The superconducting filaments in (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composite tapes have been imaged directly through the outer silver sheath of an unpolished tape by means of a magneto-optical imaging technique. The images reveal the morphology and alignment of the uppermost layer of filaments located as much as 112 μm below the unpolished tape surface, the depths of these filaments, and the homogeneity of the magnetic flux distribution within these filaments. These results demonstrate that the magneto-optical technique is a valuable nondestructive tool for analyzing (Bi, Pb)2Sr2Ca2Cu3Ox composite tapes.

Ultrafine silicon carbide powder with an average particle size of 90 nm was densified by hot-processing with the addition of Al2O3, Y2O3, and CaO at 1750 °C. Silicon carbide nanoceramics with an average grain size of 110 nm were prepared by liquid phase sintering at low temperature. The materials showed superplastic deformation at a strain rate of 5.0 × 10-4/s at 1700 °C, which is the lowest temperature published. The microstructure and deformation behavior of materials from a submicrometer powder were also investigated as a reference.

Methanol decomposition on a clean polycrystalline copper oxide surface was studied by x-ray photoelectron spectroscopy (XPS). Methanol was adsorbed at 133 K and desorbed over a broad temperature range. When CuO was exposed to a very low dose of methanol vapor, dissociative adsorption takes place, leading to the formation of CH3O and H2O. This is attributed to the presence of preadsorbed oxygen on the CuO surface.

Films of Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 have been grown using Atomic-Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been combined with layers of closely related metastable compounds like Bi2Sr2Ca7Cu8O20 (2278) and rare-earth-doped compounds like Bi2Sr2DyxCa1–xCu2O8 (Dy: 2212) to form heterostructures with unique superconducting properties, including superconductor/insulator multilayers and tunnel junctions. Transmission electron microscopy (TEM) has been used to study the morphology and microstructure of these heterostructures. These TEM studies shed light on the physical properties of the films, and give insight into the growth mode of highly anisotropic solids like Bi2Sr2CaCu2O8.

The addition of Y2BaCuO5 (211) particles to large grain melt textured YBa2Cu3O7–δ(Y123) has significantly improved the critical current density (Jc) of this material. Here, a systematic quantitative analysis on the effects of the 211 addition was performed on a microscopic scale with a systematic variation of the initial volume percent of 211. From the correlation between critical current measurements and quantitative microscopy of both (001) and (110) sections, a maximum value of Jc is observed, corresponding to a measured Y123 volume percent of 20% ± 3%. Accounting for the loss of liquid phase for the present processing, the corresponding optimum initial volume of 211 for the highest measured Jc is 40%. Further comparison between the weighted Jc and the true flux pinning force (Fp) also shows a maximum pinning force for an initial 211 addition of 40%. Although the weighted Jc starts to decrease with an initial 211 volume of above 40%, the pinning efficiency at higher magnetic fields (2–4 T) of the superconducting Y123 matrix was actually improved with an ever increasing 211 addition to at least 50%. Though an increasing addition of 211 is effective in producing efficient flux pinning sites in the Y123 matrix, percolation paths in the Y123 matrix become limited for supercurrent. Hence, a measured 211 volume corresponding to 80% 211 is proved to give the best possible critical current density. Furthermore, crack opening and crack spacing of the superficial cracks are found to decrease with an increasing 211 addition and with a decreasing 211 interparticle spacing. The penetration and surface length of each of these superficial cracks are hence reduced, which leads to a better electrical connectivity in the Y123 matrix.

The thermal expansion coefficient of Bi-based 2223 and 2212 ceramics has been measured using dilatometric apparatus. Different typologies of bulk superconducting samples have been tested, in particular (2223) phase fully dense hot-pressed samples both parallel and perpendicular to the direction of applied pressure, pressureless sintered samples, and finally hot-pressed (2212) phase specimen, in order to gather information on the contribution of secondary phase to thermal expansion behavior. From the observed α (thermal expansion coefficient) values, accounting for the sample orientation degree, it was possible to distinguish the contributions along the basic crystallographic directions and to determine the following for (2223) phase: αa = 12.2 × 10-6 °C-1, and αc = 20.8 × 10-6 °C-1 for temperatures 200–600 °C. Theoretical α values were then calculated for the different samples and successfully compared with the measured ones. As regards (2212) phase, thermal expansion coefficient was evaluated for the oriented sample, and a value for random one extrapolated; the results are very similar to that of (2223), but lower with respect to previously reported data in air atmosphere.

The thermodynamic stability of TlBa2Ca2Cu3O9–y (1223) and substitutionally related phases has been studied by performing extended high-temperature anneals in a two-zone furnace. This approach allows for independent control of each of the thermodynamic variables: the oxygen and thallous oxide partial pressures [P(O2) and P(Tl2O)], the sample temperature, and the sample composition. P(Tl2O) determines which of several superconducting phases form in the unsubstituted Tl–Ba–Ca–Cu–O system. TlBa2Ca2Cu3O9–y is stable only within a narrow window of P(Tl2O). Partially replacing Tl with Pb and Ba with Sr substantially increases the stability of the 1223 phase. The composition (TlxPb0.5) (Sr1.6Ba0.4)Ca2Cu3O9–y yields only the 1223 phase under two-zone conditions when P(Tl2O) exceeds a lower bound. The stability of Pb- and Sr-substituted 1223 relative to the 1212 phase is related to the substitutional stoichiometry, rather than P(Tl2O).

The inherently weak mechanical properties of bulk monolithic high-temperature superconductors (HTS) have been a concern. Properly selected reinforcements in fiber and whisker forms have been introduced to the HTS ceramics to improve their mechanical properties. In this paper, mechanical behavior of a MgO-whisker reinforced Pb-doped Bi-2223 (BPSCCO) HTS composite fabricated by a solid-state processing method is studied. The (MgO)w/BPSCCO HTS composite has been shown to exhibit excellent superconducting properties. Elastic properties, strengths, and notched fracture toughnesses of both the monolithic BPSCCO and the (MgO)w/BPSCCO HTS composite are investigated. Detailed mechanical properties are reported for the first time for the (MgO)w/BPSCCO HTS composite. Mechanisms of strengthening and toughening in the MgO-whisker-reinforced HTS composite are also discussed.

We examine the formation of Si1-xCx (x = 0.04–0.2) by means of CFy (y = 0,1,3) implantation in p-type Si, for application as a wide-bandgap emitter in a Si heterojunc-tion bipolar transistor. Upon implantation with 2.5 × 1016 CF+/cm2 at 45 keV, and subsequently with 2.5 × 1016 C+/cm2 at 30 keV, an amorphous top layer is formed. Annealing at temperatures up to 900 °C leads to a layer consisting of nanocrystalline material. High resolution transmission electron microscopy and secondary ion mass spectrometry show that a well-defined nanocrystalline/crystalline interface is created at an anneal temperature of 550 °C. At higher temperatures lattice defects start to develop. Preliminary attempts to dope the material via phosphorus or arsenic implantation indicate that temperatures of at least 900 °C are required to activate a fraction of the implanted dopants. This, however, adversely affects the adlayer/substrate interface.

Doped zinc oxide thin films were prepared by rf magnetron sputtering using the dopants Al, Ga, In, and Ge. The best results were obtained with Al and Ga doping where room temperature conductivities were as high as 1600 and 1800 ohm-1 cm-1, respectively. Hall measurements were performed at 77 K and 298 K. The Hall mobility as in the range of 9 to 22 cm2/Vs, and there was generally very little temperature dependence of the mobility or conductivity. Cation doping levels were as high as 10 at. %, but the conductivities did not increase beyond 3 at. % doping level. For films with high conductivity, electron carrier concentrations from Hall measurements were significantly lower than the concentrations of dopants. Optical measurements on the films showed that the average transmittance though the visible range is higher than 85%. The measurements also indicated a blueshift of the absorption edge with doping.

The ball-milling of pure Fe and Zn elemental powders corresponding to the Г-(Fe3Zn10), Г1-(Fe5Zn21), δ-(FeZn7), and ζ-(FeZn13) compositions yields metastable crystalline phases. This is demonstrated by the peaks observed in the DSC measurements of the different phases. These crystalline phases evolve differently with distinct or characteristic stages with heat treatments. Cold-welding and powder agglomeration are extensive, while the milled materials are completely homogeneous.

Blended elemental W–7 wt.%Ni–3 wt. %Fe powders were mechanically alloyed in a planetary ball mill and a heavy duty attritor. The structural and morphological characteristics of the as-milled powders were characterized by x-ray diffraction and electron microscopy techniques. A ternary solid solution of Fe and Ni in W formed in both the cases; the amount of Ni and Fe dissolved is higher in the attritor-milled powder than in the ball-milled powder. Morphologically, the W-rich particles in the attritor-milled powders were spheroidal, smaller in size, and showed a narrower size distribution than in the ball-milled condition. These differences led to increased density in the attritor-milled powder compact and significant differences in chemical composition of the matrix region and W-rich grains. Transmission electron microscopy investigations of the matrix region in the compacts revealed the presence of Fe2W precipitates uniformly distributed in an Ni(Fe, W) matrix.

A systematic experimental study of solute migration during thermal annealing and oxidation of type 2011 aluminum alloy is described. Specimens of this alloy were implanted with Ti, Cr, or Al ions to doses in the range 2 × 1015–2 × 1017 ions cm-2. The implanted substrates were annealed at 500 °C in vacuum or an oxygen atmosphere and analyzed with Rutherford backscattering and scanning electron microscopy. Changes to the alloy composition resulting from segregation of constituents in the near surface region occurred for both implanted and unimplanted specimens, though the effect was substantially more pronounced following implantation. In addition, segregation was affected by the type and dose of the implanted ion. For the Ti implants under oxidizing conditions, the Ti ions were found to diffuse toward the surface and form a thick oxide layer. Segregation of Cu and Pb/Bi then occurred below this oxide layer. In contrast, implanted Cr ions under similar conditions were observed to diffuse into the substrate with only a thin oxide layer being formed at the surface. Consequently, Cu and Pb/Bi segregated close to the surface.

An intermetallic Fe3Al alloy was cast, hot rolled, annealed (870 K), and finally quenched. After this treatment, the alloy had an imperfectly ordered B2 structure. The polycrystalline sample was then warm rolled at 800–830 K. The crystallographic texture of the rolled specimen was quantitatively studied within the range, ∈ = 20–80%. Even at large strains (∈ = 80%), recrystallization was not observed in the microstructure. It was found that the rolling texture of Fe3 Al is very inhomogeneous through the sample thickness. In the center layer, a large volume fraction of grains with a {111} lattice plane parallel to the sheet surface, {111}〈uvw〉, and a weak {001} 〈110〉 component were observed. In contrast, close to the sheet surface layer, a weak texture containing the {11 11 8} 〈4 4 11〉 and the {012} 〈110〉 orientations was formed. The results are interpreted in terms of the activation of {110} 〈111〉 and {112} 〈111〉 slip systems. The through-thickness texture gradient was attributed to the inhomogeneous strain distribution during rolling, leading to plane strain in the center layer and to shear strains close to the surface.

The structure of a stable decagonal quasicrystal with 0.4 nm periodicity, formed in a conventionally solidified alloy with composition Al71.6Ni23.7Fe4.7, was investigated by high-resolution electron microscopy. It was found that this decagonal phase is one of the best-ordered quasicrystals, without any detectable linear phason strain and with only weak random phason strain. The structure is interpreted as an aperiodic tiling of decagonal atom columns with a diameter of about 1.2 nm. The atomic arrangements in special local regions are discussed on the basis of computer simulations.

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO3)3 · 9H2O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al2O3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO2, as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al2O3 between 900 and 1000 °C and its further reaction with amorphous SiO2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

Surface grinding was performed on two silicon nitrides with different microstructures. The ground surfaces of both materials were observed with scanning electron microscopy (SEM) to consist of areas of microfracture, smeared areas, and areas covered with fine debris particles. It was determined that microfracture is the primary mechanism for material removal. Subsurface grinding damage was revealed by a bonded-interface technique to take the form of median-type cracks extending from the plastic zones. Distributed intergranular microcracks and intragrain twin/slip bands were observed within the plastic zones. The strengths of transverse-ground specimens were measured in four-point flexure. For the silicon nitride with a fine grain size and a mildly rising toughness-curve, grinding damage resulted in a drastic strength degradation compared to polished specimens. In contrast, the silicon nitride with large and elongated grains and a steeply rising toughness curve showed relatively little strength loss. The relationship between the ceramic microstructure and the damage tolerance in abrasive machining is discussed in light of these results.

Dislocation loops and stacking fault formation mechanism in α–Si3N4 have been studied by annealing α–Si3N4 powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si3N4. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si3N4 lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si3N4 fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si3N4 lattice arisen from the fact that the observed unit cell dimension of α–Si3N4 has a wide variation, and also to some related phenomena in processing of Si3N4.

A special form of the Debye formula for calculating the powder x-ray diffraction of a turbostratically stacked layer system is derived, and calculated diffraction patterns for turbostratically stacked graphite and MoS2 layers are presented. Single-molecular-layer MoS2, prepared by exfoliation of lithium-intercalated MoS2 in water or alcohols, has been deposited on various supports, and x-ray diffraction patterns show that the restacking of the MoS2 layers can be perfectly turbostratic. The restacked MoS2 may or may not have water or organic bilayers between them, depending on the deposition conditions.

Microstructure, microchemistry and mechanical properties of hardened macro-defect-free (MDF) composites processed at various rotor rates in a Banbury mixer were investigated. A quiescently formed calcium aluminate-polyvinyl alcohol composite served as a substitute for an unmixed system. Results from the Banbury studies in conjunction with microchemical analysis of the unmixed composite showed evidence that the polymer-particle interaction is a mechanically induced crosslinking reaction. The rate of the mechano-chemistry increases with mixing speeds. Scanning electron micrographs (SEM) and transmission electron micrographs (TEM) of hardened composites mixed for 15 min at 30, 50, 100, and 200 rpm indicate that much of the mechanical strength of MDF is due to the crosslinked interphase zones that blanket the cement grains. Stresses in the paste due to mixing can destroy the interphase layer, leading to a weaker hardened composite. Microchemical analysis revealed that the mechano-chemistry of the system did not vary with changes in the mixing conditions studied.