It is observed that in sol-gel derived oxide systems, chemical processes lead to the formation of photoluminescent centers analogous to those produced by neutron or γ-irradiation of oxide crystals, fused silica, and other glasses. The initial observations about the phenomenon and its proposed mechanism are reported here.

A single-wafer multiprocessing technology has been developed based on the use of lamp heating and remote microwave plasma process energy sources for fabrication of in-situ-doped homoepitaxial Si and heteroepitaxial Si/GexSi1−x multilayer structures via chemical-vapor deposition. Some effective low-temperature (650°–800°C) processes were developed for in-situ pre-epitaxial growth surface cleaning. These chemical cleaning processes employ GeH4 + H2 or GeH4 + H2 + (HF or HCl) gas mixtures with very small GeH4-to-H2 gas flow rate ratios. Multilayer heteroepitaxial structures with controlled doping and Ge fractions consisting of strained Ge4Si1−x layers were fabricated and characterized.

Highly oriented 2212 BSCCO thick films were prepared on polycrystalline MgO substrates using a melt/crystallization technique. Results compare very favorably with those on single crystal materials.1,2 The melting, quenching, and annealing processes were all found to be important in the development of a good microstructure and good superconducting properties. The best results (Jc ∼ 2000 A/cm2 at 64 K and 6000 A/cm2 at 4.2 K) were obtained on films which had been melted, quenched to room temperature, heated to 860°C where they were annealed before slow cooling to room temperature in oxygen, lightly polished, and reannealed at 860°C.

Films containing the metals copper, yttrium, calcium, strontium, barium, and bismuth were grown by organometallic chemical vapor deposition (OMCVD). Depositions were carried out at atmospheric pressure in an oxygen-rich environment using metal beta-diketonates and triphenylbismuth. The films were characterized by Auger electron spectroscopy, Nomarski and scanning electron microscopy, and x-ray diffraction. The results show that films containing yttrium consisted of Y2O3 with a small amount of carbidic carbon, those with copper and bismuth were mixtures of oxides with no detectable carbon, and those with calcium, strontium, and barium contained carbonates. Use of a partially fluorinated barium beta-diketonate gave films of BaF2 with small amounts of BaCO3.

Magnetic susceptibility measurements are used to show that the superconducting transition temperature of yttrium barium cuprate is lowered by carbon trapped in the microstructure of dense polycrystalline materials during sintering. We show that carbon is retained in the material as a result of the porosity closing off during the sintering process. X-ray photoelectron spectroscopy and electron energy loss spectroscopy are used to show that the retained carbon forms a solid solution with YBa2Cu3O7–δ and resides in a barium carbonate-like configuration in the crystal structure. The origin of the lowering of the superconducting transition temperature and processing strategies for preventing carbon retention are discussed.

A wide variety of cation substitutions have been tried in the 1-2-3 compound, YBa2Cu3Ox, in the hope that its superconducting properties can be improved. While significant improvement has not been achieved, the response of the material to such substitutions can still be helpful in understanding its defect chemistry. In this paper, we report on measurements of the equilibrium oxygen content, by thermogravimetry, and the electrical conductivity of YBa2−zLazCu3Ox, with z = 0, 0.1, and 0.2. The results are consistent with the view that the stoichiometric composition for this system, YBa2Cu3O6, is a highly acceptor-doped material.

The microstructure and mechanical properties of several Ni–Al–Hf alloys in the composition range between NiAl (β) and Ni2AlHf (Heusler phase) have been studied. The volume fraction of Heusler phase, Vf, in these alloys varies from about 15 to 96%. The lattice misfit between the β and Heusler phases in two-phase alloys is larger than 5%, indicating no coherency between them. The yield strength increases with increasing Vf at all temperatures to 1000°C. Compressive ductilities of 4 and 7% were obtained for the alloy with Vf of 15% at room temperature and 500°C, respectively, but they decreased to 0% with increasing Vf to 96%. The corresponding fracture mode is basically transgranular cleavage. However, all the alloys can be deformed extensively without fracture at 1000°C. The hardness of the Heusler alloy is very high (8.3 GPa) at room temperature, and it decreases gently with temperature to 600°C, followed by a rapid decrease to 1000°C. The brittleness and high hardness of the Ni2AlHf Heusler phase at low temperatures are interpreted in terms of internal lattice distortion resulting from its crystal structure. The thermally activated process of deformation takes place above 600°C, which is responsible for the rapid drop of the hardness of the alloys.

The large number of constituent elements and high symmetry of the ordered Fe–Co−V alloys make a complete solution of its structure impossible from a single diffraction experiment. We have carried out a Rietveld refinement of the site occupancies for a partially ordered Fe–Co–V alloy using both neutron and anomalous dispersion x-ray powder diffraction data in order to obtain a complete crystallographic solution to its structure. Contrary to previous assumptions that V occupies both sites randomly or magnetic and Mössbauer studies that suggest that V has a site preference for the Fe sublattice, we find that the V dopant preferentially occupies the Co sites.

The kinetics of crystallization of four amorphous (or partially amorphous) melt spun Nd–Fe–B alloys induced by thermal treatment is studied by means of differential scanning calorimetry and scanning electron microscopy, In the range of temperatures explored experimentally, the crystallization process is thermally activated and generally proceeds in various stages. The Curie temperature and the crystallization behavior have been measured. The apparent activation energy of crystallization of most of the crystallization stages has been determined for each melt spun alloy. The explicit form of the kinetic equation that best describes the first stage of crystallization has been found. It follows in general the Johnson-Mehl-Avrami-Erofe'ev model, but clear deviations to that model occur for one alloy. Scanning electron microscopy demonstrates that preferentially hetereogeneous nucleation occurs at the ribbon surface which was in contact with the wheel. From crystallization kinetics results the lower part of the experimental time-temperature-transformation curves for all studied alloys are deduced and extrapolated to the high temperature limit of their range of validity, also deduced.

An excimer laser was used to mix Fe/Ti/C multilayered films on 304 stainless steel substrates. The samples were processed at both 1.1 and 1.7 J/cm2 with the number of pulses at each position varied between 1 and 10. Composition, microstructure, phase evolution, and tribological properties were observed to correlate with total laser fluence. Increases in Fe concentration from substrate interdiffusion and loss of C content were observed with increasing total laser fluence. The best tribological properties were observed in films possessing a combination of an amorphous or Fe3C phase plus fine grain TiC following processing at low and intermediate total laser fluence. At higher total fluences a combination of α-Fe, Fe3C, and fine-grain TiC was observed along with degradation in the wear and friction properties. Under optimum laser processing conditions the modified surface had a friction coefficient under dry sliding conditions reduced by a factor of 2 relative to uncoated 304 stainless steel and was significantly more wear resistant. These improvements in wear and friction appear to be related to the reduced chemical reactivity of the amorphous and carbide phases and to the influence of microstructure on improved mechanical properties.

Chalcogenide glasses of the systems Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te have been prepared. Several compositions were found suitable for drawing fibers for CO2 laser radiation (λ = 10.6 μm) transmission. The glasses were characterized by x-ray diffraction, DSC (Differential Scanning Calorimetry), SEM with EDX analysis, FTIR spectrometry, density, and microhardness measurements. The glass transition temperature and microhardness of Ge–Se–Sn and Ge–Sn–Se–Te glasses decreased with increasing Sn content, for most of the samples. The region of high IR transparency of Ge–Se–Sn, Ge–Se–Te, and Ge–Sn–Se–Te glasses was slightly expanded (1–2 μm) toward longer wavelengths, compared to Ge–Se glasses, mainly for the glasses containing 70 at.% Se. The intensity of the impurity absorption peak of Ge–O (at λ ∼ 12.8 μm), which usually appears in Ge–Se glasses, was reduced or absent in Ge–Sn–Se–Te glasses. The best fibers were produced with the glass composition Ge–0.8Sn0.2Se3.5Te0.5. An attenuation of 20 dB/m at 10.6 μm, and a transmitted maximum power density of 2.4 ⊠ 106 W/m2 were measured. The mechanical and optical characteristics of these glasses have been related to the glasses structure. Corresponding to the reduced masses of the bonds formed in the Ge–Sn–Se–Te system (in the amorphous region), it is expected that the multiphonon edge is slightly shifted. As a consequence, as was measured, the transparency region has been expanded by less than 2 μm toward longer wavelengths.

Post-deposition rapid vacuum annealing of tantalum nitride (Ta2N) thin film resistors (TFR) was successful in improving the temperature coefficient of resistance (TCR) to ±5 ppm/°C with starting TCR at about −140 ppm/°C. A subsequent aging study revealed degradation of the nichrome (NiCr) contact interlayer. Two improved contact layers, TiW and Tamelox (Ta/NiCr), were compared. The structural grain growth induced by the annealing effect resulted in Ta2N films having 100–1000 Å polycrystals in an amorphous matrix. The corresponding current conduction mechanisms were identified with a substrate-assisted tunneling model. The frequency response predicted potential applications to 100 GHz.

The thermal analyses of iron nitrate in stagnant and flowing air using different heating rates were conducted to establish the intermediate phases and reactions during its decomposition. In view of the thermal results, the degree of pyrolysis of the aerosol formed by atomizing ferric nitrate aqueous solution was studied. Hollow spherical particles were obtained and varied from noncrystalline to crystalline materials, depending on the pyrolysis temperature used. The decomposition efficiency of resulting particles increased with the pyrolysis temperature.

The Nb donor concentration and cation stoichiometry dependence of grain growth in SrTiO3 has been studied. The so-called donor anomaly, where grain growth is enhanced at low donor but suppressed at high donor concentrations, is observed only in nonstoichiometric compositions with an excess of B-site cations. Scanning transmission electron microscopy (STEM) observations indicate that this phenomenon is entirely a result of changes in the distribution of residual silicate phases. Exaggerated grain growth at low donor concentrations results from the presence of a continuously wetting grain boundary silicate, whereas inhibited growth at higher donor concentrations occurs in microstructures where the silicate phase is nonwetting. In stoichiometric compositions, however, grain growth rates are both slower and independent of donor concentration. In this composition regime grain growth appears to be limited by solid solution drag. The presence of residual silicates only in nonstoichiometric compositions implies a strong stoichiometry dependence of the silica solubility.

A Raman microprobe study of as-compacted nanophase TiO2 was carried out to investigate the spatial inhomogeneity of its anatase and rutile phases. Also, changes in the observed Raman spectra (line shifts and broadening) were investigated as a function of annealing at temperatures up to 600°C in argon or air. Microscopic phase inhomogeneity is observed and Raman spectral changes are shown to result from inhomogeneous oxygen deficiency in the nanophase TiO2. The line positions corresponding to the Raman active Eg modes in both anatase and rutile are found to be sensitive to this oxygen deficiency and are potential quantitative indicators of such deviations from stoichiometry.

LiyV2O5 films were produced by reactive de magnetron sputtering followed by electrochemical posttreatment in LiClO4. X-ray diffraction showed an orthorhombic structure. Spectrophotometric transmittance and reflectance measurements demonstrated that the luminous and solar absorptance increased moderately when y increased from zero to unity. It is argued that LiyV2O5 is useful as an ion storage material operating in conjunction with electrochromic films.

Monocrystals of LiF, ion implanted with Ar+, were exposed to thermal shock in a plasma of different intensities. Ion implantation substantially alters the fracture pattern and characteristics of the material, particularly in reducing the thermal shock resistance parameter, S′, and in increasing the damage resistance parameter, S″. The former parameter indicates that ion implantation allows fracture to be initiated at lower thermal shock temperature differences and the latter parameter is associated with higher crack densities and lower crack penetration depths. The increase in the parameter S″ indicates that ion implantation can result in a higher mechanical stability and greater durability of the crystals damaged by thermal shock. Surface melting at very high heat fluxes eliminates any effect of ion implantation.

Tin-lead (40 wt. % Pb) solder-matrix composites containing 8–54 vol.% continuous unidirectional copper plated carbon fibers were fabricated by squeeze casting for use as low thermal expansion solder preforms. The low thermal expansion greatly increased the thermal fatigue life for solder joints between materials with low thermal expansion coefficients. For example, for 29 vol.% fibers, the thermal expansion coefficient was 8 ⊠ 10−6/°C (25–105°C) in the direction parallel to the fibers compared to a corresponding value of 24 ⊠ 10−6/°C for plain solder. The thermal fatigue life for cycling 2 cm long alumina-to-alumina solder joints between 25 and 100°C was increased from 98 to 183 cycles by using 29 vol.% carbon fibers in the composite solder. The fibers also increased the tensile modulus and tensile strength of the solder, but the ductility was decreased. The copper coating on the carbon fibers increased the tensile strength and ductility of the composite.

Spinning condition dependences of the microstructures of a pitch precursor fiber which is a raw material for carbon fiber preparation were studied in detail. The degree of preferred orientation of the molecules in a pitch precursor fiber along the fiber axis was higher when spinning was done at a lower mesophase pitch viscosity. An intermediate diameter gave the highest degree of preferred orientation. The degree of preferred orientation of the molecules in an extruded pitch rod was especially low. The crystallite size Lc(002) of the pitch precursor fiber also was varied by controlling the spinning conditions, and exhibited a good correlation with the degree of preferred orientation. Mesophase pitch at a higher temperature possessed a smaller Lc(002) and a larger d002. The small Lc(002) observed at high temperature was maintained by a rapid cooling to room temperature, but the large d002 relaxed to a small value at room temperature, even with rapid cooling. A qualitative model for the formation of a preferred orientation through spinning is proposed.

Small-angle x-ray and neutron scattering experiments were performed in several polymer-containing portland cement pastes with the same w/c ratio. The nature of the results is discussed in terms of the role of the polymer upon the properties of the materials. A comparison with other works seems to indicate that the capillary pores are strongly affected whereas the gel porosity remains unchanged by the polymer solutions.