bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Luminescence Properties of Neodymium(III) Oxide Nanocrystals Dispersed in Sol-gel Titania/ (γ-glycidoxypropyl)Trimethoxysilane Composite Thin Films
Authors: Que Wenxiu , Hu X. , Gan L. H. , Deen G. Roshan
Published: March 2008

Neodymium(III) oxide nanocrystals prepared by an inverse microemulsion technique have been dispersed in sol-gel titania/(γ-glycidoxypropyl)trimethoxysilane composite thin films at low temperature. Transmission electron microscopy and x-ray diffraction were used to characterize the phosphor nanoparticles and show that the neodymium(III) oxide nanoparticles have a nanocrystal structure and the size of the nanoparticles is in the range from 5 to 60 nm. An intense up-conversion emission in violet (399 nm) color from neodymium(III) oxide nanocrystals upon excitation with a yellow light (577 nm) has been observed. Two ultraviolet emissions at 347 and 372 nm and a blue emission at 466 nm have also been observed, and those are assigned to electronic transitions appropriately. A relatively strong room-temperature photoluminescence emission at 1064 nm corresponding to the 4F3/2 → 4I11/12 transition of neodymium ion has been measured as a function of the heat treatment temperature. In addition to this emission, two other emissions at 890 and 1336 nm have also been observed. Especially, a clear shoulder peak at 1145 nm, which could probably be resulting from the host matrix, was observed in all measured samples, and this shoulder peak reached a maximum intensity after a heat treatment at 300 °C.
Crystal Structure of the Compound Bi2Zn2/3Nb4/3O7
Authors: Levin Igor , Amos Tammy G. , Nino Juan C. , Vanderah Terrell A. , Reaney Ian M. , Randall Clive A. , Lanagan Michael T.
Published: March 2008

The crystal structure of Bi2Zn2/3Nb4/3O7 was determined using a combination of electron, x-ray, and neutron powder diffraction. The compound crystallizes with a monoclinic zirconolite-like structure [C2/c (No.15) space group, a = 13.1037(9) Å, b = 7.6735(3) Å, c = 12.1584(6) Å, β = 101.318(5)°]. According to structural refinement using neutron diffraction data, Nb preferentially occupies six-fold coordinated sites in octahedral sheets parallel to the (001) planes, while Zn is statistically distributed between two half-occupied (5 + 1)-fold coordinated sites near the centers of six-membered rings of [Nb(Zn)O6] octahedra. The Nb/Zn cation layers alternate along the c-axis with Bi-layers, in which Bi cations occupy both eight- and seven-fold coordinated sites. The eight-fold coordinated Bi atoms exhibited strongly anisotropic thermal displacements with an abnormally large component directed approximately along the c-axis (normal to the octahedral layers).
Substitution Effect of Ta5+ by Nb5+ on Photocatalytic, Photophysical, and Structural Properties of BiTa1–xNbxO4(0 ≦ x≦ 1.0)
Authors: Zou Zhigang , Arakawa Hironori , Ye Jinhua
Published: March 2008

Substitution effects of Ta5+ by Nb5+ in BiTa1−xNbxO4(0 ≦ x ≧ 1.0) on photocatalytic, photophysical, and structural properties were investigated. The powder x-ray diffraction and Rietveld structural refinement showed that the structure of BiTa1−xNbxO4 at R = Nb/Bi = 0.0 and 0.5 is a triclinic system with space group P1. However, the structure at R = 0.2, 0.8, and 1.0 is an orthorhombic system with space group Pnna. Ultraviolet-visible diffuse reflectance spectroscopy measurement revealed that the band gap of orthorhombic samples is narrower than that of triclinic compounds. The H2 evolution was obtained from an aqueous CH3OH/H2O solution and pure H2O with BiTa1−xNbxO4 under ultraviolet irradiation. The orthorhombic samples exhibit much higher activity than that of triclinic compounds. The orthorhombic compound at R = 0.2 showed the highest activity, which is higher than that of the well-known TiO2 photocatalyst.
(200)-predominant Growth of Radio-frequency Sputtered SrBi2Ta2O9 Thin Films
Authors: Lee Si-Hyung , Lee Jeon-Kook , Yoon Ki Hyun
Published: March 2008

SrBi2Ta2O9 (SBT) thin films were prepared by the radio-frequency (rf ) magnetron sputtering method on Pt/Ti/SiO2/Si substrates. The composition and orientation of SBT thin films were changed by the control of sputtering parameters such as pressure and rf power. As the sputtering pressure increased from 2.5 to 300 mtorr, the film was changed from Sr- and Bi-deficient SBT film to stoichiometric film. The SBT thin films with stoichiometric composition showed good electrical properties. As the rf power increased from 25 to 40 W, the Sr content decreased. However, the Bi content was maximized in the power of 30 W, where the (200)-predominant SBT thin films were fabricated. In lower power of 25 W, typical polycrystalline SBT films were obtained. The Sr and Bi contents in both films were not deficient. However, at the higher power of 35 and 40 W, the secondary phase appeared due to the Sr deficiency. The Bi content of (200)-predominant SBT film was higher than that of polycrystalline films. The degree of the (200) orientation depended on the magnitude of excess Bi content. It is also suggested that the (200)-predominant SBT films were formed by the decomposition of SBT phase to the Bi and Sr atoms caused by rf power control and the lower atomic migration energy along the a axis.
Reactive Sputter Deposition of Highly Oriented AlN Films at Room Temperature
Authors: Iriarte G. F. , Engelmark F. , Katardjiev I. V.
Published: March 2008

Textured as well as epitaxial thin AlN films are of great interest for a wide range of electro-acoustic and optoelectronic applications. Reduction of the deposition temperature is of vital importance in a number of applications due to thermal budget limitations. In this work we systematically studied the influence of the process parameters on the film properties and identified the factors leading to improved film quality as well as reduced deposition temperature with pulsed direct current sputtering in an Ar/N2 atmosphere. We demonstrated that fully textured (0002) films can be grown under a wide range of conditions. At the same time the full width at half-maximum (FWHM) of the rocking curve of the (0002) XRD peak was found to vary systematically with process conditions—depostion rate, process pressure, gas composition, and substrate temperature. The best films showed a FWHM of 1.2°. We found that by far the most important factor is the arrival energy of the sputtered Al atoms, which is primarily controlled by the process pressure. We report for the first time that fully textured AlN films with a FWHM of under 2° can be grown at room temperature. Other important factors are the ion and electron bombardment of the films and substrate temperature as well as gas composition, although their influence is not as dramatic. Generally, the film quality increases with temperature. Bias and electron bombardment within a certain range also lead to better films.
Isothermal Capacitance Transient Spectroscopy for Deep Levels in Co- and Mn-doped ZnO Single Crystals
Authors: Ohashi Naoki , Tanaka Junzo , Ohgaki Takeshi , Haneda Hajime , Ozawa Mio , Tsurumi Takaaki
Published: March 2008

Deep donor levels in ZnO single crystals doped with transition metal (TM; Co or Mn) were characterized by isothermal capacitance transient spectroscopy (ICTS) applied to ZnO-based Schottky junctions, Au/ZnO (0001) or Ag/ZnO (0001). The barrier height at the junction and donor concentration was not influenced by TM. A deep donor level at 0.28 eV was detected by ICTS; however, its energy dispersion and concentration was composition independent. The effect of doping with TM was found in the magnitude of leakage current; in other words, the leakage current at the Au/ZnO:Mn junction was lower than the other junctions on undoped or Co-doped crystals.
Chemical Solution Deposition of Lanthanum Zirconate Buffer Layers on Biaxially Textured Ni–1.7% Fe–3% W Alloy Substrates for Coated-conductor Fabrication
Authors: Sathyamurthy S. , Paranthaman M. , Aytug T. , Kang B. W. , Martin P. M. , Goyal A. , Kroeger D. M. , Christen D. K.
Published: March 2008

Sol-gel processing of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni–1.7% Fe–3% W alloy substrates using a continuous reel-to-reel dip-coating unit has been studied. The epitaxial LZO films obtained have a strong cube texture and uniform microstructure. The effects of increasing the annealing speed on the texture, microstructure, and carbon content retained in the film were studied. On top of the LZO films, epitaxial layers of yttria-stabilized zirconia and Ceria (CeO2) were deposited using rf sputtering, and YBa2Cu3Ox (YBCO) films were then deposited using pulsed laser deposition. Critical current densities (Jc) of 1.9 MA/cm2 at 77 K and self-field and 0.34 MA/cm2at 77 K and 0.5 T have been obtained on these films. These values are comparable to those obtained on YBCO films deposited on all-vacuum deposited buffer layers and the highest ever obtained using solution seed layers.
Rapid Prototyping of Micropatterned Substrates Using Conventional Laser Printers
Authors: Branham Michael L. , Tran-Son-Tay Roger , Schoonover Christopher , Davis Patrick S. , Allen Susan D. , Shyy Wei
Published: March 2008

We demonstrated rapid prototyping of templates for replica molding using a conventional laser printer. A polymer, polydimethylsiloxane, was cast directly on the transparency templates to make the replicas. The templates and replicas were characterized by scanning electron microscopy, profilometry, and optical microscopy. Four patterns, including an Electronic Industries Association resolution test pattern, were printed on transparencies at 600 dots per inch on a HP LaserJet 4M printer (Hewlett-Packard, Palo Alto, CA). Optimal precision and clarity occurred between intensity settings of 50–100. Mean pattern height/depth ranged from 8–13 μm, and width was as small as a few tenths of a millimeter. Mean surface roughness of the template patterns ranged from 1 to 4 μm on the top surface and from 5 to 10 nm on the bare transparency surface. This method provides access to microfabricated patterns for the broader research community without the need for sophisticated micromachining facilities.
Crystal Structure and Properties of a New Organic Nonlinear Optical Material
Authors: Rai R. N. , Lan C. W.
Published: March 2008

The single crystals of a binary organic 1:1 molecular complex were grown from different solvents. The single crystal x-ray diffraction study revealed that the binary material has crystallized with a noncentrosymmetric space group (P21) entirely different from that of the parent components. Second harmonic generation measurement on polycrystalline material shows green light emission with the molecular complex. The differential scanning calorimeter and the thermogravimetric analysis show eminent higher melting point and decomposition temperature, respectively for the binary molecular complex compared to that of urea and m-nitrobenzoic acid. The optical spectrum of newly grown crystal shows the cutoff wavelength (398 nm) near the UV region, and the micro hardness measurement confirmed the greater hardness of the binary crystal.
Interfacial Microstructure Evolution Between Eutectic SnAgCu Solder and Al/Ni(V)/Cu Thin Films
Authors: Li M. , Zhang F. , Chen W. T. , Zeng K. , Tu K. N. , Balkan H. , Elenius P.
Published: March 2008

The evolution of interfacial microstructure of eutectic SnAgCu and SnPb solders on Al/Ni(V)/Cu thin films was investigated after various heat treatments. In the eutectic SnPb system, the Ni(V) layer was well protected after 20 reflow cycles at 220 °C. In the SnAgCu solder system, after 5 reflow cycles at 260 °C, the (Cu,Ni)6Sn5 ternary phase formed and Sn was detected in the Ni(V) layer. After 20 reflow cycles, the Ni(V) layer disappeared and spalling of the (Cu,Ni)6Sn5 was observed, which explains the transition to brittle failure mode after ball shear testing. The different interfacial reactions that occurred in the molten SnAgCu and SnPb systems were explained in terms of different solubilities of Cu in the two systems. The dissolution and formation of the (Cu,Ni)6Sn5phase were discussed on the basis of a Sn–Ni–Cu phase diagram. In the solid-state aging study of the SnAgCu samples annealed at 150 °C for up to 1000 h, the Ni(V) layer was intact and the intermetallic compound formed was Cu6Sn5 and not (Cu,Ni)6Sn5, which is the same as was observed for the eutectic SnPb system.
Toward Rational Design of Fast Ion Conductors: Molecular Dynamics Modeling of Interfaces of Nanoscale Planar Heterostructures
Authors: Liang J-J. , Kung P.W-C.
Published: March 2008

Increased ionic conductivity at nanoscale planar interfaces of the CaF2|BaF2 system was successfully modeled using molecular dynamics simulations. A criterion was established to construct simulation cells containing any arbitrarily lattice-mismatched interfaces while permitting periodic boundary condition. The relative (to the bulk) ionic conductivity increase at the 111 (CaF2)|111 (BaF2) interface was qualitatively reproduced. Higher conductivity, by a factor of 7.6, was predicted for the 001 (CaF2)|001 (BaF2) interface. A crystalline nanocomposite of the CaF2|BaF2 system, in which the [001] morphology is encouraged and crystallite dimensions are approximately 4 nm, was proposed to give ionic conductivity approaching that predicted for the 001 (CaF2)|001 (BaF2) interface.
Synthesis and Microstructure of Antimony Oxide Nanorods
Authors: Zhang Zaoli
Published: March 2008

Antimony oxide nanorods were synthesized by the microemulsion method. The nanorods had diameter in the range of 507–175 nm and a length of up to several micrometers. The microstructure of the nanorods was examined by analytical transmission electron microscopy and high-resolution transmission electron microscopy (HRTEM). Large-angle tilt diffraction experiments on the normal nanorods (about 90 nm in diameter) showed that they have an orthorhombic structure. Combining the results of internal standards using the silicon single crystal, it could be concluded that the synthesized nanorod is Sb2O4. The common growth direction of the nanorods was along the long axis. HRTEM images showed it had a periodic layer structure, and some defects and a layer of amorphous on the nanorods surface were found. The formation mechanism of Sb2O4 nanorods is briefly discussed.
Mechanically Alloyed Amorphous Ti50(Cu0.45Ni0.55)44–xAlxSi4B2 Alloys with Supercooled Liquid Region
Authors: Zhang L. C. , Xu J. , Ma E.
Published: March 2008

A high-energy ball milling procedure has been developed to produce amorphous alloys in Ti50(Cu0.45Ni0.55)44−xAlxSi4B2 (x= 0, 4, 8, 12) powder mixtures. The milling products were characterized using x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The Ti-based amorphous alloy powders prepared through this solid-state process exhibit a well-defined glass transition and a supercooled liquid region (ΔTx =64 K) close to the largest achieved so far for Ti-based undercooled melts. The substitution of Al for Cu and Ni has beneficial effects on stabilizing the supercooled liquid. Residual nanocrystals of the αTi structure are uniformly dispersed in the amorphous matrix. The composite alloy powders offer the potential for consolidation in the supercooled liquid region to bulk lightweight amorphous alloys and the possibility to attain desirable mechanical properties.
Effect of Thermal Treatment on the Photocatalytic Activity of TiO2 Coatings for Photocatalytic Oxidation of Benzoic Acid
Authors: Chan Alex H. C. , Porter John F. , Barford John P. , Chan Chak K.
Published: March 2008

The effects of thermal treatment on the properties and photoactivities of TiO2 catalysts supported on 316 stainless steel plates were examined. Degussa P-25 was immobilized on 316 stainless steel plates by electrophoretic deposition. These TiO2-coated plates were heated at 473, 673, and 873 K for 1 h. The photoactivities of these TiO2 coatings were determined based on the removal of benzoic acid as the model pollutant. In particular, the photoactivity decreased by 52% in the sample heated at 873 K compared with the unheated sample. The results of x-ray diffraction showed that the crystallinity and the crystallite sizes of the catalysts supported on the plates did not significantly vary with increasing temperature over the range examined. Negligible change in the catalyst phase (the anatase-to-rutile ratio) was indicated from x-ray diffraction and micro-Raman spectroscopy. However, it was found that the Brunauer–Emmett–Teller surface area of the scraped catalysts heated at 873 K decreased by nearly 13% compared with the unheated sample. In addition, scanning electron microscopy/energy dispersive x-ray and x-ray photoelectron spectroscopy analyses also detected the presence of Fe3+ ions at the surface of the supported catalysts heated at 873 K. The drop in surface area and the presence of Fe3+ ions at the catalyst surface, which were considered to function as electron–hole recombination centers, were possible factors leading to the drop in the photoactivity exhibited by the sample. A lower temperature for thermal treatment such as 473 K was proposed to ensure the coating stability and the catalyst photoactivity.
Low-energy Electron Exposure Effects on the Optical Properties of ZnO/K2SiO3 Thermal Control Coating
Authors: Wang X. D. , He S. Y. , Yang D. Z.
Published: March 2008

An experimental investigation was undertaken to study low-energy electron exposure effects upon ZnO/K2SiO3 thermal control coating. The specimens were exposed to 10-, 30-, 50-, and 70-keV electrons, respectively. The spectral reflectance of each specimen was measured in situ before and after electron exposures. The solar absorptance was calculated by assuming a Johnson solar spectral irradiance distribution. Electron paramagnetic resonance and photoluminescence measurements were made before and after electron exposures to explain physical changes induced by the electron exposures. All the specimens exhibited a reflectance decrease throughout the visible and the near-infrared regions, and also the induced optical degradation was found to be electron energy dependent, with increased damage for increasing electron energy. It is believed that the optical degradation of ZnO/K2SiO3 thermal control coating, induced by the low-energy electron exposures, is mainly due to the ionization process of the ZnO pigment.
Sintering of a Crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 Glass with Titania Present
Authors: Jean Jau-Ho , Fang Yu-Ching , Dai Steve X. , Wilcox David L.
Published: March 2008

Crystallization and reaction kinetics of a crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder with 17–40 vol% titania powder were investigated. The initially amorphous K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder formed cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] during firing. The above crystalline phases were completely replaced by a crystalline phase of titanite [(Ca, Sr, Ba)TiSiO5] when the amount of added titania was greater than a critical value, e.g., 10 vol%, at 99–1100 °C. A chemical reaction taking place at the interface between titania and the glass was attributed to the above observation. The dissolved titania changed the composition of the glass, and the dissolution kinetics was much faster than the formation of cristobalite and pseudowollastonite. Activation energy analysis showed that the crystallization of titanite [(Ca,Sr,Ba)TiSiO5] was controlled by a reaction-limiting kinetics of formation for the Ti–O bond.
Pressure Dependence of Elastic Constants and Debye Temperature for Zr50.5Ti4.8Cu19.0Ni11.4Al14.3Bulk Metallic Glass
Authors: Wen Ping , Wang Ru Ju , Wang Wei Hua
Published: March 2008

The microstructure of Zr50.5Ti4.8Cu19.0Ni11.4Al14.3bulk metallic glass (BMG) was investigated by high-resolution electron microscopy. The microstructure of the BMG is of homogeneous composition and short-range ordered microstructure. Using an ultrasonic technique with the pulse echo overlap method, the pressure-dependent acoustic velocities of the BMG have been measured up to 0.5 GPa. The elastic constants and their pressure dependence have been obtained. The isothermal equation of state (EOS) of the BMG is determined in terms of the Murnaghan form. With the results of the elastic constants and the EOS for those of its metallic components, the atomic configuration of the BMG is discussed.
Transport in the Al71Pd21Mn8−XReX Quasicrystalline System
Authors: Pope A. L. , Tritt T. M. , Gagnon R. , Strom-Olsen J. , Legault S. , Schneidmiller R. , Kolis J.
Published: March 2008

In an effort to understand the effects of a quartenary element introduced into a ternary quasicrystalline system, quartenary Al71Pd21Mn8−XReX quasicrystals were grown, where X had values of 0, 0.08, 0.25, 0.4, 0.8, 2, 5, and 8. X-ray data confirm that the addition of a fourth element does not alter the quasiperiodicity of the sample. Because electronic transport is governed by different mechanisms in the parent systems (Al71Pd21Mn8 and Al71Pd21Re8), electrical and thermal transport measurements in the alloyed system have been performed on these samples and are presented here.
Nitrogen diffusion in the Si growth on GaN by low-pressure chemical vapor deposition
Authors: Chen P. , Zheng Y. D. , Zhu S. M. , Xi D. J. , Zhao Z. M. , Gu S. L. , Han P. , Zhang R.
Published: March 2008

Si film has been grown on a wurtzite gallium nitride layer on sapphire by low-pressure chemical vapor deposition. Uniform nitrogen incorporation was found in the Si film at the concentration of 5%, indicating an incorporation-limited process through interstitial diffusion from GaN layer to Si layer. The nitrogen occupied the substitutional sites in the Si film, leading this Si layer to be n-type doping with the carrier concentration of 1.42 × 1018/cm3 and the hall mobility of 158 cm2/(V s). This is consistent with other calculated and experimental results, which suggest that only 5% nitrogen can occupy the substitutional sites in the nitrogen-doped Si materials.
Low-temperature fabrication of high-quality (Ba, Sr)TiO3films using charged liquid cluster beam method
Authors: Choi Hyungsoo , Park Sungho , Yang Yi , Kang HoChul , Kim Kyekyoon (Kevin) , Sung M. Y. , Jang Ho G.
Published: March 2008

Low-temperature deposition of high-quality (Ba, Sr)TiO3(BST) thin films was achieved in air on Pt/Ti/SiO2/Si substrates using the charged liquid cluster beam (CLCB) method. The Ba, Sr, and Ti precursors were synthesized using alkoxy carboxylate ligands to tailor their physical properties to the CLCB process. The as-deposited BST films fabricated at substrate temperatures as low as 280 °C exhibited high purity. The leakage current density and dielectric constant of the film, deposited at 300 °C and subsequently annealed at 700 °C, were 2.5 × 10−9A/cm2at 1.5 V and 305, respectively.
Catalytic effects on carbon/carbon composites fabricated by a film boiling chemical vapor infiltration process
Authors: Okuno H. , Trinquecoste M. , Derré A. , Monthioux M. , Delhaès P.
Published: March 2008

Chemical vapor infiltration (CVI) has been widely studied under several conditions to obtain C/C composites. A “film boiling technique” (so-called Kalamazoo), by the use of liquid precursor, based on thermal gradient CVI has been recently developed as one of the very effective techniques to increase the carbon yield and the densification rate. A small cold wall type laboratory reactor has been realized to analyze the kinetics of reactions and the deposited pyrocarbon matrix. In this study, ferrocene, as the source of catalyst, is mixed to the liquid precursor to induce a catalytic effect on the film boiling technique since the transition metals are known to increase the carbon deposition rate. In addition to an important increase of the densification rate, it is revealed that the deposition mechanism and microtextures are completely modified by the presence of catalyst, with the presence of multiwall nanotubes within the matrix. A model has been adapted from Allendorff and Hunt's work to interpret this peculiar deposition mechanism.
Microstructural investigation of BaTiO3thin films deposited on (001) MgO
Authors: Lei C. H. , Van Tendeloo G. , Siegert M. , Schubert J.
Published: March 2008

The microstructure of BaTiO3thin films, epitaxially deposited on (001) MgO by pulsed laser ablation, has been investigated by transmission electron microscopy. The films are always c-axis-orientated, but dislocations, {111} stacking faults, and antiphase boundaries are frequently observed. Conventional TEM and high-resolution microscopy allow one to deduce the Burgers vectors of dislocations as b1= 〈100〉 or b2= 〈110〉, both being perfect dislocations. Most extrinsic stacking faults are ending at 1/3〈112〉 or 1/3〈111〉 partial dislocations; the displacement vector of the antiphase boundaries is 1/2〈101〉. Studying the interfacial structure by means of zone images taken along [100] and [110] shows that the misfit is mainly released by dislocations with Burgers vectors of 1/2〈110〉 and 1/2〈101〉.
Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process
Authors: Wang Moo-Chin , Wu Nan-Chung , Yang Sheng , Wen Shaw-Bing
Published: March 2008

β-Spodumene (Li2O · Al2O · 4SiO2, LAS4) precursor powders were obtained through a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS4 precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li2O · Al2O3 · 2SiO2, LAS2) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS4 precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.
Combustion synthesis of mechanically activated powders in the Nb–Si system
Authors: Maglia Filippo , Milanese Chiara , Anselmi-Tamburini Umberto , Doppiu Stefania , Cocco Giorgio
Published: March 2008

The effect of the mechanical activation of the reactants on the self-propagating high-temperature synthesis (SHS) of niobium silicides was investigated. SHS experiments were performed on reactant powder blends of composition Nb:Si = 1:2 and Nb:Si = 5:3 pretreated for selected milling times. A self-sustaining reaction could be initiated when a sufficiently long milling time was employed. At short milling times, the reactions self-extinguished or propagated in an unsteady mode. Combustion peak temperature, wave velocity, and product composition were markedly influenced by the length of the milling treatment. Single-phase products could be obtained for sufficiently long milling times. Observation of microstructural evolution in quenched reactions together with isothermal experiments allowed clarification of the mechanism of the combustion process and the role played by the mechanical activation of the reactants.
Ferromagnetism discovered on heat-treating the aromatic polyimide film Kapton
Authors: Kaburagi Yutaka , Hishiyama Yoshihiro
Published: March 2008

A commercially available aromatic polyimide film Kapton H 25-μm thick was heat-treated at temperatures between 490 and 540 °C in a nitrogen flow. Magnetization was measured as a function of magnetic field at 5 and 300 K and function of temperature in a field of 1 T. Diamagnetic and paramagnetic components were observed for all heat-treated films. Ferromagnetism was discovered even at 300 K in the films heat-treated at 490–520 °C. The saturation magnetization, coercive force, and residual magnetization for the 520 °C treated film were 0.059 J T−1 kg−1, 0.004 T, and 9 × 10−4 J T−1 kg−1, respectively, at 300 K. The ferromagnetism has been maintained 5 months after. Original Kapton H and the heated films were found to contain no metallic elements. The ferromagnetism should be caused by a long-range magnetic spin ordering of unpaired electrons located on slightly decomposed imide molecules with defects or on intermediates with free radicals formed by thermal decomposition. The ordering is probably established three dimensionally throughout the heat-treated films with a structural regularity similar to that of the original Kapton H.
Redox equilibrium and spectral hole burning in Sm2+-doped Al2O3–SiO2 glasses
Authors: Nogami Masayuki , Eto Toyonori , Suzuki Kazuhiro , Hayakawa Tomokatsu
Published: March 2008

Sm2+ ion-doped Al2O3–SiO2 glasses were prepared using sol-gel and melt-quenching methods; the redox equilibrium and spectral hole burning were investigated. The Sm3+ ions were reduced into Sm2+ by heating in H2 gas or x-ray irradiation. The redox between the Sm3+ and Sm2+ obeyed first-order kinetics, the rate of which was larger for the sol-gel glasses. The Sm3+ ions were also reduced by x-ray irradiation and the activation energy for redox equilibrium was half of that for the glasses treated in H2 gas. Two different mechanisms were proposed for the redox reaction of the samarium ions. In the x-ray irradiated glasses, the Sm3+ ions were reduced into Sm2+ by electron transfer from the oxygen defect center, whereas the H2-gas reaction removed the oxygen ions to reduce the Sm3+ ions. The spectral hole burning of the x-ray-irradiated glasses could be burned by the reverse reaction of the reduction of the Sm3+ ions; that is, the electron transfer from the excited Sm2+ into the surrounding oxygen. A short distance between the Sm2+ and oxygen defect centers allowed fast hole burning. On the other hand, the hole burning in the H2-treated glasses was performed by electron transfer between Sm2+ and another trapping center such as Sm3+.
Preparation, characterization, and micropatterning of laser-dye-doped sol-gel films
Authors: Arena A. , Patanè S. , Saitta G. , Rizzo G. , Galvagno S. , Neri G.
Published: March 2008

Planar thin films of dye-doped silica were prepared by sol-gel synthesis. The optical properties of the films were characterized by transmittance measurements in the visible-infrared range and by photoluminescence. Micropatterns whose feature size was on the order of 2.4 μm, were imprinted on the film surface by a simple soft lithography approach. An optical microscope interfaced to a charge-coupled device camera was used to image the imprinted patterns and to analyze the patterned films photoluminescence. A sensitive spectral narrowing of the emission, which occurred only in micropatterned films, was attributed to the lateral confinement of the luminescence due to the micrometer-scale modulation of refractive index produced by the embossing procedure.
Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing
Authors: Zhou Yizhou , Zhang Wei , Wang Baoquan , He Guanhu , Guo Jingdong
Published: March 2008

High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.
Optical properties of Ho3+-, Er3+-, and Tm3+-doped BaIn2S4 and BaIn2Se4 single crystals
Authors: Park Sang-An , Kim Mi-Yang , Kim Wha-Tek , Jin Moon-Seog , Choe Sung-Hyu , Park Tae-Young , Park Kwang-Ho , Kim Duck-Tae
Published: March 2008

BaIn2S4, BaIn2S4:Ho3+, BaIn2S4:Er3+, BaIn2S4:Tm3+, BaIn2Se4, BaIn2Se4:Ho3+, BaIn2Se4:Er3+, and BaIn2Se4:Tm3+ single crystals were grown by the chemical transport reaction method. The optical energy gap of the single crystals was found to be 3.057, 2.987, 2.967, 2.907, 2.625, 2.545, 2.515, and 2.415 eV, respectively, at 11 K. The temperature dependence of the optical energy gap was well fitted by the Varshni equation. Broad emission peaks were observed in the photoluminescence spectra of the single crystals. They were assigned to donor–acceptor pair recombination. Sharp emission peaks were observed in the doped single crystals. They were attributed to be due to radiation recombination between the Stark levels of the Ho3+, Er3+, and Tm3+ ions sited in C1 symmetry.
High-pressure, high-temperature sintering of diamond–SiC composites by ball-milled diamond–Si mixtures
Authors: Qian J. , Voronin G. , Zerda T. W. , He D. , Zhao Y.
Published: March 2008

A new method of sintering diamond-silicon carbide composites is proposed. This method is an alternate to the liquid silicon infiltration technique and is based on simultaneous ball milling of diamond and silicon powder mixtures. Composites with fine-grain diamonds embedded in a diamond–SiC nanocrystalline matrix were sintered from these mixtures. Scanning electron microscopy, x-ray diffraction, and Raman scattering were used to characterize the ball-milled precursors and the sintered composites. It was found that the presence of diamond micron-size particles in the initial powder mixture promotes milling of silicone particles and their transformation into the amorphous state. Mechanical properties of the composites, sintered from mixtures of different ball-milling history at different pressure–temperature conditions, (6 GPa/1400 °C and 8 GPa/2000 °C) were studied.
Elastoplastic load–depth hysteresis in pyramidal indentation
Authors: Sakai M. , Nakano Y.
Published: March 2008

Extensive indentation tests were conducted for nineteen different engineering materials ranging from brittle to ductile materials, and including hard ceramics, ductile metals, and a soft organic polymer. Three tetrahedral pyramid indenters with specific face angles β [shallow pyramid (β = 10°), Vickers (β = 22°), and sharp pyramid (β = 40°) indenters] were used. All the materials tested were subjected to the quadratic load P and penetration depth h relationship P = k1h2 on loading, and most of the tested materials to the quadratic unloading relationship of P = k2(h − hr)2 with the residual depth hr after a complete unload. To determine the contact area at peak indentation load, a specially designed depth-sensing instrument was constructed, on which the contact behavior during loading/unloading was examined by through thickness observation of transparent specimens. All the characteristic indentation parameters were investigated on the basis of simple elastoplastic model, and correlated well with the nondimensional strain E′ tan β/H, in which the elastic modulus E′ was a measure for elasticity, true hardness H was a measure for plasticity, and the inclined face angle β characterized the indenter. The ratio of the conventional Meyer hardness HM to the true hardness H of the materials tested ranged from 0.2 to 0.9 as a function of E′ tan β/H. The cavity model suggested that true hardness H is expressed by the yield stress Y through a constraint factor C as H = C · Y with C ≈ 5.
Effects of manganese on microstructure and mechanical properties of A206 alloys containing iron
Authors: Tseng Chien-Jung , Lee Sheng-Long , Tsai Sheng-Chuan , Cheng Chia-Jen
Published: March 2008

The effects of Mn and Fe contents on the mechanical properties of aluminum-based A206 alloys were investigated quantitatively. Results showed that the addition of Fe caused a loss in both ductility and yield strength. Further addition of Mn could recover the ductility, but it caused a further loss in yield strength. In low-Mn alloys (0.29 wt% Mn) the primary constituent was the needle shape of Cu2FeAl7. Upon further addition of Mn, the Chinese script configuration of Mn-bearing particles formed instead. The Cu2Mn3Al20 particles formed in high-Mn alloys during solution treatment and resulted in grain-growth inhibition. The needle, Mn-bearing, and Cu2Mn3Al20 particles caused the solid solution level of copper in the matrix to decrease; meanwhile, increasing the Mn solution level retarded the precipitation of the strengthening phase. Differential scanning calorimetry analyses showed the kinetics and amount of decrease in θ′ phase precipitation when the contents of Fe and/or Mn were increased. The smaller grain size induced by the Cu2Mn3Al20 particles and the θ′ phase were the factors that determined the hardness of A206 alloys under as-quenched and T7-treated conditions, respectively.
Cellular automaton model to simulate nucleation and growth of ferrite grains for low-carbon steels
Authors: Zhang L. , Zhang C. C. , Wang Y. Y. , Liu X. X. , Wang G. G.
Published: March 2008

A two-dimensional cellular automaton model was developed for the simulation of nucleation and growth of ferrite grains at various cooling rates in low-carbon steels. The model calculates the diffusion of the solute and temperature fields in an explicit finite method and incorporates local temperature and concentration changes into a nucleation or growth function, which is utilized by the automaton in a probabilistic fashion. The modeling provides an efficient way to understand how those physical processes dynamically progress and affect nucleation and growth of ferrite grains.
Thermal stability of nanometer-sized NiO and Sm-doped ceria powders
Authors: Okawa Yoshihiro , Matsumoto Toshitatsu , Doi Toshiya , Hirata Yoshihiro
Published: March 2008

A fine NiO powder and a Sm-doped ceria powder with a composition of Ce0.8Sm0.2O1.9 were synthesized by heating the oxalate precursors at 300–1200 °C in air to produce a cermet (anode material) for solid oxide fuel cell. A 0.2 M Ni(NO3)2 solution and a 0.2 M Ce(NO3)3–Sm(NO3)3 solution were mixed with 0.4 M oxalate solution, respectively, to produce the oxalate precursors. Only the cubic phase of Ce0.8Sm0.2O1.9 was formed in the calcined powders from the Sm-doped cerium oxalate. However, the mixed phases of NiO and Ni were produced in the NiO precursor after the calcination at 300–600 °C. At higher temperatures, only NiO was detected. The primary particle sizes, which were determined from the Brunauer-Emmett-Teller analysis surface areas, were 60 nm for NiO and 10 nm for Ru/Sm-doped ceria (SDC) after the heat treatment at 400 °C. The oxalate precursors of SDC and NiO provided 433 and 259 kJ/mol of the activation energy, respectively, for sintering/grain growth in the temperature range from 600 to 1200 °C. As-produced SDC precursor formed platelike secondary particles of 0.5–2-μm length by the heating at 800 °C. Heating of Ni oxalate at 800 °C produced isotropic fine NiO secondary particles of 0.5–2-μm sizes.
Crystal growth of Bi2Sr2Ca2Cu3O10+x and (Bi,Pb)2Sr2Ca2Cu3O10+x by the KCl flux method
Authors: Lee Sergey , Yamamoto Ayako , Tajima Setsuko
Published: March 2008

Bi2Sr2Ca2Cu3O10+x and (Bi,Pb)2Sr2Ca2Cu3O10+x single crystals with a sharp superconducting transition at Tc = 109 K were grown using a modified KCl flux technique. The crystals show platelike morphology with typical dimensions of 0.5 × 0.5 × 0.002 mm3 and 0.25 × 0.25 × 0.001 mm3 for Pb-free and Pb-doped compositions, respectively. The formation of Bi-2212 intergrowth in the crystals is suppressed by utilization of a stable MgO crucible, suppression of the KCl evaporation, and isothermal heat treatment at a temperature close to the melting temperature of the oxide precursor in the flux. Morphology, phase purity, and chemical composition of grown crystals were determined by various analysis methods while the superconducting properties were studied by magnetization and resistivity measurements.
Improvement of oxidation resistance of Si3N4 by heat treatment in a wet H2 atmosphere
Authors: Koh Young-Hag , Kim Hae-Won , Kim Hyoun-Ee
Published: March 2008

To improve the oxidation resistance of Si3N4 material, a dense and continuous layer, composed of small Y2Si2O7 crystallites and silicate glass, was formed on the surface. The surface layer was formed by exposing the specimens in a flowing H2 atmosphere containing 0.1% H2O at 1450 °C for 1 h. For the purpose of comparison, specimens of the same material were heat treated in air at 1450 °C for 1 h. Small equiaxed Y2Si2O7 crystallites were formed when the specimen was heat treated in the wet H2 atmosphere, while relatively large and elongated Y2Si2O7 crystallites developed when the specimens were heat treated in air. The oxidation resistance of Si3N4 material was improved remarkably by the heat treatment in the wet H2, while no improvement in oxidation resistance was observed from the specimen heat treated in air. The improvement was attributed to the retardation of the transport of oxidants through the dense and continuous layer formed on the surface.
Effects of heat treatment and sintering additives on thermal conductivity and electrical resistivity in fine-grained SiC ceramics
Authors: Zhan Guo-Dong , Mitomo Mamoru , Mukherjee Amiya K.
Published: March 2008

The effects of heat treatment and sintering additives on the thermal conductivity and electrical resistivity of fine-grained SiC materials were investigated. The thermal conductivity and the electrical resistivity of dense SiC materials were measured at room temperature by a laser flash technique and a current-voltage method, respectively. The results indicated that the thermal conductivity and electrical resistivity of the SiC materials were dependent on the sintering additives and the resultant microstructure. Annealed materials with oxide additives developed microstructures consisting of elongated grains of various α/β–SiC polytypes. In contrast, annealed materials with oxynitride additives had microstructures consisting of fine equiaxed grains entirely of β–SiC phase. For the annealed materials with oxide additives the observed thermal conductivity was over 110 W/mK. For the annealed materials with oxynitride additives the observed value was 47 W/mK. The electrical resistivity of a hot-pressed material with oxide sintering additives decreased after annealing. For annealed materials with oxynitride additives, the electrical resistivity was even lower. High-resolution electron microscopy revealed a thin amorphous phase along the grain boundaries. Energy dispersive x-ray spectroscopy results showed that there was segregation of both Al and O atoms and a very small amount of Y atoms at grain boundaries. The results indicated that the chemistry and structure of the grain boundary has significant influence on thermal and electrical properties in SiC.
Superplasticity in NiAl and NiAl-based alloys
Authors: Guo J. J. , Du X. X. , Zhou L. L. , Zhou B. D. , Qi Y. Y. , Li G. G.
Published: March 2008

Superplastic deformation was realized on NiAl and NiAl-based alloys prepared by both common casting and directional solidification. Directionally solidified NiAl–27Fe–3Nb alloy as well as conventionally cast NiAl, NiAl–25Cr, NiAl–9Mo, NiAl–20Fe–Y.Ce, and NiAl–30Fe–Y alloys exhibited typical deformation characteristics shown in conventionally superplastic materials. NiAl and NiAl-based alloys could be divided into three categories depending on their different superplastic behavior: finely grained structure (NiAl–9Mo, NiAl–25Cr, NiAl–20.4Fe–Y.Ce, NiAl–30Fe–Y), coarsely grained structure (NiAl), and columnar structure (NiAl–27Fe–3Nb). The corresponding deformation mechanisms for fine-grained structure, coarsely grained structure, and columnar structure were grain boundary sliding or grain boundary sliding accompanied by dynamic recrystallization, dynamic recovery and recrystallization, and intragrain dislocation slip, respectively.
Preparation of titanium(IV) oxide film on a hard alumite substrate
Authors: Ishikawa Yoshie , Hayashi Yasunori , Matsumoto Yasumichi
Published: March 2008

TiO2 was deposited onto hard alumite (Al/Al2O3/TiO2) by alternating current electrolysis and precipitation in (NH4)2[TiO(C2O4)2] solution at various temperatures, where the hard alumite was prepared by the anodic oxidation of aluminum in sulfuric acid (Al/Al2O3). The TiO2 electrodeposition mainly occurred at temperatures lower than about 50 °C, while the TiO2 deposition due to TiO(C2O4)22− adsorption onto alumina predominantly occurred at temperatures higher than about 50 °C. The amount of deposited TiO2 increased with the increase in the deposition temperature, leading to high photocatalytic activity. The deposited TiO2 at 90 °C followed by heat-treatment at 550 °C had an anatase structure and showed a high photocatalytic activity for the decomposition of acetaldehyde even under fluorescent lamp illumination. The Al/Al2O3/TiO2 prepared at 50 °C was optimal for practical use, because of a relatively high activity and the sufficient adhesion strength between the TiO2 and the Al/Al2O3 substrate due to the presence of the deposited TiO2 in the pores of the alumina film.
Layered lead zirconate titanate and lanthanum-doped lead zirconate titanate ceramic thin films
Authors: Myers Todd , Banerjee Parag , Bose Susmita , Bandyopadhyay Amit
Published: March 2008

The physical layering of sol-gel-derived lead zirconate titanate (PZT) 52/48 and lanthanum-doped PZT (PLZT) 2/52/48 on platinized silicon substrates was investigated to determine if the ferroelectric properties and fatigue resistance could be influenced by different layering sequences. Monolithic thin films of PZT and PLZT were characterized to determine their ferroelectric properties. Sandwich structures of Pt/PZT/PLZT/PLZT/PZT/Au and Pt/PLZT/PZT/PZT/PLZT/Au and alternating structures of Pt/PZT/PLZT/PZT/PLZT/Au and Pt/PLZT/PZT/PLZT/PZT/Au were then fabricated and characterized. X-ray photoelectron spectroscopy depth profiles revealed that the layering sequence remained intact up to 700 °C for 45 min. It was found that the end layers in the multilayered films had a significant influence on the resulting hysteresis behavior and fatigue resistance. A direct correlation of ferroelectric properties and fatigue resistance can be made between the data obtained from the sandwiched structures and their end-layer monolithic thin film counterparts. Alternating structures also showed an improvement in the fatigue resistance while the polarization values remained between those for PZT and PLZT thin films.
Synchrotron x-ray scattering study of SnO2 thin film grown on sapphire
Authors: Rue Gi-Hong , Yoo Dae Hwang , Hwang Yoon Hwae , Kimb Hyung-Kook
Published: March 2008

From synchrotron x-ray scattering measurements, it was found that epitaxially grown SnO2 film on sapphire has a variant structure with threefold symmetry with respect to the substrate and that the ultrathin interfacial layer is formed due to the lattice mismatch between SnO2 and Al2O3. The physical properties of the top surface, such as surface morphology, height profile, and roughness, were determined by atomic force microscopy. The height profiles of the film grown at 600 °C and room temperature revealed the asymmetrical and the ordinary symmetric Gaussian distributions, respectively. The difference originates from the dominant diffusion process at high substrate temperature.