This paper presents an analysis of the collective nucleation of glide dislocation loops under the bias of a high shear stress. It introduces the concept of an ‘induced’ stress field associated with the planar distribution of glide dislocation loops. It shows that, due to the ‘induced’ field, glide dislocations nucleate in a collective, self-catalytic fashion at critical stresses and temperatures.

We report new multistriped phases at high densities in a three-state model (Si = 0, ± 1) driven by an external field E and influenced by repulsive nearest neighbor interactions. The dynamics are dictated by local Metropolis rates with the ratio of particle-particle to particle-hole exchange given by γ. In the noninteracting limit, this model shows an ordered, low-current phase above a density-dependent critical field. In this phase the two types of charges are segregated from each other and from the vacancies, forming stripes transverse to the field direction. Addition of a repulsive bilinear interaction J favors mixing of the charges. This interaction competes directly with the charge-segregated ordering and the system undergoes a nonequilibrium transition to one of four other types of striped phases, some with checkerboard ordering. We have calculated the staggered charge density and used the amplitude of its longest wavelength Fourier component along the field direction as an order parameter to characterize this new type of striped ordering. The phase diagram in the parameter space of E, J, γ, and density shows both first and second order transitions, with second order transitions most prevalent in the high-E/J, high density regions. Our study also shows a reentrant phase diagram with only second order transitions for high γ and a tricritical topology at low γ. For field strengths close to zero, the system orders in a checkerboard fashion above a J-dependent density. Results were obtained using Monte Carlo simulations on a 30×30 square lattice with periodic boundary conditions and charge conservation.

Precipitation reactions from aqueous solutions of calcium nitrate and tin(II) fluoride result in the formation of two metastable phases, depending on the reaction conditions. Crystalline CaSn2F6 and the microcrystalline Ca1-xSnxF2 solid solution are obtained, the latter crystallizing in the cubic fluorite (CaF2) type with total Ca/Sn disorder. Both phases are fluoride ion conductors. Electrical conductivity measurements versus temperature and bulk density measurements show that both phases are far from thermodynamic equilibrium at ambient conditions, and thus are metastable. Both decompose to a mixture of SnF2 and CaF2 at high temperature. In addition, CaSn2F6 is chemically unstable in an aqueous medium, in which it looses SnF2 to give the microcrystalline Ca1-xSnxF2 solid solution.

The compounds in the binary system Ag2Se-Ag2S are known to undergo a phase transition to a superionic phase at a temperature which varies with concentration. The diffusion mechanism of Ag ions have been studied in a Molecular Dynamics formalism. We have calculated the diffusion coefficient as function of temperature and concentration and have calculated the activation energy for diffusion from the Arrhenius plot of DAg vs temperature. Results obtained for the end points Ag2Se and Ag2S agree with experimental measurements.

The phonon spectrum and thermal parameters such as specific heat, effective temperature and amplitude of vibration of solid C60 are studied from ab-initio calculations. The relative orientations between the C60 balls are taken into account in a sc phase below 261.4K. The same properties are studied above the transition temperature (261.4K) where the balls are randomly oriented in a fcc structure. A difference is found in some of the thermal parameters due to the relative inter-molecular orientation. In particular, the low energy vibrational spectrum (which is separated by a ∼20meV gap from the intra-molecular spectrum) is changed.

It is often incorrectly assumed that temperature alone defines the equilibrium state of a crystal. However, the Gibbs phase rule shows that the number of independent thermodynamic variables required to define the equilibrium state depends upon the experimental design. In most practical cases, this means that temperature and components of the external phase or phases in proximate contact with the sample will determine the equilibrium state, e.g., the equilibrium native defect concentrations, impurity solubility, etc. If native defect concentrations approach their equilibrium values in a time which is short compared to the time of an experiment, then impurity diffusion can be described well by a thermodynamic model and impurity diffusion is analogous to classic tracer diffusion. If native defect concentrations require a long time to approach their equilibrium values, then diffusivities will exhibit significant time dependence and simple models do not apply. However, multi-phase, multi-component systems generally have several possible equilibrium regions within their phase diagram. Relating the phase diagram to a given experimental design allows one to qualitatively understand how the native defect concentrations change as a crystal in a nonequilibrium state relaxes toward one (of several possible) well-defined equilibrium states. Examples will focus largely on the diffusion of impurities in single crystal GaAs. Evidence will be presented that native defect concentrations can rapidly approach equilibrium in a limited group of experimental designs. We shall show why a description of diffusivity in terms of carrier concentration, a dependent thermodynamic variable, sometimes succeeds but often fails. Examples of commonly used experimental designs, in which there is inadequate control over the independent variables, will demonstrate some large variations in measured diffusivity. An enormous range of reported diffusivities, in GaAs covered by SiO2 or Si3N4 encapsulant layers, will demonstrate the difficulty and the futility of measuring diffusion when the solid is cut off from the external phases which define the equilibrium state.

L12-long-range ordering (LRO) was studied by residual resistometry in Cu3Au. Variations of LRO-parameter were produced by isochronal and isothermal heat treatments for different initial states of order. By comparison of order-order and disorder-order relaxations, the contributions to ordering of atomic jumps within ordered domains and of antiphase boundaries were separated. Analysing isothermal annealings yielded ordering energies of vacancies involved.

Thin films of In2O3 and Fe2O3 have been deposited on (001) MgO using pulsed-laser deposition (PLD). These thin-film diffusion couples were then reacted in an applied electric field at elevated temperatures. In this type of solid-state reaction, both the reaction rate and the interfacial stability are affected by the transport properties of the reacting ions. The electric field provides a very large external driving force that influences the diffusion of the cations in the constitutive layers. This induced ionic current causes changes in the reaction rates, interfacial stability and distribution of the phases. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated in these spinel-forming systems, to gain a better understanding of the influence of an electric field on solid-state reactions.

A theoretical analysis of the transformation kinetics which accounts for nuclei, either prequenched or created homogeneously, and whose growth are controlled by diffusion is presented. The change in growth habit intervening during the transformation is analysed in terms of the evolution of the free energy difference between the precipitate and the matrix at the interface, ΔG1. In the Avrami formalism, this quantity accounts for the competition between interface and diffusion controlled growth whereas the nucleation events are driven by the free energy difference between the precipitate and the bulk matrix. Competition and selection of precipitate phases in highly undercooled melts using the CALPHAD approach for the evaluation of the free energies and the changes in diffusivity with concentration are analysed. Experimental vs. calculated data are discussed in some rapidly solidified metallic systems.

The crystallographic and morphological aspect associated with the formation of γ hydride phase (fct) from the β phase in β abilized Zr-20%Nb alloy has been reported. In this paper the βto γ transformation has been considered in the terms of the phenomenological theory of martensitic crystallography in order to predict the crystallographic features of the γ hydride in the β to γ transformation. The prediction made in the present analysis has been found to match very closely to the experimentally observed habit plane. The possibility of the α to γ transition through the formation of a transient β configuration has been examined.

Various kinds of phase transformations, viz., spinodal decomposition, omega transformation, precipitation reactions and martensitic transformation can be induced in ternary (Zr3Al) -Nb alloys in conditions far removed from equilibrium. Transformation sequences in alloys containing 3% niobium are described and rationalized in terms of some basic tendencies such as phase separation and chemical ordering in the β (bcc) phase and displacive omega and β to α (hcp) transformations. Microstructures of rapidly solidified alloy showed a distribution of cuboidal (D88 phase) particles in the β matrix. The periodic arrangement of these particles along the <100>β directions was indicative of a spinodal transformation which preceded their formation. The β → D88 transformation could be accomplished by the superimposition of three processes, namely, chemical ordering, lattice collapse akin to ω transformation and vacancy ordering. During isothermal aging the D88 phase transformed into the B82 phase. The observed lattice correspondence and transformation morphology suggested that the D88 to B82 structural change involved the replacement of structural vacancies in the former by zirconium atoms without any reconstitution of the lattice. The evolution of the equilibrium Zr3Al (L12 structure) phase during prolonged aging were also studied.

The purpose of this work is to study precipitation kinetics in air-cooled aluminum alloy 339 by both differential scanning calorimetry (DSC) and differential isothermal calorimetry (DIC) and thereby establish the equivalence of the two methods. To accomplish this, precipitation time constants, τ and activation energies, Eact, were determined by both techniques. Kissinger analysis of the DSC data yielded Eact and τ values. Using DIC we measured precipitation time constants, Arrhenius plots of which gave Eact. Activation energies and τ values from both methods agree provided DSC temperature scan rates are slow compared to the instrumental lag time. Thus, DSC and DIC have been shown to be equivalent (at least for this test case).

The effects of aging and thermal cycling treatments on the damping capacity and microstructure of Cu-(47, 55, 65)%Mn alloys and Cu-65%Mn-4.5%Ni alloy have been studied using an optical microscope, a transmission electron microscope (TEM), and a cantilever type damping measuring apparatus. The maximum damping capacity appeared after aging at 400°C for 18 hours in Cu-47%Mn, 8 hours in Cu-55%Mn, 4 hours in Cu-65%Mn, and 36 hours in Cu-65%Mn-4.5%Ni alloy, respectively. Storage at 100°C slightly reduced damping capacity of these alloys, and the higher the Mn content, the smaller the amount of the degradation. This result might be ascribed to α-Mn precipitation inside microtwins in Cu-65%Mn alloy, and to the microstructural change from tweed structure to mottled structure in the other alloys. The thermal cycling treatment between room temperature (20°C) and 250°C led to an increase in damping capacity, which is probably due to the refinement of microstructure(tweed or twin).

The initial stages of copper electrodeposition on glassy carbon were studied from a solution of 1 M CuSO4 in 0.5 M H2SO4 by the methods of potentiostatic current transients and pulse experiments. The experimental data were analyzed according to the theory of potentiostatic current transients for three-dimensional multiple nucleation with diffusion controlled growth. The theory was found to be in good agreement with experimental data for instantaneous copper nucleation in the cathodic overpotential range η = −0.18 – −0.40 V. It is shown that in case of progressive nucleation at η ≤ −0.16 V, this theory can be used only for trend analysis of copper nucleation process parameters. An important influence of the initial state of glassy carbon surface on the nucleation rate was found determined by the underpotential. It is shown that the dependence of nucleation rate on the underpotential is inadequate and is determined by cathodic overpotential.

A quantitative analysis of the phase changes of iron in silicon from interstitial to precipitate phase and vice-versa is presented. Temperature dependent iron precipitation and dissolution in float-zone grown silicon wafers is experimentally investigated. A quantitative analysis of iron silicide precipitate stability and dissolution with respect to time and temperature is also presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photo voltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 1011 to 1013 atoms/cm3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500°C to 600°C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 minutes. Iron silicide precipitates were found to dissolve above a temperature of 760°C restoring iron back to an interstitial phase in the silicon matrix.

Argonne National Laboratory has developed a composite ceramic waste form for the disposition of high level radioactive waste produced during electrometallurgical conditioning of spent nuclear fuel. The electrorefiner LiCl/KCl eutectic salt, containing fission products and transuranics in the chloride form, is contacted with a zeolite material which removes the fission products from the salt. After salt contact, the zeolite is mixed with a glass binder. The zeolite/glass mixture is then hot isostatic pressed (HIPed) to produce the composite ceramic waste form. The ceramic waste form provides a durable medium that is well suited to incorporate fission products and transuranics in the chloride form. Presented are preliminary results of the process qualification and characterization studies, which include chemical and physical measurements and product durability testing, of the ceramic waste form.

Track formation in amorphous solids is treated in terms of viscoelastic shear stress relaxation in thermal spike regions which is followed by the freezing-in of the associated strain increment. The resulting strained tracks are considered to be the mesoscopic defects responsible for anisotropic creep and growth. A recently presented approximate quantitative approach to the problem is reviewed. In addition, a new set of constitutive equations describing the viscous flow in thermal spike regions is suggested and general solutions are discussed.

Starting from the radiation damage cascades, as obtained using the binary collision approximation, we derive the spatial distribution of the energy deposited into the lattice by the primary knock-on atom (PKA). We follow the time evolution of the cascade core in two ordered intermetallics Ni3Al and NiAl, using the molecular dynamics (MD) method with the embedded potential and with the liquid droplet model (LDM) in which a simplified version of the heat equation is solved. Moreover, the MD was used to determine the evolution of the local structure and to identify the disordered zones. The LDM allows us, after a calibration with MD results, to estimate the dependence of the molten volume on the PKA energy up to 1 MeV. The results show good agreement with other published simulations and the available transmission electron microscopy (TEM) observation experiments.

A detailed study has been conducted of the effect of Kr ion irradiation on phase formation in Zr-Fe metallic multilayers, using the Intermediate Voltage Electron Microscopy (IVEM) at Argonne National Laboratory. Metallic multilayers were prepared with different overall compositions (near 50–50 and Fe-rich), and with different wavelengths (repetition thicknesses). These samples were irradiated with 300 keV Kr ions at various temperatures to investigate the final products, as well as the kinetics of phase formation. For the shorter wavelength samples, the final product was in all cases an amorphous Zr-Fe phase, in combination with Fe, while specially for the larger wavelength samples, in the Fe-rich samples the intermetallic compounds ZrFe2 and Zr3Fe were formed in addition to the amorphous phase. The dose to full reaction decreases with temperature, and with wavelength in a manner consistent with a diffusion-controlled reaction.

Segregation under irradiation in austenitic steels is due to a permanent flux of vacancies and interstitials produced by irradiation towards sinks like surfaces and interfaces. A model based on a mean field lattice rate theory is proposed where kinetics and thermodynamics are treated in a mutually consistent way. For a Fe-Ni-Cr ternary alloy, the 15 parameters defining the jump frequencies of vacancies were fitted on equilibrium properties including ordering energies and tracer diffusion experiments with no use of segregation data. Measurements of RIS by Auger Electron Spectroscopy (AES) were used in the last step of the fitting procedure in order to choose the best set of the 27 interstitial jump frequencies. This fitting procedure strongly supports the idea that the interstitials are contributing to RIS in Fe-Cr-Ni alloys. We also simulate the trapping of interstitials by an impurity model and reproduce the total inhibition of RIS by this impurity as observed experimentally [1].