Co2+ of 1.5:1.0) were superparamagnetic with magnetization M (of the particle-resin system) in the range of 3.0 to 4.4 emu/g at 10 kOe of applied field. The least upper bound of the magnetic size was about 3 nm in diameter. Ratios of Fe3+ to Co2+ within the matrix of the resin before and after precipitation were investigated by x-ray fluorescence spectrometry and were found to be sensitive to the initial salt solution mixture. The ratio Fe3+:Co2+ of 1.5:1.0 was found to be a better mixture in terms of magnetization value. Spherical shape cobalt ferrite particles 2–8 nm in diameter were observed using transmission electron microscopy. The close agreement between the physical and crystallite size indicated that the particles are largely monocrystals.
Growth of silver nanowires using mica structure as a template and ultrahigh dielectric permittivity of the nanocomposite
Authors: Mukherjee P. K. , Chakravorty D.
Published: March 2008

Fluorphlogopite mica crystallites of dimensions in the range 0.5 to 24 µm were grown within silicate glass of suitable compositions by heat treatment at 1168 K. After an ion exchange treatment (K+ ⇆ Ag+) the specimens were subjected to an electrodeposition reaction. With the optimum concentration of K+ ions in the precursor glass, electrodeposition brought about the growth of silver nanowires about 0.5 nm diameter within the nanochannels of the fluorphlogopite mica structure. By applying a voltage pulse of 20 volts of duration 3 s, break junctions could be induced in the nanowires. A high dielectric constant of around 1.0 × 107was found in the resultant specimen. This was shown to be quantum mechanical in origin and arose due to the presence of metal filaments about 1280 nm in length. An asymmetric voltage–current characteristic was recorded at 114 K in the case of the specimen containing silver nanowires grown within the mica structure. This is believed to arise due to formation of a nanojunction between the metal nanowire and silver nanoparticles with diameters of less than 3 nm. The latter were earlier shown to behave as insulators
Growth, microstructure, charge transport, and transparency of random polycrystalline and heteroepitaxial metalorganic chemical vapor deposition-derived gallium–indium–oxide thin films
Authors: Wang Anchuan , Edleman Nikki L. , Babcock Jason R. , Marks Tobin J. , Lane Melissa A. , Brazis Paul R. , Kannewurf Carl R.
Published: March 2008

Gallium–indium–oxide films (GaxIn2⊟xO3), where x = 0.0–1.1, were grown by low-pressure metalorganic chemical vapor deposition using the volatile metalorganic precursors In(dpm)3 and Ga(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato). The films were smooth (root mean square roughness = 50–65 Å) with a homogeneously Ga-substituted, cubic In2O3 microstructure, randomly oriented on quartz or heteroepitaxial on (100) yttria-stabilized zirconia single-crystal substrates. The highest conductivity of the as-grown films was found at x = 0.12, with σ = 700 S/cm [n-type; carrier density = 8.1 × 1019 cm⊟3; mobility = 55.2 cm2/(V s); dσ/dT<0]. The optical transmission window of such films is considerably broader than that of Sn-doped In2O3, and the absolute transparency rival or exceeds that of the most transparent conductive oxides known. Reductive annealing, carried out at 400–425 C° in a flowing gas mixture of H2 (4%) and N2, resulted in increased conductivity (σ 1400 S/cm; n-type), carrier density (1.4 × 1020 cm⊟3), and mobility as high as 64.6 cm2/(V s), with little loss in optical transparency. No significant difference in carrier mobility or conductivity is observed between randomly oriented and heteroepitaxial films, arguing in combination with other data that carrier scattering effects at high-angle grain/domain boundaries play a minor role in the conductivity mechanism.
Nanostructure and mechanical properties of WC–SiC thin films
Authors: Endrino Jose L. , Krzanowski James E.
Published: March 2008

The mechanical properties of WC–SiC thin films deposited by dual radio frequency magnetron sputtering were investigated. The films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), and transmission electron microscopy (TEM) to evaluate the details of the microstructure and degree of amorphization. The results indicate that small additions of SiC (<25%) can significantly increase hardness compared to a pure WC film, but higher SiC contents do not strongly affect hardness. XRD studies show the SiC had a disordering effect. TEM results showed that WC films had coarse porous structure, but films with a low silicon carbide content (approximately 10 to 25 at%) had a denser nanocrystalline structure. Samples with greater than 25% SiC were amorphous. The initial hardness increase at lower SiC contents correlated well with the observed densification, but the transition to an amorphous structure did not strongly affect hardness.
Synthesis and dielectric properties of barium tantalates and niobates with complex perovskite structure
Authors: Kolodiazhnyi T. , Petric A. , Belous A. , V'yunov O. , Yanchevskij O.
Published: March 2008

Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1/3B"2/3)O3, where B′ = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed. It was found that all the studied complex perovskites attained high degrees of 1:2 cation ordering at temperatures specific to each composition. A high temperature order–disorder phase transition in Ba(Zn1/3Nb2/3)O3 occurred below 1380 °C. Ba(Ni1/3Nb2/3)O3 (BNN) and Ba(Mg1/3Nb2/3)O3 (BMN) pervoskites remained 100% ordered at temperatures as high as 1500 and 1620 °C, respectively. It was found that in BMN and BNN extrinsic factors, such as the second phase (i.e., Ba3Nb5O15) and point defects, dominated the dielectric loss at microwave frequencies. Ba(Mg1/3Ta2/3)O3 (BMT) remained single phase up to 1630 °C. Above this temperature, the Ba3Ta5O15 second phase was detected. A decrease in the 1:2 cation ordering and increase of dielectric loss in BMT occurred at sintering temperatures above 1590 °C. It was also revealed by electron paramagnetic resonance that all samples studied contained a substantial amount of paramagnetic point defects. These defects contributed to extrinsic dielectric loss at microwave frequencies, thus degrading the Q factor.
Mechanically induced devitrifications of ball-milled Zr70Pd20Ni10 glassy alloy powders
Authors: El-Eskandarany M. Sherif , Saida J. , Inoue A.
Published: March 2008

Mechanical alloying using a high-energy ball milling technique was used to fabricate a single glassy phase of Zr70Pd20Ni10 alloy powders after 100 h milling time. Annealing the glassy powders at a temperature just below the crystallization onset temperature led to thermally enhanced devitrification and the formation of a metastable big-cube phase with a lattice constant of 1.2289 nm. The same metastable phase was obtained upon subjecting the end product of the glassy powders to further ball milling time (150 h). This metastable big-cube phase could no longer withstand the shear and impact stresses generated by the milling media and transformed into a new metastable phase of face-centered cubic Zr70Pd20Ni10. The lattice constant of this metastable phase was calculated to be 0.56838 nm. These metastable phases are new and have never been, so far as we know, reported for the ternary Zr–Pd–Ni system or its binary phase relations.
Microstructure and thermal stability of an ultrafine Al/Al2O3 composite
Authors: Yang Zhiqing , He Lianlong , Chen Ji , Cong Hongtao , Ye Hengqiang
Published: March 2008

Studies were carried out on the microstructure and thermal stability of an ultrafine Al/Al2O3 composite with high strength and low density. Transmission electron microscopy indicated that Al2O3 shells remained undeformed below 550 °C, which limited grain growth of Al. Both transmission electron microscopy and x-ray diffraction analysis indicated that no obvious grain growth of Al with time occurred upon annealing at 620 °C. After almost all the alumina shells were destroyed following annealing at 620 °C, the Al2O3 fragments with various morphologies distributed in the material could still limit the migration of Al grain boundaries to increase the thermal stability of the material. After Al melted and resolidified, the grain sizes of Al were still about 200 nm. The bulk composite sample showed good dimensional stability. Even if the Al grains melted, the network of Al2O3 fragments kept the sample from deforming due to the wetting of Al2O3 network with liquid Al.
Effect of combined metal-carbon additions on the microstructure and structure of Sm2Fe17
Authors: Meacham B.E. , Shield J.E.
Published: March 2008

The effect of combined alloying additions on the structure and scale of rapidly solidified Sm–Fe alloys was investigated. Transition metal additions tend to promote the formation of the disordered TbCu7-type structure in Sm2Fe17 alloys, as determined by monitoring the long-range order parameter. Essentially no order was observed for M = Ti, Zr, V, or Nb. Thus, the structure was close to the prototypical TbCu7-type structure. With M = Si, a large amount of order was observed (S = 0.62), resulting in a structure closer to the well-ordered Th2Zn17-type. The microstructural scale was also affected by alloying. In this case, refinement depended on the substituent and also on carbon for microstructural refinement. The scale of the as-solidified grain structures ranged from 100 nm for SiC-modified alloys to 13 nm for NbC-modified alloys. The degree of refinement was directly related to the atomic size of the M addition. The refinement was the result of solute partitioning to grain boundaries, resulting in a solute drag effect that lowered the growth rates.
Surface-oxidation studies of cube-textured, pure nickel to form NiO as a potential YBa2Cu3O7−x-coated conductor buffer layer
Authors: Lockman Z. , Berenov A. , Goldacker W. , Nast R. , deBoer B. , Holzapfel B. , MacManus-Driscoll J.L.
Published: March 2008

The growth of nickel oxide (NiO) on {100}〈001〉 cube textured, rolling-assisted biaxially textured substrates (RABiTS) of pure nickel was studied. Single-phase (100) NiO formed only in a narrow temperature range at 1250 ± 5 °C. At lower or higher temperatures, other orientations, namely (111), (311), and (220), also formed. At 1250 °C, practically single phase (100) NiO was observed for short oxidation times t of 0.2–10 min (oxide thickness < 10 μm). For 10 < t < 120 min, small quantities of (111) NiO formed in addition to (100), but near-single-phase (100) NiO formed once again after oxidation for >150 min (thickness > 35 μm). The ratio of (100) to (111) textures with oxidation time is explained in terms of epitaxial constraints, growth rates, and oxygen absorption on the (100) and (111) grains. The optimum oxidation conditions are oxidation for approximately 0.5 min at 1250 °C in flowing oxygen, yielding (100) NiO, a few microns in thickness, and root-mean-square roughness of approximately 40 nm on the length-scale of the grain size.
Sol-gel synthesis of textured lanthanum titanate thin films
Authors: Sandstrom Mary M. , Fuierer Paul
Published: March 2008

Control over crystallographic orientation in thin films is important, particularly with highly anisotropic structures. Because of its ferroelectric nature, the layered perovskite La2Ti2O7has interesting piezoelectric and electrooptic properties that may be exploited when films are highly textured. Sol-gel films with an orientation factor of greater than 95% were fabricated without relying on epitaxial (lattice-matching) growth from the substrate. Film orientation and crystallization were confirmed by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and optical measurements. The particle sizes in all precursor solutions were measured by dynamic light scattering experiments. Experimental results indicate that film orientation is a function of precursor solution concentration, size of the molecular clusters in the solution, and film thickness.
Fabrication of mesoporous CdS nanorods by chemical etching
Authors: Yang Lin , Yang Jian , Wang Zheng-Hua , Zeng Jing-Hui , Yang Li , Qian Yi-Tai
Published: March 2008

One-dimensional CdS nanocrystallites were used as precursors for preparation of mesoporous CdS nanorods through an ion-exchange process at room temperature. The results from x-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive x-ray analysis, and x-ray powder diffraction techniques showed that Ag+ did not affect the electronic structure of CdS or cause the disorder of crystal structure although the product contained a considerable amount of Ag2S. The visible absorption of Ag2S nanoparticles in the mesoporous structure led to the result that the intensities of Raman scattering peaks of the mesoporous nanorods were weaker than those of CdS initial nanorods.
Room-temperature preparation of biaxially textured indium tin oxide thin films with ion-beam-assisted deposition
Authors: Thiele Karola , Sievers Sibylle , Jooss Christian , Hoffmann Jörg , Freyhardt Herbert C.
Published: March 2008

Biaxially aligned indium tin oxide (ITO) thin films were prepared by an ion-beamassisted deposition (IBAD) process at room temperature. Films with a transmittance at 550 nm of 90% and an electrical resistivity of 1.1 × 10−3 Ωcm for 300 and 250 nm thickness were obtained. Investigations of the texture evolution during IBAD film growth were carried out and compared to the well-established texture development in yttria-stabilized zirconia. An in-plane texture of 12.6° full width at half-maximum (FWHM) for a 1-μm-thick IBAD-ITO film was achieved. The quality of these films as electrically conductive buffer layers for YBa2Cu3O7-δ (YBCO) high-temperature superconductors was demonstrated by the subsequent deposition of high-currentcarrying YBCO films by thermal co-evaporation using a 3–5-nm-thick Y2O3 interlayer.A Jc of 0.76 MA/cm2 (77K, 0 T) was obtained for a 1 × 1 cm sample with ITO of 20° FWHM.
Canonical-glass-like behavior of the polycrystalline relaxor ferroelectric (1–x)PbMg1/3Nb2/3O3–xPbZrO3: Heat-capacity study
Authors: Singh Gurvinderjit , Tiwari V.S. , Kumar Arun , Wadhawan V.K.
Published: March 2008

A solid solution of lead magnesium niobate (PMN), a relaxor ferroelectric, with lead zirconate (PZ), an antiferroelectric, gives rise to a system that behaves like a relaxor ferroelectric for lower concentrations of PZ, and like a normal ferroelectric above 50% substitution by PZ. This paper reports the heat-capacity behavior of (1 –x)PMN–xPZ for the composition rangex= 0.30 to 0.95 and temperature range 300–600 K. It was observed that, although the atomic structure of the material is basically crystalline throughout, with sharp x-ray diffraction peaks, the crossover from normal–ferroelectric behavior to relaxor–ferroelectric behavior (on decreasingx) is accompanied by a matching crossover from crystalline behavior to glassy behavior, as exhibited in the heat-capacity plots. In other words, the heat-capacity curves for the relaxor compositions bear resemblance to those observed for canonical or conventional glasses, with the glass-transition temperature and the continuous step in specific heat changing gradually as a function of the composition parameterx. However, not all properties match those for canonical glasses. For example, soaking for 24 h at a temperature or 10 to 20 K below the mean glass-transition temperature does not raise the specific heat to a value nearly equal to the value in the unfrozen state. Similarly, the glass-transition temperature (for 0.7PMN–0.3PZ) increases, though only marginally (from 337 K to 343 K), when the rate of heating across the transition is increased by a factor of 50 (from 0.1 K per minute to 5 K per min.). Further, the temperature interval ΔT over which most of the glass transition occurs in the relaxor ferroelectric is typically as large as 30–40 K, compared to only about 10 K for canonical glasses.
Temperature dependence of piezoelectric properties of 0.67 Pb(Mg1/3Nb2/3)O3–0.33 PbTiO3 single crystals
Authors: Wang Ping-chu , Pan Xiao-ming , Li Dong-lin , Song Yuan-wei , Luo Hao-su , Yin Zhi-wen
Published: March 2008

Piezoelectric properties k33 and d33 of 0.67 Pb(Mg1/3Nb2/3)O3–0.33 PbTiO3 single crystals grown by a modified Bridgman method were measured in the temperature range of 20–150 °C. Recoverability of the properties after the samples were heated to 110 °C, above the ferroelectric–ferroelectric (F–F) phase transition temperature of the composition, was found. From 20 to approximately 80 °C, k33 increases slightly, while d33 is almost doubled. Between approximately 90 and 100 °C, k33 decreases sharply to roughly a level of PZT-5 ceramics and d33 decreases to about 700 pC/N. They increase again with further increase of temperature; at 140 °C they attain 0.74 and approximately 1300 pC/N, respectively, and then decrease quickly and approach zero at about 150 °C. When heating to 110 °C followed by cooling to room temperature, the property decay is small. After more than one dozen heating–cooling cycles, k33 and d33 tend to be stable at 0.89 and approximately 1220 pC/N, respectively. The results might be helpful for device design and applications of PMN–PT single crystals.
Interaction of surface acoustic waves and ultraviolet light in ZnO films
Authors: Sharma Parmanand , Kumar Sanjeev , Sreenivas K.
Published: March 2008

The frequency response of a 37 MHz bulk LiNbO3 surface acoustic wave (SAW) filter with a 200-nm-thick ZnO overlayer exhibited a downshift in the frequency with ultraviolet (UV) light due to acoustoelectric interactions between the photo-generated carriers in the semiconducting ZnO and the surface acoustic waves. In contrast, a 36 MHz ZnO thin film SAW delay-line with insulating ZnO films exhibited an upshift in the frequency. The response was more pronounced at higher harmonics (130–315 MHz) and was attributed to changes in the elastic/dielectric properties in the upper surface layer of ZnO. A linear change in the frequency with UV intensity shows immense applicability for wireless ultraviolet sensor applications.
Influence of the emulsification conditions on the microstructures and electrochemical characteristics of spinel lithium manganese oxide powders
Authors: Lu Chung-Hsin , Lin Yueh
Published: March 2008

Lithium manganese oxide powders (LiMn2O4) with a spinel structure were synthesized via an optimized water-in-oil emulsion process. The influence of the emulsification conditions on the microstructures and physicochemical properties of LiMn2O4 powders was investigated. The phase purity of the synthesized powders significantly depends on the water-to-oil volume ratio in the emulsion. Increasing the water-to-oil ratio tends to decrease the stability of the emulsion that in turn leads to a segregation of water and oil phases. The unstable emulsion system results in the formation of an impure phase—Li2MnO3—that markedly decreases the charge and discharge capacities of the cathode materials. When water/oil volume ratio equals 1/5 or 1/10, monophasic spinel powders are formed at temperatures as low as 400 °C. In addition, decreasing the concentration of the aqueous phase substantially reduces the particle size of LiMn2O4 powders. Nanometered-LiMn2O4 powders with a particle size of 50 nm are obtained when the concentration of the aqueous phase is 1.0 M and the water-to-oil volume ratio is 1/5. Decreasing the particle size of LiMn2O4 powders was demonstrated to effectively increase the specific capacity and improve the cyclability of LiMn2O4 powders.
Polymorphism in ZrP crystal
Authors: Iwanaga Hiroshi , Hashishin Takeshi , Motojima Seiji , Ichihara Masaki , Takeuchi Shin
Published: March 2008

Electron microscopy observations of α–ZrP whiskers with the NaCl structure, grown by chemical vapor deposition at 1300 °C, showed that there exists a hexagonal structure region (a = 0.369 nm and c = 1.248 nm) near the surface of the whiskers. High-resolution lattice image observations revealed that the method of stacking the eight-layered hexagonal structure is different from the reported hexagonal β–ZrP. In addition to the eight-layered structure, 12-layered and 16-layered structures were also observed, indicating a variety of ZrP polymorphisms.
Synthesis and characterization of TiO2 nanocrystalline powder prepared by homogeneous precipitation using urea
Authors: Seo Dong Seok , Kim Hwan , Jung Hang Chul , Lee Jong Kook
Published: March 2008

TiO2 nanocrystalline powder was synthesized by homogeneous precipitation method using urea, and its characteristics were investigated through comparison with the powder prepared by conventional precipitation using ammonia. The homogeneously precipitated powder was anatase-type TiO2 with a particle size of 4–5 nm and a uniform spherical particle shape. The fact that the transformation from anatase to rutile was prohibited at elevated temperatures in the homogeneously precipitated powder can be useful to prepare anatase-type TiO2 thin films by calcination at high temperatures. With increasing heat-treatment temperature, the particle size of the homogeneously precipitated powder was smaller than that of the conventionally precipitated powder, and the particle shape was more uniform. The homogeneously precipitated powder showed good photocatalytic activity for Ag ion photoadsorption because the powder had both good crystallinity and a large specific surface area of 280 m2/g.
Electron microscopy study of tin whisker growth
Authors: LeBret J. B. , Norton M. G.
Published: March 2008

The growth of tin whiskers formed on sputtered tin layers deposited on brass was studied using electron microscopy. The occurrence of whiskers appeared to be largely independent of the macroscopic stress state in the film; rather it was microscopic compressive stresses arising from the formation of an intermetallic phase that appeared to be the necessary precursor. Whisker morphology was a result of whether nucleation had occurred on single grains or on multiple grains. In the latter case, the whiskers had a fluted or striated surface. The formation of whiskers on electron transparent samples was demonstrated. These samples showed the whiskers were monocrystalline and defect free, and that the growth direction could be determined.
Strong green and red emission of a newly developed calcium fluoroaluminate: Eu3+ phosphor
Authors: Sahoo R. , Bhattacharya S. K. , Debnath R.
Published: March 2008

A phase of new bichromatic (green, red) phosphor Ca2Al3O6F:Eu(III), was found to grow in a small fraction along with Ca5(PO4)3F:Eu(III) phase if aluminum is previously added to the reaction mixture of the latter and flourish to a sizable concentration on subsequent heat treatment. The luminescence spectrum of the as-prepared sample, where Ca5(PO4)3F:Eu(III) is the dominant phase, shows a strong band at 612 nm along with a series of less intense bands at 573, 584, 644, and 692 nm due to different 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions and indicates that the presence of aluminum in the system forces the Eu(III) ions to occupy exclusively one type of site rather than multiple types of sites. As the aluminate phase grows, a strong green emission band around 520 nm due to the 5D2 → 7F3 transition of Eu(III) occurs concomitant with a splitting of almost all the 5D0 → 7FJ bands. The excitation spectrum of the green emission (520 nm) shows a strong absorption band at 393 nm, and the electron spin resonance spectrum of this material shows existence of a fluorine-related hole center of (F2n)− type in the matrix. It is argued that the (F2n)− holes are localized in the interstitial of the Ca2Al3O6F phase near the calcium-substituted Eu(III) ions to maintain the charge balance and form a complex with the latter, which plays a vital role in the process of green emission.
Resistance to vacuum ultraviolet irradiation of nano-TiO2 modified carbon/epoxy composites
Authors: Jiang Lixiang , He Shiyu , Yang Dezhuang
Published: March 2008

Nano-TiO2 modified composites, including TiO2 + EP648 and M40/TiO2 + EP648, were fabricated, in which the nano-TiO2 particles were dispersed in an EP648 epoxy matrix using a high-speed shearing emulsification technique. A jet type of vacuum ultraviolet (VUV) source was used to simulate the VUV spectrum in space and acquire various doses of VUV irradiation. In terms of the changes in specific-area mass loss and surface morphology, the resistance to VUV irradiation of the TiO2 + EP648 and M40/TiO2 + EP648 nanocomposites was evaluated. Experimental results showed that compared to the EP648 epoxy and M40/EP648 composite, the specific-area mass loss of the TiO2 + EP648 was decreased by 44% and that of M40/TiO2 + EP648 composite by 38%, respectively. By increasing the dose of VUV irradiation, the internal layer shear strength of the M40/TiO2 + EP648 increased gradually, while that of the M40/EP648 showed a decreasing trend. After irradiation, the surface of the M40/TiO2 + EP648 changed a little, but that of the M40/EP648 was damaged severely. It was indicated by means of scanning electron microscopy and atomic force microscopy observations that the VUV damage occurred mainly in the epoxy matrix, while the carbon fibers showed good resistance to irradiation.
Fabrication of high-critical current density Yba2Cu3O7−δfilms using a fluorine-free sol gel approach
Authors: Xu Y. , Goyal A. , Rutter N. A. , Shi D. , Paranthaman M. , Sathyamurthy S. , Martin P. M. , Kroeger D. M.
Published: March 2008

Superconducting Yba2Cu3O7−δ(YBCO) films with critical transition temperatureTc(0) of 90 K were fabricated via a fluorine-free, metal trimethylacetate based sol-gel route. Precursor films were spin-coated onto single-crystal (001) LaAlO3(LAO) and (001) SrTiO3(STO) substrates. Optimization of the burnout process resulted in films with excellent out-of-plane and in-plane texture. Transport critical current densities,Jc, of 1.6 and 1.1 MA/cm2were obtained at 77 K in self-field on films grown on LAO and STO substrates, respectively. This is the first demonstration of high-JcYBCO film fabrication using a fluorine-free,ex-situprocess.
Polarization of plastic deformation modes in polysynthetically twinned TiAl crystals
Authors: Paidar V. , Kishida K. , Yamaguchi M.
Published: March 2008

Polarization of deformation twinning (its propagation in a certain sense but not in the opposite one) is taken for granted. However, the same phenomenon can occur for a superdislocation glide as well, as is demonstrated in this paper. The consequences for plastic deformation of polysynthetically twinned TiAl crystals with the lamellar interfaces parallel to the loading direction are discussed. It is not the interface itself that is an obstacle for propagating deformation but also the fact that a deformation mode with the parallel Burgers vector cannot be activated in the neighboring lamella due to the directionality of superdislocation motion leading to additional stress increase.
Ultrasound-induced change of microstructure and photochromic properties of polyacrylamide thin films containing a polyoxometalate
Authors: Feng Wei , Zhang Tierui , Liu Jun , Lu Ran , Zhao Yingying , Yao Jiannian
Published: March 2008

Novel photochromic nanocomposite thin films were prepared by entrapping polyoxometalate in a polyacrylamide matrix via the ultrasound technique. The ultrasound irradiation has a great effect on the microstructure and photochromic properties of the hybrid films. The polyoxometalate nanoparticles are finely dispersed in the polymer matrix after ultrasound treatment, instead of agglomeration in the unirradiated film with ultrasound. Consequently, the photochromic behaviors of the hybrid films can be controlled from irreversible heteropolybrown to reversible heteropolyblue by ultrasound. The influence of ultrasound on microstructure and photochromic properties is due to the sonochemical controlling interfacial interactions in the hybrid system.
Photocatalytic properties of rutile TiO2 acicular particles in aqueous 4-chlorophenol solution
Authors: Kim Sun-Jae , Lee Jong-Kuk , Lee Eun Gu , Lee Hee-Gyoun , Kim Seon-Jin , Lee Kyoung Sub
Published: March 2008

The photocatalytic properties of TiO2 rutile powder with acicular primary particles were characterized using the photocatalytic reaction in aqueous 4-chlorophenol (4CP) solution and compared to those of TiO2 anatase with almost the same surface area of approximately 200 m2g. The characteristics of commercial P-25 TiO2 powders with the surface area of approximately 55 m2/g were also compared to rutile and anatase powders. The rutile phase powders surpassed both anatase and P-25 ones in decomposition rate for 4CP. The excellent photo-oxidative ability of the powder was dependent on the specific powder-preparation method, which led to a direct crystallization in aqueous solution, regardless of the crystalline structures of the powders.
Thermally stable high-strength porous alumina
Authors: Jayaseelan D. Doni , Ueno S. , She J. H. , Ohji T. , Kanzaki S.
Published: March 2008

A two-step heating schedule involving pulse electric current sintering, a kind of pressure-assisted vacuum sintering, and a subsequent postsintering in air was used to fabricate sintered porous alumina compacts. During pressure-assisted vacuum sintering, a dense microstructure of the Al2O3–C system was obtained and in the second stage (i.e., during postsintering in air at different temperatures ranging from 800 to 1300 °C for more than 10 h) carbon particles present in the Al2O3–C system burned out to form a highly porous Al2O3 compact. In this work, the porosity (30%) was successfully controlled and did not change with the postsintering temperature. The intriguing aspect of this study is that porous alumina compacts are fabricated with high strength and remain stable against the postsintering temperature and extended soaking time. This behavior merits the material fabricated here as a potential porous compact, mechanically withstanding for high-temperature applications.
Raman study of gaseous bubble inclusions in bismuth germanate and bismuth germanium silicon oxide single crystals
Authors: Vaithianathan V. , Kesavamoorthy R. , Kannan C. V. , Santhanaraghavan P. , Ramasamy P.
Published: March 2008

Gaseous bubble inclusions in bismuth germanate (BGO) and bismuth germanium silicon oxide (BGSO) crystals were studied by means of Raman spectroscopy at room temperature. Their Raman spectra in the range from 60 to 70 cm−1 showed three peaks for the rotational Raman modes of O2 and N2. Vibrational Raman modes of O2 and N2 were also recorded for BGO and BGSO crystals. It was found that all the rotational and vibrational modes were blue shifted from those of free molecules due to the hydrostatic pressure in the bubbles. Internal pressure in the bubbles was estimated from the rotational and vibrational Raman mode frequencies. O2 gas pressure in the bubble was estimated as 140 GPa, and N2 gas pressure, as 31 GPa. The pressure coefficient of the vibrational mode frequency of O2 (0.368 cm−1/GPa for O2 vibrational mode of 1580 cm−1) and N2 (0.322 cm−1/GPa for N2 vibrational mode of 2331 cm−1) was also obtained from the blue shift and the calculated bubble pressure.
Fabrication of TiO2 nanospheres by template replication in porous carbon networks
Authors: Kim J. C. , Kim Y. N. , Chi E. O. , Hur N. H. , Yoon S. B. , Yu J-S.
Published: March 2008

A silica-colloidal template approach was used to prepare monodisperse nanospheres of TiO2. Close-packed arrays of silica spheres were infiltrated with a sucrose precursor used as a source of carbon. The infiltrated sucrose was carbonized by calcination at 800 °C in flowing argon. After removal of the silica spheres by washing with HF, a porous carbon replica remained. The resulting pores in the replica were then filled with a chloroform solution of titanium alkoxide. Nanospheres of TiO2 approximately 200 nm in diameter were obtained after calcination of the organic component at 600 °C in an argon atmosphere and subsequent sintering in air at 700 °C.
Highly localized acoustic emission monitoring of nanoscale indentation contacts
Authors: Tymiak Natalia I. , Daugela Antanas , Wyrobek Thomas J. , Warren Oden L.
Published: March 2008

This study evaluated a novel approach for acoustic emission (AE) monitoring of nanoindentation. The technique utilizes a miniature AE sensor integrated into a calibrated diamond indenter tip on a commercial nanoindentation system. The evaluation focused on the yield -point phenomenon in W (100); MgO (100); and sapphire C (0001); R (1012); A (1210); and M (1010) single-crystal surfaces. The minimum amount of elastic energy release sufficient to produce AE signal detectable with the indenter tip sensor was nearly two orders of magnitude lower than the minimum energy level required for conventional AE sensors. Wave forms detected with the indenter tip sensor were independent of sample size. A linear relationship between released elastic energies and the corresponding AE energies was observed for all three evaluated materials. The scaling coefficient of the linear relationship was independent of indenter tip size/shape and indentation depth. The differences between the mechanisms of the initial stages of plasticity for the various crystallographic orientations of sapphire were reflected in the following aspects of AE activity: detection of a specific type of AE wave form that correlated to the presence of linear surface features near the indentation sites; AE signal associated with the yield point, consisting either of one or two distinct wave forms; and presence or absence of AE signals after the yield point. The possibility of plasticity onset in sapphire involving both slip and twinning is discussed.
Investigation on the arc erosion behavior of new silver matrix composites: Part I. Reinforced by particles
Authors: Chang Shou-Yi , Hsu Chia-Jung , Hsu Cher-Hao , Lin Su-Jien
Published: March 2008

Static-gap, single-spark tests were used to investigate the arc erosion behavior of newly developed silicon carbide and alumina particle reinforced silver matrix composites (SiCp/Ag, Al2O3p/Ag). Craters and hills exist on the surfaces of eroded silver matrix composites, and their depths and sizes decrease as the particle content increases and the particle size decreases. Obvious melting, flow, severe splash of molten silver, and the segregation of particles are present on the surfaces of eroded composites containing low volume percents of large particles. Easier silver flow results in smooth surfaces and reduces the total surface areas of the eroded composites containing large particles. The flow and splash of silver decreased with increasing particle content and decreasing particle size, exhibiting a better erosion resistance to single-spark tests. The static-gap, single-spark erosion behavior of silver matrix composites is dominated by the flow and splash of molten composites. A high viscosity of the liquids provides the composites a good arc erosion resistance.
Study on the nature of the electrochemically synthesized hard Fe–15.4 mass% Ni–0.70 mass% C alloy film
Authors: Haseeb A. S. M. A. , Hayashi Y. , Masuda M. , Arita M.
Published: March 2008

Electrochemical synthesis of hard Fe–15.4 mass% Ni–0.70 mass% C alloy film with a hardness 750 HV was carried out from sulfate-based bath containing a small amount of citric acid and L-ascorbic acid. The nature of the alloy was investigated by different characterization techniques including x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy, differential scanning calorimetry, and magnetic measurements. The decomposition behavior of the alloy was also studied and compared with that of thermally prepared martensite. It was found that the electrochemically deposited Fe–Ni–C alloy exists in a state that is ahead of the freshly quenched state of martensite. It is suggested that the state of the electrochemically deposited Fe–15.4 mass% Ni–0.70 mass% C alloy corresponds to the state of thermal martensite, which had been heated to the preprecipitation stage of tempering.
Thermal stress characteristics of two-level Al(Cu) interconnect structure
Authors: Rhee Seung-Hyun , Ho Paul S.
Published: March 2008

Thermal stress characteristics of single-level and two-level Al(Cu) interconnects passivated with tetraethyl orthosilicate oxide were measured using x-ray diffraction. Thermal stresses of the second-level metal lines were deduced from the experimental data based on an analysis of the x-ray absorption in a two-level interconnect structure. The confinement effect from the substrate on the stress characteristics of metal lines at different interconnect levels was investigated. Thermal stress behavior of the second-level lines indicated that the confinement effect from the Si substrate is reduced compared to the single-level lines, resulting in reduced levels of hydrostatic and shear stresses.
Thermal properties of kinetic spray Al–SiC metal-matrix composite
Authors: Eesley Gary L. , Elmoursi Alaa , Patel Nilesh
Published: March 2008

Kinetic spray deposition provides a new means for producing composite materials with tailored physical properties. We report on measurements of the thermal conductivity and thermal-expansion coefficient for several compositional variations of kinetically sprayed Al–SiC metal-matrix composites. As a result of the deposition process, inclusion of SiC particles saturates in the 30–40% volume fraction range.
Effects of additive and impurity species on the oxide morphology of silicon nitride
Authors: Tsarenko I. V. , Du H. , Lee W. Y.
Published: March 2008

Si3N4 sintered with Lu2O3 was exposed to 1 atm of oxygen and steam environments at 1200–1400 °C. The effects of additive and impurity species on the morphological development of the oxide layer were examined. Oxide layers grown on as-received samples in oxygen generally contained bubbles and cracks and underwent spallation due to the presence of an initial impurity-laden oxide layer. Oxide layers grown on as-received samples in steam exhibited layered morphology: a glassy outer layer and a cristobalite inner layer with a high population density of Lu2Si2O7 particles between. The Lu2Si2O7 particles accumulated at the interface led to extensive spallation of the upper oxide layer. Removal of the initial oxide by polishing resulted in improved oxidation resistance and oxide morphology in oxygen and in steam.
Crystallization of Cu60Ti20Zr20 metallic glass with and without pressure
Authors: Jiang J. Z. , Yang B. , Saksl K. , Franz H. , Pryds N.
Published: March 2008

Structural stability of a Cu60Ti20Zr20 metallic glass under pressure up to 4.5 GPa was investigated by x-ray diffraction. The sample exhibited a supercooled liquid region of 33 K and a ratio of the glass-transition temperature to the liquidus temperature of 0.63. The glass crystallized in two-step transformation processes in the pressure range of 0–4.5 GPa; the first was a primary reaction to form a Cu51Zr14-type structure crystalline phase with a spacing group P6/m (175) and lattice parameters a=11.235 Å and c=8.271 Å, and then the residual amorphous phase crystallized into a MgZn2-type structure crystalline phase with a spacing group P63/mmc (194) and lattice parameters a=5.105 Å and c=8.231 Å. Both crystallization temperatures increased with pressure having a slope of 19 K/GPa. The increase of the first crystallization temperature with increasing pressure in the glass can be explained by the suppression of atomic mobility. No significant structural change was detected in the Cu60Ti20Zr20 glass annealed in vacuum at 697 K for 1 h as compared to the as-prepared sample from x-ray diffraction measurements.
Control of crystallization and crystal orientation of alkoxy-derived SrBi2Ta2O9 thin films by ultraviolet irradiation
Authors: Nishizawa Kaori , Miki Takeshi , Suzuki Kazuyuki , Kato Kazumi
Published: March 2008

A 650 °C annealed thin film was found to be a single phase of SrBi2Ta2O9 (SBT) and showed the c-axis orientation without ultraviolet irradiation. The crystallinity and crystal orientation of the thin films were improved by ultraviolet irradiation using an ultrahigh-pressure mercury lamp (UHPML) or a low-pressure mercury lamp (LPML) under three conditions. In particular, the crystal orientation of the 650 °C annealed thin films dramatically changed by ultraviolet irradiation using a LPML at room temperature or using an UHPML at 150 °C. The 650 °C annealed SBT thin film prepared by ultraviolet irradiation using an UHPML at 150 °C showed a remanent polarization (Pr) of 4.3 μC/cm2 and a coercive electric field (Ec) of 101 kV/cm at 10 V.
Enthalpy of formation of cubic yttria-stabilized zirconia
Authors: Lee T. A. , Navrotsky A. , Molodetsky I.
Published: March 2008

Oxide melt solution calorimetric measurements were made to determine the enthalpy of formation of cubic-yttria-stabilized zirconia (c-YSZ) with respect to the oxides m-ZrO2 and C-type YO1.5. The enthalpy of formation can be fit either by a quadratic equation or by two straight line segments about the minimum near x = 0.40. The quadratic fit gives a strongly negative interaction parameter, Ω=-93.7 ± 12.0 kJ/mol, but does not imply regular solution behavior because of extensive short-range order. In this fit, the enthalpy of transition of m-ZrO2 to c-ZrO2, 9.7 ± 1.1 kJ/mol, is in reasonable agreement with earlier estimates and that of C-type to cubic fluorite YO1.5, 24.3 ±14.4 kJ/mol, is consistent with an essentially random distribution of oxide ions and anion vacancies in the high-temperature fluorite phase. The two straight-line segments give 6.1 ± 0.6 kJ/mol and 5.5 ± 2.5 kJ/mol for these transitions, respectively. The latter value would imply strong short-range order in cubic fluorite YO1.5. Clearly more complex solution thermodynamic descriptions need to be developed. The enthalpy of transition from the disordered c-YSZ phase to the ordered δ-phase at 25 °C was also measured and was 0.4 ± 1.6 kJ/mol. No energetic difference between the disordered c-YSZ phase and the ordered δ-phase underscores the importance of short-range order in c-YSZ. Enthalpy data were combined with Gibbs free energy data to calculate entropies of mixing. Using the quadratic fit, negative excess entropy of mixing in the cubic solid solution, relative to a system with maximum randomness on cation and anion sublattices, was found and was another indication of extensive short-range order in c-YSZ.
New approach to depositing yttria-stabilized zirconia buffer layers for coated conductors
Authors: Sambasivan S. , Kim I. , Barnett S. , Zurbuchen M. A. , Ji J. , Kang B. W. , Goyal A. , Barnes P. N. , Oberly C. E.
Published: March 2008

A new approach for the production of yttria-stabilized zirconia (YSZ) oxide buffer layers directly on metal rolling-assisted biaxially textured substrates (RABiTS) is described in this paper. This represents a significant advance over existing techniques and avoids the need for complicated steps to avoid substrate oxidation during direct deposition of oxides. Current densities of about 1 MA/cm2 have been achieved for YBa2Cu3O7-δ layers on the YSZ buffer, with an intermediate CeO2 layer. The process consists of reactive sputtering of a YxZr1−xN film directly on the RABiTS, which adopts its biaxial texture. This nitride film is then converted to YSZ via a thermal oxidation step. The YSZ films retain the texture of the nitride film (and of the RABiTS) through local syntaxy. In many cases, YSZ films exhibit improved biaxial texture over that of the RABiTS substrate. Nitrides can be sputter deposited at much higher rates relative to oxides, making the approach industrially scalable and economical.
Determination of the interfacial fracture energies of cathodes and glass ceramic sealants in a planar solid-oxide fuel cell design
Authors: Malzbender Jürgen , Steinbrech Rolf W. , Singheiser Lorenz
Published: March 2008

A notched bimaterial bar bend test was applied to identify weak interfaces that influence the thermomechanical performance of solid-oxide fuel cell (SOFC) stacks with planar design. The experiments were focused on the weakest interface of the multilayered cells and on the rigid glass ceramic sealants between metallic interconnects of SOFC stacks. The fracture energies of these interfaces were determined. To test interfaces within the cells, they were glued to steel strips, and the notched cell was used as a stiffener in the test. The weakest part of the cells with composite cathodes was the interface between the functional part of the cathode and the remaining current collector. Values for the interfacial fracture energies of composite cathodes both freshly prepared and after aging were determined. Taking advantage of the crack extension within the anode from the notch-tip to the interface, the fracture energy of the oxidized and reduced anodes was calculated. Sandwich specimens with glass ceramic between the interconnect steel were used to determine the fracture energies for different glass ceramic–steel interfaces. Different combinations of ferritic steel and glass ceramic were tested. The fracture path developed partly along the interface and partly in the glass ceramic, which did not influence the fracture energy. However, a significant improvement of the fracture energy with annealing time was found.