We report the results on x-ray diffraction and magnetic susceptibility study of Y–Ba–(Cu1−xScx)–O. The materials were prepared in a stoichiometry corresponding to Y1Ba2(Cu1−xScx)3O7. Although x-ray analysis reveals the increasing presence of a subtle second phase with increasing Sc content, the superconducting transition temperature and resistivity did not change substantially in the composition range 0.0  x ≤ 0.15. In contrast, the magnetic susceptibility studies showed dramatic changes. Although Sc3+ has no spin by itself, an enhanced paramagnetic Curie susceptibility was observed above Tc with a moment of 1.5 μB per Sc. At 16 K a sharp cusp is observed in the temperature dependent susceptibility corresponding to the onset of a three-dimensionally ordered antiferromagnetic state. These results are discussed in terms of an additional previously unreported phase of Y–Ba–(Cu–Sc)–O that has an antiferromagnetic Néel temperature of 16 K. For composition of x = 1.0, a new phase is formed which is nonmagnetic.

The lower yield strengths of Ni3Al and mild steel and their respective relationships to (grain size)−0.8 and (grain size)−0.5 are explained in terms of work hardening within Lüders bands.

Fourier transform infrared (FTIR) absorption spectra were measured for various glasses in the Bi–Zn–Fe–B–O system, and interpreted upon the basis of glass structure. Spectral changes were noted with variations in the composition for these glasses that were related to changes in the atomic arrangement of the boron oxide portion of the glass network. The changes in glass transformation temperature with changes in glass composition were discussed in terms of structural data.

Thick (20–300 μm) freestanding polycrystalline films of ceramic YBa2Cu3O6.9 have been obtained by resintering YBa2Cu3O6.9 powder in air after screen printing onto fused silica substrates. An interfacial reaction occurs between the powder and the silica substrate which efficiently detaches the resintered film upon cooling. The magnetization and transport properties of these films are comparable to those for high quality bulk ceramic samples.

The possibility of site-selective substitution of 18O into YBa2Cu3O7 was explored. Samples containing various quantities of 18O were prepared by processing in 18O2 both at 950 °C and at 400 °C. The samples were characterized by secondary ion mass spectroscopy (SIMS), temperature programmed desorption (TPD) and reduction (TPR), Raman spectroscopy, and magnetization measurements. Measurements of the shifts in the Raman active modes with 18O substitution and of the ratios of 18O to 16O by TPD, TPR, and SIMS show that even for temperatures as low as 400 °C and times as short as 2 h. 18O is not substituted exclusively into the chain site (O1) in YBa2Cu3O7. In addition, there is no consistent variation in the shifts in Tc with the degree of substitution; therefore, the isotope effect for a sample with 100% 18O cannot be predicted by a linear extrapolation of data obtained for samples with partial 18O substitution. The mechanism of oxygen substitution, the difficulties of measuring the true magnitude of the oxygen isotope shift, and the meaning of the small isotope shift are discussed.

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd–Ba–Cu–O superconductor alloy. The GdBa2Cu3O7−x phase in the oxygen annealed sample is orthorhombic while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the [001] zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

The Raman line at 1430 cm−1 (M-line) in single crystal La2CuO4−y was studied as a function of doping, temperature, magnetic field, and excitation wavelength. Upon Li doping the line becomes broader, and it vanishes rapidly with Sr-doping. The line also broadens with increasing temperature and increasing applied magnetic field. Resonance enhancement was found for decreasing laser excitation energies but was not as pronounced as the enhancement of several alleged two-phonon lines. Many of these features are correlated with the 2D antiferromagnetic ordering measured in this system by neutron scattering. The possible identification of this line as a one-spin excitation is favored by the data though a two-phonon excitation is also considered.

Alloys of Nb73Al12Si14.5B0.5 were rapidly solidified into amorphous ribbons using the melt spinning technique. These were isothermally annealed at temperatures ranging from 660 to 780 °C. The A15 phase began to crystallize at 700 °C and small amounts of second phases appeared at the higher temperatures. Crystallization was dependent on quenching rate as well as annealing conditions. Below 750 °C nucleation was nonuniform and was enhanced by surfaces and quenched-in nuclei. Above 750 °C nucleation became more uniform and completely crystalline ribbons with equiaxed grains ∼30 nm in diameter were obtained. These ultra fine grained ribbons had extremely high superconducting critical current densities of 8 × 1010 A/m2 and 5 × 1010 A/m2 at magnetic fields of 0.5 and 15 tesla, respectively, at 4.2 K.

Potential and current distributions and local energy dissipation due to Joule heating in metal-superconductor junctions have been computed as a function of geometric parameters and interfacial resistance. The primary current distribution and power dissipation are highly nonuniform in the system. The secondary current distribution and power dissipation, however, become more uniform as the interfacial resistance increases. Analysis indicates that zero contact resistance is not a stable situation since the primary distribution leads to local current densities exceeding the critical current density of the superconducting phase near the corner of the junction. Local contact failure might then initiate. A finite contact resistance is necessary for a practical application, and the minimum value of the contact resistance can be estimated from the operating current density (javg) of the device and the critical current density (jcri) of the superconducting phase. To obtain an optimum value of the contact resistance, however, one further has to take into consideration the stability and reliability of the device performance, which is, in turn, directly related to the uniformity of the current distribution and power dissipation, to temperature fluctuation of the superconducting phases brought about by local power dissipation, and to the thermal management of the system. Furthermore, a nonuniform contact resistance layer of appropriate profile can redistribute the current more effectively and more uniformly and hence reduce the total power dissipation in the system for a given jmax/javg ratio obtained by a uniform resistance layer.

Rapidly solidified Al–Cr alloys up to 20 at. % Cr were studied to delineate the extent of crystalline and quasicrystalline phase formation in these alloys in comparison with as-cast alloys by using transmission electron microscopy and x-ray diffraction technique. The icosahedral quasicrystals are observed from 7 to 15 at. % Cr alloys, while equilibrium η–Al11Cr2 phase is completely absent. Both rapid solidification and subsequent thermal decomposition studies indicate that the main competing phase is θ–Al2Cr up to 15 at. % Cr. Beyond this composition ∊–Al4Cr is the dominant phase together with a small amount of γ4–Al7Cr3. We have shown that the electron diffraction patterns of Al–Cr quasicrystals are often associated with a diffuse intensity distribution, indicative of short-range order. The change in quasilattice constant with composition suggests the existence of structural vacancies. Further, a sudden change from coarse to ultrafine quasicrystalline grain structure in Al-7 at. % Cr alloy points to a change in nucleation mechanism from heterogeneous to homogeneous mode during the rapid solidification.

The Embedded Atom Model (EAM) was utilized to analyze the energy and strain surrounding Au and Pt atoms substituted into a Ni crystal. Au substituted into Ni has a large positive size difference and a positive heat of mixing; Pt substituted into Ni has a large positive size difference and a negative heat of mixing. The EAM predicted highly anisotropic strain fields around the substitutional atom with large positive strains in the [110] direction and small or negative strains in the [100] and [111] directions. This is in contrast to the normal assumption that the strain around a substitution atom is spherically symmetric. The cohesive energy of the atoms around the substitutional atom was found to depend upon the crystallographic direction relative to the substitutional atom in addition to the radial distance from the substitutional atom. The EAM predicted an energy increase for Au substituted into Ni and an energy decrease for Pt substituted into Ni. The EAM results were compared with an elastic analysis.

A melting point depression, δTM, has been observed for Sn in Ge/Sn (50 at.% Sn) dispersions which were prepared by mechanical milling of Ge and Sn powders. Sn and Ge are immiscible and form a fine dispersion of the pure components when milled in a high energy ball mill. The magnitude of δTM, as measured by DSC, increases with milling time, i.e., with refinement of the dispersion. Melting is observed to begin as low as 36 °C below the equilibrium bulk melting temperature. The magnitude of δTM is reduced by about 25% after melting the Sn. Subsequent remelts do not change δTM further. Impurities cannot account for δTM. While stored energy of cold work may contribute to 25% of δTM before Sn is melted, it is concluded that the major contribution to δTM comes from the nucleation of disorder/melting at the Ge/Sn interfaces.

The intermetallic compounds NiTi, NiTi2, CuZr, CuTi2, and Zr3Al were irradiated by 2 McV protons at various temperatures between –175 °C and –44 °C to a fluence of 1.9 × 1022 H+/m2. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi2) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surfaces of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfaces of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is considerable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr3Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.

Molecular dynamics simulations of energetic displacement cascades in Cu and Ni were performed with primary-knock-on-atom (PKA) energies up to 5 keV. The interatomic forces were represented by the Gibson II (Cu) and the Johnson-Erginsoy (Ni) potentials. Our results indicate that the primary state of damage produced by displacement cascades is controlled basically by two phenomena: replacement collision sequences during the ballistic phase, and melting and resolidification during the thermal spike. The thermal-spike phase is of longer duration and has a more marked effect in Cu than in Ni. Results for atomic mixing, defect production, and defect clustering are presented and compared with experiment. Simulations of “heat spikes” in these metals suggest a model for “cascade collapse” based on the regrowth kinetics of the molten cascade core.

Strain hardening dominates the deformation process in fine-grained A1-7475 alloy in the temperature range 400 to 515 °C. It is shown that anomalously low stress exponents are obtained as a result of strain hardening in strain-rate-change tests. In order to measure stress exponents in a quasi-steady state condition, the samples must be initially deformed at a relatively high stress (≍ 10 MPa) to a relatively high strain (∊ ≍ 0.5) before initiating a strain-rate-change test. Such a procedure revealed that a stress exponent about equal to two and an activation energy (141 kJ/mole) nearly equal to the activation energy for lattice diffusion are obtained. The results are interpreted in terms of a model involving grain boundary sliding accommodated by slip following the Gifkins' “core and mantle” concept. It is proposed that strain hardening is associated with the development of a boundary-dislocation structure in the mantle region in a manner similar to the development of subgrains in the core of a grain when slip is the principal deformation mode.

The room temperature deformation behavior and microstructure of Ti48Al52 and Ti52Al48 alloys are compared. The material was fabricated by rapid solidification melt spinning, and examined in both as-cast and consolidated forms. The Ti52Al48 alloy exhibited enhanced strength and ductility in both forms in bend tests compared with the Ti48Al52 alloy. The microstructure of the Ti52Al48 alloy was two-phase γ–TiAl and α2–Ti3Al. The Ti48Al52 alloy was single-phase γ–TiAl and had a larger grain size than the previous alloy. The microstructure of the Ti52Al48 alloy after room temperature deformation consisted primarily of {111} mechanical twins and a/2〈110〉 perfect dislocations. The comparable Ti48Al52 alloy microstructure contained fewer twins, and many more a〈101〉 and a/2〈112〉 superdislocations were present in addition to a/2〈110〉 dislocations. The superdislocations had dissociated and formed sessile faulted dipoles. The possible reasons for the differences in microstructure and mechanical behavior between these two alloys are discussed.

Diffusion of several impurity atoms (Cu, Al, Au, and Sb) has been studied in Zr61Ni39 and Fe82B18 amorphous alloys. A definite correlation between the diffusion coefficient (D) and the atomic size of the diffusant is seen for the metal-metal (M–M) alloy, while it is not clear for the metal-metalloid (M–Me) alloy. Based on the present data, as well as other published data in binary amorphous alloys, empirical correlations have been found between (i) the activation energy (Q) and the energy required to form a hole of the size of the diffusing atom in the host alloy, and (ii) the pre-exponential factor (D0) and Q. While the former correlation is seen only for binary M–M type of amorphous alloys, the latter correlation is more general and holds for all types of amorphous alloys. Based on the correlation between D0 and Q, it is proposed that there are two distinct mechanisms of diffusion in amorphous alloys.

The difference in density between liquid and solid is shown to be altered at the interface of a rough surface. Since it has been argued previously by the author that density difference plays a major role in interface velocity, I conclude that the rough (100) surface of silicon can have both a larger slope and less asymmetry in the freezing-melting velocity versus temperature relation than does the smooth (111) surface. This may provide partial explanation for some recent experimental results and apparent controversy.

The nature of the disordered state of hydrogenated amorphous silicon is examined for the first time by measurement of anelastic relaxation behavior. It is demonstrated that local structural units and their modifications control the relaxations in these films under different conditions of deposition, aging, and light exposure. Specifically, the light-induced state in this material is shown to be characterized by four distinct relaxations.

The depth distribution, chemical bonding, and electrical behavior of N quenched into Si by pulsed laser-induced melting have been investigated by secondary ion mass spectroscopy, infrared (ir) absorption, transmission electron microscopy (TEM), and electrical conductivity. The results demonstrate that laser-induced melting of N-implanted layers provides access to a useful range of otherwise inaccessible conditions for the study of N in Si. Nitrogen concentrations four orders of magnitude above equilibrium solid solubility are retained in implanted layers with limited diffusion during laser-induced melt and rapid solidification. The N is incorporated predominantly as N–N pairs bonded to Si, similar to the bonding configuration for equilibrium concentrations introduced during ingot growth. Formation of SixNy clusters is suggested to explain ir absorption bands, features in TEM, and shallow donor activity observed after furnace annealing near 750 °C. These cluster effects are removed by a melt/solidification sequence which restores the N to N–N pair centers together with a small fraction of off-center substitutional N.