The hydrogen storage performance of a single body-centered-cubic phase Ti-40V-10Cr-10Mn alloy was investigated. A hydrogen absorption capacity of 4.2 wt.% (H/M = 2.1), which is the highest value at room temperature reported so far, was achieved at 293 K under modest pressure (3 MPa) for this as-cast alloy. The effective hydrogen capacities of this alloy were 2.6, 2.8, and 3.2 wt.%, respectively, at 353, 393, and 523 K, which gave hope of bringing Ti-V-based alloys into the reach of practical application for onboard hydrogen storage systems in fuel cell-powered vehicles.

The effect of chemical etching on the surface roughness and fracture strength of Nd:yttrium-aluminum-garnet single crystals was investigated. Etching the laser host material in a 1:1 mixture of concentrated sulfuric and phosphoric acid at elevated temperatures enabled material removal from the surface of laser rods cored from single-crystal boules. The roughness on the rod surface increased from the as-drilled condition after etching, but after 17 μm of material was removed, the roughness remained approximately constant. The modulus of rupture increased from 133-530 MPa when 87 μm of material was removed by the chemical etching procedure.

The interface microstructures of Sn-Ag and Sn-Ag-Cu solders with Au/Ni-6P plating were studied primarily using transmission electron microscopy. During soldering at 230°C, Au dissolved into molten solder, and double reaction layers of Ni3Sn4/η–Ni3SnP formed between Sn-3.5Ag solder and Ni-6P layer. P content increases in the surface region of the Ni-6P layer due to the depletion of Ni diffused into molten solder, resulting in the formation of Ni3P+Ni layer. For Sn-3.5Ag-0.7Cu solder, an η-(Ni,Cu)3Sn2 single layer, containing Cu of about 50 at.%, formed as a reaction layer.

An electromigration failure mechanism in flip chip solder joints is reported in this communication. The solder joints failed by a very rapid, asymmetrical, and localized dissolution of the Cu metallization on the cathode side. The average dissolution rate was about 1 μm/min. The dissolved Cu included not only the Cu under bump metallurgy but also the on-chip Cu conducting trace. From the location and geometry of the dissolved Cu, it can be concluded that current crowding plays a critical role in the rapid dissolution. The dissolved Cu atoms were driven to the anode side by electromigration, and a large amount of Cu6Sn5 was formed there.

Composites consisting of particles of α-iron dispersed in silicon carbonitride (SiCN) were fabricated by a polymer route. The composites had iron inclusions with the same magnetization as bulk iron, but they resisted oxidation up to 500°C and had a hardness of 5-7 GPa. The composites behaved as ferromagnets, albeit with a low susceptibility attributed to the pinning of the domains by imperfect interfaces and to the elastic resistance from the SiCN matrix. This low-cost, low-temperature processing method can be used to make different kinds of ceramic composites with multifunctional properties.

Carbon nitride nanocrystals were synthesized on Co/Ni-covered Si(100) wafers using a nitrogen-atom-beam-assisted pulsed laser ablation deposition method. Transmission electron miscroscopy, x-ray diffraction, and Raman spectroscopy showed that as-deposited films were constructed primarily from nanometer-sized β-C3N4 and CNx crystallites. The co-catalyzation by the cobalt and nickel in the synthesis process is considered to play an important role in the formation of nanocrystalline β-C3N4. The reasons for the formation of carbon nitride nanocrystals were analyzed.

La0.8Sr0.2MnO3 (LSMO) and LaMnO3 (LMO) thin films epitaxially grown on (001) LaAlO3 substrate at 700 and 800°C were studied using cross-section and plan-view transmission electron microscopy. In both LSMO and LMO films deposited at 700°C, a two-layered structure was observed: a continuous cubic perovskite layer epitaxially grown on the substrate followed by epitaxially grown orthorhombic column nanostructures. The orthogonal nano columns in LSMO were very well defined with a narrow size distribution. The LMO films exhibited a somewhat distorted orthogonal shape for the nanostructured columns and a wider size distribution. LSMO and LMO epitaxial films deposited at 800°C consisted of only a continuous single layer of cubic perovskite. These results reveal that formation of epitaxial column nanostructures in the La1-xSrxMnO3 thin films strongly depends on the growth temperature. Sr substitution on La sites in La1-xSrxMnO3 can improve uniformity of column size distribution and perfection of the orthogonal shape of nano columns.

The evolution of an interfacial microstructure between Cu/Ni/Au bond-pad metallization and Pb-free or Pb-containing solder bumps during solid-state aging was investigated. A distinctive difference between the Pb-containing and Pb-free solder bumps was observed. A continuous (Au,Ni)Sn4 intermetallic compound layer was readily detected in the Pb-containing solder bump on the bond-pad. No such layer exists in the Pb-free case; instead a large number of (Au,Ni)Sn4 particles scatter in the bulk of the solder. The different morphologies of the (Au,Ni)Sn4 have been explained on the basis of the contact angle in Young's equation and of the growth of a flat layer by ripening. A simple kinetic analysis of ripening between a set of monosize spheres and a flat surface is given to describe the layered growth having a time dependence around 0.5.

Alkali activation of dehydroxylated kaolin or clay yielded high-strength polymeric materials, so-called geopolymers. They were synthesized by mixing the aluminosilicate with solutions of sodium metasilicate and KOH followed by adding 45 wt.% of ground-granulated blast furnace slag. The influence of the aluminosilicate source, its activation temperature, and the order of mixing raw materials were studied on the workability of the blending paste, the microstructure, and the Vickers hardness of the geopolymer samples. The polymeric material is completely amorphous according to x-ray diffraction. Solid-state 27Al and 29Si magic-angle-spinning nuclear magnetic resonance showed that the geopolymer consists of AlO4 and SiO4 tetrahedra linked together through a polymeric network constituted by branched entities SiQ4(4Al) and SiQ4(3Al), but also by less-polymerized silicates SiQ1 and SiQ2. Scanning electron microscopy showed a homogeneous polymeric gel matrix containing unreacted slag (and quartz) grains; thermogravimetric analysis and differential scanning calorimetry exhibited a high content of water and an elevated melting point (1260°C). Vickers hardness values are in the range of 200 MPa.

We report an effective procedure for fabricating carbon microcoils and nanocoils with three-dimensional spiral structures in high yield by nickel (Ni)-catalyzed thermal decomposition of acetylene. The Ni catalyst particles used in this preparation were electrochemically deposited onto tungsten substrates. Springlike coils having low pitch and micrometer-scale diameters and ropelike coils having higher pitch and nanometer-scale diameters were observed. Electrical and optical properties were investigated by employing a field-emission probe system equipped with an optical spectrometer. In an applied field above 1.5 V/μm, significant electron emission was observed from individual ropelike nanocoils. The approximately linear slope of the corresponding Fowler-Nordheim plot denotes predominately field-emission behavior. During measurement, individual carbon coils aligned themselves along the electric field, exhibiting a natural resonance on some occasions. As the field strength increased above 2.5 V/μm, the emission-current density for a single nanocoil was measured to be on the order of 104 A/cm2. This high-current density caused Joule heating, resulting in strong photon emission by incandescence.

Using anodic oxidation with a time-dependent linearly varying anodization voltage, we have made films of tapered, conical-shaped titania nanotubes. The tapered, conical-shaped nanotubes were obtained by anodizing titanium foil in a 0.5% hydrofluoric acid electrolyte, with the anodization voltage linearly increased from 10-23 V at rates varying from 2.0-0.43 V/min. The linearly increasing anodization voltage results in a linearly increasing nanotube diameter, with the outcome being an array of conical-shaped nanotubes approximately 500 nm in length. Evidence provided by scanning electron-microscope images of the titanium substrate during the initial stages of the anodization process enabled us to propose a mechanism of nanotube formation.

The solid-state reaction of SrNb2O6, BaNb2O6, and CeO2 to form Sr0.5Ba0.5CexNb2O6+δ at different temperatures and heating rates was investigated. A nonisothermal kinetic empirical model was used to evaluate the activation energy and rate constant of Sr0.5Ba0.5CexNb2O6+δ. The values of the activation energy evaluated from the slopes are 762, 800, and 844 kJ/mol, respectively, for S50, 1CeS50, and 2CeS50, which increase with the increase in Ce doping. The order of reaction was found to decrease with the increase of the Ce doping. A kinetic equation was developed based on the parameters evaluated from the nonisothermal reaction model, which was successfully used to predict the isothermal reaction of Ce-doped strontium barium niobate.

Ba2MeWO6 (Me=Mg, Ni, Zn) double perovskites were prepared by the conventional solid-state reaction in a wide temperature range. Single-phase ceramics were obtained only at low temperatures approximately 1200°C, whereas a small amount of second phases existed in the samples sintered at higher temperatures. All the compounds are characterized by the cubic perovskite structure (space group Fm3m) with a complete NaCl type ordering between B-site ions. Anomalous temperature variation of the dielectric loss tangent found in the Ba2NiWO6 perovskite is supposed to be connected with a dielectric relaxation due to electronic hopping within thermally activated Ni3+-6W(6-1/6)+/W5+-6Ni(2+1/6)+ clusters. Dielectric measurements showed that the other two perovskites—Ba2ZnWO6 and Ba2MgWO6—exhibit a positive value of the temperature coefficient of permittivity. Such temperature variation is assumed to be caused by a considerable influence of the second polar mode involving B-site ion vibrations on the low-frequency dielectric properties.

Liquid-phase sintered SiC, doped with 3 vol% AlN, Al2OC, Y3Al5O12, revealed a variation in electrical resistivity of more than five orders of magnitude (<102-107 Ω cm) upon slight variations in the sintering process. The materials were characterized using various transmission electron microscopy techniques such as high-resolution transmission electron microscopy (HRTEM), Fresnel fringe imaging, analytical electron microscopy, and electron holography. The main focus of this study was to verify whether there is a correlation between interface structure and electrical resistivity. Scanning electron microscopy (SEM) of polished and plasma-etched surfaces showed interface features similar to those observed in Si3N4 ceramics containing amorphous grain-boundary films. Such films are expected to act as an insulating barrier for electric current. However, in contrast to the SEM results, HRTEM of SiC grain boundaries revealed no intergranular film in any of the SiC materials studied. Elemental analysis (i.e., energy dispersive x-ray and electron energy loss spectroscopy) of these “clean” SiC interfaces showed the segregation of secondary phase elements at grain boundaries. Electron holography and the Fresnel fringe technique were used to determine the change in the mean inner potential across SiC interfaces, which could be associated with the spatial charge distribution of a double Schottky barrier. The height of the potential barrier correlates with the electrical resistivity recorded via impedance spectroscopy.

A controlled introduction of second-phase Y2BaCuO5 (211) nanoparticles into YBa2Cu3O7−δ (123) thin films was achieved for the first time for the purpose of increasing flux pinning. The island-growth mode of 211 on 123 was utilized to obtain an area particle density >1011 cm-2 of 211 thick-disk-shaped nanoparticles in individual layers. Composite layered structures of (211y nanoparticles/123z)×N were deposited by pulsed laser deposition on LaAlO3 substrates, with N bilayers = 24 to 100, y thickness = 1 to 2 nm, and z thickness = 6 to 15 nm (assuming continuous layer coverage). With 211 addition, the critical current densities at 77 K were higher at magnetic fields as low as 0.1 T and increased as much as approximately 300% at 1.5 T. The superconducting transition temperature was reduced by approximately 2 to 4 K for 211 volume fraction <20%. Reinitiation of 123 growth after every 211 layer resulted in a smooth and flat surface finish on the films and also greatly reduced surface particulate formation especially in thicker films (∼ μm).

Highly conductive cubic (Y0.25Bi0.75)2O3 tends to transform to rhombohedral (Y0.25Bi0.75)2O3 when annealed at 600°C for more than 200 h. Although the rhombohedral phase of (Y0.25Bi0.75)2O3 was known to be the stable phase at temperatures ≤600°C, it was found that the annealed (Y0.25Bi0.75)2O3 was not thermodynamically stable in the water-containing environment. From x-ray diffraction and transmission electron microscopy analysis, it was observed that the annealed (Y0.25Bi0.75)2O3 easily decomposed into monoclinic α-Bi2O3 and yttrium hydroxide at a temperature as low as 50°C. The monoclinic α-Bi2O3 further reacted with CO2 and formed Bi2O2CO3. Consequently, the annealed (Y0.25Bi0.75)2O3 degraded and became flaky powder. Scanning electron microscopy micrographs of water-reacted (Y0.25Bi0.75)2O3 also showed surface swelling and peeling. Such surface deterioration was caused by a large volume increase during the water reaction. Similar reaction was also observed when the annealed (Y0.25Bi0.75)2O3 was exposed in the humidified air at 300°C. As the temperature was raised to 500°C, little reaction was observed between water vapor and (Y0.25Bi0.75)2O3. The better stability of (Y0.25Bi0.75)2O3 at elevated temperature was observed.

The microstructural changes in the initial stage of a conversion process of α-tricalcium phosphate [α-Ca3(PO4)2] (α-TCP) to hydroxyapatite [Ca10(PO4)6(OH)2] (HAp) by the hydrolysis method were investigated by transmission electron microscopy (TEM). To investigate the microstructural changes that take place during the conversion process, we prepared two types of α-TCP specimens for TEM: α-TCP powder and sintered α-TCP thin film. According to our results, the microstructural changes can be summarized as follows. At first, the surface of the α-TCP was covered with an amorphous calcium phosphate layer, resulting from hydration or the dissolution of α-TCP. Subsequently, the nucleation of HAp occurred on the amorphous layer, and then dendritic structures appeared on the layer. Thereafter, the dendritic structures would grow into needlelike fine HAp crystals.

The effect of the layer-charge density of clay on the orientation and aggregation of a cationic dye, methylene blue (MB), in MB/clay films was investigated using a series of layer-charge-controlled montmorillonites as host materials. Polarized ultraviolet-visible spectroscopy and x-ray diffraction were used for the characterization of the arrangement and orientation of dye cations in host interlayer spaces. It was revealed that high charge densities of layers induced the formation of relatively ordered and homogeneous phases with dye dimers. The reduction of the charge led to the formation of disordered, mixed phases with large amounts of monomers (isolated dye cations). Dimers and monomers were slightly tilted against the plane of the clay surface, and their angles were not affected by the layer charge.

The light diffusion behavior in a glass particle-dispersed epoxy matrix composite was evaluated using a pico-second order light pulse. Change in pulse profile was detected, and this change in different detection areas is discussed. The light scattering behavior in the composite was directly observed, and the result was compared with the pulse profile change. This change appeared in the pulse shape, and depended on the particle volume fraction and the area of light detected. The maximum probable light path extension and the light transmittance were strongly correlated with the direct observation result of spatial spreading behavior of light in the composite. The combination use of (i) maximum probable light path extension and (ii) light transmittance was effective in evaluating the light-scattering behavior of the composite. The method is applicable to evaluation of the light-scattering process in light-transmitting materials.

The microstructure of the Ni-based superalloy IN100 processed by a powder metallurgy route was evaluated to reveal the structures, volume fractions, distributions, and chemistries of the various phases present. These data were compared with those predicted by computational thermodynamics. It is shown that the microstructural parameters expected on the basis of global equilibrium conditions differ significantly from those measured experimentally. However, modification of these calculations by use of constrained and successive equilibria compensated for kinetic effects and led to accurate (or better) predictions of phase volume fractions and chemistries in this alloy. This demonstrated that such modified phase equilibria calculations could be powerful tools for modeling microstructures, even in complex multicomponent alloys processed under nonequilibrium conditions.