bluuebunny/crossref_metadata_2025 huggingface dataset:
A Morphological Approach to Constructing Interatomic Potentials: An Application to Silicon.
Authors: Dallot P. , Bristowe P. D.
Published: March 2011

A framework for constructing interatomic potentials is proposed and applied to the case of silicon. The construction relies on a geometrical approach in which we try to reproduce the morphology of the Born-Oppenheimer surface. In particular, we develop a new technique for constructing four body terms. It consists of building invariant coordinate systems on the configuration space of four atoms, thus allowing the choice of the four body term morphology. The potential that we develop has a two and a four body part. It is adjusted to match the only geometrical information known from the Born-Oppenheimer surface which is the position of its minimum of energy and its curvature at that point, as given by the dynamical matrix. The potential is then tested on point defects and surface structures in silicon.
Anisotropic Displacement Threshold Energies in Silicon by Molecular Dynamics Simulations
Authors: Miller LeAnn A. , Brice David K. , Prinja Anil K. , Thomas Picraux S.
Published: March 2011

A combination of molecular dynamics simulations and theoretical modeling was used to examine the orientation dependent threshold energies for displacement of silicon atoms from their lattice site due to energetic particle collisions. These results are important for a detailed understanding of both radiation effects in silicon devices and beam-enhanced stimulation of molecular beam epitaxial growth.

The molecular dynamics code developed for this study, which employs a Tersoff interaction potential, as well as the theoretical model that incorporates the symmetry of the crystal are described.

Bulk displacement threshold energies were determined by the molecular dynamics code for four directions through the open face in the <111>. These values were then incorporated into the theoretical model for the average bulk displacement threshold energy. The average bulk displacement threshold energy was found to be 14.8 eV in 30° about <111> and 11.1 eV in 20° about <100>.
Dislocation Mobilities in NiAl From Molecular Dynamics Simulations
Authors: Moncevicz A. , Clapp P. C. , Rifkin J. A.
Published: March 2011

Using the Voter-Chen Embedded Atom Method (EAM) potentials for the Ni-Al alloy system,the Peierls stress (σp) and velocity of edge dislocations (b=[100]) have been estimated in stoichiometric perfectly ordered B2 NiAIat a temperature of 10 K, by the use of molecular dynamics simulations employing approximately 4000 atoms. σp was determined to be about 3×1010 dynes/cm2, or about 2%of the shear modulus, C44. The steady state velocity was found to be about 1.6×105 cm/s (or 65% of the (001) shear velocity) under an applied shear stress of 3.9×1010 dynes/cm2. Stress induced martensite (SIM) was nucleated in some of the simulations after the dislocation had begun to move, and in all cases when the SIM reached the immediate neighborhood of the dislocation core the motion of the dislocation was arrested.
Atomic-Scale Simulation of Adhesion Between Metallic Surfaces
Authors: Taylor Paul A.
Published: March 2011

We have performed MD simulations of adhesive phenomena, on an atomic scale, between metals possessing both smooth and stepped-surfaces. Studies of adhesion between identical metals, consisting of either Au, Cu, or Ni, with (001) or (111) orientations, reveal the existence of adhesive avalanches as the bodies are brought to within a critical separation (˜2Å). That is, as the surfaces approach one another, one or both surface layers becomes unstable, and abruptly moves towards the other. This signals a transition from an initial system with two distinct surfaces to one possessing no identifiable surfaces. Th presence of adhesive avalanches will pose difficulties in determining adhesive forces and energies by means of atomic forcemicroscopy at sub-nanometer separations of probe tip and sample surface.
Hot Electrons Relaxation
Authors: Mazzone A.M.
Published: March 2011

This work represents the first attempt of a direct simulation of the processes of electron-phonon interaction and lattice excitation which follow the formation of an excited electron gas such as, for instance, is the one produced by high-energy implants. The simulation method is of the type molecular dynamics and is based on a quantum mechanical representation. The results suggest a lattice disorder similar to the one of a thermal spike.
Defect Dynamics of a Nematic Polymer in a Magnetic Field
Authors: Rey Alejandro D.
Published: March 2011

Analysis of the nonlinear dynamical response of a rod-like nematic liquid crystalline polymer, between parallel untreate plates, in a magnetic field is presented. Numerical solutions to the torque balance equations showthat when a uniformly aligned polymer is acted by a magnetic field normal to the initial polymer orientation an array of inversion walls develops. Stability analysis shows that the inversion walls are unstable to localized perturbations. The nonlinear resolution ofthe instability leads to the nucleation of an array of disclination line pairs of strength ±1/2. A perturbation analysis is used to obtain the evolution of the polymer structure towards equilibrium
Dislocation Dynamics In B.C.C. Metals: A Nuclear Magnetic Resonance and Transmission Electron Microscopic Study
Authors: De Hosson J. Th. M. , Kanert O.
Published: March 2011

Pulsed nuclear magnetic resonance proved to be a complementary new technique for the study of moving dislocations in b.c.c. metals. From the motion induced part of the spin-lattice relaxation rate the mean jump distance of mobile dislocationshas been measured in Vanadium as a function of temperature. The NMR experiments are combined with transmission electron microscopic investigations to reveal the static structure of defects in the samples. The NMR experiments show that the mean jump distance is nearly constant below 230 K whereas it decreases substantially above 230 K to 300 K indicating a transition that marks two different mechanisms. NMR observations in combination with TEM support the physical picture that above that transition temperature dislocation segments are stopped between localized obstacles whereas below Tcthe latticefriction controls the plastic behaviour.
Dislocation Density Determination in Polycrystalline Copper by Neutron Diffraction Extinction Measurements.
Authors: Palacios Gomez. J.
Published: March 2011

(200), (111) AND (311) neutron diffraction peaks were measured on polycrystalline Cu samples with varying degrees of deformation by compression: O%. 0.8%. 1.2%,, 1.5% and 2%. The first two reflections were measured with wavelength 2.358Å and the third one with wavelength 1.55Å.

Integrated intensities vary more less monotonically and they tend to reach the kinematical value. This limit was estimated by extrapolation and used to evaluate extinction. To obtain dislocation densities a simple model was proposed which divides the crystal in regions of perfect periodicity and regions perturbed by dislocations, and evaluates the integratedintensity from perfect regions by the general theory of X-Ray diffraction of Zachariasen (1967).

Dislocation densities result between 1.2×1O7 cm−2 for the sample without deformation, and approximately 5.0×1O7 cm−2 for the 2%. deformed sample. These results are in the expected range.
Extrinsic Gettering of Copper in Silicon: Heterogeneous Precipitation on Near-Surface Dislocations
Authors: Rice P.M. , Kim M.J. , Carpenter R.W.
Published: March 2011

Copper was precipitated on extrinsic near-surface dislocations in {100} Si wafers. Several types of precipitates were heterogeneously nucleated on low index planar arrays. Large crystalline precipitates with visible strain fields proved to bea silicide. Large weakly diffracting precipitates without strain fields proved to be voids. Small, thin, partially crystalline particles of unknown composition also precipitated on the arrays. Point defects played an important role in the precipitation reaction.
Majority Carrier Transport Across Semiconductor Grain Boundaries
Authors: Nelson S.F. , Evans P.V. , Sass S.L. , Smith D.A.
Published: March 2011

Majority carrier transport measurements were made across the potential barriers at (100) twist boundaries in silicon. The bicrystals were prepared by hot-pressing single crystals of lightly doped float-zone material, under ultra-high vacuum conditions. The current - voltage measurements were analyzed using combined drift-diffusion and thermionic emission transport mechanisms, and incorporating some inhomogeneity in the charge distribution at the boundary. Evidence has been found for a small, Nd = 3 × 1010 cm−2, density of mono-energetic defect states near midgap, in bicrystals characterized by a variety of misorientation angles. This density is too small to result from the intrinsic structure of the boundary. In addition, no dependence was found on misorientation angle.
X-Ray Topography Studies of Oxygen Precipitates in MCZ Silicon
Authors: Holland Anthony J. , Green G. Stephan , Tanner Brian K. , Zhenhong Mai
Published: March 2011

X-ray section topography has been used to study the distribution and size of precipitates resulting from heat treatment of MCZ silicon. A low density of precipitates was found, enabling individual precipitate images to be studied. Images have been simulated by numerical solution of Takagi's equations and the magnitude of the strain field deduced by comparison with experiment. Excellent agreement has been found in the details of simulated and experimental images. The effective defect volume increased monotonically with annealing temperature. The effect of surface relaxation and long range curvature on the accuracy of determining the microscopic strain field by matching simulated and experimental images has been investigated.
Analysis for the Characterization of Oxygen Implanted Silicon (SIMOX) by Spectroscopic Ellipsometry
Authors: Doss M.G. , Chandler-Horowitz D. , Marchiando J. F. , Krause S. , Seraphin S.
Published: March 2011

Samples of SIMOX have been prepared by implantation in a high-current implanter (density ≍ 1 mA/cm2) and by annealing at 1300°C for 6 hours. Transmission electron microscopy reveals unusual structure in these samples. Spectroscopic ellipsometry has been used to analyze these structures. Ellipsometric measurements were collected at an angle of incidence of 75. deg, with photon energies from 1.5 to 5.0 eV, and using a rotating polarizer configuration. The measurements were analyzed with three models: a three-layer model, a four-layer model, and a five-layer model. The five-layer model provided the best fit of the three. This model identified a layer of crystalline Si inclusions (“islands”) within the SiO2 layer. A method is presented that provides initial estimates for the thicknesses of the top three layers to help start the regression analysis.
Structural Defects in Laser Annealed Arsenic Implanted Silicon
Authors: Tonnerre J. M. , Matsuura M. , Cargill III G. S. , Hobbs L. W.
Published: March 2011

Laser annealed arsenic implanted silicon specimens with doses ranging from 6×1015 to 7×1016 As/cm 2 have been investigated by transmission electron microscopy (TEM) and double crystal xray diffractometry (DCD). For the highest implant dose, laser powers ranging from 1.1 to 2.2 J/cm 2 have been used. Experimental observations show two new features for this kind of specimen. First, in some cases, TEM micrographs evidence small (˜50Å diameter) precipitate-like defects and/or dislocation loops confined within the heavily doped region. Second, in some cases, DCD shows a positive strain in addition to the negative strain attributed to 90% As in substitutional sites. X-ray rocking-curve simulations reveal that the negative strain drops to zero around 1000Å before the end of the As distribution. This might be related to the presence of Si interstitials in the deepest region of the As distribution.
Synchrotron Topographic Studies of the Influence of Rapid Thermal Processing on Defect Structures in Single Crystal Silicon.
Authors: Dudley Michael , Wang Franklin F.Y. , Fanning Thomas , Tolis Georgios , Wu Jun , Hodul David T.
Published: March 2011

Synchrotron white beam X-ray diffraction topography in transmission geometry has been used to non-destructively investigate defect structures in silicon single crystal wafers, both prior and subsequent to a 60 second rapid thermal processing (RTP) treatment at 1050°C. Prior to RTP dislocations, precipitates and swirl defects were observed and characterized. Following RTP the following effects were observed: glide of individual dislocations and dislocation multiplication; and the enhancement of the strain field associated with the swirl defects. Precipitates appeared unaffected by RTP. This work shows that synchrotron topography is capable of non-destructively revealing significant dislocation motion induced by RTP under conditions were such motion is not thought to occur. This dislocation motion is likely to be detrimental to device performance. The technique enables determination of the conditions required to avoid such dislocation motion.
Modifications in Gap State Distribution Upon High Energy Electron Bombardment in n Type Hydrogenated Amorphous Silicon
Authors: Babras Suvarna , Bhoraskar S.V. , Bhide V.G.
Published: March 2011

Modifications in the structural parameters of n type a-Si:H due to bombardment of different doses of 10 keV and 1 MeV electrons and the consequent changes in the gap state distribution are studied. A systematic dependance of the changes on the energy and dosage of electrons is observed. The Deep Level Transient Spectroscopy results reveal that apart from increasing the gap state density over a broad energy range, the electron bombardment also modifies the charge state of the defect, which is conclusively brought out by the result of C-V measurements. An understanding of the reason behind such modifications is sought by studying the structural parameters of the bombarded films directly with the help of Laser Raman Spectroscopy.
A Scanning Tunneling Microscopy Study of the Reduced Tio2(110)Surface
Authors: Rohrer Gregory S. , Henrich Victor E. , Bonnell Dawn A.
Published: March 2011

The scanning tunneling microscope has been used to image a reduced TiO2(110) surface in ultrahigh vacuum. Structural units with periodicities ranging from 21Å to 3.4Å have been clearly imaged and the observed surface structures can be explained by a model involving ordered arrangements of two dimensional defects known as crystallographic shear planes. An electronic state 0.5 eV below the conduction band edge, detected in tunneling spectra, has been assigned to reduced Ti cations which reside along the crystallographic shear planes. This state appears to be empty at the surface, possibly due to asmall amount of band bending. The results indicate that the topography of nonstoichiometric oxide surfaces can be rather complex and that the tunneling microscope provides an effective tool for studying the tomic scale surface features of wide band gap semiconductors.
HREm Study of Al-Si Interfaces
Authors: Shamsuzzoha Mohammad , Deymier Pierre A. , Smith David J.
Published: March 2011

Interfaces between aluminum and silicon in samples prepared by solidification of an Al-Si eutectic liquid have been studied by high-resolution electron microscopy. The Al and Si grains have a common [110] axis with a misorientation between grains of 70.5°, thus aligning the (lll)si plane with the (111)ALplane. In general, theinterfaces have a complex structurewith numerous interfacial dislocations and considerable facetting. The core structurescan be characterized in terms of structural unit models. The nature of the facetting has also been investigated, in particular one facet which lies approximately along the (111)AL, and (l15)si planes and another which lies approximately along the (110)AL and (l14)si planes.
Tilt Boundaries In BCC Metals:Comparison of Results Using Different Interatomic Interactions
Authors: Foiles S. M. , Daw M. S. , Phillips R. B.
Published: March 2011

Two classes of interatomic interactions, the embedded atom method and the model generalized pseudopotential theory are used to calculate the structure of tilt boundaries in bcc metals.These interactions differ in the inclusion of explicitlyangular dependent interactions. The results show that these different models of the interactions can lead to qualitatively different predictions for the atomic structure of the boundary. The applicability of the embedded atom method to bcc transition metals is also discussed.
Threading Dislocation Densities in Mismatched Heteroepitaxial (001) Semiconductors
Authors: Ayers J. E. , Ghandhi S.K. , Schowalter L. J.
Published: March 2011

In this paper we propose a theory which accounts for the thickness dependence of threading dislocation densities in mismatched heteroepitaxial (001) semiconductors. This theory predicts that, for thick, planar, highly-mismatched heteroepitaxial layers with equilibrium strain, the threading dislocation density should be proportional to f/h, where f is thelattice mismatch and h is the film thickness. These predictions are in good agreement with experimental resultsin the GaAs on Si(001) system.
Short Range Order Strucrures in Y-Pr-Ba-Cu-O System Studied by X-Ray Absorption Fine Structure (XAFS) Techniques
Authors: Kao Y.H. , Krol A. , Ming Z.H. , Lin C.S. , Soo Y.L. , Gu C.X. , Yang I.S. , Tsuei C.C.
Published: March 2011

Local structure around the constituent atoms in the compound system Y1-xPrxBa2CU3O7-y has been investigated by means of x-ray absorption fine structure (XAFS) techniques. By comparing the local structure in the compound x=1 with its counterpart x=0, the XAFS results provide a direct evidence that Pr has replaced Y in the material. The nearest-neighbor structure in the CuO2 planes seems to remain intact as × varies from 0 to 1, indicating that substitution of Pr for Y does not disturb the local distribution of holes in the CuO2 planes. We suggest that local disorder and distortions in the second-neighbor bonding configuration could be responsible for suppression of superconductivity with increasing Pr content in the system.
Oxygen Diffusion in La2−Xsrxcuo4−Y
Authors: Opila Elizabeth J. , Tuller Harry L. , Wuensch Bernhardt J. , Maier Joachim
Published: March 2011

Oxygen diffusivities in La2−xSrxCuO4−y (x×0, 0.07, 0.09, 0.12) single crystals were measured using an is 02 exchange technique followed by SIMS profiling. An interstitial diffusion model is proposed to explain the decrease in the oxygen diffusivity with increasing strontium content.
Oxygen In-Diffusion and Out-Diffusion in Single Crystal Yba2Cu3O7−δ
Authors: Lagraff John R. , Han Pengdi , Payne David A.
Published: March 2011

Isothermal resistance measurements were used to monitor oxygen indiffusion and out-diffusion in single crystal YBa2Cu3O7−δ from 600-780°C. Measurements on single crystals reveal that oxygen out-diffusion is intrinsically faster than in-diffusion, which is contrary to the rates observed in other studies for polycrystalline ceramics. Oxygen out-diffusion measurements suggest two different mechanisms, one above an4 one below ˜680°C,which have activation energies of 1.57±0.06eV and 1.00±0.04eV, respectively. Calculation of relaxation times for oxygen in-diffusion into initially tetragonal YBa2Cu3O7−δ suggest a single mechanism from 600-780°C with an activation energy of 1.16±0.06eV.
Nonstoichiometry, Defect Structure and Energetics in T (La2MO4; M=Cu, Ni) and T′ (Nd2CuO4) Structures
Authors: Dwivedi Anurag , Cormack A. N.
Published: March 2011

Atomistic computer simulation is performed to investigate the extent and nature of nonstoichiometry in La2CuO4, and La2NiO4. Results suggest anion Frenkel to be the dominant intrinsic defect in both compounds. Spontaneous oxidation is predicted for La2NiO4 but not for La2CuO4; however, both compounds are more easily oxidised than reduced, as opposed to Nd2CuO4, a superconducting compound with same generic formula. Oxidation takes place via accommodation of oxygen interstitials; however, the possibility of metal vacancies can not be completely ignored in La2CuO4. There is only one favorable oxygen interstitial site which is same in both the compounds La2MO4 (M=Cu, Ni). We found a favorable oxygen interstitial site in T′ structure too. Relaxed structures around an oxygen interstitial in these compounds are reported.
Metastable Phases and Defect Microstructures in Melt-Spun Ribbons of Nb3Al
Authors: Aindow M. , Shyue J. , Gaspar T.A. , Fraser H.L.
Published: March 2011

The phases and defects produced in a binary alloy, with nominal composition Nb-18at.% Al, have been studied using transmission electron microscopy (TEM). In addition to the equilibrium A15 phase (Nb3Al) a previously unreported Nb-rich B2 phase is present. A significant number of grow-in dislocations were observed in the A15 phase, these have b= a<100> and are predominantly screw on character. They are dissociated into two partial dislocations which bound a stacking fault according to the reaction;

<100> → > 1/2 <100> + SF + 1/2 <100>

The habit plane of the fault is shown to be {012}. These observations are compared with previous studies performed on the isostructual compound V3Si. The consequences of the observed dissociation for the plastic deformation of Nb3Al are discussed.
Comparison of Superstructure Phases of Rb2ZnBr4 Type Compounds
Authors: Hogervorst A.C.R.
Published: March 2011

Nine crystal structures, taken from literature, are compared with each other and with the room temperature structure of Rb2ZnBr4. Compared are the modulation functions and some pronounced local distortions. It appears that the ten structures have strikingly similar cooperative rotations of the anion tetrahedra.
Modulated Phases and Domain Structure in Double Niobates With Tetragonal Tungsten Bronze - Like Structure
Authors: Manolikas C.
Published: March 2011

The domain structure and the commensurate - incommensurate transition of some niobates, with general formula A2BNb5O15 where A = Ba, Sr or Pb and B = Na or K, are examined by using electron microscopy and electron diffraction methods. A model of the commensurate phase at room temperature is proposed and the natureof the incommensurate phase is discussed.
Electron Microscopic Study of Long Period Modulated Structures with Continuously Variable Periodicity
Authors: Colaitis D. , Dyck Van , Conde-Amiano C. , Amelinckx S.
Published: March 2011

Some systems show continuous and reversible phase transitions which are characterised by the appearance of irrational sunerlattice reflections with a position that shifts continuously and reversibly with temperature. This diffraction feature is not necessarily caused by a deformation modulation but can also originate from the reneated occurrence of planar defects with a variable “average” periodicity. The planar defects can be of different type (e.g. planes of different composition, antiphase boundaries, twin planes) as shown for the systems Ni3+xTe2, Cu3−xTe2, Cu2−S, mPbS-nBi2S3 ( > 2) and Cu 0.75VS2, using electron-microscopy and electron diffraction.
Long-Period Ordered Structures of the Au-Rich Au-Mn Alloys
Authors: Watanabe D. , Terasaki O.
Published: March 2011

Changes in the ordered structures of the Au-Mn system, existing at temperatures below 400°C, with composition have been studied in the range of 20–28 at.% Mn by high-resolution electron microscopy. The superstructures, Au4Mn, Au22Mn6, Au31Mn9 and 2d-APS(I), exist in the range of 20–23 at.% Mn. The Au22Mn6 and Au31Mn9 are the one-dimensional (ld) and two-dimensional (2d) antiphase structure (APS), respectively, based on the Au4Mn, and the 2d-APS(I) is based on the DO22 structure and consists of parallelogram and lozenge shaped domains. When Mn content increases, the Mn-Mn nearest-neighbour pairs are formed across the antiphase boundaries of the 2d-APS(I), and the structure changes to orthorhombic 2d-Au3Mn at about 24 at.% Mn. When Mn content increases further, the Mn-Mn pairs align in the <120> direction and the structure transforms continuously to the monoclinic Au5Mn2.
Two-Dimensional Antiphase Structure in The Ordered Ternary Alloy Cu-Zn-Au
Authors: Watanabe D. , Sato K. , Miida R.
Published: March 2011

Ordered structures of Cu-Zn-Au alloys were studied by electron diffraction. Two-dimensional antiphase structures exist at the compositions, Cu55Zn15Au30, Cu80-xZnxAu20 (10 ≤ x ≤ 35) and Cu85-xZnxAu15(25 ≤ x ≤ 35). The domain sizes M's measured in terms of the basic L12 cell along the two orthogonal directions are always the same, and they change from 3.4 to 1.6 as Zn content increases from 10 to 35 at.%. Based on the superstructure image of the Cu55Zn25Au20 with M=2.0 taken with high-resolution electron microscope, a structure model is derived, which explains intensities of all the superlattice spots on the diffraction pattern.
Configuration of Antiphase Domains in One-Dimensional Long Period Superstructural Alloys
Authors: Kuwano N. , Tomokiyo Y. , Oki K. , Eguchi T.
Published: March 2011

The configuration of antiphase domains in a one-dimensional long period superstructure (LPS) was examined theoretically. As LPS is composed of two kinds of antiphase domains, the domain-arrangement is described by f(n) , where f(n) is the existence probability of n which is the number of the majority domains between two minority ones. The equations for f(n) were derived using statistical approaches or thermodynamical ones, and f(n) predicted from the equations were compared with those obtained experimentally.
Calculations of Densities of States for Nonrandom, Substitutionally Disordered Alloys
Authors: Gonis A. , Freeman A.J.
Published: March 2011

Disordered systems have received a great deal of theoretical attention in the last fifteen years or so, and many advances in our understanding of such systems have been made. The greatest progress has been made in connection with substitutionally disordered alloys in which atoms of various species are randomly distributed over the sites of a regular lattice. The most satisfactory single-site theory for studying the properties of random substitutionally disordered alloys, in particular the one-particle properties such as the density of states (DOS), is the coherent potential approximation (CPA) [1,2]. In the CPA, one considers that the real disordered material is replaced by a self-consistently determined effective medium which is characterized by an energy-dependent site-diagonal selfenergy, and which preserves all symmetries of the lattice. The CPA yields unique and analytic results, i.e., yields DOS and spectral weight functions that are nonnegative and satisfy the fundamental sum rules. There exist several reviews of the CPA [3-5] both for systems describable by tight binding (TB) and by muffin-tin (MT) Hamiltonians.
An Explanation of the Influence of the Order-Disorder B2-B.C.C Transformation of the Self-Diffusion Behaviour in Alloys
Authors: Bakker H.
Published: March 2011

Theories describing the kinetics of ordered B2 and disordered b.c.c. alloys are applied to the effect of the order-disorder transition on tracer diffusion. Both tracer self-diffusion coefficients and isotope effects in βCuZn and equiatomic FeCo are considered.
The Role of Chemical Driving Force in Discontinuous Coarsening
Authors: Hillert M.
Published: March 2011

The precipitation of a new phase sometimes results in the simultaneous growth of one of the matrix grains at the expense of another one, so called discontinuous precipitation. The two growing crystals may arrange themselves in the lamellar fashion, known from eutectoid transformations. The mathematical analysis of this diffusion-controlled reaction would be incomplete if the nature of the driving force for the matrix grain is not identified.

There have been many suggestions regarding the nature of the driving force. The recent discovery that grain boundaries in a single-phase material can migrate in connection with grain boundary diffusion supports the hypothesis of a chemical driving force, acting in discontinuous precipitation.

Another reaction where the chemical driving force may be important is discontinuous coarsening. The theory for this reaction is developed in sufficient detail to show the role of the chemical driving force.
Coexisting Ordering and Phase Separation in Binary Fcc Alloys
Authors: Rossiter P.L. , Lawrence P.J.
Published: March 2011

Consideration of only nearest neighbour pairwise interactions Vij in a binary alloy leads to the classification of the system as ordering (unlike near neighbours) or clustering (like near neighbours), depending upon the sign of Vij However, this simple classification loses meaning when multi-atom correlations, many-body interactions or a longer range interaction are considered. For example, the first nearest neighbour interaction may favour ordering while the second, which may be of comparable magnitude, may favour clustering. By extending the Bragg-Williams model to include second near-neighbour interactions in fcc alloys, it is shown that a miscibility gap may form in the region of the orderdisorder solvus, leading to a complicated sequence of atomicrearrangement upon slow cooling. Despite the well-known failings of the point approximation when applied to fcc alloys, the results are shown to be consistent with the unusual behaviour exhibited by some systems.
A Study of the Kinetic of Precipitation and the Morphology of Precipitates Induced by Plastic Deformation in Al-Zn Alloys
Authors: Mai C. , Merle P. , Merlin J. , Livet F.
Published: March 2011

The influence of plastic deformation on the kinetic of precipitation and the morphology of precipitates in an Al-Zn 4.4 % at. studied by T.E.P. and SAXS is reported. Some results can be pointed out ; after a given amount plastic deformation at room temperature by tensile strength:

i - the precipitates have a flat shape (instead of the spherical or ellipsoidal shape usualy observed in this alloys.

ii - the precipitate volume fraction is a function of strain (ε) and strain rate (ė). For a given ė, the higher precipitate volume fraction is obtained with the higher ε. For a given ε, the lower ė the higher the volume fraction of precipitates.

iii - the scattering intensities at small angle for three orientations of the sample (α =0,45°, 90° where α is the angle between the axis of tensile and the scattering vector- are different. A calculation for an anisotropic orientation of flat discs shows that precipitates have a preferential texture. The orientation is about 50° from the tensile axis.
Initial Stages of Precipitation in the Cu-Be Alloys
Authors: Pelletier J.M. , Vigier G. , Mai C.
Published: March 2011

The clustering in Cu-Be alloys lead to large modifications of the X-ray scattering curves and to increases of both electrical resistivity and thermopower. The microstructure is investigated in the initial stages of precipitation : small clusters exist in the quenched state, but no spherical precursor precipitates are observed before the formation of plate-like G.P. zones. The evolution of the transport properties is qualitatively analyzed and the deformation effect induced by anisotropic particles is considered.
Diffuse and Small Angle Neutron Scattering Studies of Clustering and Decomposition in Electron-Irradiated Cu-Ni-Fe Alloys
Authors: Gölling H.W. , Poerschke R. , Schwahn D. , Wollenberger H.
Published: March 2011

Earlier investigations of short range clustering (SRC) and long range decomposition (LRD) in Cu-Ni alloys upon electron irradiation [1,2] have been extended to alloys containing 0.5 and 2 at.% Fe. Moreover, quenching instead of furnace cooling was applied to achieve a well defined homophase equilibrium state with a small degree of SRC. Under subsequent irradiation at temperatures between 373 K and 623 K the decomposition kinetics of the alloys have been followed by diffuse and small angle neutron scattering experiments within a momentum transfer range of 0.001 < κ(Å−1) < 8. The addition of Fe is found to extend the miscibility gap to higher temperatures. The observed scattering curves are discussed in terms of the existing models for the initial stages of spinodal decomposition, irradiation enhanced diffusion and phase stability under irradiation.
Metastable Phases Obtained by Laser Surface Melting of a Chromium High-Carbon Steel
Authors: Ramous E. , Giordano L. , Principi G. , Tiziani A.
Published: March 2011

The power laser has been applied to the surface melting of a high-carbon alloy steel with laser operating parameters leading to structures which cannot be produced by the usual heat-treatments. The subsequent annealing of these structures has also been investigated. Optical and scanning electron microscopy, X-ray diffraction and Mössbauer spectroscopy have been used as methods of analysis.
Microstructural and Property Changes During Short-Term Ageing of Cast Austenitic Stainless Steels
Authors: Hodgkinson M. , Towers T.A.
Published: March 2011

The Charpy ν-notch impact properties at -196°C of casts of Type 316 austenitic stainless steel have been compared, after ageing at 650°C for time periods up to 90 minutes. The impact energy of all steels depends on ageing time; the degree of response to ageing depends on original delta ferrite content, which varied from −0.5% to 5.0% in the steels studied. For steels with delta ferrite content in the lower half of this range the impact energy, during ageing, initially decreases to a minimum, subsequently rises to a maximum and finally decreases. Steels with delta ferrite contents near 5% suffer a continuous decrease in impact energy as ageing time increases.

Microstructural investigation reveals, during early stages of ageing, the rapid formation of sigma phase, at the ferrite-austenite interphase boundaries. Some delta concurrently transforms to new austenite. Microfractographs indicate a change in the nature of the fracture as ageing progresses. Initially, fractures have large dimples, but as ageing progresses, a finer dimpling appears and extends in area. These dimples contain fine particles, identified mainly as MnS. The variations in impact behaviour are explained on the basis of the structural changes observed.
A Study of the Strengthening and the Production of Sigma Phase in 20–9–3 Austenitic Stainless Steel Weld Metals
Authors: Honeyman G.A. , Towers T.A.
Published: March 2011

It is general practice to weld bullet proof steels with 20Cr-9Ni-3Mo Duplex stainless alloy. Little information is available regarding increasing the strength of these weldments or their response to time at temperatures used for heat treatments. This investigation sought to study possible strengthening mechanisms involving silicon additions and the effects of heat treating such welds at 1050°C.

A 2% silicon addition gave a 16% increase in strength with approximately equal contributions from stacking fault energy, solute and second phase hardening. However, the ductility was significantly reduced by a high ferrite content. When this δ ferrite content was corrected by cobalt additions a 26% increase in strength was achieved, giving properties very similar to bullet proof steels.

A 1050°C heat treatment programme showed rapid sigma phase formation from δ ferrite but the process was reversed on further heating. This phenomenon was attributed to alloy migration as the weld microstructure approached equilibrium, the hardness of the alloys followed the variation in δ ferrite content being at their heightest at the beginning and end of heat treatment.
Phase Diagrams for Incommensurate Systems
Authors: Toledano P.
Published: March 2011

Phase diagrams, for systems undergoing one or several incommensurate and lock-in transitions, are discussed in the framework of the Landau theory of phase transitions. It is shown that their essential features can be deduced from the explicit forms of the free-energy density ø and the k-dispersion of the coefficient α(→k)of the quadratic contribution of the order-parameter components in ø. Two families of phase diagrams are distinguished depending on symmetry considerations.
The Semi-Conductor ⇌ Metal Transition in Tin
Authors: Smith R.W. , Vnuk F.
Published: March 2011

It is well known that silicon, germanium and other diamond-cubic semi-conductors may transform to a metal when a pressure of the order of 100 kilobars is applied. This renders the detailed study of the transformation experimentally difficult. Grey tin transforms to the more common (white) metal allotrope at room temperature and pressure and so provides a means of studying readily this type of transformation. This paper describes the influence of pressure on the transformation characteristics of tin and dilute tin-germanium alloys.
Melt Spinning and Phase Transformations of V2CrA11-xBx and Ti3Nb6Mo3Si4 Alloys
Authors: Smith B.S. , Smith R.A. , Clapp M T.
Published: March 2011

Melt spinning was used to rapidly quench V2CrA11-xBx and Ti3Nb6Mo3Si4 alloys. Melt spinning had very little effect on the crystal structure of the V2CrA11-xBx alloys. However, a new (NbTiMo)3 Si A–15 phase was found by rapid quenching of the Ti3Nb6Mo3Si4 alloys; the lattice parameter was 5.08 Å. Melt spinning increased the Vickers microhardness values of the V2CrA11-xBx alloys from 500 to 750, and of the Ti3Nb6Mo3Si4 alloys from 1000 to as high as 1675. Melt spinning increased the superconducting transition temperature of the Ti3Nb6Mo3Si4 alloys from 1.9 to 3.4K.
Electronic Energy Bands in γ-InSe with and without Intercalated Lithium
Authors: Costa P. Gomes Da , Balkanski M. , WALLIS R. F.
Published: March 2011

The effect of intercalated lithium on the electronic band structure of the γ-polytype of InSe has been investigated using a tight-binding method. The energy bands of the pure polytype were calculated and the results compared with previous work. The modifications of the energy bands produced by the introduction of one lithium atom per unit cell were calculated for the lowest potential energy position of the lithium atom in the Van der Waals gap between layers. The results for the changes in the smallest and next-to-smallest direct band gaps are compared with experimental data. An interpretation of a photoluminescence peak produced by lithium intercalation is given.
Ion-Ion Pairs in the Superionic Conductors
Authors: Sigaryov Sergei E.
Published: March 2011

On the base of numerous experimental data and theoretical approaches it is shown that ion-ion pairs with the intrapair distance about a sum of the corresponding ionic radii is the feature of charge transfer in the superionic conductors.
Electrochemical Properties and Applications of Ionically and Electronically Conducting Polymers
Authors: Croce Fausto , Panero Stefania , Scrosati Bruno
Published: March 2011

Various types of polymeric materials with enhanced electrical properties have been characterized recently. Many of these conducting polymers are of specific interest in solid state electrochemistry and in solid state ionics since they act as novel electrode and electrolyte materials. Indeed, these materials are currently used as improved polymer electrolytes and polymer electrodes for the development of advanced-design electrochemical devices. However, there are still some problems which prevent the wide utilization of these conductors. In this paper we attempt to identify the nature of these problems and discuss their possible solutions.
Factors Controlling Ionic Conductivity of Plasticized and Non-Plasticized Crosslinked Polyether Electrolytes
Authors: MacFarlane Douglas R. , Hey Jeffrey M. , Forsyth Maria
Published: March 2011

A series of elastomeric (urethane crosslinked) polyether electrolytes have been prepared in order to investigate the influence on conductivity of crosslink density, length of uninterrupted polyether chain, number of side chains and plasticizer content. Crosslink density was found to only weakly influence conductivity, but had the expected major effect on elastic modulus. Increases in uninterrupted polyether chain length were also found to enhance conductivity. The number of side chains (acting as an internal plasticizer) was not found to have a marked effect on conductivity within the range studied. The highest room temperature conductivity observed in these non-plasticized elastomers was 3 × 10-5 Ω-1 cm-1. Addition of a low molecular weight plasticizer such as tetraglyme was found to markedly increase the conductivity and lower Tg. The highest room temperature conductivity observed in 50% plasticized elastomeric materials was 10-3 Ω-1cm-1.
MD Studies of Transport in Polymer-Salt Complexes: A Progress Report
Authors: Forsyth M. , Payne V. A. , Ratner M. A. , Leeuw S. W. De , Shriver D. F.
Published: March 2011

Molecular dynamics simulations performed on highly concentrated Coulomb/solvent systems are used to help interpret the transport mechanism in polymer ionics. Using simple Coulomb and Lennard-Jones forces among the ions and a solvent model of a fixed dipole contained in a spherical solvent particle, we investigated the nature of ion pair formation and stability. For a model NaI system, we find that ion pairs decrease with increase in solvent dipole moment or temperature. The latter observation is at variance with experimental results on polymer electrolytes, probably because of entropy terms that do not occur with our simple solvent molecule.
Mixed Divalent Polymer Electrolytes
Authors: Cole Michael , Latham Roger J. , Linford Roger G. , Sheldon Mark H.
Published: March 2011

Some features of interest for divalent polymer electrolytes are described. Attention is focussed on two contrasting roles for cations: providing chemical cross-links within the polymer matrix and offering a source of mobile charge carriers. The possible merits of using mixtures of two types of cation, one type for each role, is discussed. Alternative mixed salt systems containing two anions with a common cation are considered. Another class of mixed polymer electrolyte systems involving two divalent cations in conjunction with two monovalent anions is also examined in the context of illustrating competitive anion-cation interactions within the polymer matrix by EXAFS local structure techniques. Results for the systems PE015:ZnI2/Mg(CIO4)2, PEO15:ZnI2/Mg(CF3SO3)2, PEO15:CaI2/ZnI2 and PEO15:CaI2/CaBr2 are discussed.
Solid Polymers Doped with Neodymium. Complex Formation and Morphology in NdCl3 and Nd(DPM)3-Poly(Ethylene Oxide) Systems
Authors: Twomey Conor J. , Chen Shaw H.
Published: March 2011

The complex formation and morphology of the NdCI3—PEO system are presented together with some preliminary results on the Nd(DPM)3 \Nd—tris—2,2,6,6—tetramethyl —3,5—heptane dionate]—PEO system. Although the NdCl3—PEO complex is found to be highly hygroscopic, it is shown that residual moisture can be removed reversibly, thereby permitting the role of water in affecting the morphology of the solid to be examined. It is concluded that complexation is a competitive process between the ether oxygens on the polymer backbone and water. Under anhydrous conditions the resultant complex is amorphous at a \EO]/\NdCl3] molar ratio approximately less than ca. 8, but above this critical value the PEO in excess of the stoichiometric ratio presents a second partially crystalline phase. The glass transition temperatures were found to increase sigmoidally with increasing salt content. Despite the hygroscopic nature of Nd(DPM)3 the resultant complexes were found to be moisture resistant upon prolonged exposure to the atmosphere.
Intercalation in 3D-Skeleton Structures : Ionic and Electronic Features
Authors: Hagenmuller Paul , Delmas Claude
Published: March 2011

The voltage of an electrochemical cell, i.e. the difference between the chemical potentials of the two electrodes, may play the role of a sensor which allows to display the structural modifications and the physical properties. The electrochemical processes involved in an alkali metal (A) intercalation electrode emphasize the influence of the ionic and/or electronic features. The A+-lattice and A+-A+ interactions as well as electronic band-filling may lead to phase transitions or even limit the intercalation reaction.

The shape of the cell voltage vs. intercalation rate curve depends on the number of vacant sites available for intercalation, the number and the oxidation state of the reducible cations, the band structure of the material and the covalency of the framework.

Alkali ion intercalation in 3D-structures related to perovskite (Ln⅓ NbO3), hexagonal tungsten bronze (LiW3O9F) and Nasicon-type (AM2 (PO4)3) is discussed from that point of view.

In Ln⅓NBO3 (Ln = La, Nd) (i.e. ▭ ½Ln⅓ ▭, ⅙NbO3) L1+-intercalation in various sites is related to the rare earth size.

Two extra lithium atoms can be introduced into LiW3O9F in which four sites are available, but only one out of two is occupied in order to reduce the electrostatic interactions. Moreover the change in the discharge curves can be associated to the modifications with intercalation rate of the Li+-lattice interactions.

Within the Nasicon derived structures of ATi2 (PO4)3 and Fe2 (MoO4)3 the intercalation process is limited by the lowest stable oxidation state of titanium or iron. In both systems the strong electronic localization leads to formation of large two phase-domains.

The relevance of using 3D-intercalation electrodes in electrochemical power batteries will be discussed as far factors such as electrical behavior or absence of significant unit cell modifications of the positive electrodes during the intercalation process are essential for many cycle utilizations.
Intercalation Processes in Cobalt Substituted Nickel Oxyhydroxides
Authors: Delmas Claude
Published: March 2011

Chimie douce reactions (hydrolysis and reduction) from layered oxides : NaNiO2, NaxCoO2 and NaNil-xCoxO2 lead to numerous oxyhydroxides and hydroxides which differ by the composition of the intersheet space.

According to the experimental conditions of the hydrolysis reaction, the oxyhydroxides can be unhydrated or intercalated with one or two layers of water molecules. From the most hydrated phases, the other ones can be obtained by chemical, thermal and even mechanical treatment.

The reduction of Co-substituted nickel oxyhydroxides leads to hydroxides in which nickel and cobalt ions are respectively divalent and trivalent. In order to compensate the excess of positive charge in the (Ni, Co)O2 sheet, anions (OH-, CO32-, SO42-, NO3-) are inserted in the Van der Waals gap.

For the highest anion amounts, well ordered α*-type materials are obtained. Water molecules are simultaneously inserted in the interslab space. Their structure is strongly related to the hydrotalcite one. When the amouit of anions in the intersheet space is not sufficient, interstratified materials are obtained. In this case the (Ni,Co)(OH)2 slabs are separated by a layer of CO32- anions and water molecules (α*-type) or by an empty Van der Waals gap (β(II)-type). The amount of α*-type planes in the structure increases with the cobalt amount. All these materials have been characterized by IR spectroscopy which allows to detect the existence of two types of O-H bonds (free in α*-type plane or hydrogen bonded in ²(II)-type plane).