The embedded atom method (EAM) has been used to compare the stability of a series of small palladium clusters with 5–60 atoms and a variety of shapes. It is found that the 13- and 55-atom icosahedra and cubo-octahedra are stable at 0 K. However, other sized icosahedra and cubo-octahedra are unstable at 0 K. Upon annealing, the icosahedra and cubo-octahedra reconstruct into nonpolyhedral structures which are highly strained. The strained structures are much more stable than the icosahedron or cubo-octahedron except when there are 13 or 55 atoms in the cluster. Further, there are many disordered shapes which are within 0.01 eV of the minimum energy structures at all cluster sizes including 13 and 55 atoms. We observe transitions between these low energy structures in Monte Carlo calculations. These results suggest that at equilibrium one should rarely observe polyhedral palladium particles. Instead, most of the particles should be disordered. Further, there should be a wide distribution of particle shapes in agreement with experiment.

Nanocrystalline FeTi has been prepared in two ways: by ball milling the intermetallic compound and mechanically alloying a mixture of the elemental powders. The materials obtained in each case are identical. The reaction proceeds via the formation of interfacial β–Ti(Fe) which then grows to include all of the material present. Oxygen levels above 3 at. % suppress this reaction and lead to the formation of amorphous Fe–Ti.

Crystal structure and superconductivity of the Tl–Ba–Ca–Cu–O powder prepared by a solid-state reaction were studied. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicate that the powder of a major single 1223 phase was synthesized with a cauliflower-like morphology; by grinding, the powder was partially transformed to an amorphous phase. The measurement of magnetic hysteresis was also performed in the temperature range of 7–75 K up to 5 T from which the weak field-dependent behavior of critical current density was observed. The as-synthesized powder, with Tc = 110 K measured from magnetometer and susceptometer, is considered to consist of weak-linked regions. The results obtained from comparing the as-synthesized and the ground powder imply that in the Tl-1223 system, the Ag-sheathed tapes fabricated by the powder-in-tube process may be benefited by forming other intermediate phases with plate-like morphologies to give better densification or grain alignment.

A new interpretation of the reaction mechanism between active metal thin-film filler and ceramic substrate is proposed. The authors predict the possibility of prebonding reactions, prior to melting of the filler, at the interface of the system described above. To prove this, solid-state reactions of Ag–Cu–Ti thin films on sapphire substrates have been studied with Auger electron spectroscopy (AES) and x-ray diffraction (XRD). Reaction process and products have been clarified at the temperature just below the melting point of the filler. It is evident that Cu3Ti3O (diamond structure of Fd3m) is formed by the reaction between Cu3Ti and O which results from the reduction of sapphire. It seems that Cu3Ti3O contributes to bonding between metals and sapphire as an intermediate phase.

Heat-treatment temperature/time and ambient effects on the properties of YBa2Cu3O7−x superconducting films derived from carboxylate precursors were investigated. The thin films were processed under O2, N2, or N2/O2 mixed atmosphere. The use of N2 or N2-rich atmosphere facilitated the 123 phase formation, grain growth, and orientation due to liquid phase assist sintering. Thin films with Tc(zero) = 87.8 and Jc > 105 A/cm2 at 77 K were prepared under such atmosphere at T ≤ 920 °C. Higher temperatures were required for thin films processed under O2 atmosphere and inferior transport properties were obtained. Processing above the melting temperature resulted in highly oriented films with dense microstructures and large grains, but significant post annealing was needed to obtain good film properties.

The results of high-temperature compressive deformation tests on a two-phase alloy consisting of Cr2Nb, a C15 Laves phase, and a soft Nb-based solid solution, are presented along with measurements of oxidation kinetics at 1273 K in air. These alloys are deformable only at temperatures above 1273 K. The measured 0.2% yield stress decreases steadily with increasing temperature and is only slightly sensitive to alloy composition. The steady state flow stress decreases steadily with increasing temperature and depends on alloy composition. A constitutive equation was fitted to the experimental data with a composition-independent stress exponent of about 2.7 and an apparent activation energy which ranges between 477 and 391 kJ/mol, also depending on alloy composition. Microstructural examination shows that cracking (cavitation) and interfacial sliding between the two constituent phases, in addition to bulk deformation of the constituent phases, are responsible for the deformation. The oxidation resistance of these alloys is very good.

Ti−50.8% Al has been cast using unidirectional solidification to produce specimens with a highly directional structure. Each specimen consisted of the intermetallic phases, TiAl and Ti3Al. Both phases existed as single crystal lamellae which were parallel to each other throughout the specimen and aligned along specific crystallographic orientations. Mechanical properties were assessed by deforming specimens such that slip occurred in different directions relative to the lamellae. High-temperature stability was assessed by heating for various times and examining the microstructure. Deformation revealed a highly anisotropic structure since ductility depended upon the principal direction of slip. Poor slip, occurring in a direction through the lamellae, was attributed to the Ti3Al phase where cracking initiated. Heating at 1200 °C resulted in recrystallization of the TiAl phase. The recrystallization started at the ends of the specimens as a result of residual mechanical damage, before spreading along individual lamellae into the bulk.

The 2212 phase formation during annealing of melt textured Bi–2212 (Bi2Sr2CaCu2Ox) was investigated using differential thermal analysis, thermal gravimetric analysis, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and high resolution transmission electron microscopy. After zone melting, the material is multiphase consisting of 2212, 2201, Sr1−xCaxCuO2, and the eutectic. The 2212 phase formed is highly perfect with less than 5% intergrowths of 2201 layers; the 2201 phase shows no intergrowth of 2212 at all. In the first period of the annealing, remelting of the eutectic leads to fast oxygen diffusion and a high 2212 formation rate. The 2201 → 2212 transformation proceeds via intermediate states of high defect density. The 2212 grains contain up to 30–70% 2201 intergrowths. Further heat treatments lead to an annihilation of the great majority of intergrown 2201 layers. We propose a model for the formation of 2212 grains with a low planar defect density, based on frequent stacking faults, that allows diffusion of Ca- and Cu-atoms over a short distance. The model provides a schematic description of this solid-state process and correlates it to the characteristic microstructural features of melt-processed Bi–2212.

In order to understand the effects of the thermodynamic stability on superconductivity, the thermodynamic stability of the Bi2Sr2CaCu2-xLixOy system and the Bi2Sr2YCu2-xLixOy system was studied. It is found that the broad ranges (0 ≤ x ≤ 0.6) of solid solution may be thermodynamically stable at high temperatures for the Bi2Sr2CaCu2-xLixOy), system and the Bi2Sr2YCu2-xLixOy), system. At equilibrium at low temperatures, however, solid solubility is eliminated, and only the end member compounds and possibly intermediate compounds of fixed composition remain for 0.3 ≤ x ≤ 0.6. It suggests that Li can destroy the thermodynamic stability. Superconductivity is improved by Li-doping, which may be related to the thermodynamic instability.

We have studied the superconducting Bi–Sr–Ca–Cu–O thin films prepared by metalorganic chemical vapor deposition (MOCVD). The thin films fabricated on an MgO(110) single crystal substrate show a preferential (110) orientation. The fabrication of (110)-oriented film was dependent on the chemical composition and the existence of a Sr–Ca–Cu–O buffer layer. The zero resistance temperature (Tc0) was obtained at 60 K for the 1 μm thick film and 23 K for the 300 nm thick film. The critical current density (Jc) of this film at 4.2 K was about 1 × 104 A/cm2 for the film of 1 μm thickness.

Ferromagnetic europium (EuO) films have been made by oxidizing europium (Eu) metal films deposited on glass substrates using a thermal evaporation technique. It has been found that the quality of the films is sensitive to substrate temperature. Stable EuO films were formed only if Eu metal films were annealed at temperatures of 320 to 380 °C. Both x-ray diffraction pattern (XRD) and magnetization measurements indicate that a significant amount of EuO phase has been formed in the films. These films undergo a phase transition from paramagnetic to ferromagnetic phase at temperatures between 60 and 70 K and exhibit the magneto-optical Faraday effect. The saturation magnetic moment at 10 K is about 40% of the theoretical value, and the coercive force, Hc, for slow sweeping field is about 70 Oe.

High quality Al-Cu-Fe quasicrystals have been studied at the atomic level with a high resolution microscope operating at 400 kV. When the incident beam is parallel to the fivefold axis, experimental bright-field images in thin regions of the specimen are found to be of two types, depending on the electron optical parameters employed. One of these images is of greater contrast than the other, but both types yield decagon-like image features. Close agreement is found between both types of contrast-enhanced micrographs and microscope image simulations of a realistic atomic model. This model involves the placement of overlapping Mackay icosahedra on a perfect quasicrystalline network. The limitation of resolving the projected atomic structure is discussed in terms of the contribution of different diffraction orders, considerations of specimen thickness, and optimal adjustment of the microscope objective lens defocus. A similar treatment is also applied to the threefold orientation where micrographs were taken under coherent imaging conditions. For the threefold pattern, fine modulations of the quasicrystalline lattice are obtained which are not observed under less coherent conditions.

A methodology is presented to characterize the crystallography of individual fracture surface facets. Electron backscatter patterns (EBSP's) from a metallographic section through a facet identify grain orientation, and quantitative tilt fractography identifies facet orientation; these results are combined to establish fracture facet crystallography. For this technique, facet electropolishing is not required, the facet alignment procedure is accurate and quick, and the method can be generalized to different microstructures, test environments, or facet orientations. Method accuracy is illustrated for 25 to 50 μm fatigue crack facets in an unrecrystallized Al–Li–Cu alloy (AA2090) that has 5 μm thick subgrains in elongated grains that are 10 to 200 μm thick. The fine subgrain structure and tortuous fatigue crack profile precludes the use of other diffraction techniques for determining AA2090 facet crystallography. EBSP and tilt fractography results demonstrate that vacuum fatigue cracks in AA2090 are nearly parallel to local {111} planes.

Thick film (1.2 μm) YBCO superconductors grown by pulsed laser deposition on unbuffered and CeO2-buffered single crystal (001)-oriented yttria-stabilized zirconia (YSZ) substrates have been investigated. YBCO and YSZ react to form BaZrO3 (BZO), whereas YBCO and CeO2 react to form BaCeO3. Reaction phases were examined by θ-2θ and four-circle x-ray diffraction and high resolution electron microscopy. Three orientation relationships identified for the unbuffered films were (i) (001)YBCO ‖ (011)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, (ii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [110]YBCO ‖ [100]BZO ‖ [100]YSZ, and (iii) (001)YBCO ‖ (001)BZO ‖ (001)YSZ with [100]YBCO ‖ [100]BZO ‖ [100]YSZ. The results suggest that for films grown at typical deposition temperatures, YBCO epitaxy is established before the interfacial reaction occurs. The presence of BaCeO3 in buffered films grown at high temperatures (790 °C) was confirmed by θ-2θ scans and selected area diffraction patterns.

The effect of silver (Ag) addition on the resistance to thermal shock and delayed failure of YBa2Cu3O7−δ superconducting wires has been evaluated. Resistance to thermal shock was evaluated by measuring the critical-current density (Jc) as a function of the number of thermal cycles for YBCO and its composites with 15 vol. % Ag additions. Composite YBCO-Ag wires show a slower decrease in Jc than does monolithic YBCO as the number of thermal cycles increases. The nature of delayed failure was studied by measuring strength (σf) as a function of loading rate (σ) and evaluating the value of the subcritical crack growth parameter N[σf = Aσ1/(N+1)]. The value of the N parameter was observed to increase slightly from 35 for YBCO to 41 for YBCO-Ag composites. The improved resistance to thermal shock and subcritical crack growth is believed to be due to improvements in mechanical properties (strength and fracture toughness) and thermal conductivity of YBCO as a result of Ag addition.

The microstructure of mixed phase, c-axis oriented Tl–Ca–Ba–Cu–O thin films, exhibiting excellent superconducting properties, has been examined by transmission electron microscopy and x-ray diffraction. Although the stoichiometry of the as-deposited films corresponds to the Tl2Ca2Ba2Cu3O10 phase (Tl-2223, c = 3.6 nm), x-ray diffraction showed these films contain up to 50% of the Tl2CaBa2Cu2O8 phase (Tl-2122, c ≍ 2.9 nm). The x-ray diffraction peaks of the 3.6 nm phase are noticeably broader than those of the 2.9 nm phase, suggesting a smaller coherent size along the c-axis for the 3.6 nm phase Lattice-fringe images of the 2.9 nm phase typically show only an occasional or no defect layer; however, such layer defects are more abundant in the 3.6 nm phase and, though random, occur with sufficiently wide separation and regularity to be consistent with an average coherency of ∼40 nm. The coherent sizes along the c-axis, as determined by x-ray line profile analysis, were 140 nm and 40 nm, respectively, for the 2.9 nm and 3.6 nm phases, in good agreement with those determined by electron microscopy. The estimated width of the layer defects observed in the lattice-fringe images is suggestive, for the most part, of the four Cu-layered phases (Tl-1324 or Tl-2324) and to a lesser degree the two Cu-layered phases (Tl-1122 or Tl-2122).

Ac susceptibility measurements have been used to monitor the changes in the superconductive properties of sintered and uniaxially pressed samples of Pb-stabilized 2223-phase bismuth cuprate ceramic as the structural damage was annealed in air in a sequence of steps in temperature between 500 and 850 °C. It is concluded that below 600 °C a relaxation of residual stresses is responsible for a 2% shrinkage in sample volume and a small improvement in bulk superconductive transition temperature, Tc. Above 700 °C, a recovery of the original properties occurs through grain regrowth governed by an activation energy of ∼200 kJ/mol. However, in the region between 600 and 700 °C, a decrease in Tc of ∼40 K appears to be the result of plastic flow and amorphization associated with local decomposition of 2223 which reduces the effective grain size and weakens the intergranular superconductive coupling.

Copper- and yttrium-rich YBa2Cu3O7 bulk superconductors have been prepared by mixing copper oxide or yttrium oxide in nitric acid and adding the solution to premade stoichiometric YBa2Cu3O7 followed by annealing. In contrast to materials made by mixing oxide powders, both samples contain copper-rich defects spread homogeneously throughout the grains, either small platelet copper oxide precipitates or bundles of planar defects (Cu–O double planes). These materials also show large magnetic hysteresis at 77 K, comparable to the results obtained from decomposed YBa2Cu4O8. This implies that small copper oxide precipitates and bundles of planar defects are strong flux pinners, and indicates a processing route to producing large amounts of strongly intragranular pinned superconductors. However, the materials also show clean grain boundaries, so an equally valid interpretation is that there is a substantial component of intergranular superconductivity in field, enhancing the effective circuit size to a value far larger than the grain size.

The present work has examined the effect of pulsed excimer laser irradiation (λ = 308 nm, τ = 26 ns, E = 100 mJ/pulse, N = 1, 5, 10 laser pulses/spot, repetition rate 1 Hz) on the magnetic anisotropy of Fe81B13.5Si3.5C2, Fe78B13Si9, Fe40Ni38Mo4B18, and Fe40Ni40P14B6 metallic glasses. The transmission Mössbauer spectra yielded the intensity ratio R21 of the second to the first line as a function of the number of applied laser pulses. On these grounds, it was found that in the higher magnetostriction samples, controlled changes in the magnetic anisotropy could be induced without onset of bulk crystallization; in the lower magnetostriction samples, a random distribution of the magnetic moment directions was obtained. The conversion electron Mössbauer spectra were characteristic of the amorphous state but showed the same texture as the nonirradiated samples. SEM examinations of the laser-treated surfaces revealed the presence of molten zones subsequently solidified. It is suggested that the correspondingly induced stresses may account for the observed changes in the bulk magnetization orientation, and the model of closure domain structure is supported.

A study of the quasicrystalline phases obtained from a quaternary alloy of Al–Cu–Co–Fe is carried out. The formation of these phases is based on a gravity chill-casting technique. The alloy was cast in a wedge-shaped copper mold. Optical and scanning electron micrographs show a characteristic dendritic growing in regions close to the wedge edge. These types of dendrites display apparent symmetries that resemble the tenfold, fivefold, and eightfold symmetries obtained in quasicrystalline materials. Electron diffraction patterns, in addition to x-ray diffraction patterns, show two kinds of quasicrystalline phases. The icosahedral and decagonal phases coexist in these types of alloys also with binary and ternary compounds of intermetallic nature.