Hydrostatic pressure measurements of the superconducting transition temperature were made as a function of x in La2−xSrx CuO4. A sharp change in the behavior occurs between x = 0.2 and 0.25 in that the pressure derivative goes from positive to essentially zero. This result is discussed in the context of band structure models.

Black crystals, displaying a micaccous habit, result from heating the 90 K superconducting phase YBa2Cu3O7−x above 1050°C. The crystals are tetragonal, P4/mmm, a = 3.863 (2) Å, c = 11.830 (4) Å, Z = 1, ρcal = 6.115 g/cm3. The 184 independent single-crystal reflections were used to refine the structure by least squares to R = 0.0374, wR = 0.0347. The structure contains Cu+ in twofold coordination and corrugated layers of Cu2+–O. The Ba2+ is in eightfold coordination between the Cu+ and Cu2+ layers and Y is in eightfold coordination between the Cu2+ layers.

The alloy Al70Si17Fe13 was subjected to a range of rapid solidification conditions and the resulting microstructures were evaluated. It was found that when solidification was sufficiently rapid to bypass the formation of primary intermetallic phases, the alloy consisted of spherical regions of amorphous (or microquasicrystalline) material surrounded by a crystalline phase(s). This microstructure is interpreted as the result of solidification of the amorphous phase from the melt by a first-order transformation. The structure of the amorphous phase is different from that of a liquid (or usual metallic glass).

Nuclear magnetic resonance (NMR) results are presented for several aluminum alloy samples prepared using the melt-spinning technique including orthorhombic Al6Mn, Al–Mn quasicrystals both with and without doping with Si and Ru, and a T-phase alloy of Al and Pt. With the exception of the orthorhombic material, all of the NMR spectra show a broad distribution of sites. No features unique to the quasicrystal phase are observed. For the orthorhombic material the quadrupole field parameters are found to be ∥VQ∥ − 1.0±0.1 MHz and η = 0.4±0.1.

The effect of boron on the mechanism of strain transfer across grain boundaries in Ni3Al has been investigated by dynamic recording of events occurring during in-situ straining in the transmission electron microscope. Boundaries in both doped and undoped material can act as effective barriers to dislocation motion, large numbers of dislocations being incorporated into the boundary without any plastic strain occurring in the adjacent grain. In the undoped material, the grain-boundary strain is relieved by the sudden failure of the grain boundary. In the doped material the strain is relieved by the sudden generation and emission of large numbers of dislocations from the grain boundary. This effect may be understood by boron either increasing the grain-boundary cohesion or reducing the stress required to operate grain-boundary dislocation sources, rather than easing the passage of slip dislocations through the grain boundary.

The interactions of the Pt/Ni/Cu and Au/Ni/Cu structures and their ambient dependence are studied. Comparison of the Pt–Cu interdiffusion with that of Au–Cu across the Ni layer shows an interesting relation between the interactions and their ambient dependence. According to the surface potential model, which has been shown to correlate the ambient effects for many systems, diffusion of both Pt and Au into the Cu layer via the Ni layer should be enhanced by oxygen. This is observed for Au but not for Pt. On the other hand, the anticipated oxygen-enhanced diffusion of Cu into Pt and Au layers via the Ni layer is observed in both structures. The difference between the Pt and Au diffusion via Ni is attributed to the presence of competing interdiffusion between Pt and Ni in the Pt/Ni/Cu structure, which is reduced by oxygen, whereas little diffusion of Ni into the Au layer is observed for the Au/Ni/Cu structure. The ambient effects on the trilayer structures are compared with those on the binary Au/Ni, Au/Cu, Ni/Cu, Pt/Ni, and Pt/Cu structures. The diffusion mechanisms are discussed, and relations among various systems are suggested.

Low-energy ion-beam cleaning of the substrates prior to a deposition greatly enhances the quality of ultrathin (< 100 Å) refractory superconducting (Nb, V) films. Using this technique Nb films as thin as 7 Å have been grown, from which good tunnel junctions have been fabricated. Both the native films and the tunnel junctions are sturdy and can be thermally recycled without any degradation. In-situ surface study along with transmission electron microscopy (TEM) results suggest the removal of the carbon atoms from the surface of the substrate without an apparent surface damage as the causes of the improvement. The TEM results indicate that the Nb films grow perfectly lattice matched to the sapphire substrate when the substrate is ion-beam cleaned. This strained-layer epitaxy is observed up to 40 Å, the maximum thickness investigated through TEM.

Analytical expressions describing the various thermodynamic phases in binary systems can be derived by the CALPHAD approach, whereby the parameters in these expressions are obtained from fits to measured phase equilibrium data. Extrapolations of these models can be used to predict metastable equilibria. Different thermodynamic models proposed for the Ni–Ti and the Cu–Ti systems are used to calculate the T0 curves that are relevant to the prediction of the glass-forming range in rapidly cooled molten alloys. Although all the models give acceptable fits for the equilibrium range for which they were derived, significant differences are found for the metastable regime. The problems that need to be addressed in order to improve the extrapolations into the metastable regime are discussed. Simple thermodynamic considerations predict that the glass-forming range for rapidly quenched alloys exceeds that for amorphous alloys synthesized by isothermal solid-state interdiffusion reactions.

The low-temperature (120°–245°C) structural relaxation of Metglas¯ 2826B (Ni49Fe29P14B6Si2) amorphous alloy was investigated for samples subjected to a tensile stress in the range of 20–400 MPa during annealing. The stress-annealed samples demonstrated a much smaller increase of microhardness than was observed in similarly annealed ribbons without a stress. Further heat treatment of the stress-annealed specimens, this time without the stress, was capable of increasing the microhardnesses of only some ribbons to values equal to those of samples similarly heat treated initially without a stress. An additional exothermic peak in the differential scanning calorimetry (DSC) thermograms of the stress-annealed specimens indicated the presence of a more disordered structure at room temperature, which was found to correlate with the lower microhardness values. Otherwise, those artifacts of the DSC thermograms that were characteristic of samples annealed without a stress were still present in the stress-annealed ribbons. No effect on the crystallization temperature was noted but the glass transition temperature was increased in the stress-annealed case with respect to values attained when the stress was absent during heat treatment. A reduction in the degree of embrittlement of those samples annealed with a tensile stress was a further indication of more disorder in the stress-annealed ribbons.

A method using synchrotron radiation parallel beam x-ray optics with a small incidence angle α on the specimen and 2Θ-detector scanning is described for depth profiling analysis of thin films. The instrumentation is the same as used for Θ:2Θ synchrotron parallel beam powder diffractometry, except that the specimen is uncoupled from the detector. There is no profile distortion. Below the critical angle for total reflection αc, the top tens of Angstroms are sampled. Depth profiling is controlled to a few Angstroms using a small α and 0.005° steps. The penetration depth increases to several hundred Angstroms as α approaches αc. Above αc there is a rapid increase in penetration depth to a thousand Angstroms or more and the profiling cannot be sensitively controlled. At grazing incidence the peaks are shifted several tenths of a degree by the x-ray refraction and an experimental procedure for calculating the shifts is described. The method is illustrated with an analysis of iron oxide films.

An original preparation of ZnO is described where the powder is obtained by precipitaton from zinc nitrate in aqueous solution followed by a calcination. Scanning electron microscopy reveals a close relation between the initial density and the morphology of the powder, the latter being also strongly dependent on the calcining conditions. The investigation of the densification process shows the extreme sensitivity of the final density to sintering conditions. A physical model based on the competitive influences of shrinkage and evaporation successfully describes the observed phenomena.

Lithium fluoride added to BaTiO3 as a sintering additive can be worthwhile for realizing cheap multilayer ceramic capacitors. Such an addition leads to a decrease both in sintering and Curie temperatures from 1400°–930°C and from 120°–10°C, respectively. A transmission electron microscopy (TEM) study of thin samples quenched from intermediary stages has shown the microstructure of the sintered material to be complex. A liquid-phase sintering, mechanism occurring at temperatures slightly lower than 730°C has been proposed. Volatility accounts for partial or complete disappearance of the liquid during heat treatments.

The use of structurally and/or compositionally diphasic gels has been shown earlier to have profound effects in lowering the crystallization temperature and enhancing densification in several systems. In this study of solid-state epitaxy the ThSiO4 composition has been investigated. The use of compositional diphasicity allows one to lower the huttonite (β-ThSiO4) crystallization temperature by as much as 200°C. Using crystalline thorite (α-ThSiO4) as second phase nuclei partially stabilizes this phase (hypothetically metastable), while the introduction of huttonite nuclei completely inhibits the formation of the α form, which appears in detectable quantities in the unseeded precursors. This confirms the structural (epitaxial) control of the solid-state reaction. The use of structural or compositional nanoheterogeneity clearly helps to lower the crystallization temperature and to stabilize a particular polymorph in ccramics processed by the sol-gel route, and this principle can certainly be utilized more generally.

Materials derived by precipitation or polymerization chemistry (e.g., “sol-gel” methods) are usually obtained in noncrystalline or otherwise metastable phases, and transformation to more thermodynamically stable phases generally occurs by a nucleation and growth process. In a fully reconstructive transformation, such as occurs in the alumina system, the activation energy for nucleation may be higher than that for simple short-range diffusion. Hence nucleation frequency can be a controlling factor in the development of microstructurc. The efficacy of seeding as a method of microstructural and phase control in solution-derived or so-called sol-gel materials has been clearly demonstrated for the alumina system. The epitaxial nature of this phenomenon is explored, using the polarizing microscope to follow the crystallographic orientation of the transformed material as the transformation proceeds, showing that this is epitaxial in nature, and that the nucleation frequency in unseeded material is relatively low (∼ 1010 cm−3). The microscope was then used to demonstrate the effect on nucleation frequency of seeding with materials selected to be isostructural, isotypic, and having little or no similarity to the corundum structure. Using these and other methods, the seeding phenomenon in alumina gels is shown to result from epitaxial growth of the stable corundum phase on isostructural or isotypic nuclei in the solid state. This approach is applied to formulate hypotheses for the mechanisms by which some of the previously reported effects of seeding, e.g., enhanced densification and microstructural refinement, can be understood and to formulate a set of generalizations for its potential application to other systems.

A previous bulk thermodynamic model, which used enthalpies of compound and alloy formation to predict metal/compound–semiconductor interface reactivity, is extended to include entropy. It is shown that, for most metals on CdTe, GaAs, GaSe, InP, and MoS2, solid-state reactions are energetically favored up to semiconductor dissociation temperatures and, consequently, entropy effects are minimal. Gold and silver, with their small enthalpies of metal–semiconductor anion compound formation, can be exceptions. Even here, the results for gold/III–V systems favor solid-state reaction at room temperature, but at higher temperatures entropy drives the reaction via vapor-phase production of the group V element. The binary phase bulk thermodynamic model is not sufficient to predict absolute reactivity, but can rank the reactivity of the various metal–semiconductor combinations successfully, as long as possible alloy formation is included. It is suggested that the limitations of the model are due to the specific effects of the interface.

An atomistic model for the dependence on interface orientation and velocity v of the solute partition coefficient k during rapid solidification is developed in detail. Starting with a simple stepwise growth model, the simple continuous growth model result is obtained for k(v) when the growth steps are assumed to pass at random intervals rather than periodically. The model is applied to rapid solidification of silicon. Crystal growth at all orientations is assumed to occur by the rapid lateral passage of (111) steps at speeds determined by the interface velocity and orientation. Solute escape is parametrized by a diffusion coefficient at the edge of the moving step and a diffusion coefficient at the terrace, far from the step edge. The model results in an excellent fit to data for the velocity and orientation dependence of k of Bi in Si.

The optoelectronic properties of the II-IV-V2 semiconductor ZnSnP2 are studied as a function of the cooling rate of the crystal growth melt. The structure of the material, as studied by x-ray diffraction, is seen to change from chalcopyrite to sphalerite as the cooling rate is increased. Photoelectrochemical measurements show that the bandgap of the material decreases from 1.64 eV for the chalcopyrite to 1.25 eV as the structure approaches sphalerite. The 119Sn Mössbauer spectroscopy shows both an isomer shift and a broadening of the 119Sn resonance as a result of new tin environments produced by disordering of zinc and tin sites at the faster cooling rates. The 31P solid-state nuclear magnetic resonance spectroscopy clearly shows new resonances associated with the additional phosphorus environments produced by metal site disordering. A model based on zinc and tin site exchange with the introduction of compensating donor and acceptor states is proposed and discussed.

R. B. Fair et al. have analyzed original data on the effect of heavy, uniform background doping with As and B on the diffusivity of Sb in Si at 1000°–1200°C. Their analysis attributed a role to “electric fields” and led to the conclusion that, for n-type background doping, Sb diffusion is dominated by double-negatively charged vacancies with no contribution from V−. For p-type backgrounds they concluded that donor-acceptor pairing alone retards the diffusion. Here it is shown (1) that electric fields do not play a role in their experiments, (2) that the contribution of V− to Sb diffusion in an n-type background is not zero but is roughly equal to that of V= for n/ni = 10, and (3) that the retardation of Sb diffusion in p-type Si is due both to donor-acceptor pairing and, principally, to the elimination of the contributions of V− and V=.

The expression used for electric field in the article being discussed is not appropriate for the experimental conditions, but there is a built-in electric field present that affects Sb diffusion. Thus the calculated values of D=i are reasonably within the experimental error of the data on which the calculations are based. Our conclusions that V− vacancies do not play an important role in Sb diffusion and that Sb–B pairs are responsible for retarded Sb diffusion in high-concentration B-doped Si are supported.