To clarify the effect of undercooling on the crystal growth of Y-123, the growth rate was measured with different undercoolings. The growth rate of the {100} face shows a quadratic dependence of undercooling, while that of the {001} face shows a linear dependence in the sample with nominal 123 composition. In the case with 211-rich composition, the growth rate of each face was larger than that compared with nominal 123 composition since the mass flux from 211 particle for peritectic reaction becomes large. Addition of excess 211 alters the undercooling dependence of Ra from quadratic to linear. It is considered that the entrapment of 211 particles into 123 crystals supplies step sources beside screw dislocations. The growth rate of the {001} face is larger than that of the {100} face up to 26° of undercooling.

EuO thin films with the cubic NaCl structure were fabricated by a sol-gel technique. The composition and crystal structure of the films were investigated as a function of firing temperature. The preparation of the stock solution and the coating and firing of the films are described. The firing of the gel film and the reduction of the Eu2O3 phase are also discussed.

Stage 2 CsC24 graphite-cesium derivatives were synthesized and characterized using x-ray diffraction. Pure CsC24 specimens are single phase stage 2 in the range 77–300 K. From the 00l scans, we observed on samples slightly polluted during the transfer in the glove box, the tridimensional segregation of stage 2 in a main CsC26 structure and an additional dense CsC20 structure. The 2D Laue diffraction photographs are the same as already reported, but are interpreted as a mixture of 2 × 2 R 0° lattice commensurate and 2.54 × 2.54 R 14.5° lattice incommensurate structures. In oxidized compounds, we identified another 2.23 × 2.23 R 25.5° 2D additional incommensurate structure corresponding to the composition CsC20 already evidenced by analysis of the 00l diffractograms. We suggest that oxygen impurities are at the origin of this particular stiff and dense structure at low temperature.

The microstructure of large grain melt-processed YBa2Cu3O7−δ containing 10 molar% excess Y2BaCuO5 prepared and oxygenated under atmospheric pressure has been investigated by transmission electron microscopy (TEM) and optical microscopy. These materials always contain parallel structural and microscopic platelet-like features in the crystallographic a-b plane of a few microns spacing which have been variously described as grain boundaries or microcracks. We have observed such features, which clearly influence the flow of current in melt-processed YBCO, to consist of copper deficient, impurity phase material which can be either amorphous or crystalline in nature. A variety of defects have been observed by high-resolution electron microscopy (HREM) in the vicinity of these platelet boundaries, including double and triple CuO layer stacking faults, which may constitute effective flux pinning sites.

The grain boundary topography and grain boundary dislocation network structure of a 6° [001] bicrystal of YBa2Cu3O7−δ were studied using diffraction-contrast transmission electron microscopy (TEM). Saw-tooth-shaped arrays of facets composed of facets with lengths of a few tens of nanometers were observed in each of two widely separated sections of the boundary. The facet planes were {110}, {310}, and {221}. Further subfaceting of the (130) facets into a smaller-scale (a few nanometers) saw-tooth configuration of (010) and (110) facets produced a hierarchy of facets in at least one boundary section. The dislocation content observed in each type of facet agreed well with Frank's formula. However, the dislocations within individual facets frequently were inhomogeneously distributed, contrasting the picture of evenly spaced dislocations that is derived for boundaries of infinite extent. Certain types of dislocations repeatedly were grouped near the facet centers and ends. Well-separated partial dislocations frequently were observed near the facet midsections, but not near the facet junctions. Extended (∼30 nm) strain contrast was observed at all of the facet junctions formed by facets with dimensions on the order of tens of nanometers. This long-range strain may be due to the finite extent of the individual facets. These results all suggest that structural inhomogeneities occur on various length scales ranging from macroscopic to just a few nanometers. Such structural heterogeneity is consistent with the electrical heterogeneity that is indicated for many YBa2Cu3O7−δ grain boundaries.

We present the numerical formulation of the thermal stress driven steady-state dislocation generation during the growth of shaped crystals from the melt, with Czochralski (CZ) growth of solid cylinder III–V compound semiconductors as an example. We use and compare the Haasen–Alexander model, coupling dislocation multiplication and creep strain rates, and the Jordan model, based on thermoelastic stresses. Growth parameters may be chosen so as to produce an overall approximately flat interface, leading to reduced dislocation density in the majority of the crystal's cross section. Calculation of final dislocation density requires the initial dislocation density and all stress components along the solid-liquid interface, microstructural features which depend on the physical processes leading to solidification. The final dislocation density is not sensitive to the initial dislocation density along the solid-liquid interface, but strongly depends on the interface stress. Significant stress relaxation at the interface is required to produce experimentally observed “W” shaped dislocation patterns. Crystal growth direction and crystalline anisotropy couple elastic (lattice) and plastic (slip systems) crystalline anisotropy.

The diffusion zone between a U–23 at. % Zr alloy and a Ni–16.4 at. % Cr alloy exhibited nine distinct phase layers, many of which were mixtures of two phases. Four single-phase regions were less than 10 μm wide. To identify these phases by diffractometry, a synchrotron x-ray beam was collimated by a 50 μm by 1 mm slit. This beam was translated across the sample to obtain diffraction patterns throughout the diffusion zone. In this way, only a few phases were simultaneously within the beam, easing identification of the phases. Strains in the lattice due to solid solution were also observed. These microdiffraction techniques are applicable to a wide range of material systems.

This paper describes a new application of two complementary surface characterization techniques to study solid-state bonding in an Al–Li alloy. Through the two mentioned techniques, Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS), important findings about what takes place in the bond interface have been determined. These findings enclose both the formation of discontinuous mixed oxides and the evolution of Li through the bond line and into theadjacent diffusion affected zones. Homogenization of Li and Cu alloyelements has been detected even in those cases where a metallic interlayer was used to favor the union.

An ultrahigh-carbon (1.25 wt.%) steel alloy containing 10 wt.% aluminum (UHCS–10Al) was processed by a powder metallurgy technique. Gas-atomized powders were subjected to ball-milling in an attritor in order to obtain a submicrometer grain size. Powder material was consolidated by both hot isostatic pressing (HIP) and by hot isopressure extrusion (HIE). Bulk material with submicrometer grain sizes was produced from attrited powders. The chemical composition and microstructure of this material are characterized at each processing step, from atomization through consolidation. Tensile tests show that a high strength results from the submicrometer grain size produced in the bulk material.

Analytical transmission electron microscopy was used to study specimens of a low-Cu dental amalgam (Velvalloy), prepared using the “wedge technique.” Analysis confirmed that the microstructure consists of a Ag2Hg3(γ1)/HgSn7−9(γ2) matrix surrounding unreacted Ag3Sn(γ) particles. In addition a hitherto uncharacterized reaction layer of fine grains between Ag3Sn(γ) and Ag2Hg3(γ1) is a mixture of Ag3Sn(γ), Ag–Hg–Sn (β1), Ag2Hg3 (γ1), and occasionally Cu6Sn5 (η′). An Ag–Hg–Sn (β1) phase was clearly identified for the first time. Since Velvalloy is a simple commercial dental amalgam, it is a reasonable starting point for characterizing more complex dental amalgam microstructures.

The effect of sintering periods for monocore (Bi, Pb)2Sr2Ca2Cu3O10+x (Bi-2223) tapes on microstructure and critical current density (Jc) have been studied. The results show that long sintering periods (of duration ≥100 h) give better grain growth, but greater misalignment. Prolonged sintering also necessitates the increase in porosity of the core due to random grain growth, increasing the chance of penetrating into the silver matrix and oxide core interface. Critical currents for long sintering periods are found to be lower in comparison with those obtained for slightly shorter sintering periods. The increase in frequency of intermediate cold uniaxial pressing between sintering periods assists grain alignment. However, when the sintering period is further reduced by increasing the frequency of intermediate deformation, it is found that microcracks are unable to heal as there is not enough time for grain regrowth. The tapes made using “three-to-four-sinter-period” (each period ∼60 h) show superior electrical transport properties which are attributable to the fact that their oxide core is more dense and better aligned relative to the “two-sinter-period” (each period ≥100 h) tapes and contain less cracks relative to the “five-to-six-sinter-period” (each period ∼40 h) tapes.

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 interruption of long-range polar order in rhombohedral ferroelectricPb(Zr1−xTix)O3 (PZT) ceramics has been systematically studied by incorporating La onto the A-site of the perovskite (ABO3) structure for Zr/Ti ratios of 65/35 and 80/20 and various La contents. Studies have been performed by hot-stage transmission electron microscopy, dielectric spectroscopy, and Sawyer–Tower polarization (P-E) techniques. The evolution of a polar nanodomain state from a normal micron-sized domain state with increasing La content was observed. The emergence of this polar cluster state was characterized by the onset of strong frequency dispersion in the dielectric response, indicative of relaxor behavior. The La content that drives the structure into the relaxor state was found to be related to the lattice distortion of the undoped base composition.

Using transmission electron microscopy, we have found stacking faults on the cation sublattice in the chalcopyrite structure of CuInSe2. These films are grown by molecular beam epitaxy under Cu-rich conditions. These stacking faults are found to extend large distances in the plane of the film, and are not found to be present in samples not grown in Cu-rich conditions. We suggest that this defect is triggered by a Cu-induced transformation of the surface structure of the growing film.

Fe–29Al–2Cr powders with nanoscale grain sizes were produced by mechanical milling of prealloyed intermetallic powders. A consolidation procedure employing high-pressure, low strain rate hot forging (sinter-forging) has been developed to consolidate the powders into full-density compacts. The relative density and average grain size of the compact have been studied as a function of consolidation temperature at constant pressure. Fully dense compacts (>99.5% theoretical density) were produced at a relatively low temperature of 545°C with a pressure of 1.25 GPa. Transmission electron microscopy and x-ray diffraction analysis indicate that the average grain size has been maintained to the order of 30 nm in samples consolidated under these conditions. By using protective Ar atmosphere during mechanical milling and consolidation, contamination of oxygen and carbon in consolidated samples has been controlled to below a small fraction of an atomic percent. Microhardness tests of nanocrystalline Fe–29Al–2Cr samples indicate a significant strengthening effect due to grain size refinement and a monotonic hardness increase with decreasing residual porosity. Our work demonstrates the feasibility of using mechanically milled powders as the source of nanocrystalline materials for the production of fully dense, low-impurity, nanocrystalline bulk samples needed for reliable mechanical property measurements and practical applications.

This paper describes the application of dynamic secondary ion mass spectrometry (SIMS) to the study of the chemistry of welds in V–Cr–Ti alloys and presents preliminary data on the distribution of minor and trace elements (H, C, N, O, P, S, and C1) in welds produced by gas tungsten arc (GTA) and electron beam techniques. The motivation for this research is to develop techniques that determine correlations between the concentration and distribution of trace elements in alloy metal welds and the physical properties of the weld. To this end, quantitative SIMS techniques were developed for N, O, and S analysis in vanadium alloy welds using an ion implantation/relative sensitivity factor methodology. The data presented in this paper demonstrate that trace compositions and distributions of selected welds correlate, at least qualitatively, with such properties as microhardness and tensile elongation. These data support continuing these investigations to develop microanalysis methods that quantitatively correlate weld composition with mechanical properties.

The morphology and microstructure of an Al2O3 glass composite (trade name In-Ceram, Vita Zahnfabrik) were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was produced by infiltration of a lanthanum-based glass throughout a porous Al2O3 body. This alumina body was formed by three classes of particles differing in size and shape: faceted particles typically ≤4 μm in diameter, platelets of average diameter 8 μm, 1.5 μm thickness, and small spheres 0.4 μm in diameter. The outstanding strength properties of the composite (600 MPa, ball-on-ring test) are a result of the high wetting capability of the glass phase on the Al2O3 surface. In addition, plastic strain relaxation in the faceted particles by dislocation formation compensates partially for residual stresses and impedes crack formation at the glass/Al2O3 interface.

High resolution transmission electron microscopy (HRTEM) was used to characterize nanostructures in soots produced in flames of benzene, acetylene, or ethylene premixed with oxygen and an inert diluent gas. The nanostructures ranged from ∼2 nm to ∼30 nm in size with a hollow core measuring about ∼ 1 nm to ∼10 nm in diameter and containing 5 to 20 shells. The shapes of the nanostructures included spherical, spheroidal, tubular, and trigonous.

The solidification of a series of Al–Cu–Fe alloys containing an icosahedral phase has been studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, powder x-ray diffraction, and differential thermal analysis. The constitution and morphology of alloys solidified at different rates are presented. The overall compositional range of the icosahedral phase was determined in as-cast, slowly solidified alloys and those annealed at 800 and 600 °C. The solidification of this phase follows closely the Al3Fe–AlCu compositional direction. The first icosahedral phase solidified close to Al65.5Cu21.5Fe13; its compositional region at 800 °C lies between about Al64.5Cu23Fe12.5 and Al62Cu26.5Fe11.5, while at 600 °C it lies between Al62Cu26.5Fe11.5 and Al60.5Cu29.5Fe10. The formation of the icosahedral and related structures observed in Al–Cu–Fe alloys is discussed.

X-ray single crystal diffraction data were used for structural refinement of the title compounds with different x (0.15, 0.27, 0.49, and 0.89). Crystals were grown in alumina crucibles using the self-flux method. Aluminum, which originates from the crucibles, substitutes only Cu(1), and thus induces tetragonal symmetry which was observed in all four crystals. The main structural effect of praseodymium is an increased separation of superconducting layers. Substituent concentrations (x and y in the formula) have been refined and compared with the values obtained by EDX (energy dispersive x-ray analysis) in an electron microscope. It was indicated that the refined values of Y: Pr ratio and the oxygen content are more reliable than those obtained by EDX while the refinement is less sensitive for Cu(1): Al ratio, and this value is more uncertain. This is in accordance with the result of wet chemical analysis.