bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal Relaxation of a Thermally Stressed Fiber by Prismatic Dislocation Punching
Authors: Dunand David C. , Mortensen Andreas
Published: March 2011

A model predicting the number of prismatic loops dislocation punched at the ends of a cylindrical fiber by thermal mismatch stresses is presented and compared to another based on a mismatching ellipsoid. The longitudinal stress in the fiber and the interfacial shear stress are derived by adapting a shear-lag model to the plastic portion of the interface. In certain cases, the central part of the fiber is strained by plastic and elastic interfacial shear until it exhibits no mismatch with the matrix. This leads to a critical fiber length above which the number of punched loops is constant.
Effect of Particle Size on the Plastic Zone Formation in Front of Mode I Crack in ABS Polymers
Authors: Ni Beta Y. , Li J. C. M.
Published: March 2011

Two different sizes (0.4 and 0.1 μm) of rubber particles (polybutadiene) are usually used to toughen the glassy SAN (styrene acrylonitrile) matrix in ABS copolymers. Experiments on a batch of specimens without the large particles confirmedour previous contention that cavitation of large particles within a zone of cardioid shape is an important part of crack tip plasticity which protects the crack tip from the applied stress field. Large rubber particles require a less strong applied stress field than small rubber particles to initiate crazes so that the large rubber particles help avoid brittlefracture which occurs without crazes.
Theory of Hydrogen Complexes in Si
Authors: Zhang S. B. , Jackson W. B.
Published: March 2011

The predominance of Si-H bonding and the origin of {111} platelets in hydrogenated Si remain important unsolvedproblems in the study of H in Si.Recent theoretical and experimental results indicate that H predominately enters the Si network in pairs. A promising diatomic H configuration consists of a bond centered H closely associated with an antibonding centered H. In this work, we show that adjacent diatomic H pairs have a binding energy of 0.2 eV/2H. The binding originates from relaxation of strained Si-Si backbonds. Further clustering of the H pairs eliminates all strained bonds, forming a hydrogenated platelet oriented along the {111} plane. The binding energy of 3.95 eV/2H for the platelet is 0.15 eV lower than that for interstitial H2 molecules in c-Si. Lattice expansion makes the platelets energetically more competitivewith the lowest energy Si-H bonding confi gration at hydrogenated Si (111) surfaces. These higher level complexes explainthe formation of platelets, Raman spectra, and absence of gap states in hydrogenated c- Si as well as the clustered phaseseen in NMR and of H evolution and diffusion in hydrogenated amorphous Si.
The Precipitation of Nickel and Copper at Grain Boundaries in Silicon
Authors: Möller H. J. , Jendrich U. , Huang L. , Foitzik A.
Published: March 2011

The precipitation of copper and nickel at grain boundaries in cast polycrystalline silicon is investigated. The metals are diffused into the specimens from a surface source between 800 – 1000 °C and the precipitation after cooling is studied by TEM. Copper precipitates in form of colonies containing hundreds of particles with a size between 5–6 nm. In the grain boundary they nucleate preferentially at dislocations and steps. The distribution and size of the precipitates depend on the cooling rate after the diffusion. Nickel forms only few large (micrometer size) plate-like or three dimensional precipitates at and near grain boundaries. The main features of the results and the differences between the two elements are explained under the assumption that the precipitation requires the transport of native point defects.
On the Distribution Mechanism of Voids in Si-Implanted GaAs
Authors: Chen Samuel , Lee S.-Tong , Braunstein G. , Ko K. Y. , Tan T. Y.
Published: March 2011

Voids, formed by the condensation of an excess of implantation-induced vacancies, have been recently identified as the defect directly responsible for dopant diffusion and electrical activation anomalies in Si-implanted and annealed GaAs and GaAs/AlGaAs superlattice materials. Depending on the implanted dose, voids can be distributed either throughout the implanted region or in two bands. We have examined the origin of this void distribution difference. In the asimplanted sample associated with the latter case, a buried continuous band of amorphous GaAs has formed. GaAs formed by the recrystallization of amorphous GaAs does not contain excess vacancies, and therefore cannot form voids. However, on either side of the amorphous layer, the excess vacancies can condense to form the observed banded distribution of voids. In the as-implanted sample associated with the former case, a continuous amorphous GaAs layer did not form and therefore, upon annealing, voids are seen throughout the implanted region.
Frequency Dependence of Hopping Conductance in Crystalline Electron Irradiated Semiconductors
Authors: Kouimtzi S.D.
Published: March 2011

Extensive irradiations were carried on crystalline semiconductors InSb, GaAs and InAs. At low temperatures the frequency dependence of the conductivity is observed to be sublinear (σαωs). where s<1. The dependence of s on both the degree of the induced damage and on temperature is studied and discussed in terms of the quatum mechanical tunnelling and of correlated barrier hopping mechanisms.

At fairly low doses of irradiation activated conductance is observed with s having a weak temperature dependence. As the degree of damage is further increased conduction at helium temperatures takes place by variable range hopping, σαexp(-b/T1/4). The constant b is observed to depend on the effective mass for different semiconductors.

At higher temperatures activated conduction is observed again. The observed activation energies E are Eg 1/4 <E<Eg 1/2 and we believe they could represent hopping of single and double carriers.
Phonons in Mixed II-VI Compound Semiconductors
Authors: Talwar D. N. , Coleman Alan C. , Amirtharaj P. M. , Perkowitz S. , Feng Z. C. , Becla P.
Published: March 2011

We have analysed the far infrared reflectivity and Raman scattering spectra of phonons in Cd1−xMnxTe, Zn1−xMnxTe, Hg1−xMnxTe, and Hg1−xZnxTe for low composition of x. Unlike CdMnTe and ZnMnTe, weak impurity induced peaks are observed in HgZnTe and HgMnTe, near ˜ 96 and 98 cm−1, well above the LA-phonon band of HgTe. Comprehensive calculation of lattice dynamics based on a semi-empirical Green's function theory has provided convincing arguments to support the above features as gap modes of Zn and Mn in HgTe. The theory also predicts the possibility of resonance modes, above the TA cutoff of HgTe, in HgMnTe and HgZnTe to be observed by IR spectroscopy.
Effect of the Extinction Distance in X-Ray Rocking Curve Analyses of II-VI Compounds
Authors: Moran P.D. , Matyi R.J.
Published: March 2011

Double crystal x-ray rocking curves from single crystal CdTe and CdZnTe of various degrees of crystalline perfection were recorded under diffraction conditions in which the extinction distance varied from under 10 microns to more than 100 microns. In crystals of intermediate quality the rocking curves recorded under conditions of long extinction length showed structure not evident in those recorded under conditions of short extinction length. Integrated reflectivity measurements were performed at both long and short extinction lengths. The results have been interpreted within the framework of a transition from kinematic to dynamical diffraction.
PAC Studies of Defects in AgCI and II-VI Compounds
Authors: Austin J.C. , Swanson M.L. , Hughes W.C. , Choi S.S.
Published: March 2011

The Perturbed Angular Correlation (PAC) method has been used to study In -vacancy complexes in AgCl and II - VI compounds. Although these materials are quite different in structure and properties, they are related by photoconductive properties which make them interesting intrinsically and for application to photography (silver halides) and to the design of photodetectors and photovoltaic cells (II - VI compounds). We have obtained the first PAC results for silver halides and ternary II-VI compounds.

For AgCl, measurement at 77 K clearly reveals two different 111In - vacancy complexes characterized by quadrupole interaction frequencies Vq1 = 21.5 MHz and Vq2=43 MHz, both having axially symmetric electric field gradient (EFG) tensors with principle axes along <100> directions. Temperature dependence of the PAC signal allows a determination of the activation energy and attempt frequency for vacancy motion by measurement of the damping arising from dynamic effects.

For 4% Zn - doped bulk CdTe samples, vacuum annealed in the range 400°C to 550°C, PAC shows that a large fraction of the 111 In probe atoms occupy non-cubic lattice sites having an EFG characterized by vQ = 60 MHz, η = 0.2. The concentration of this complex was decreased by annealing between 400°C and 600°C in a Cd overpressure, suggesting tha the observed EFG is caused by a 111In - cadmium vacancy complex. Similar measurements of Cd0.8Mn0.2Te showed an identical EFG which, however, appeared at a lower annealing temperature.
Point Defect Injection and Enhanced Sb Diffusion in Si During Co-Si and Ti-Si Reactions
Authors: Honeycutr J.W. , Rozgonyi G.A.
Published: March 2011

The effects of Co and Ti silicide film formation on diffusion of buried Sb-doped layers in Si have been investigated. Sb profile analysis by secondary ion mass spectrometry shows that greatly enhanced, non-uniform Sb diffusion occurs during reactions of various thicknesses (30- 300 nm) of Co and Ti by rapid thermal annealing. A simple non-equilibrium intrinsic diffusion model is invoked to estimate time-averaged excess vacancy concentrations. Vacancy concentrations of about 107 times equilibrium values are shown to exist during CoSi2 formation by reaction of a 30 nm Co film at 700°C for 5 min in Ar.Diffusion enhancements at large distances from silicide stripe edges are observed by bevel and etch techniques. These effects tend to decrease with increasing annealing time, indicating that film stresses may play an important role in the interfacial point defect injection process.
Investigation of Deep Level Defects in Mercuric Iodide by Thermally Stimulated Current Spectroscopy
Authors: Bao X.J. , Schlesinger T.E. , James R.B. , Cheng A.Y. , Olrtale C. , Van Den Berg L.
Published: March 2011

Mercuric iodide (HgI2) single crystals deposited with semitransparent Pd, Al and Ag contacts were studied by thermally stimulated current spectroscopy (TSC). Distinct differences were found among spectra obtained friom samples withdifferentmetal contacts, indicating that interactions between the metal contacts and mercuric iodide substrates have strong effects on the deep defect levels in mercuric iodide. The activation energies of some of these defect levels were estimated bytaking TSC spectra with different heating rates. In addition, a pyroelectric effect was observed in Ag-contactedsamplesbythermally stimulated depolarization current technique (TSDC). The implications of these results in device applicationsof mercuric iodide are discussed.
Hydrogen Diffusion in N-Type Silicon.Comparison With P-Type Silicon
Authors: Rizk R. , De Mierry P. , Ballutaud D. , Aucouturier M. , Mathiot D.
Published: March 2011

Deuterium diffusion profiles in medium phosphorus doped silicon (1016 and 1017 cm−3) at two different deuteration temperatures (120 and 150°C) are simulated with an improved version of a previously reported model. The new approach which excludes the H2 molecule formation, as applied recently to ptype silicon, allows the determination of kinetic and thermodynamic parameters such as diffusion coefficients, activation and dissociation energies. These parameters 6re compared with those found for p-type silicon and discussed in the light ofavailable data for n-type material.
The Accommodation of Lattice Mismatch on the (111) Interphase Boundary Plane in FCC Metals
Authors: Gumbsch P. , Fischmeister H.F.
Published: March 2011

Using the embedded atom method we atomistically model the accommodation of the lattice nismatch and study the propertiesof the misfit dislocations in parallel oriented bicrystals. We calculate and analyze in detail the excess interfacial energies on the (100) and (111) boundary planes. The Ag/Ni system is chosen as a model system for metal/metal interfaces with a large lattice mismatch.

Among the possible boundary planes in parallel oriented fcc bicrystals, the ones with terminating {111} planes arc energetically most favourable and are most often observed in experiments. This can be explained by a detailed analysis of the elastic strain fields in the interfaces, which correspond to networks of misfit dislocations. While the misfit dislocations on the (100) and (011) planes have a ½[01ī] Burgers vector, those on (111) can dissociate into misfit partials. The elastic strains connected with the misfit partials are, of course, much smaller than those for other types of misfit dislocations. The misfit partials form a triangular network within the boundary plane.
Imaging of Cracks in Semiconductor Surfaces Using Scanning Tunneling Microscopy
Authors: Foecke T. , King R. , Dale A. , Gerberich W.W.
Published: March 2011

Scanning Tunneling Microscopy (STM) has developed into a useful tool for atomic-scale characterization of material surfaces. It is proving especially useful in the field of fracture, as the vast majority of high-resolution images of fracture processes are made in the transmission electron microscope, where thin film effects and sample preparation may greatly modify crack tip stresses and dislocation structures. This investigation involved imaging of cracks introduced in Si at room temperature and single crystals of galena (PbS) by rapid indentation at 77K. Images were obtained at the arrested cracktip, around the indentation, and along the flanks of the crack in the dynamic growth region. Measurements were made of both crack-tip morphology and upsets observed along the flanks of the cracks in PbS. Interesting results concerning crack tip geometry in Si, the effect of STM tip geometry and scan conditions on the resulting image of the cleavage crack, as well as work in progress on other material systems, will be discussed.
Combined Tem and X-Ray Topographic Characterization of InxGa1−xAs/GaAs Strained Layer Systems.
Authors: Dudley Michael , Yao Gong-Da , Paine David , Howard David , Sacks Robert N.
Published: March 2011

Novel application of a combination of TEM and non-destructive synchrotron X-ray topography in both Bragg and grazing Bragg-Laue geometries to the characterization of InxGa1−xAs/GaAs strained layer films is reported. Specialized epilayer lift-off procedures enabled TEM characterization of the defect distributions in macroscopic area films, effectively increasing the field of view of the technique by several orders of magnitude. These lateral distributions correlated well with those observed on both Bragg and grazing Bragg- Laue topographs. Grazing Bragg-Laue images also afforded depth sensitivity. Excellent correlations exist between results obtained with all these techniques for systems with a wide range of In concentrations, corresponding to a broad range of interfacial dislocation densities, although only results for x=;0.085 are presented. This work demonstrates that it is possible to bridge the gap that has traditionally existed between the areas of application of these two generic techniques, in terms of both tolerable defect densities and fields of view. This gap also spans the range of defect densities which is of interest in this and other systems.
Wrong Bonds at Compound Semiconductor Grain Boundaries
Authors: Lambrecht W. R. L. , Lee C. H. , Methfessel M. , Van Schilfgaarde M. , Amador C. , Segall B.
Published: March 2011

The role of cation-cation and anion-anion “wrong” bonds at compound semiconductor grain boundaries is investigated. Results are presented for the {110} and {001} inversion domain boundaries in SiC and GaAs. The role of electrostatic effects, compensation of over- and undersaturated bonds, “chemical” reconstructions andbond length relaxations are discussed.
Interface Structure of Epitaxial Nb Films on Sapphire: Grazing Incidence X-Ray Diffraction and X-Ray Reflectivity Studies
Authors: Lee C. H. , Liang K. S. , Shieu F. S. , Sass S.L. , Flynn C. P.
Published: March 2011

The interface structure of MBE grown Nb films on sapphire substrates was studied using grazing incidence x-ray diffraction and x-ray reflectivity measurements. Specifically, the use of these x-ray techniques in probing the buried interfaces was demonstrated. Diffraction effects were observed which are consistent with the presence of misfit dislocations in the interface.
Deep Level Defect Characterization of MBE Grown Ingaas/Gaas Heterostructures.
Authors: Buchwald W.R. , Zhao J.H. , Rong F.C.
Published: March 2011

Deep level transient spectroscopy (DLTS) measurements have been performed on Schottky diodes fabricated on MBE grown InGaAs/GaAs heterostructures. The dominant electron trap in this material is found at a depth of 0.30eV below the GaAs conduction band and is believed to be the previously observed M3 defect. Two other defects, at depths of 0.50eV and 0.58eV below the GaAs conduction band, were also observed. Defect depth profiling shows the 0.50eV defect to be spatially locatednear the heterointerface. The 0.58eV defect is not observed near the heterointerface but is observed in large concentrations deep in the GaAs epilayer. Optical DLTS measurements reveal deep defects at 0.54eV and 0.31eV above the InGaAs valence band as well as a large, broad peak, most likely consisting of several energy levels with varying capture cross sections,located at the heterointerface. Two carrier accumulation peaks were also seen in the CV carrier profiling measurements and are suggested to be due to two heterointerface defects located at 0.68eV and 0.87eV below the GaAs conduction band.Thermally stimulated capacitance measurements also indicate minority hole emission in this n-InGaAs/N-GaAs heterostructure.
High Quality GaAs Mis Diodes With Very Low Surface State Density
Authors: Fujisaki Yoshihisa , Sakai Sumiko , Ataka Saburo , Shibata Kenji
Published: March 2011

High quality GaAs/SiO2 MIS( Metal Insulator Semiconductor ) diodes were fabricated using (NH4)2S treatment and photo-assisted CVD( Chemical Vapor Deposition ). The density of states at the GaAs and SiO2 interface is the order of 1011 cm-2eV-1 throughout the forbidden energy range, which is smaller by the order of two than that of the MIS devices made by the conventional CVD process. The mechanism attributable to the interface improvement was investigated through XPS( X-ray Photoelectron Spectroscopy ) analyses.
Influence of Surface Relaxation on X-Ray Topographic Imaging of Interfacial Dislocations in Heterosystems.
Authors: Yao Gong-Da , Wu Jun , Dudley Michael , Shastry Vijay , Anderson Peter
Published: March 2011

The influence of surface relaxation on the imaging of dislocations in thin single crystal films, using white beam synchrotron radiation topography in grazing Bragg-Laue geometry, has been assessed. The predicted visibility of dislocation images on grazing Bragg- Laue topographs, for the particular case of interfacial edge dislocations in a GaAs/Si heterostructure, is shown to be strongly influenced. Agreement between predicted and observed visibility could only be obtained by incorporating the surface relaxation effects, which thus strongly influence the depth sensitivity of the technique, i.e. the ability to pinpoint the depth of a dislocation. Dislocation image widths are also influenced by these effects.
Antiphase Boundary Calculations for the L12 Structure Using an Embedded Atom Method Model
Authors: Brown Jeanne R. , Johnson Robert A.
Published: March 2011

A model based on the embedded atom method [1] has been used to calculate antiphase boundary (APB) energies of three low-index planes for alloys having the L12 structure. The lattice constant, cohesive energy, unrelaxed vacancy formation energy, bulk modulus, and average shear modulus for each element are used as inputs into the model. Effects of the APB orientation and of the range of interaction in the model are examined. Both unrelaxed and relaxed APB energies are compared with available experimental values and earlier theoretical results. A strong anisotropy was found in six of the seven alloys studied. The {111} APB energy was consistently smaller than that for the {110} APB, while the {100} APB energy was found to be very close to zero with very little difference between the unrelaxed and relaxed values. For both energy and relaxation amounts, the results did not vary much with the range of interaction, so that 3rd nearest-neighbor calculations were found to be satisfactory approximations.
Comparison Between Homo-And Hetero-Epitaxial Layers by Photoreflectance Spectroscopy
Authors: Jiao K.L. , Shi Z.Q. , Anderson Wa.
Published: March 2011

MOCVD grown GaAs and InP epitaxial layers have been studied using photoreflectance spectroscopy. Homogeneous and heterogeneous structures were employed to investigate the influence of the mismatch induced strain and dislocations. All the tested spectra contained a sharp peak related to the fundamental absorption edge and a pronounced Franz-Keldysh oscillation. The data analysis revealed a consistent difference in bandgap, temperature coefficients of the bandgap, and surface electric
field, in the order of the degree of mismatch. For GaAs/GaAs and GaAs/Si samples, the bandgaps derived from the three point method were 1.436 and 1.324eV, respectively. Values of 1.334, 1.325, and 1.294 eV for the bandgap were found for InP/InP, InP/GaAs, and InP/GaAs/Si, respectively. For GaAs epitaxial layers, the intensity of the surface
field bore a ratio of 1.18:1 between GaAs and Si substrates. For InP epitaxial layers, the ratio was 1.23:1.12:1 in the sequence of InP, GaAs, and GaAs/Si substrates. Such a measure must be related to the mismatch in the heteroepitaxy structures. A shoulderlike peak, 18-23 meV below the gap-energy peak (Eo), was found for GaAs samples, which could be impurity related. A broad shoulder-like peak 30 meV below the fundamental absorption edge was also observed only for InP/GaAs/Si and hence attributed to some shallow defect levels induced by antiphase disorder.
Defect Network in Superconducting Ceramic Oxides Studied by Neutron and Proton Irradiation
Authors: Mezzetti E. , Andreone D. , Castagno G. , Cherubini R. , Colombo S. , Gerbaldo R. , Minetti B.
Published: March 2011

This paper investigates both transport properties and nature of superconductivity breakdown or, conversely, enhancement in oxide ceramics, due to radiation-induced defects.

Low-fluence neutrons (≈107 n cm-2 at 3 MeV) can sensitively damage the samples, giving experimental evidence that the breakdown of coherent percolating paths produces decoupled domains. A set of preliminary measurements shows that high-fluence proton implantation can either damage or enhance critical current density in a currently non controllable way. In both cases strongly damaged or enhanced superconducting paths short-circuit the unaffected bulk network.
X-Ray Scattering from Highly Distorted Lattices Undergoing Phase Separation
Authors: Rao Satish I. , Wu C.H. , Houska C.R.
Published: March 2011

Calculations by Krivogtaz [1] dealing with quasiline formation in highly distorted lattices undergoing phase separation have been extended for randomly arranged particles. Qualitative experimental evidence from powder patterns, already in the literature for Cu-Be,Ni-Be,Cu-Ti and Nimonic alloys[2-5], have demonstrated the existence of quasilines. This extended calculation deals with ellipsoids of revolution and allows one to examine different shapes and transformation strains in an anisotropic medium. it is shown that the precipitate transformation strains play a very important role in shaping the Bragg-like profiles. This is most obvious in the intermediate stage which includes Bragg scattering from the lattice, regular static diffuse scattering and the quasiline. For precipitate sizes associated with maximum age hardening, all three normally become scrambled into a broad assymetrically shaped Bragg-like peak. However, a comparison of the theoretical calculations with experimental data from an age hardened Cu-Be alloy shows qualitative agreement, which we believe is due to the non-random nature of precipitation in this system.
Effect of 120 MeV Oxygen Ion Irradiation on Current-Voltage Characteristics in YBaCuO
Authors: Iwase A. , Masaki N. , Iwata T. , Nihira T.
Published: March 2011

The effect of 120 MeV oxygen ion irradiation on the current-voltage(I-V) characteristics has been studied at 77.3 K in YBaCuO superconductors. In the small current region, the voltage V against the current I and the ion-fluence Φ can be described by the following simple form; ln(V/VO)=αln(I/IO)×ln(Φ/ΦO), where α, VO, IO and ΦO are constants. The experimental results have been discussed in terms of current-induced unbinding of thermally excited vortex pairs.
Unstable Plane in Bi-Sr-Ca-Cu-O System by TGA
Authors: Zhang H. , Feng Q.R. , Feng S. Q. , Zhu X. , Gan Z. Z.
Published: March 2011

By thermogravimetry analysis (TGA), x-ray diffraction and R(T) relationship determination, the BiSrCaCuO system superconductors with composition of 2201, 2212 and 2223 were studied systematically. The experiments discovered that there is an unstable plane in 2223 sample, but not in 2201 and 2212. Comparing this result with the structure and property of 123 phase in YBCO-system, analyzing carefully, we found that only those superconductors which have the unstable plane are of higher Tc value. The role of the unstable plane in a superconductor is discussed. It is possible that 110K superconductivity in Bi-system has a close relationship with the existence of this unstable plane.
Quantitative Analysis of Diffuse Scattering from Concentrated Alloys: The Last Two Decades
Authors: Cohen J. B. , Georgopoulos P.
Published: March 2011

The techniques for measurement and analysis of the absolute intensity from concentrated alloys have now improved to the point where reliable analysis for local order and displacements can be performed in reasonable times, for both clustering and ordering. Coupling the results with computer simulation provides information on the details of chemical fluctuations and, as well, tests of modern theories of transformations. In some cases, the results have been confirmed via direct imaging (FIM, HRTEM). The role of this information in our understanding of phase transformations is reviewed, and suggestions for future studies are given.
Phase Transitions in and Ferroelasticity of 9-Hydroxyphenalenone
Authors: Svensson Christer , Abrahams S. C.
Published: March 2011

Crystalline 9-hydroxyphenalenone is monoclinic between 145 K and the melting point at 475 K. The space group is P21 below 255 K, P21/c between 255 K and 380 K, and I2/c above 385 K. A model for the 255 K transition involves inplane rotations of about 40° for one quarter of the molecules. Further rotation and translation takes place at the 380–385 K phase transitions. All three phases are expected to be ferroelastic, but at present only the unit cell of the room temperature phase has been reversibly reoriented. The spontaneous strain decreases from 0.24 at 145 K through 0.18 at room temperature to 0.14 at 430 K, assuming a tetragonal prototype. Domain walls are temperature dependent with orientation (1.86, 0, 1) and (1, 0, −1.86) at 298 K. Ferroelastic transformation proceeds by a slip process, approximately in the molecular planes. A prototype common to all three phases can be derived with space group P41. Macroscopically, the transformation is accompanied by a remarkable change of shape; if unfractured, the crystals exhibit shape memory.
The Role of Phonon Dispersion in Controlling Atomic Rearrangement in Solid Solutions
Authors: Wu T.B.
Published: March 2011

The elastic energy of a solid solution of atoms of different sizes can be written as a Fourier sum with coefficients as a function of position in reciprocal space. Each coefficient is made up of three components. The first one is an energy associated with taking atoms of the pure elements and placing them randomly on the average lattice o f the alloy. The second one is an elastic gradient energy associated with composition fluctuations and which is proportional to the second derivative of the dispersion curve. The third is the relaxation energy concerned with the motion of atoms away from the average lattice to more comfortable positions. Because of the contribution of the elastic gradient energy, it is shown that the shape of the phonon dispersion curve can affect precipitation or ordering in a solid solution.
A Tem Study of the Metakaolin-to-Mullite Transformation in Kaolinite
Authors: Horner J.A. , Martinez W.A. , Greenhut V.A.
Published: March 2011

Two different kaolinites were heated in the range 850–1000°C and subsequently analyzed using TEM to study the metakaolinite-to-mullite reaction sequence. Metakaolinite was found to exist as amorphous relics of the original kaolinites. Small particles of a spinel composition appeared and grew to a maximum size of ∼50Å at temperatures below the 980°C exothermic reaction. Mullite was detected at and above 980°C which accounts for the 980°C exothermic reaction of these kaolinites.
Phase Transitions in Hoalga
Authors: Doukoure M. , Gignoux D. , Sayetat F.
Published: March 2011

HoAlGa is hexagonal at room temperature. It undergoes two magnetic transitions succesively at TN = 32 K from a paramagnetic to a triangular antiferromagnetic state where the Ho moments lie in the basal plane and at Tt = 18 K in the course of which the moments rotate toward c giving rise to a colinear antiferromagnetic arrangement. X-ray experiments performed between 5 and 300 K allow to determine the crystal evolution through the two transitions. The hexagonal symmetry is not lowered through the transitions; this result is compatible with the observed magnetic groups. The thermal expansion curves show a very anisotropic behaviour of the lattice parameters. The “c” parameter shrinks below TN and this anomaly is to be related to the magnetic order. Along a, a positive thermal anomaly appears below 70 K and this can be interpreted by crystal field effects. Stability of magnetic structures is discussed with regard to exchange interactions and magnetocrystalline anisotropy.
Anisotropic Effects in Antiferromagnetic MnSb2O4 and NiSb2O4 : Structural and Vibrational Evolution Studies
Authors: Gavarri J.R. , Chater R. , Genet F.
Published: March 2011

Powdered samples and crystals of the antimony isomorphous MnSb2O4 and NiSb2O4 have been prepared using hydrothermal synthesis. The anisotropic elastic and magnetic properties of these tetragonal structures are compared, using low temperature diffraction techniques (X-ray and neutron) and Raman scattering experiments. Magnetostrictive effects in MnSb2O4 are interpreted. An anomalous frequency shift is observed below 70 K and the change of the Grüuneisen constant is interpreted.
Effects of the Tahir-Kheli,Intermediate-Temperature Teriis on the Clapp and Moss, High–Temperature Formulation of Short Range Order (Sro) in Li-Mg Alloys
Authors: Gilder H.M. , Vignesoult S.
Published: March 2011

Present calculations of the Cowley-Warren SRO parameters, using the Rasolt-Taylor-Dagens, first principles pair potential for Li-Mg alloys show that the higher order terms of Tahir-Keli's intermediate-temperature solution of the Ising, spin-1/2 ferromagnet modify the Clapp and Moss, hightemperature solution in a very significant way. The present results are compared to previous calculations and measurements on Li-10 at.% Mg and Li-50 at.%Mg alloys.
A New Ordered Structure of the off-Stoichiometric Laves Phase Having C15- Type Structure in Mg-Cu-Si System
Authors: Komura Y. , Matsunaga T.
Published: March 2011

A new ordered structure has been found in a ternary Mg-Cu-Si Laves phase whose composition is around Mg(Cu0.80Si0.20)2.50. The ordering between Cu and Si of Cl5-type Mg(Cu0.81Si0.19)2.53 specimen was analysed by a single crystal X-ray diffraction method. It belongs to a space group P41 32(or P4 332) having a=6.9598Å contrary to the disordered structure of Fd3m. The ordered structure is characterized by the ordered 4-fold screw arrangements of Cu and Si atoms located on four tetrahedra in the unit cell leaving Mg atoms on 8c sites. The order parameter S= αl−α2 was found to be 0.74 in this specimen, where αland α2 are occupancy factors of Cu for 12d and 4a sitesof the space group P4 132, respectively. The order parameters were measured as a function of annealing temperature by using Warren's method for quenched powder specimens of Mg(Cu 0.80 Si 0.20)2.40. The maximum value of S reached to 0.75 at 200°C, which is a little lower than the expected value of perfect order, S=0.85. The order parameter then decreases continuously with increasing annealed temperature and become zero at about 600°C, indicating order-disorder transformation temperature.
Determination of Short Range Order Parameters in 62Ni0.765Fe0.235 At 600°C Effect of a Quench
Authors: Lefebvre S. , Bley F. , Cenedese P.
Published: March 2011

Different states of local order have been previously measured at room temperature on water quenched crystal of Ni0.76562 Fe0.235 [1−2]. The Cowley' parameters and the interaction pair potentials in a Clapp and floss approximation have been determined at : 385° C, 470°C, 507°C, 535°C, 685°C that is under and above Tc which is equal to 500°C for this composition.

The kinetic of long range order establishment is, in this alloy, very sluggish even near Tc [3]; the kinetic of short range order (SRO) is completely different and may be more complex [4]. In the previous experiments it has been supposed that the state of high temperature was retained during the quench. The following experiments check this hypothesis.
Ordered Structures in Ti Al Alloys in the Composition Range from Ab To Ab3
Authors: Loiseau A. , Lasalmonie A. , Van Tendeloo G. , Van Landuyt J.
Published: March 2011

This paper describes crystal structures of Ti1−x, Alx alloys containing from 40 to 75 % at. Aluminum observed by electron microscopy. Two new phases are in particular discussed : Ti2 Al and a phase denoted X, which is a non stoichiometric Ti3Al5.
Order-Disorder Transition at High Temperature and Microdomain Formation in Oxidized Ferrites
Authors: Grenier J.C. , Pouchard M. , Hagenmuller P. , Henche M.J.R. , Vallet M. , Calbet J.M.G. , Alario-Franco M. A.
Published: March 2011

At high temperature, nonstoichiometric perovskite-type related ferrites can be oxidized in air. At first sight, this phenomenon appears rather surprising since it corresponds to a partial formation of iron +IV. Moreover a structural transition occurs from a vacancy ordering state to a pseudodisordering one characterized by a cubic perovskite-type X-ray diffraction pattern. A TEM study has shown in fact a more complex situation attributed to a microdomain texture. This is explained from a crystallographic point of view and correlated to the existence of mixed valencies of iron.
Evidence of a Coupling Between Magnetic and Chemical Interactions in Iron-based Alloys
Authors: Pierron-Bohnes V. , Cadeville M.C. , Gautier F.
Published: March 2011

The simultaneous occurrence of chemical and magnetic interactions in transition metal alloys greatly influences their thermodynamic properties. However the experimental evidence of the Coupling between both interactions has not been demonstrated so far. The present study shows that such a coupling exists in iron-based alloys (FeCo, FeMn, FeV) and that it modifies qualitatively the chemical short range order. This is evidenced from its temperature dependence in both ferromagnetic and paramagnetic phases which displays a marked change of behaviour at the Curie temperature (Tcm). Theoretical models which account qualitatively for the whole of the observed behaviours are briefly discussed.
Towards a True Fe-Ni Phase Diagram
Authors: Rossiter P L. , Jago R. A
Published: March 2011

A modification to the existing Fe-Ni phase equilibrium diagram is proposed that takes account of the low-temperature ordering reaction to FeNi. It is shown that true equilibrium is never attained during slow cooling of Fe-Ni alloys, even for iron meteorites (which cool extremely slowly). In all real cases, a metastable phase diagram applies, in which the depressed γ/α+γ solvus produces a more extensive γ+ FeNi phase field than for the equilibrium case. This enlarged phase field is used to explain the decomposition of supersaturated Fe-Ni to γ+ FeNi, which is observed only in iron meteorites.
Statistical Mechanics of Phase Coarsening
Authors: Glicksman M.E. , Voorhees P.W.
Published: March 2011

Phase coarsening, also termed Ostwald ripening, is generally thought to be a slow, diffusion-controlled process which occurs subsequent to phase separation under extremely small under- or over-saturation levels. The theory due to Lifshitz, Slyzov, and Wagner (LSW), which predicts the coarsening kinetics and the particle distribution function is applicable to dilute systems only, in which particle-particle interactions are unimportant. Most practical systems, however, have large enough volume fractions of the dispersed phase to violate the essential assumptions of LSW theory. Recent progress will be described on simulating Ostwald ripening in randomly dispersed, high volume fraction systems. A fast algorithm for solving the multiparticle diffusion problem (MDP) will be described, permitting simulation of coarsening dynamics by cyclic time-stepping and updating the diffusion solution for large random particle arrays. The rate constants, controlling the growth of the average particle, and the particle distribution functions were obtained by numerical simulations up to a volume fraction of 0.55. A new statistical mechanics theory has now been developed which reproduces the MDP simulation data accurately, and finally makes clear how the linear mean-field approximations employed by LSW theory must be modified to describe real systems. The new theory provides a comprehensive approach to understanding microstructural coarsening in two-phase systems.
Coarsening of Cobalt Precipitates in Copper- Cobalt Alloys
Authors: Eguchi T. , Tomokiyo Y. , Oki K. , Seno Y.
Published: March 2011

The Ostwald ripening of precipitates in Cu-Co alloys was investigated by electron microscopic observation. The variation of the mean particle radius r, and the distribution of relative particle sizes, f(r/r) , were obtained as functions of the aging time at 873K . The shape of f(r/r)was rather sharp and symmetrical around r = T in the early stage. It became broad with the aging and was similar, in the late stage, to the theoretical distribution of Ardell. It appeared that the shape of f(r/r) depends on the volume fraction but the growth rate of F scarcely depends on it. The rate of change of r was proportional to the cube root of the aging time from the early stage of aging.
Test of Some Statistical Approximations (Quasi Chemical, Cvm) in Bcc and Fcc Binary Alloys by Monte Carlo Simulation. Validity Range of the Clapp and Moss Approximation.
Authors: Cenedese P. , Gaspard J.P.
Published: March 2011

In the framework of regular solution model, we test the validity of some usual approximations (QC, CVM) of entropy in (disordered) binary alloys by Monte Carlo simulation. The validity range of these approximations are explored both in alternant and nonalternant lattice with ferro- and antiferromagnetic coupling. The CVM tetrahedron approximation is also analysed on a structure containing only tetrahedra : the 120 polytope [8] in 3d curved space.
Diffusion Along Migrating and Stationary Grain Boundaries: The Al-Zn System
Authors: Gust W. , Hintz M.B. , LuČić R. , PREDEL B.
Published: March 2011

The discontinuous precipitation reaction has been studied in an Al-28a/o Zn solid solution. It appears that the diffusion rates determined by us for migrating grain boundaries are of the same order of magnitude as the values determined by Häβner (1974) for stationary grain boundaries. To the same statement have led results from the discontinuous coarsening reaction in an Al-29a/o Zn alloy (Fournelle et al., 1982) as well as from the eutectoid reaction in an Al-60a/o Zn alloy (Cheetham et al., 1971).
The Effect of Applied Stress of the Decomposition Cu-15Ni-8Sn Spinodal Alloy
Authors: Ahn S. , Tsakalakos T.
Published: March 2011

The effect of stress on spinodal decomposition in Cu-15Ni-8Sn alloy was investigated at various temperatures and stresses. As the aging temperature approached the coherent spinodal temperature about 500°C, the anisotropy among the three equivalent <100> modulations of the stress aged specimens became pronounced. The wavelength of the [001] modulation along the tensile stress axis was smaller than that of the [100] or [010] modulation perpendicular to the stress axis. TEM diffraction patterns also showed the anisotropy effect of the applied stress to the composition modulation. A theoretical model based on micromechanics concepts was employed to explain the experimental results.
Spinodal Decomposition in Fe - 32Cr
Authors: Lasalle J. C. , Spooner S. , Schwartz L. H.
Published: March 2011

Spinodal decomposition in iron-chromium alloys has been studied for various compositions and aging temperatures by several workers using small angle neutron scattering. The data of the present study and that of previous workers are reviewed in order to better define the coexistence curve of this system as well as to provide an experimental basis for comparison with current nonlinear theories of spinodal decomposition. Regarding the coexistence curve, it is argued that the qualitative changes in the scattering pattern with composition and aging temperature are consistent with the experimentally determined boundary, rather than those calculated for this system. Quantitative analysis of the kinetic development of scattering from Fe-32Cr samples allows direct comparison with predictions of nonlinear theories of spinodal decomposition. The time dependence of the position of the peak maximum has been given by several theories as t−. The value of ø found for Fe-32Cr increased with increasing aging temperature, extrapolating near the value of 1/6 at the estimated spinodal temperature.
Irreversible and Reversible Behavior of Spin Glasses: Broken Ergodicity
Authors: Soukoulis C. M. , Grest G.S. , Levin K.
Published: March 2011

Over the past decade, a great deal of effort has gone into understanding the properties of spin glasses [1,2]. However, because these are rather unique systems which show simultaneously apparent phase transition as well as metastable or glassy behavior, progress has been slow. Though it was initially believed that spin glasses could be treated as if they had a true equilibrium phase transition, we now recognize that this cannot be the whole story. Recently, it has become clear that spin glasses are very complex systems, in which irreversible and time dependent effects play an important role. We now know that one must go beyond the regime of validity of equilibrium thermodynamics. In this paper, we will discuss the mountinq evidence, both experimental and theoretical, for why nonequilibrium approaches are essential in order to understand spin glasses.
An Order-Wave Description of the Kinetics of Spinodal Ordering
Authors: Cammarata R. C. , Greer A. L. , Lobb C. J.
Published: March 2011

Several authors have modeled the order-disorder transformation as a continuous process, not occurring by nucleation and growth. Their approaches are based either on treating the transformation as a second-order chemical reaction [1,2], or on discrete formulations of the phenomenological diffusion equations [3–8]. Extending the work of Gorsky [9] and of Bragg and Williams [10], Dienes [2] used the chemical reaction model with absolute reaction rate theory to derive numerically the time-dependence of the longrange order parameter. As his thermodynamic model he used the Bragg-Williams (B-W) approximation, assuming that the solid was uniformly ordered and ignoring inhomogeneity effects such as the excess interface and coherency strain energies that arise if antiphase domains exist.
Kinetics of Ordering with Phase Separation
Authors: Eguchi T. , Oki K. , Matsumura S.
Published: March 2011

An attempt is made to investigate theoretically the kinetics of ordering accompanying phase separation in an alloy as a continuous medium. A set of coupled equations for the local composition and the degree of order are derived from the first principles of thermodynamics of irreversible processes, under an appropriate assumption as to the free energy of the system. Under certain circumstances a periodic deviation of local order parameter in the disordered state induces that of the composition, leading to a spinodal decomposition, and the resonance conditions for enhancement of such an induction are examined in the perturbation approximation. In a uniform state of imperfect degree of order disturbances of the local composition and degree of order develop in-phase.
Influence of Surface Magnetism on the Surface Segregation Near TC in NiX Cu1-x Alloys
Authors: Urias J. , Moran-Lopez J.L.
Published: March 2011

The influence of surface magnetization on the surface segregation in binary alloys with one magnetic component is studied. Based in a model in which the local magnetic moment on the ferromagnetic atoms is determined by the local environment, the internal energy is calculated within the mean field approximation. We applied the model to dilute CuNi alloys and we find that magnetism favors the segregation of Ni, contrary to what it is found in the paramagnetic phase.
Artificial Semiconductor Superlattices
Authors: Döhler G.H.
Published: March 2011

Artificial superlattices are multilayer structures consisting of a onedimensional sequence of ultrathin layers of different semiconductors (compositional or hetero junction superlattices) or layers of the same material, modulated by periodic n- and p-doping (doping or p-n junction superlattices). The electronic properties of these new materials differ qualitatively from those of their components and can be tailored within wide limits by appropriate choice of the design parameters (i.e. superlattice period, alloy composition, and/or doping concentration). Different electronic phases (insulating, semiconducting, semimetallic, metallic, e.g.) may be obtained in this way.
Martensite Lattice Correspondence and Twinning in Uranium Alloys
Authors: Speer J.G. , Edmonds D.V.
Published: March 2011

A new lattice correspondence has been deduced for the γ→a′ martensite reaction in dilute uranium alloys. The new correspondence involves a lattice deformation with significantly smaller principal strains than those previously considered, although more atomic shuffles are required.

From an analysis of possible transformation twinning modes based on the new correspondence, the further possibility of a deformation twinning mode in these alloys is theoretically predicted. The mode is compound, described by (021)(023) [012] [032], and involves a twinning shear (g = .044) which is smaller than any value previously predicted or observed, although again a larger number of shuffles would be required. The significance of these results is discussed.
The use of Phase Transformations in the Design of Alloy Steel
Authors: Morris J. W.
Published: March 2011

This paper is intended to describe and illustrate the use of phase transformations in the design of new alloy steels. The general method of alloy design is described. Two examples are discussed: the development of new ferritic structural steels for use at cryogenic temperature, and the development of ‘dual phase’ steels for automotive use.