Aluminum gallium nitride (AlxGa1−xN) films, grown by metalorganic chemical vapor deposition on sapphire, were characterized by low-temperature cathodoluminescence (CL) and photoluminescence (PL), and room-temperature optical absorbance. The aluminum fractions are estimated to range from x = 0 to x = 0.444. Most films were silicon-doped. The absorption spectra have a Urbach (exponential) form below the bandgap. The width of the Urbach edge, EU, increases with Al fraction, x, as EU = (0.045 +1 0.104x) eV. The luminescence (CL or PL) spectra show a relatively narrow band-edge peak and a broad deep-level peak. The full-widths at half-maximum of the band-edge CL peaks (measured at T = 15 K) are remarkably similar to the Urbach absorption widths, EU (measured at T = 300 K). PL spectra were obtained from the top surfaces and the film-substrate interfaces of several films. The interface PL spectra of some films show an extra peak 0.15 eV to 0.45 eV below the bandgap, which is ascribed to structural defects or impurity phases localized near the interface. The energy of the band-edge luminescence peak shifts with excitation mode (CL, top-surface PL, or interface PL). This effect is attributed to the variation of the excitation depth, between the top surface and film-substrate interface, with excitation mode, together with the depth variation of film properties such as residual stress or aluminum fraction.

The effects of chloromethane on diamond nucleation and growth were studied by employing laser reflective interferometry. Chloromethane enhances the film-growth rate only slightly compared to methane. However, chloromethane greatly enhances the nucleation density and shortens the film-forming stage, more significantly at a lower temperature. Thus, chloromethane facilitates the low temperature growth mainly through the enhancement of nucleation. Nucleation density is strongly dependent on the compositions of H atoms and carbon species prior to diamond growth. The residual diamond seeds by diamond-grit scratching are suggested to be the major nucleation sites. Chloromethane can enhance diamond nucleation by protecting the residual seeds from being etched by H atoms.

The alloying effect on microstructure and stability of the NbCr2 Laves phases is investigated using x-ray diffraction (XRD) and transmission electron microscopy (TEM). In as-cast condition, the binary alloy as well as the ternary alloy containing V consisted of the C15 phase while the ternary alloys containing Mo, Ti, and W consisted of both the C14 (or C36) and the C15 phases, accompanied by a number of stacking faults and microtwins in their constituent phases. By a prolonged heat treatment at 1673 K, the retained C14 (or C36) phase is completely transformed to the C15 phase. However, their kinetics is slower in the sequence of the ternary alloys containing Mo > Ti > W. The alloying effect on the stability of the C15 (or the C14) phase and the associated transformation process is discussed on the basis of phase stability and kinetics.

The emissions of CO2, SOx, and NOx of various steel alloys in the production stage were calculated by using the unit requirement of each subsystem of the steel-making process, in order to compare the superiority from the viewpoint of the environmental issue among various types of steel alloys. As steel production is a typical integrated system with multiproducts, allocation of emissions to each product, effect of the composition, and sharing the load by the by-product gases are considered. Calculated values of emission were arranged for fifteen kinds of finished steel products and for arbitrary contents of alloying elements.

Nb75M25 (M = Al, Si, Ga, Ge, and Sn) alloy ingots were prepared by the conventional arc-melting method and then were directly reacted with high purity hydrogen of 0.1 MPa in an arc-;melting chamber without exposing the ingots to air. As the clean surface of the arc-;melted ingots is preserved, the ingots rapidly absorb a large amount of hydrogen without any activation treatments and disintegrate violently into fine particles. The disintegration of ingots depends on the M element. The collected particles are investigated by x-ray diffraction, electron microscopy, chemical analysis, and thermal analysis. The particles are hydrides of Nb75M25 after hydrogenation and have a sharp-edged polygonal appearance. After dehydriding, fine Nb3M powders with A15 crystalline structure are obtained except for Nb75Si25. In comparison with the atomized Nb3M powders, the Nb3M powders prepared by the present study have a smaller average particle size and lower impurity contents.

Preparation of β–SiC nanorods with and without amorphous SiO2 wrapping layers was achieved by carbothermal reduction of sol-gel derived silica xerogels containing carbon nanoparticles. The β–SiC nanorods with amorphous SiO2 wrapping layers were obtained by carboreduction at 1650 °C for 1.5 h, and at the end of 1.5 h the temperature was steeply raised to 1800 °C and held for 30 min; they are typically up to 20 µm in length. The diameters of the center thinner β–SiC nanorods within the amorphous SiO2 wrapping layers are in the range 10–30 nm, while the outer diameters of the corresponding amorphous SiO2 wrapping layers are between 20 and 70 nm. The β–SiC nanorods without amorphous SiO2 wrapping layers were produced by carbothermal reduction only at 1650 °C for 2.5 h, and their diameters are in agreement with those of the center thinner β–SiC nanorods wrapped in amorphous SiO2 layers. Large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are both favorable to the formation of much thinner β–SiC nanorods. The formation of the outer amorphous SiO2 wrapping layer is from the combination reaction of decomposed SiO vapor and O2.

In situ observations of crack propagation in an applied moment double cantilever beam specimen were used previously to obtain the R-curve behavior of ceramic composites. To predict the R-curve using constitutive models, knowledge of the crack profile is required to derive the bridging stress distribution along the crack length and to analyze the toughening effect. To predict the crack profile in an applied moment double cantilever beam test, both the deformation of the crack surface due to the bending moment and the movement of the crack surface due to the rigid body motion of the loading fixture need to be considered. The analytical solution for the crack profile is derived in the present study. The predicted crack profiles agree well with experimental measurements.

By systematically varying the carbon content, chamber pressure, arc current, and blowing gas velocity in a tungsten-arc encapsulation setup, the effects of each of these variables on the encapsulation of nickel in graphite layers were observed. The data from these optimally designed experiments revealed that the properties of the arc translate into changes in the encapsulated product. Specifically, a larger, hotter arc results in more encapsulation in the final sample. These findings, along with evidence of graphite layers which have formed on precrystallized particles, indicate that the graphite layers may form by two sequential formation steps. The first step is the simple phase segregation of carbon from a cooling liquid particle, resulting in surface graphite. The second step is the growth of carbon on a crystallized nickel particle, regardless of the temperature at which this occurs. The proposed formation mechanism has significant implications for both a scientific understanding of the encapsulation phenomena, and possible commercial applications.

During the heat treatment of an anatase nanocrystalline powder at a high temperature, the two processes of anatase-to-rutile (A → R) transformation and grain growth would occur simultaneously and affect each other. With decrease of the original anatase grain size, the A → R transformation temperature range became extended on both sides, which may be partially attributed to the prevention effect of grain growth on this transformation. On the other hand, the grain growth process could be significantly enhanced by the A → R transformation, which can be ascribed to the higher atomic mobility because of the bond breakage during the transformation.

Ar+ ions with 1 keV energy were irradiated on aluminum nitride in an O2 environment and on aluminum oxide in a N2 environment. AlON on AlN and AlN on Al2O3 are formed by the Ar1 irradiation in O2 gas and N2 gas environments, respectively, and the formation of new surface layers is confirmed on the basis of Al2p near core levels and O1s, N1s core levels XPS depth profile analysis. Cu(1000 Å) films were deposited by ion-beam sputtering on Ar+ irradiated/unirradiated AlN surfaces, and the change of the adhesion strength was investigated by a scratch test. Cu films deposited on the irradiated AlN under an O2 environment showed higher bond strength than that on the unirradiated AlN. The improvement of bond strength of Cu films on the AlN surface resulted from the interface bonds between Cu and the surface layers. The bending strength of polycrystalline Al2O3 irradiated by Ar+ ions in N2 environment was also increased and the formation of nitride layer on the alumina was confirmed. A possible new surface layer formation mechanism on ceramics by the ion assisted reaction has been discussed in terms of surface analysis, chemical bond, and mechanical strength.

Ceramics based on the composition Bi2SrNb2O9 with isomorphic substitutions of cations in the Bi2O22+ and the perovskite layers, Bi2−xTexSr1−xNa(K)xNb2O9, have been prepared by solid state reaction. The ferroelectricity of this Aurivillius type structure has been studied. Dielectric measurements as a function of the temperature show a low temperature maximum in the dielectric constant that would correspond to a ferro-;paraelectric phase transition. The temperature of this maximum increases when the radius of the ion that substitutes Sr for decreases. A second maximum in the dielectric constant is found at higher temperature possibly corresponding to a relaxor ferroelectric. Measurements of remanent polarization as a function of the temperature seem to confirm the relaxor behavior, because the polarization disappears at temperatures between the two maxima of the dielectric constant. Saturated hysteresis loops are obtained for all the substituted samples at temperatures above 300 °C. Ferroelectric parameters such as the polarization, coercive field, and coupling factors of the BSN family compounds were obtained for the first time. The ac electric conductivity shows anomalies at temperatures close to those where the remanent polarization disappears. Activation energies calculated from measurements of dc electric conductivity, impedance arcs, and dielectric modulus data may be associated with thermally activated oxygen vacancies.

Laser-induced fluorescence, thermophoretic sampling, laser light scattering, and emission spectroscopy have been used to probe low pressure hydrogen/oxygen flames in which 3–50 nm, loosely agglomerated oxide nanopowders have been synthesized at high production rates by the pyrolysis of precursor vapors, followed by condensation in the gas phase. These measurements have enabled the identification of pyrolysis, condensations, and particle growth regions in the flame. Flame simulations using a one-dimensional stagnation flow model, with complex chemistry, demonstrate that the chemical and thermal flame structure can be accurately predicted for flames without a precursor. Furthermore, some flame structure changes induced by the addition of a precursor can be simulated by addition of analogous species to the chemical mechanism.

The characteristics of nanosized silicon nitride powders with doped Y2O3 and Al2O3 fabricated by a plasma-reacted chemical process were investigated. The chemical compositions of the powders were analyzed by wet chemical analysis. The morphology and the size distribution were determined by transmission electron microscopy (TEM). TEM with energy dispersive spectroscopy (EDS) was used to verify the existence of sintering additives in each individual particle. The crystal structure of the powders was identified by the selected area diffraction pattern (SADP). X-ray diffraction (XRD) technique was used for phase analysis and the measurement of degree of crystallinity. The characteristics of chemical bonding was analyzed by using Fourier transform infrared spectroscopy (FTIR).

The low temperature pressureless sintering of a nanosized Si3N4 powder with doped sintering additives was investigated. The microstructural evolution during sintering at different temperatures was analyzed using x-ray diffraction and scanning electron microscopy. The effect of using nanosized Si3N4 powder as a catalyst to accelerate the α→β–Si3N4 transformation of a commercial Si3N4 powder with larger particle sizes was also investigated. Finally, two stage sintering was used to study the feasibility of controlling the microstructure and the mechanical properties of the nanosized silicon nitride.

High-temperature creep in undoped Al2O3 and La2O3- or Y2O3- or Lu2O3-doped Al2O3 with a grain size of about 1 µm is examined in uniaxial compression testing at temperatures between 1150 and 1350 °C. The high-temperature creep resistance in Al2O3 is highly improved by the rare-earth oxide doping in the level of 0.045 mol %, and the creep rate is suppressed in the order La2O3 <Y2O3 <Lu2O3. Rare-earth ions in each doped Al2O3 are found to segregate in Al2O3 grain boundaries without forming amorphous phase or second-phase particles. The activation energy for creep in undoped Al2O3 is estimated to be 410 kJ/mol, while it is about 800 kJ/mol in the three rare-earth oxide-doped Al2O3. The grain boundary diffusivity must be highly reduced by the segregation of the dopant cation in Al2O3 grain boundaries.

Micro-Raman analysis was used to study the structure of TiO2 powders produced at low (260 °C) and high (600–900 °C) temperatures by vapor hydrolysis of titanium tetraisopropoxide (TTIP). Spatial inhomogeneity was discovered after the amorphous TiO2 powders produced at low temperature were calcined at 700, 800, and 900 °C for 3 h. The TiO2 powders produced at high temperatures (from 600 to 900 °C) were found to be spatially homogeneous and predominately anatase in structure. Small amounts of rutile and brookite are found for powders produced at 700, 800, and 900 °C after calcination at 600 °C for 3 h. The rutile and brookite impurities are believed to be concentrated on the surface of anatase based on a comparison of results of Raman and x-ray diffraction studies.

The self-propagating high temperature synthesis (SHS) of Al–Zr–N system composite ceramics was investigated in this paper. The melting point of Al was low (Tm = 660 °C), while that of Zr was high (Tm =1855 °C). Therefore, Al will melt and coalesce during reaction, which inhibit diffusion of nitrogen from outside the metal compact to interior due to collapse of the pore openings, while Zr will not melt under the combustion temperature which is lower than its melting point. It will not affect the permeation of nitrogen under the conditions. Accordingly, the ratio of Al and Zr in the initial mixed powders will affect the permeation of nitrogen from outside the sample to the interior, which results in different phase formation of the products. In this study, the relationship between the combustion parameters and the phase formation of the products will be experimentally determined through XRD analysis, and then thermodynamically analyzed.

Carbon ions were implanted with energies between 50 and 150 keV into thin iron layers at temperatures of –10 °C and –70 °C. Formation of iron carbide phases was studied as a function of fluence, which was varied from 1.2 × 1017 C+-ions/cm2 up to 1.4 × 1018 C+-ions/cm2. The sequence of phase transformation during subsequent annealing to temperatures of up to 450 °C was also investigated. Detailed analysis of structure and morphology was done by cross-sectional transmission electron microscopy and electron diffraction experiments. The existence of metastable iron carbide phases, θ-Fe3C, Χ-Fe5C2, η-Fe2C, and also the amorphous phase Fe(C), after high-fluence carbon ion implantation and the transformation of the formed metastable phases by subsequent annealing into the θ-Fe3C phase are demonstrated.

We report here on the preparation of La2/3Sr1/3MnO3 magnetoresistive thick films on polycrystalline Al2O3 substates by using the screen printing technique. It is shown that films can be obtained using high temperature sintering. While there is a reacted layer, this improves adhesion and is not too troublesome if the films are made thick enough. It is shown that PbO–B2O3 –SiO2 glass additives allow sintering at lower temperatures and can be used to improve the mechanical stress of the films. However, it is found that glass concentrations large enough to significantly improve the film adherence result in a weak low field magnetoresistance probably because grains are coated with high resistivity material. Strategies to overcome these difficulties are discussed.

Texture evolution in Si/SiC multilayers deposited by atmospheric pressure chemical vapor deposition on carbonized Si(001) substrates was investigated using x-ray diffraction and transmission electron microscopy. SiC layers were epitaxial and (001)-oriented. Si layers deposited on the SiC exhibited a columnar structure with predominantly (110) orientation which could be related to the nucleation. Orientational relationships were Si[111] ║ SiC[110] and Si[112] ║ SiC[110]. Also, a low density of (112)-oriented columns was present. Extensive twinning on the vertical {111} planes within the Si columns led to domains of hexagonal stacking up to 10 nm in size with the presence of 2H-Si and 4H-Si. Subsequent SiC layer growth on the (110)-oriented Si layer resulted in a (110)-oriented SiC layer if the Si layer was carbonized prior to growth.