Amorphous spherical particles of magnesium and potassium niobates were produced by homogeneous precipitation in solutions of magnesium and potassium salts, respectively, in the presence of polymeric niobium oxo-hydroxide ions. At pH 9 solids of definitive compositions were achieved and converted to crystalline powders of MgNb2O6 and KNbO3 on calcination. Chemical mechanisms for the formation and transformation of such colloidal particles are offered.

A model has been previously proposed to describe the energy associated with emission of dissociated superlattice dislocations from crack tips in ordered intermetallic alloys. In the present paper, the model is applied to several B2 intermetallic alloys. The results of the analysis reveal a correlation between the range of slip system orientations for which emission of a dislocation from a crack tip is energetically favorable and the macroscopic fracture mode of the alloy. Additionally, the effects of changing the active slip system, increasing the thermal energy available for thermally activated dislocation emission, and changing the {111} APB energy on the fracture mode of NiAl and FeAl are discussed.

The chemical diffusion in thin trilayer films of TM–TM100−xZrx–TM with an amorphous middle layer where TM = Co, Ni, or Fe and in amorphous Fe–Zr and Ni–Zr films with composition gradients has been investigated using Rutherford backscattering spectrometry. The growth of the amorphous layer in the trilayers, due to in-diffusion of cobalt and nickel, is initially found to be proportional to the square root of the time, t1/2, and subsequently found to level off before the compositions corresponding to metastable equilibria are reached. Irradiation, with 500 keV Xe+ ions, is found to promote the in-diffusion. This behavior is discussed in terms of structural relaxation effects and their influence on the metastable equilibrium. In amorphous Fe–Zr the chemical diffusivity is observed to be very sluggish. Contrary to the behavior in Co–Zr and Ni–Zr trilayers, the direction of the iron diffusion in Fe–Zr trilayers suggests a broad positive peak in the Gibbs free energy at a composition around 50 at. % Zr. It is argued that the sluggish chemical diffusivity of iron is directly related to the unusual composition-dependence of the Gibbs free energy for amorphous Fe–Zr.

We performed diamond deposition experiments from a gas phase containing H2, CH4, and sometimes CO, using a microwave plasma ball reactor operating at 400 mbar pressure. The molybdenum substrates were stamped with a suitable tool to form a number of flattened cones on its surface. A strong preference for crystal growth on top of the cones was observed. Numerical calculations were used to solve the underlying thermal conduction and diffusion problems. At the substrate, the flow of the active species entering by diffusion from the bulk of the gas phase was balanced by those leaving the system due to incorporation in the crystals. Comparison with the experiments showed that at least 10% of the active species striking the surface are incorporated. Thus, the limitation of diamond growth in our investigation lies in gas phase transport and not in incorporation difficulties at the growing surface.

The electronic transition from localized to delocalized states of carriers in a disordered carbon material is investigated by photoconductivity measurements. Phenol-derived activated carbon fibers, where the carriers are strongly localized due to disorder, are heat treated in the range 300–2500 °C to give rise to the insulator-metal transition. Dark conductivity, Raman spectra, and x-ray diffraction patterns are also measured to characterize their structural changes. As a result, the transition temperature was determined to be rather low, around 1000 °C, considering the rapid decrease in the photoconductivity above this temperature. This decrease was ascribed to a fast recombination between the photoexcited carriers and the delocalized carriers generated by heat treatment.

The kinetics of disorder → B2 order transformations in ternary alloys were studied in the pair approximation. The predictions of two sets of rate equations were compared, one based on an atom-atom interchange mechanism and the other based on an atom-vacancy interchange mechanism. Examples are presented to show how the evolution of order is affected by differences in interatomic potentials, differences in activation barrier heights, and effects of vacancy ordering. A wide variety of states of order are possible during the disorder → order transformation in ternary alloys, and qualitative features of the sequences of these states are discussed. The sequences of states, or “kinetic paths”, are much less intuitive than for binary alloys.

Isothermal sections of the In–Ni–P phase diagram have been determined at 600 °C and 470 °C. Two new ternary phases not previously identified in bulk samples were found. A phase with the composition Ni57In22P21 is present at both 600 °C and 470 °C and was found by differential thermal analysis to melt at 736 °C. The phase Ni2InP was found to be in equilibrium with InP at 470 °C, but it does not appear in the 600 °C isotherm since it melts at 526 °C. The phases (In), Ni2P, Ni5P4, and NiP2 are in equilibrium with InP at both temperatures studied.

The effects of indentation on the electrical resistance of rectifying gold-chromium contacts on silicon and germanium have been studied using nanoindentation techniques. The DC resistance of circuits consisting of positively and negatively biased contacts with silicon and germanium in the intervening gap was measured while indenting either directly in the gap or on the contacts. Previous experiments showed that a large decrease in resistance occurs when an indentation bridges a gap, which was used to support the notion that a transformation from the semiconducting to the metallic state occurs beneath the indenter. The experimental results reported here, however, show that a large portion of the resistance drop is due to decreases in the resistance of the metal-to-semiconductor interface rather than the bulk semiconductor. Experimental evidence supporting this is presented, and a simple explanation for the physical processes involved is developed which still relies on the concept of an indentation-induced, semiconducting-to-metallic phase transformation.

A number of nanocrystalline ceramics have been fabricated by the gas phase condensation technique. The mechanical properties of one of the first ceramics produced by this method, nanophase TiO2, have been discussed in an earlier study.1 This paper reports a similar study undertaken to examine the properties of nanocrystalline ZnO. Nanoindenter techniques are used to determine hardness, Young's modulus, and strain rate sensitivity in ultra-fine grained ZnO. Significant properties variations are experienced within a given sample, indicating a large degree of microstructural inhomogeneity. Nevertheless, a distinct evolution in properties can be observed as a function of sintering temperature. Young's modulus and hardness values increase almost linearly with increasing sintering temperature, and, in addition, there also appears to be a linear correlation between the development of the two materials properties. In contrast, strain rate sensitivity is shown to have an inverse dependence on sintering temperature. This dependence appears to be linked to the strong influence of grain size on strain rate sensitivity, so that the lower sintering temperatures, which provide the finer grain sizes, tend to promote strain rate sensitivity. The results of this study are strikingly similar to those obtained earlier for nanophase TiO2, and they indicate that the earlier results could probably be generalized to a much broader range of nanocrystalline ceramics.

TiO2 single crystal fibers in the 1 mm diameter range were pulled from different alloy melts using the laser heated pedestal melting technique. The alloying elements studied were CaO, MnO, MgO, SiO2, FeO, and Al2O3. Phase diagram solute partition coefficient, k0, maximum solid solubility limit, CS(max), eutectic concentration, CE, and eutectic temperature, TE, were determined for each of these alloys. Solute redistribution effects in the solid, controlled precipitation in the solid, smooth solid-liquid interfaces in the presence of high melt concentrations and substantial crystal broadening by fluid migration up the solid from the melt all indicated the existence of a very strong thermodynamic field and a large solid diffusion coefficient operating in the solid behind the solid/liquid interface.

Homogeneous and stoichiometric PbTiO3 and PbZr0.52Ti0.48O3 gel fibers were drawn from viscous solutions prepared by sol-gel processing of alkoxide precursors. The fibrous gels on heating at 450 and 600 °C, respectively, formed the well-crystallized phases of PbTiO3 and PbZr0.52Ti0.48O3. Fibers heat treated at 700 °C are a few centimeters long and 50 to 150 μm in diameter. PbZr0.52Ti0.48O3 fibers subjected to heat treatment at 700 °C for 1 h consisted of fully dense submicron grains (0.15 to 0.2 μm). However, PbTiO3 fibers under analogous conditions showed a few micropores with grains of ∼0.1 μm. Dielectric constants of these PbTiO3 and PbZr0.52Ti0.48O3 fibers were approximately 300 and 800, respectively.

In as-sintered silicon nitride with yttria as a sintering aid, the intergranular glassy phase contains Y, Si, O, and N. Results of crystallization of partly crystalline, as-quenched melt samples containing 28–40 mol% Y2O3 in the Y2O3–SiO2 system are presented. Three different compositions were melted in tungsten crucibles at 2100 °C in 1 and 50 atm nitrogen and heat treated in air in the temperature range of 1200 to 1600 °C. Phase identification by x-ray diffraction (XRD) and transmission electron microscopy (TEM) showed crystallization to β, γ, and δ polymorphs of Y2Si2O7.

The effect of the interfacial thermal resistance and the laser energy density on film morphology and the extent of evaporation was studied in the excimer laser processing of copper-sapphire couples. Copper films of 80 nm thickness were sputter-deposited on sapphire substrates and laser-irradiated with energy densities in the range of 0.2 to 3.5 J/cm2. The changes in film morphology and thickness as a function of laser energy density were analyzed by energy dispersive x-ray spectroscopy. Four regimes can be established as a function of the laser energy density. First, for low energy densities up to a critical value, the film is partially removed by thermal stresses. Second, as the energy density is increased above that critical value, larger portions of the film remain attached to the substrate. In this regime adhesion enhancement takes place. Third, a further increase in the energy density results in film evaporation. Finally, the decrease in the specific mass removal rate of copper is related to the formation of a laser generated plasma that shields the sample from the incoming radiation. In this last regime, an intermediate compound may form at the substrate surface. The data were correlated with results from a computer model of the heat flow during laser processing of metal-ceramic couples.

The photoelastic stress-freezing technique is applied to observe the stress distribution inside two spheres of different sizes compressed together elastically. After the stress is frozen in, thin slices of the material containing the symmetry axis are prepared for observation through a polariscope. The stress distribution is compared with both the finite element numerical analysis and the Hertz analytical theory which is limited to small deformations. Among the three, the agreement between the experimental results and the finite element analysis is the best. The deviation from the Hertz theory is less in the larger sphere contacting a smaller one than in the smaller sphere contacting a larger one.

A method for calculating lattice statics Green's function is described for a bimaterial lattice or a bicrystal containing a plane interface. The method involves creation of two half space lattices containing free surfaces and then joining them to form a bicrystal. The two half space lattices may have different structures as in a two-phase bicrystal or may be of the same type but joined at different orientations to form a grain boundary interface. The method is quite general but, in this paper, has been applied only to a simple model bicrystal formed by two simple cubic lattices with nearest neighbor interactions. The bimaterial Green's function is modified to account for an interfacial crack that is used to calculate the displacement field due to an applied external force. It is found that the displacement field, as calculated by using the lattice theory, does not have the unphysical oscillations predicted by the continuum theory.

The equilibrium shapes of stress free inclusions with a small mismatch and possibly a small rotation from the matrix phase are studied. The model used includes both bond-breaking and elastic contributions to the interface energy. The unrotated shape contains only facets. Rotated inclusions sometimes contain smoothly curved parts as well. Interface phase diagrams are used to characterize the stable phase behavior of flat interfaces of fixed orientation.