In order to understand the formation mechanism of the Y2BaCuO5 free region, microstructures concerning incongraent mehing and peritectic reaction were studied in melt-textured Y–Ba–Cu–O oxides. It is found that spherical pores form during incongruent melting of the YBa2Cu3O7−y phase into Y2BaCuO3 and a Ba–Cu–O liquid phase. As the melting goes on, liquid phase flows into the pores and then produces spherical liquid pockets containing a few Y2BaCuO5 particles. During slow cooling of the sample from the peritectic temperature to the temperature where YBa2Cu3O7−y phase is formed, the liquid pockets are converted into YBa2Cu3O7−y phase containing a few Y2BaCuO5 particles. Sometimes, remnant Ba–Cu–O liquid phase is present at the center part of the Y2BaCuO5 free regions due to the incomplete peritectic reaction. It is concluded that formation of spherical pores during incongruent melting of YBa2Cu3O7−y is responsible for the formation of the Y2BaCuO5 free regions.

We deposited (Mn,Zn,Fe)1−xO thin films of a wüstite structure on SiO2/Si(100) by ion beam sputtering using a single-crystal Mn-Zn ferrite target. The wüstite structure of the as-deposited film, confirmed by XRD, TEM, and XPS analysis, appeared to originate from an oxygen-deficit ambient and also from the preferential resputtering of the oxygen ions in films during deposition. The as-deposited films showed ferrimagnetic characteristics having quite a large Ms in spite of their crystallographic structure, wüstite. Such an unusual phenomenon is presumably due to the different magnetic moments of the constituent cations with disordered distribution. This wüstite phase could be transformed into the spinel ferrite phase with the same preferred orientation during postannealing under an appropriate oxygen partial pressure. The interplanar distance of the as-deposited films decreased with increasing Ts due to a release of compressive stress. The Ms of the film had a maximum value at about 275 °C, while the resistivity, mainly governed by the grain boundaries, was almost the same irrespective of Ts.

Partially carbonized polyacrylonitrile fibers were observed to undergo a resistivity change of 2 to 4 orders of magnitude at a transition temperature typically in the range of 98 °C to 200 °C. The current-voltage curves exhibited an initial supercurrent-like increase, followed by a rapid drop to a high resistance state, and then a rise in current again at a later stage. These phenomena cannot be interpreted by existing theories on switching in inorganic amorphous semiconductors. They are explainable if the microstructure of the pyrolyzed fiber is viewed as comprising nanometer-scale superconducting phases interspersed with semiconducting phases, much like a large number of Josephson junctions connected in series.

Using transmission electron microscopy, we investigate Si3N4 grown in situ on GaAs metal-insulator-semiconductor (MIS) device structures with a Si interlayer, which has been previously shown to improve the electrical properties of field-effect transistors with Si3N4 gates on GaAs. We find that the primary role of the Si interlayer is to prevent the reaction between the nitride or nitrogen used for growth and GaAs. The interlayer thickness dependence of this microstructure, and its relationship to electrical properties, are discussed. The optimal thickness of the thin pseudomorphic Si interlayer appears to be around 0.4 nm. The growth temperature dependence of the critical thickness for morphological instability is demonstrated.

Diamond-like carbon (DLC) films were deposited on (100) silicon wafers and silicon nitride balls by RF plasma-assisted chemical vapor deposition at a pressure of 700 mTorr and a substrate temperature of 360 K. The friction coefficient and the wear rates were measured using a pin-on-disk tribometer in 40% humid and dry air. Friction coefficients are near 0.05 in all cases measured. In dry air, the wear of silicon nitride and steel against DLC is below measurement capability because of a protecting DLC transfer layer, and wear of DLC is 2.5 ± 10−8 mm3/Nm against silicon nitride and 6.5 ± 10−9 mm3/Nm against steel. In humid air, the DLC transfer layer does not adhere to the solids, and wear of both bodies is larger. Unmeasurable wear is obtained when DLC slides against itself in humid air; the wear rate is 5 ± 10−9 mm3/Nm in dry air. These results are interpreted in terms of the properties of a friction-induced transformation of the surface layer of DLC.

Diamond was deposited on Si(100) substrates by the microwave plasma-assisted chemical vapor deposition method in three steps: carburization, biasing, and growth. High-resolution transmission electron microscopy in cross-sectional view has been used to observe the evolution of microstructures around the interfacial region between diamond and Si in each processing step. The chemistry near the interface was characterized with elemental mapping using an energy-filtered imaging technique with electron energy loss spectroscopy. An amorphous carbon layer, β-SiC and diamond particles, and graphite plates have been observed in the carburization stage. β-SiC can form in epitaxial orientation with Si in the following stage of biasing. Graphite and amorphous carbon were not observed after the bias was applied. Diamond grains were aligned in a strongly textured condition in the growth stage. It has been found that diamond, SiC, and Si all have (111) planes in parallel. The relation of the evolution of microstructure with the processing conditions is also discussed.

Extended dislocations including partial dislocations and a stacking fault in Al70Pd20Mn10 icosahedral quasicrystal have been observed and identified for the first time. The diffraction contrast and defocus convergent-beam electron diffraction experiments show that the dissociation of the extended dislocations is of the form 1/2<1 −2 0 0 −2 1> → 1/4<1 −3 1 −1 −1 1>+ 1/4<1 −1 −1 1 −xs3 1> with a stacking fault between these two partial dislocations. For the partial dislocations, the Burgers vector components in physical space b¶part are along different fivefold axes with a magnitude of 0.17 nm, which is about one seventh of that in complementary space. For the perfect dislocation, the Burgers vector component in physical subspace b¶perf is along a twofold axis with a magnitude of 0.183 nm, which is about an eleventh of that in complementary space.

Powders and thin films of high-yield lanthanum hexaluminate (LaAl11O18) were prepared by a sol-gel route and compared with yields obtained by conventional hot-pressing of oxide powders. X-ray diffraction and transmission electron microscopy (TEM) were used to characterize powders and thin films deposited on TEM grids. While the solid-state kinetics of formation of LaA11O18 are known to be extremely sluggish, the yield of LaAl11O18 formed by the sol-gel route was much higher than that obtained by processing under similar conditions by solid-state reaction of elemental oxides. The development of a very fine grained microstructure at 1200 °C and a coarser, much more mature microstructure at 1450 °C, with strong texturing of the magnetoplumbite phase, was observed by TEM. Isolated grains of LaAlO3 were present in all powders and films. Trace impurities, introduced most likely as impurities in the initial alumina sol, appear to have segregated to both the grain boundaries and to the external surfaces of grains in as-prepared films.

A process was developed to prepare nanocrystalline and quantum-confined particles of manganese-doped zinc sulfide. By the reaction of diethylzinc with solubilized hydrogen sulfide, particle sizes of 30–36 Å were achieved by control of reactant concentration, and size appeared to vary with the thermodynamic considerations indicative of homogeneous precipitation. Managanese doping required the development of an in situ chemical reaction compatible with the homogeneous precipitation reaction. To that end, ethylmagnesium chloride was reacted with manganese chloride to form the metastable diethylmanganese which acted as the dopant source. Quantum confinement of the particles was accomplished by using methacrylic acid and poly(methyl methacrylate) polymer of low molecular weights. These surfactants were transparent to the ultraviolet wavclcngths of light which allowed luminescent excitation of the material and provided surface passivation which enhanced phosphor brightness. The surfactant adsorption and effect of ultraviolet curing of the surfactant on the luminescent efficiency of the doped nanocrystals was investigated by infrared spectroscopy. These results indicate that the chemisorption of the surfactants to the nanoparticle surface and oxidation followed by crosslinking during curing are responsible for the improvement in luminescent efficiency.

The structure and the thermal stability of the Fe0.89B0.11 rapidly quenched alloy have been investigated. Transmission Mössbauer measurements were carried out as a function of temperature in the range from 148 K to 513 K. Room temperature x-ray diffraction and transmission and conversion-electron Mössbauer experiments, as well as 4.2 K spin-echo nuclear magnetic resonance measurements, were also performed after some selected thermal treatments for one hour between 523 K and 1273 K. Based on these experiments it is suggested that the alloy is inhomogeneous at nanoscopic scale and consists of a fine dispersion of a defective boride phase with an o-Fe3B-like short-range order, embedded in an α-Fe matrix. This result gives support to the models which indicate phase separation in the amorphous phase with o-Fe3B short-range order prevailing in the hypereutectic iron concentration range. This phase was found to be less stable than the undefective one present in the less boron concentrated alloys. The transformation into the equilibrium phases, analyzed with an Arrhenius-type temperature dependence for the increase of the relative fraction of Fe2B, led to an activation energy Ea = 1.38 ± 0.68 eV/atom.

Some aspects of the industrial development of copper-on-alumina catalytic materials for the combined removal of SO2 (DeSOx and NOx (DeNOx) from flue gas of power plants are discussed. Applications of these catalytic materials for the recovery of sulfuric acid from diluted aqueous solutions of ammonium sulfate are also outlined. In particular, the following specific topics are analyzed: (i) the relationship between textural and reactivity properties. (ii) the problem of the design of samples with improved DeSOx properties in relation to the stability of the samples over extended operations, and (iii) the optimization of the regeneration characteristics of the samples. Details on the flow sheet of the technology are also given.

Gas-phase particle size distributions and lead loss were measured during formation of (Bi,Pb)-Sr-Ca-Cu-O and pure PbO particles by spray pyrolysis at different temperatures. A differential mobility analyzer (DMA) in conjunction with a condensation particle counter (CPC) was used to monitor the gas-phase particle size distributions, and a Berner-type low-pressure impactor was used to obtain mass size distributions and size-classified samples for chemical analysis. For (Bi,Pb)-Sr-Ca-Cu-O, as the processing temperature was raised from 200 to 700 °C, the number average particle size decreased due to metal nitrate decomposition, intraparticle reactions forming mixed-metal oxides and particle densification. The geometric number mean particle diameter was 0.12 μm at 200 °C and reduced to 0.08 and 0.07 μm, respectively, at 700 and 900 °C. When the reactor temperature was raised from 700 and 800 °C to 900 °C, a large number (∼107 no./cm3) of new ultrafine particles were formed from PbO vapor released from the particles and the reactor walls. Particles made at temperatures up to 700 °C maintained their initial stoichiometry over the whole range of particle sizes monitorcd; however, those made at 800 °C and above were heavily depleted in lead in the size range 0.5–5.0 μm. The evaporative losses of lead oxide from (Bi,Pb)-Sr-Ca-Cu-O particles were compared with the losses from PbO particles to gain insight into the pathways involved in lead loss and the role of intraparticle processes in controlling it.

Ba1−xSrxTiO3 (x = 0.9) ferroelectric ceramics were prepared successfully using a new wet technique and their structure and dielectric properties compared with those synthesized by the solid-state reaction method. The voltage dependence of the dielectric constant in the paraelectric phase was examined. It was found that the dielectric constants of these materials, prepared by both methods, exhibit large changes with applied voltage in the paraelectric phase. Tunability (the percentage change of the dielectric constant from its zero-bias value in the presence of a de-biasing electric field) was observed to exceed 30% at only 1.7 kV/cm at 77 K in the samples prepared by the solid-state reaction method. The tunability was found to decrease dramatically as the operating temperatures increased above the Curie point. These observations are interpreted in light of an existing phenomenological theory. The dependence of the dielectric constant in the paraelectric state upon a de-biasing electric field is also demonstrated as a potential method for the characterization of dielectric nonuniformities in ferroelectric ceramics.

The possibility that crystal-to-amorphous phase transformations can be induced by one or more underlying instabilities of the crystalline phase has been investigated in highly supersaturated solid solutions of Nb-Pd. Several unusual properties were discovered that may be identified as precursor effects of the collapse of the bcc α-Nb terminal solution to the amorphous phase. Elastic neutron diffraction measurements of α-Nb solutions found, with increasing Pd concentration, an anomalously large increase of the average atomic root-mean-square displacement to about half of the value at which the Lindemann criterion predicts the lattice should melt. Low-temperature heat capacity measurements yielded a concomitant decrease in the Debye temperature, suggesting that supersaturation causes an elastic modulus to soften. Single crystals of α-Nb solutions at high supersaturations have a highly anisotropic structure that is visible in transmission electron microscopy images; it is consistent with the development of a soft phonon mode leading to a bcc-to-ω phase transformation. Considered together with the results of other recent experiments, these findings suggest that shear instability of the crystalline phase plays an important role in the crystal-to-amorphous transformation and that the average static mean-square displacement of atoms in the lattice acts as a useful parameter for the stability of the crystal with respect to amorphization.

Using an inductive technique, we have measured the in-plane resistivity ρa of stages 2, 4, 5, and 8 SbCl5-GIC's versus temperature T and pressure p in the ranges 130–300 K and 0–0.85 GPa. The room temperature values of ρa range from 4.0 μΩcm for the stages 5 sample to 7.7 μΩcm for the stage 8 sample. At all pressures, ρa shows a metallic temperature dependence ρa ∼ Tα, with 1 ≤ a ≤ 2, but in contrast to the c-axis resistivity ρc, it depends only very weakly on pressure and/or intercalate structural order. We show that the behavior observed is consistent with a band conduction model.

The solid state reaction between Co and Si has been studied in bulk diffusion couples between 850 and 1100 °C. At the scale of the observations made, the three phases Co2Si, CoSi, and CoSi2 are found to grow simultaneously, according to diffusion controlled kinetics. The results are analyzed in term of the Nernst-Einstein equation that directly relates diffusion fluxes to the free energy changes driving the formation. The growth rates obtained for CoSi2 at high temperatures, in the present bulk samples, are compared with those determined by others in thin films, at much lower temperatures. The comparison requires that attention should be paid to two factors. The first one is that the laws of growth are slightly different for a phase growing simultaneously with two other ones (bulk) and one phase growing alone (thin films). The second factor is the grain size of the various samples, which varies with the temperature of reaction. Once this is done, excellent agreement is obtained between the two sets of measurements. Moreover it is shown that knowing the grain size, it is possible to calculate quite accurately the growth rate from the respective isotope diffusion coefficients both for lattice and grain boundaries of Co and Si in CoSi2.

Zone-melting recrystallization (ZMR) is a lateral epitaxy technique used to recrystallize polycrystalline thin films on substrates. Large-area multilayer structures of thin films processed with ZMR are usable in microelectronics applications. During the processing, slight variations in thermal gradients can lead to different crystalline qualities. Thus, processing uniformity over the wafer is strongly affected by the sensitivity of both the melt width and the solid/liquid interface to changes in the thermal environment. Processing control must either be set initially in a stable operating range or adjusted dynamically to variations in processing. Numerical simulations of the ZMR process were conducted to evaluate the sensitivity of the process over a wide range of temperatures and materials. Results indicate that material with melting points below 900 °C are very sensitive to temperature disturbances. This is due to the increased influence of conductive heating and decreased influence of radiative heating. The increased reflectivity during phase change curbs the amount of absorbed radiation. As the absorbed radiation becomes less influential, the sensitivity of the slush width decreases. Conductive effects should be considered when processing materials with melting points at or below 900 °C.

A fiber-reinforced in situ metal matrix composite (MMC) consisting of copper (Cu) and 20 mass% niobium (Nb) was produced by large strain cold rolling. The rolled MMC revealed a very high strength combined with good electrical conductivity. The microstructure of single Nb filaments was investigated employing transmission electron microscopy (TFM). In heavily rolled specimens (∊max = 99.4%) randomly arranged dislocations as well as dislocation cells were observed. Furthermore, structurally less-ordered areas were discovered, the size of which frequently extended over the entire filament width. The shrinkage of these zones during heating was directly observed in the TEM. The impact of such structurally less-ordered areas on the strength was assessed. The discovery of the degradation of structural regularity in the Nb filaments of heavily cold-worked Cu-20 wt. % Nb shows that the underlying microstructural mechanisms responsible for the high strengths observed are far from being understood and that the strain-hardening models for Cu-based in situ composites currently discussed do not yet account for all relevant microstructural features.

We have produced and chemically analyzed a series of high purity iron-zinc alloys with iron concentrations in the range 4-27 wt. %. The technique involved slow diffusion of high purity zinc with small particle iron powder. We produced alloys within the four main iron-zinc phases, Zeta, Delta, Gamma-1, and Gamma to aid in the identification of the intermetallic phases formed in commercially produced galvanneal steel coatings. The diffusion technique produces iron-zinc alloys which are suitable as instrument calibration standards for galvanneal producers and users. A chemical titration technique which measures iron concentration to within 0.5 wt. % was also refined. In determining the bulk iron concentrations of the samples, we have compared the accuracy of the wet chemical technique with Induction Coupled Plasma spectroscopy. Homogeneity was measured using an electron microprobe and a scanning transmission electron microscope. The data show that samples are homogeneous to greater than 98% of the mean iron concentration.

Activated carbons were used to selectively remove NOx from simulated flue gas at temperatures between 25 and 125 °C. Processing conditions and physical/chemical characteristics of the carbons which affected NOx adsorption, storage, and release were investigated. Oxygen as a coreactant was necessary to maximize the conversion of NO to NO2 and condensation of NO2 within the pores of the carbons. A NO-to-NO2 conversion mechanism is presented and discussed relative to previous research. A process for selectively removing NOx and concentrating it as NO2 in an alternate process stream is outlined. The purified NO2 stream could be used for chemicals manufacturing.