In this research, the influences of the oxygen impurity contained in the commercially available nitrogen gas on the reactions of chromium pellets with nitrogen were investigated in the temperature range 600–1350 °C. A small amount of oxygen competed with the majority N2 to react with chromium in the annealing process. Analyzing the in situ oxygen partial pressure changes during annealing proved that the dissolution of oxygen in Cr and/or resultant CrxN (CrN or Cr2N) was exothermic and the solubility decreased with increasing temperature. It was found that the oxygen partial pressure decreased drastically to about 10−22 atm when specimens were annealed at 600 °C compared to a mere 10−5 atm for a blank test, while its value increased with temperature. The oxidation involved simultaneous dissolution of oxygen in specimens and formation of oxide scale. Moreover, comparing the aforementioned results with those obtained from additional annealing experiments preformed in argon gas showed that the formation of Cr2O3 might stem mainly from oxidation of the resultant nitrides instead of the metallic chromium.

The effect of Ag substitution for Cu on the glass forming ability (GFA) and mechanical properties of Mg65Cu25−xAgxGd10 (x = 0, 5, 10, 15, 20, 25) alloyswere investigated using x-ray diffractometry and differential scanning calorimetry.The partial substitution of Cu by Ag in Mg65Cu25Gd10 promoted the GFA. Mg65Cu20Ag5Gd10 bulk metallic glass (BMG) with a diameter of 11 mm could be fabricated by conventional copper-mold casting method in air atmosphere. The Mg65Cu20Ag5Gd10 BMG exhibits yielding and plastic deformation during compressive loading. The compressive fracture strength, total strain to failure, and plastic strain to failure of the Mg65Cu20Ag5Gd10 BMG were 909 MPa, 2.21% and 0.5%, respectively.

The soldering reaction and interfacial microstructure formed between liquid Sn–Zn–Ag solder and Cu at the early stage of soldering at 250 °C for 15 s were studied primarily with the aid of transmission electron microscope (TEM). To achieve the early stage reaction information, the soldered specimens, 5 mm × 5 mm × 500 μm solder on 10 mm × 10 mm × 20 μm Cu, were rapidly quenched in liquid nitrogen after soldering. The results of TEM interfacial analysis show that a Cu–Zn reaction zone, consisting of β′–CuZn and γ–Cu5Zn8, formed near Cu while a Ag–Zn zone, consisting of γ–Ag5Zn8 and ϵ–AgZn3, formed near solder. The innermost layer adjacent to the Cu substrate is an amorphous Cu-Zn diffusion region that contains dispersed β′–CuZn nanocrystalline cells. The β′–CuZn also precipitates in the γ–Ag5Zn8 and ϵ–AgZn3 layer due to the supersaturation of Cu.

A range of nitrogen-doped amorphous hydrogenated carbon samples (a-C:Nx:H, where x = 3 at.% and x = 7 at.%) have been studied using neutron diffraction, inelastic neutron scattering (INS) and Fourier transform infra-red (FTIR) spectroscopy to obtain detailed information about their atomic-scale structure, particularly the bonding environment of the hydrogen. The results show that the overall atomic scale network structure of the two samples is very similar; however, the hydrogen-bonding sites alter subtly as the nitrogen content of the samples is increased.

Solid solutions (1 − x)CeO2 − xYO1.5 (0 ≤ x ≤ 0.36) were prepared by coprecipitation and sol-gel methods. Their enthalpy of formation relative to the end-members, fluorite-type cubic CeO2 and C-type YO1.5 was determined by oxide melt solution calorimetry. The enthalpy of drop solution shows a roughly linear trend with composition. Extrapolation to x = 1 gives the transition enthalpy of C-type to cubic fluorite YO1.5 as 22.2 ± 6.7 kJ/mol. This linear behavior is in contrast to the strong curvature seen in the ZrO2 − YO1.5 and HfO2 − YO1.5 systems. The slightly positive enthalpy of formation of CeO2 − YO1.5 is strikingly different from the strongly negative enthalpies of formation of ZrO2 − YO1.5 and HfO2 − YO1.5. The thermodynamics of CeO2 − YO1.5 is analyzed in terms of defect association and oxygen vacancy distribution. Specifically, the association of oxygen vacancies with the tetravalent cations in the zirconia and hafnia systems, in contrast to the preference of vacancies for nearest neighbor yttrium sites in the ceria systems, may explain the different energetics.

Fine tubular fibers composed of C60 and C70 fullerene molecules were successfully fabricated by the liquid–liquid interfacial precipitation method. The walls of the tubular fibers were crystalline, and the fullerene molecules were densely packed along the growth axis of tube wall. The tubular structures are called “fullerene nanotubes.” The inner diameter and the outer diameter of C70 tubes showed a linear relationship, suggesting a constant wall thickness of the tubes. The tubular structures composed of C70 molecules could be formed when their diameter was larger than about 240 nm. The fullerene tubes were successfully fabricated by using a C60-C70 soot as well. The formation of fullerene nanotubes can be understood by assuming a mechanism of core dissolution of the solvated fullerene nanowhiskers.

Age-hardening behavior of a new generation of FeCo alloys [Fe–40Co–5V–0.005B–0.015C–0.5Mo–0.5Nb (at.%)] is characterized by microhardness, tensile testing, electrical resistivity, and magnetic properties. The alloy exhibits maximum hardening when aged at 600 °C. Precipitation of γ2 (V-rich face-centered cubic phase) during aging appears to be responsible for the observed hardening behavior. The alloy exhibits superior creep resistance when subjected to solutionizing in γ phase field and aged at 600 °C. On the other hand, the room temperature tensile ductility of the aged alloy depends on the grain size, which in turn can be controlled by varying the solutionizing condition. The age-hardened alloy exhibits a room temperature electrical resistivity of 70–75 μΩ cm. The higher resistivity of the present alloy as opposed to the commercial FeCo–2V alloys is attributed to the high V content of the alloy. Structure-sensitive magnetic properties like coercivity and core losses of the alloy are affected by the aging treatment, and the maximum coercivity is observed when the alloy is aged at 600 °C. High coercivity of the alloy is attributed to the fine distribution of paramagnetic γ2 precipitate, fine grain size, and internal stress arising from phase transformation.

Decagonal single quasicrystals of the composition Al70Ni15Co15 have been deformed in situ in a high-voltage transmission electron microscope at 730 °C along the 10-fold periodic axis to directly observe the dislocation motion. The deformation is carried by stress-assisted climb of dislocations with periodic Burgers vectors. These dislocations may also glide and move by a combination of glide and climb. Dislocations with Burgers vectors with components in the periodic and quasiperiodic directions probably move under the action of a chemical force. The observations are interpreted by a model established by P. Schall et al. under consideration of the activation parameters of macroscopic deformation and by analogies with the behavior of icosahedral quasicrystals.

Ultra-refractory ceramic composites of composition ZrB2 + (5 to 20) vol% MoSi2were produced by pressureless sintering at 1830 °C under argon atmosphere.Sintering cycles and microstructural analysis point out that at least 20 vol% molybdenum disilicide is necessary for obtaining a dense material. Thereafter, the composite 80 vol% ZrB2 + 20 vol% MoSi2 was used to test the thermal stabilityunder oxidizing environment. Oxidation tests were carried out in flowing syntheticair in a thermogravimetric analyzer from 700 to 1400 °C with exposure time of30 h. In the low-temperature range (700–1000 °C), the oxidation of the composite resembles that of monolithic ZrB2 ceramics, for temperatures >1200 °C the silica resulting from oxidation of molybdenum disilicide seals the sample surface, preventing zirconium diboride from fast degradation.

We report on the growth of Mg-rich cubic (Mg,Zn)O nanowires using a catalysis-driven molecular-beam-epitaxy method. Nanowires were grown on both Si and Al2O3 substrates coated with a nominally 2-nm-thick layer of Ag. The (Mg,Zn)O nanowires were grown with a Zn and Mg cation flux, with an O2/O3 mixture serving as the oxidizing species. The growth temperature was 400 °C. Under these conditions, nanowires were observed to grow on the Ag sites. The nanowire diameter was on the order of 90 nm. (Mg,Zn)O nanowires as long as 2 μm were realized. High-resolution transmission electron microscope imagery shows the nanowires had single-phase cubic rock salt structure (Mg,Zn)O with a growth direction along the [100]. The presence and compositional distribution of Mg and Zn in the single nanowire were confirmed using a compositional line-scan, profiled across the nanowire, by energy dispersive spectrometry with scanning transmission electron microscopy.

Elastic-viscoelastic correspondence, utilizing Boltzmann integral operators, was used to generate displacement–time solutions for spherical indentation testing of viscoelastic materials. Solutions were found for creep following loading at a constant loading rate and compared with step-loading solutions. Experimental creep tests were performed with different loading rate–peak load level combinations on glassy and rubbery polymeric materials. The experimental data were fit to the spherical indentation ramp–creep solutions to obtain values of shear modulus and time-constants; good agreement was found between the experimental results and known modulus values. A multiple ramp-and-hold protocol was examined for the measurement of creep responses at several loads (and depths) within the same test. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test a priori assumptions made in the correspondence solutions regarding linear viscoelastic material behavior and the creep function.

In this paper, we report the fabrication the methacryl-oligosiloxane nano hybrid films from 3-(trimethoxysilyl)propyl methacrylate (MPTS) and diphenylsilanediol (DPSD), and the investigation of the tuneability of the optical characteristics of the films through the compositional change. The viscosity of the methacryl-oligosiloxane nano hybrid resin was altered at 102 intervals by the compositional modification without any drastic changes in the reaction parameters, and thickness-controlled (from 11 to 150 μm) and uniformly coated (less than 1 nm root-mean-square roughness) films were obtained through a single coating step. The refractive indices were tunable from 1.506 to 1.543, depending on composition. On the other hand, the thermo-optic coefficients remained constant (−2 × 10−4/°C), independent of composition. Also, we demonstrated a thick (170 μm) photo pattern with a high aspect ratio (3:1). Methacryl-oligosiloxane nano hybrid materials can be promising candidates for the optical applications due to easy and wide tuneability of their optical parameters.

We grew epitaxial α–Fe2O3(1010) on TiO2(001) rutile by oxygen plasma-assisted molecular-beam epitaxy. High-resolution transmission electron microscopy (HRTEM), reflection high-energy electron diffraction (RHEED), and x-ray diffraction pole figures confirm that the film is composed of four different in-plane orientations rotated by 90° relative to one another. For a given Fe2O3 unit cell, the lattice mismatch along the parallel [0001]Fe2O3 and [100]TiO2 directions is nominally +67%. However, due to a 3-fold repetition of the slightly distorted square symmetry of anion positions within the Fe2O3 unit cell, there is a coincidental anion alignment along the [0001]Fe2O3 and [100]TiO2 directions, which results in an effective lattice mismatch of only −0.02% along this direction. The lattice mismatch is nearly 10% in the orthogonal [1120]Fe2O3 and [100]TiO2 directions. The film is highly ordered and well registered to the substrate despite a large lattice mismatch in one direction. The film grows in registry with the substrate along the parallel [0001]Fe2O3 and [100]TiO2 directions and nucleates dislocations along the orthogonal [1120]Fe2O3 [100]TiO2 directions.

Low-temperature processable inherently photosensitive polyimide was prepared from a dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and aromatic diamines, 4,4′-diamino-3,3′dimethyl-diphenylmethane, through a polycondensation reaction, followed by a chemical imidization method. The photosensitive polyimide cured at 180 °C is used as a gate dielectric to fabricate flexible organic thin-film transistors with pentacene as an active semiconductor on polyethersulfone substrate. With the inherently photosensitive polyimide, the access to the gate electrode could be created easily without complicated and expensive lithographic techniques. A field effect carrier mobility of 0.007 cm2/V s was obtained for the pentacene organic thin-film transistors (OTFTs) with the photo-patterned polyimide as a gate dielectric. More detailed analysis for the pentacene OTFTs will be given with electrical properties of the thin polyimide film. Low-temperature processability and patternability of the polyimide give us more freedom to choose plastic substrates in OTFTs and facilitate the realization of low-cost organic electronics.

Inversion boundaries (IBs) of a head-to-head or (0001)|(0001) (C+|C+) configuration bisect virtually every grain in typical commercial ZnO varistor ceramics. They are most often considered electrically inactive, and the effect on the grain growth behavior has been recently addressed. In this work, various configurations of ZnO bicrystals were prepared using different source crystals and strong barrier effects were observed in some (0001)|(0001) (C−|C−) bicrystals using crystals with higher impurity contents. The crystallographic polarity and impurity effects were systematically examined by doping C+|C+ and C−|C− bicrystals with single and double additives of Mn, Co, Ni, and Bi. Varying degrees of barrier effects including varistor-like behaviors were observed in C−|C− bicrystals depending on dopants, while C+|C+ bicrystals consistently exhibited negligible effects. Because the IBs in ZnO varistor ceramics preferentially expose C− surfaces in the grain boundaries, the superior property of commercial ZnO varistor ceramics is suggested to be assisted by the presence of IBs.

Using conventional and high-resolution transmission electron microscopy (HRTEM), the effects of rolling at room temperature on the microstructures of amorphous Al90Fe5Gd5 and Al86.8Ni3.7Y9.5 were compared. In rolled Al90Fe5Gd5, nanocrystallites were observed at shear bands, whereas none were observed in rolled Al86.8Ni3.7Y9.5. When HRTEM was combined with with Fourier transform filtering, nanoscale, low-density defects were imaged. In Al90Fe5Gd5, the shear bands contain few defects, which are concentrated at the boundary zone between the shear bands and undeformed region, whereas in Al86.8Ni3.7Y9.5, the shear bands contain a uniform distribution of defects with a density higher than the undeformed region. The preferential precipitation of nanocrystallites in rolled Al90Fe5Gd5 is attributed to a kinetic effect due to uniformly-distributed excess free volume in the shear bands.

A composite material containing uniformly distributed micrometer-sized Nb particles in a Zr-based amorphous matrix was prepared by suction cast. The resulting material exhibits high fractured strength over 1550 MPa and enhanced plastic strain of about 29.7% before failure in uniaxial compression test at room temperature. Studies of the serrations on the stress–strain curves and the shear bands on the fractured samples reveal that the amplitude of the stress drop of each serration step corresponds to the extent of the propagation of a single shear band through the materials. The composite exhibits more serration steps and smaller amplitude of stress drop due to the pinning of shear band propagation by ductile Nb particles.

Silicon carbide (SiC) microtubes were synthesized and characterized via a vapor–solid (VS) reaction of carbon fiber (Csolid) and SiO(gas). The synthesis mechanisms were investigated. The precursor led complete conversion of [SiO(gas) + C(solid)] into [SiC(solid) + CO(gas)] through overall reaction under inert gas flow at and above 1350 °C. Carbon fibers with small surface area (0.7–2.0 m2 g−1) were gradually converted to SiC microtubes with large specific surface area (45–63 m2 g−1). Inner surface of SiC microtubes indicated a villus-like morphology, which consisted of submicron-sized SiC villi. The outer surface of the SiC microtubes was smooth. Inner surface morphology of SiC microtubes was dependent upon synthesizing temperature. Thickness of villus-like layer in SiC microtubes increased with increasing synthesizing temperature, showing 0.25 and 0.5 at 1350 and 1400 °C, respectively. Both VS and gas–liquid–solid (VLS) growth mechanisms were investigated in synthesis of SiC fiber as a reaction byproduct, and the reaction was governed by both growth mechanisms.

Oxidation behavior of Ni-toughened reactively sputtered composite thin films of nanocrystalline TiN and amorphous SiNx [denoted as nc-TiN/a-SiNx(Ni)] was explored to understand the oxidation mechanism. The films were deposited on silicon substrate using a magnetron sputtering technique. Oxidation was carried out from 450 °C up to 1000 °C. The nature of the oxidation was determined using x-ray photoelectron spectroscopy. The microstructure of the oxidized films was studied using grazing incidence x-ray diffraction. The topography was characterized using atomic force microscopy. It was determined that the oxidation of the nc-TiN/a-SiNx(Ni) thin film proceeds primarily through a diffusion process, in which nickel atoms diffuse outward and oxygen ions inward. The oxidation takes place by progressive replacement of nitrogen with diffused oxygen. Five regions were identified in the oxidized layer from surface into the film. For films doped with 2.1 at.% Ni, a threshold temperature of 850 °C was determined, below which, excellent oxidation resistance prevails but above which, oxidation takes place at exponential rate, accompanied by abrupt increase of surface roughness.

Crystallization of amorphous thin films composed of doped SbxTe with x = 3.0, 3.6, and 4.2 and constant dopant level was studied by in situ heating in a transmission electron microscopy. Magnetron sputtering was used to deposit 20-nm-thick films sandwiched between two types of 3-nm-thick dielectric layers on 25-nm-thick silicon-nitride membranes. One type of dielectric layer consists of ZnS–SiO2 (ZSO), the other of GeCrN (GCN). Crystallization was studied for temperatures in-between 150 and 190 °C. The type of dielectric layer turned out to strongly influence the crystallization process. Not only did the nucleation rate appear to depend sensitively on the dielectric layer type, but also the growth rate. The velocity of the crystalline/amorphous interface is about 5 times higher for the x = 4.2 film than for the x = 3.0 film if ZSO is used. In case of GCN, the interface velocity is about 2 times higher for the x = 4.2 film than for the x = 3.0 film. The activation energy for crystal growth is not significantly dependent on the Sb/Te ratio but is clearly different for ZSO and GCN—2.9 eV and 2.0 eV, respectively. The incubation time for the crystal nuclei formation is longer for ZSO than for GCN. Although the effects of the Sb/Te ratio and the dielectric layer type on the growth rates are strong, their effects on the nucleation rate are even more pronounced. A higher Sb/Te ratio results in a lower nucleation rate and the use of GCN instead of ZSO leads to higher nucleation rates.