bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheed Oscillation During the Epitaxial Growth of Layered Materials
Authors: Shimada Toshihiro , Ohuchi Fumio S. , Koma Atsushi
Published: March 2011

RHEED intensity oscillations have been observed during the epitaxial growth of layered NbSe2, MoSe2 on GaAs(111) substrates. Monolayer- and bilayer- mode oscillations have been observed at different diffraction points. The existence of bilayer-mode oscillation is interpreted as showing the polytype of the grown films. The present report demonstrate the utility of RHEED oscillation for analyzing the structure of ultrathin films of layered materials. The epitaxial growth of TaSe2 on layered substrates is also reported.
High Energy Transmission Electron Diffraction From Surface Monolayers During Silicon Oxidation
Authors: Ross Frances M. , Gibson J. Murray
Published: March 2011

We have examined the behaviour of the clean Si (111) 7x7 reconstructed surface during exposure to oxygen over a range of temperature and pressure in a UHV transmission electron microscope (TEM). We present preliminary results of our study, discussing both the etching of the silicon surface by oxygen at elevated temperatures and lower oxygen pressures, and its roughening and oxidation at higher oxygen pressures. We achieve great sensitivity to the structure of the surface monolayers by analysing the diffraction of high energy electrons by these surface layers and can resolve the movement of individual monatomic surface steps. Our most dramatic result to date is a demonstation that surface steps do not move during the growth of native oxide.
The Enchanting Properties of Oxygen Atoms in Silicon
Authors: Needels M. , Joannopoulos J.D. , BAR-YAM Y. , Pantelides S.T. , WOLFE R.H.
Published: March 2011

In this paper we will present several new theoretical results on the properties of oxygen atoms in bulk crystalline silicon. Specifically, these properties will include (1) oxygen migration - where we will suggest that the conventional adiabatic-barrier model for oxygen migration may not be valid for this system; (2) oxygen catalysis - where we will demonstrate that certain oxygen configurations can act as “catalysts” to reactions that form silicon broken bond defects; and (3) oxygen aggregation - where we will introduce a new mechanism for the initial stages of aggregation and oxidation within the bulk of crystalline silicon.
Peculiar Doping Behavior of Si:Be.
Authors: Tarnow Eugen , Zhang S.B. , Chang K.J. , Chadi D.J.
Published: March 2011

The total energies and structures of a number of Be-induced defects in Si are investigated using ab-initio local density calculations. Our primary results are: 1) The geometry of the isoelectronic center is found to correspond to a [111] substitutionalinterstitial pair (SIP); 2) The low energy defect spectrum includes large Be complexes containing at least one substitutional atom; and 3) Simple bonding rules exist for the stability of the different types of bonds in the material. Thus the Si-Be bond is found to be stable for all defect configurations while the Be-Be bond is metastable.
A Cluster Calculation of B and P Impurities in Amorphous Silicon
Authors: Enrique Sansores L. , Valladares R.M. , Cogordan J.A. , Valladares A.A.
Published: March 2011

The local density of states and charge density contours of clusters of the type ISi20H28, where I can be Si, B or P, was calculated using the well-known pseudopotential SCF Hartree-Fock Method (and the HONDO Program). It is found that the covalent nature of the bonding in pure silicon gets altered and gives rise to an ionic component when B and P are substituted in the center of the cluster. Also, the local density of states in the neighborhood of a Si atom, nearest neighbor to the center of the cluster, show a splitting of the p-states at the top of the valence band in pure silicon when B is substituted, and a new p-state appears in the band gap when P is sustituted. These results are analyzed in the light of the local changes and its relevance to the solid state properties.
First-Principles Study of Photoexcited Defects in Polysilane Chains
Authors: Mintmire J. W. , Mowrey R. C. , Brenner D. W. , Dunlap B. I. , White C. T.
Published: March 2011

Organopolysilane materials have recently demonstrated potential technological importance as positive photoresists, photoconductors, and nonlinear optical materials. Many of the technological applications of these materials depend intimately on the photoexcitation process in these materials, possibly resulting in either bond scission or the creation of mobile charge carriers. Herein we present some preliminary results of a model simulation of the photoexcitation process in oligomeric polysilane chains using a recently developed first-principles local-density functional method for the calculation of electronic structures,total energies, and gradients of the total energy with respect to nuclear coordinates.
X-Ray Characterization of Defects in Irradiated Iron
Authors: Peisl J. , Franz H. , Schmalzbauer A. , Wallner G.
Published: March 2011

We report on a thorough X-ray study of irradiation induced defects in iron. Single crystals were irradiated at 4.6 K with reactor neutrons and at 90 K with 2 MeV electrons. After irradiation and subsequent thermal annealing, we measured the defect induced diffuse scattering of X-rays (Huang scattering) and the small angle scattering of synchrotron radiation. Simultaneously, lattice parameter and electrical resistivity changes were measured. The single defect properties are determined from low dose electron irradiated samples and yield the lattice distortions, i.e., the volume change and defect symmetry as described by the force dipole tensor. Excellent agreement of the experimental results with calculated values from literature is observed. After neutron irradiation, defects are correlated within displacement cascades. The correlations for vacanciesand interstitials are described by a spatial correlation volume. These results are compared with computer simulations usingthe Marlowe code. During thermal annealing the irradiation induced defects agglomerate at characteristic temperatures and we observe changes in the spatial correlations of the defects. There is a clear difference between electron and neutron irradiated samples concerning defect recovery in stage 1.
In-Situ NMR Investigation of Dynamical Behavior of Point and Line Defects During Deformation of NaCl
Authors: Detemple K. , Kanert O. , Linga Murty K. , Dehosson J.Th.M.
Published: March 2011

Spin lattice relaxation time in the rotating frame [T1ρ] is investigated in pure NaCl single crystals as a function of temperature in-situ during deformation. Transition from 2- phonon Raman process to atomic diffusion was noted at around 500K in the undeformed material and the activation energy was determined to be that for the diffusion of extrinsic vacancies. Enhanced spin relaxation rates were noted during constant strain-rate deformation at temperatures from ambient to about 750K. These enhancements were identified to arise from dislocation motion at lower temperatures while enhanced diffusion due to excess vacancies at higher temperatures. This excess concentration increased with increased strain-rate and in-situ annealing of deforma-tion induced excess vacancies is noted at high temperatures.
Heterocyclization of Acetylene to Thiophene at Defects on the Pd(111) Surface
Authors: Gellman Andrew J.
Published: March 2011

We have studied a novel surface reaction in which acetylene (C2H2) cyclizes with sulfur atoms on the Pd(111) surface to form thiophene (C4H4 S). The reaction occurs at defects in the (√7 ×√7)R19° sulfur overlayer that is formed on this surface. The surfaces were prepared by decomposing H2S on the clean Pd(111) surface and annealing to temperatures in the range 600K to 1100K to produce defects i the sulfur overlayer. The reaction occurs to greatest extent on surfaces annealed to high temperatures and only on surfaces with coverages approaching saturation. The defects have been characterized by adsorption of CO using both vibrational spectroscopyand measurementsof desorption kinetics. On the sulfided surface CO is bound in a linear configuration to a single Pd atom. At defects in the sulfur overlayer CO is bound in a bridging site between two atoms, as on the clean surface.
Weak Localization Effects in Fluorineintercalated Graphite Fibers
Authors: Di Vittorio S.L. , Dresselhaus M.S. , Bayot V. , Piraux L. , Issi J-P. , Endo M. , Nakajima T.
Published: March 2011

The intercalation of fluorine into graphite introduces defects into the highly crystalline pristine fibers. These defectsare studied using temperature-dependent resistivity and magnetoresistance measurements. A logarithmic increase in resistivity at low temperature is observed, whereas the high temperature behavior is metallic. At weak magnetic fields and low temperatures, a negative magnetoresistance is observed, which becomes positive at high fields. These effects are explainedusing the two theories of weak localization and hole-hole interaction. In the light of TEM pictures of the microstructure of the fluorinated fibers, the origin of the defects in the intercalated fibers is discussed.
Characterization of Activated Carbon Fibers
Authors: Fung A. W. P. , Rao A. M. , Kuriyama K. , Dresselhaus M. S. , Dresseliiaus G. , Endot M.
Published: March 2011

Low-temperature electrical conductivity and Raman scattering are studied as characterization tools for activated carbon fibers, which have a high density of defects and a huge specific surface area. The transport mechanism at low temperature is governed by variablerange hopping, as in other strongly disordered systems. From the Raman spectra obtained, we deduce that the long phenolic fibers are more disordered than the acrylic fibers and that increased specific surface area corresponds to increased disorder. The average in-plane microcrystallite size is about 20–30 Å.
Properties of Cu in GaAs
Authors: Leon Rosa , Kaminska Maria , Man Yu Kin , Weber Eicke
Published: March 2011

The electrical properties and preferred lattice sites of Cu in GaAs were studied combining electrical and optical measurements with Particle Induced X-ray Emission (PIXE) and Channeling. For electronic characterization, Deep Level Transient Spectroscopy (DLTS), Hall Effect measurements, and Photoluminescence (PL) were used. From this comprehensive study it was determined that Cu introduces two levels in the bandgap, that the concentration of electrically active copper is considerably smaller than the total copper concentration, and that most of the Cu in GaAs is not of purely substitutional character.
Evidence of Defect Levels in P and N-Type Electron Irradiated Si
Authors: Kouimtzi S.D.
Published: March 2011

Capacitance bridge measurements at low temperature on irradiated specimens of p and n-type Si are reported. Electronic defect levels are seen at Ev+0.10 eV , Ev+0.14 eV and Ec−0.11 eV. The change of the band structure caused by irradiation is also described.
Raman Studies of Znse Lattice Damage and Recovery Due to N Implantation and Annealing
Authors: Deneuville A. , Ayyub P. , Park C. H. , Anderson T. , Lowen P. , Jones K.S. , Holloway P. H.
Published: March 2011

The “bulk” and near-surface regions of N implanted heteroepitaxial ZnSe films were studied using the full width at half maximum (FWHM) of the LO phonon Raman line. The “bulk” FWHM has a minimum below an annealing temperature Ta = 400°C, and increases for higher Ta. This is attributed to the relaxation of residual stress, and to an increased stress from the formation of Zn vacancies. The surface FWHM has a deep minimum near Ta = 500°C which is attributed to the relaxation of the implantation damage at lower Ta, and stress induced by Zn vacancy formation at higher Ta. Another wider peak is found just after implantation and for Ta = 600°C, and results from a sum of two peaks attributed to the heavily damaged region around Rp and to the region with Zn vacancies.
Influence of Current Injection into a-Sin:H Films on Charge Trapping Defects
Authors: Oku Tomoki , Kawabata Kiyoshi , Higaki Yukio , Matsui Teruhito , Takano Hirozo , Otsubo Mutsuyuki
Published: March 2011

The degradation mechanism of a-SiN:H films under current injection is investigated. It is shown that the degradation of a-SiN:H films is closely related to the hole trapping into Si-Si, Si-H, and Si0 defects. It is presumably concluded that the hole trapping centers are the Si-Si defects in the valence band tail. We estimate that the hole trapping cross-section is nearly equal to 10−20cm2.
Contactless Deep Level Transient Spectroscopy Using Microwave Reflection
Authors: Wang M. S. , Borrego J. M.
Published: March 2011

Contactless deep level transient spectroscopy using microwave reflection at 35 GHz is presented and it is proved to be a powerful technique for characterizing trapping levels in semiconductors without the necessity of special sample preparation. The technique consists of measuring the transient decay in photoconductivity after a monochromatic light pulse has been applied to the semiconductor. The photoconductivity after the light pulse is caused by emission of carriers from trapping levels filled during the light pulse and by scanning the sample temperature it is possible to determine their activation energy. On Si-implanted layers on LEC grown SI-GaAs substrate we have detected three trapping levels, located at 0.15, 0.18 and 0.27 eV below the conduction band, by using a 1060 nm YAG laser, and one level, 0.13 eV below the conduction band, by using a 633 nm HeNe laser. The technique has been applied to LEC SI-GaAs and no trapping levels have been observed above the EL2 level.
Effect of Hydrogen on The Electronic Structure of a Grain Boundary In Iron
Authors: Krasko Genrich L. , Harrison Ralph J. , Olson G. B.
Published: March 2011

LMTO-ASA calculations were performed on a 26-atom supercell model of a Σ3(111) grain boundary (GB) in bcc Fe. The supercell emulated two GB's with 11 (111)planes of Fe atoms between the GB planes. One of the GB's was clean, with a structural vacancy at the GB core in the center of a trigonal prism of Fe atoms, while on the other GB this site was occupied by a H atom. The interplanar spacings of the supercell were relaxed using a modified embedded atom method. As in the case of P and S in a similar GB environment in Fe there is only a weak interaction between H and nearest Fe atoms. Almost all the Fe d-states are nonbonding. A very weak covalent bond exists between H and Fe due to s-d hybridization, the hybrid bonding part located far below the Fermi energy. This bond is mostly of σ-type, connecting H with the Fe atoms in the GB plane; the δ-component of this bond across the GB is weaker. A weak electrostatic interaction attracts Fe-atoms across the clean GB, but results in repulsion if a H atom is present. The magnetic contribution to intergranular cohesion is decreased when H is present due the suppression of the magnetic moments of the nearest Fe atoms both in the GB plane and directly across the GB.
Hyperfine and Superhyperfine Tensors as Probes of the Local Environment of Deep-Level Defect Centers
Authors: Cook Michael , White C.T.
Published: March 2011

Point defects occur in every solid material. No crystalline lattice is perfect, and no amorphous network has only unbroken sequences of bonds. Every material contains a greater or smaller number of vacancies, interstitials, substitutional atoms, and broken bonds. Many of these have only minor effects on the behavior of the material, but in a surprisingly large number of cases, point defects can have significant and even decisive effects on material performance. This can be true even when the defects are present in very small concentrations.
Evidence of Forbidden Reflections in the Diffuse Scattering of Hg0.80Cd0.20Te Single Crystals
Authors: Quintana J. P.
Published: March 2011

The x-ray diffuse scattering pattern from a commercial bulk n-type Hg0.80Cd0.20Te single crystal was measured in absolute units. Anomalous dispersion techniques near the Hg LIII edge were used to determine theintensity due to Hg interactions. Diffuse x-ray superlattice reflections are reported that are forbidden by the zinc-blende structure. The systematic absences in these peaks eliminate the possibility that they are the result of a Cu3Au ordering scheme.
Scanning Tunneling Microscopy Imaging of Defects in Layered Compounds
Authors: Van Bakell G. P. E. M. , De Hosson J. Th. M. , Hibma T.
Published: March 2011

Structural features of TiS2 were studied by scanning tunneling microscopy (STM) and single-crystal X-ray diffraction was applied as a complementary technique. STM images in air and at room temperature revealed, beside the trigonal symmetry of the lattice, several new features having this symmetry as well. We conclude that these features not only are to be described by structural defect phenomena which affect octahedral sites in the 1T-CdI2 structure but tetrahedral sites as well. Sample orientation determination by X-ray diffraction provides a unique relation between feature types and sites. A model is proposed in which displaced Ti atoms account for the observed features.
Simulations of Step Motion During Crystal Evaporation
Authors: Peter Jardine A.
Published: March 2011

The rate of decay of a macroscopic sinusoidal grating etched into a clean surface can be predicted from its surface and volume diffusion coefficients and the partial pressure of the material. The microscopic theory of crystal growth and evaporation of Hirth and Pound has produced an expression for the step velocity for a surface in equilibrium with its own vapor, which was used to simulate the decay of a sinusoidal surface. The macroscopic decay rate was determined from the measured surface diffusion coefficient and the equilibrium vapor pressure of the Ni (100) surface. The rate of decay of a model sinusoidal grating surface using the microscopic step velocities was inconsistent with the observable mnacroscopic results. Reasons for this are discussed.
Study of Surface Defects With the Reflected Electrons
Authors: Hsu Tung
Published: March 2011

Studying crystal surfaces using the forward scattered high energy electrons Is discussed.Performance and applications of the basic REM and several variations of this technique are presented.
Defects in the Structure of Σ=27 <110> Tilt Grain-Boundaries in Ge.
Authors: Mckernan Stuart , Barry Carter C. , Elgat Zvi
Published: March 2011

General high-angle tilt grain-boundaries may be described by an arrangement of repeating structural units. A particular defect in the normal arrangement of structural units in a Σ=27 <110> tilt grain-boundary in Ge is reported.The defect is characterized by a short segment of (111) facet at the interface, and is associated with a screw dislocation in the boundary plane. This defect accommodates a slight misorientation of the boundary away from the perfect tilt configuration, andmay represent a type of structural unit present in other tilt boundaries containing a small twist component.
Characterization of Interfacial Structure in Large Lattice Mismatch Heteroepitaxy: Ag/Si (111)
Authors: McKenna D.C. , Wang G.-C. , Rajan K.
Published: March 2011

The interfacial structure of a large lattice mismatched (˜25%) (111) Ag-Si system was studied by using transmission electron diffraction (SADP - Selected Area Diffraction Pattern). The epitaxial films of Ag (600–1200Å) were grown by MBE on flat Si(111) and misoriented Si(1ll) surfaces. We have examined the interfacial structures of the Ag on 2° misoriented Si(111) using diffraction patterns of cross sectional view. Through a detail analysis of thelocation and shape of the diffraction spots, we can determine the epitaxial relationship between Ag and Si, the small tilt angle of Ag(111) planes withrespect to the misoriented Si(111), the period of the finite terrace size of the misoriented Si substrate, and the size of the ordered region in the Ag film. The O-lattice analysis developed by Bollmann has beenapplied to this interface andthe result is compared with the SADP observation.
High Resolution Electron Microscopy Studies of Interfaces Between Al203 Substrates and MBE Grown NB Films
Authors: Mayer J. , Dura J. , Flynn C.P. , RüHle M.
Published: March 2011

Single crystal niobium films were grown by Molecular Beam Epitaxy (MBE) on (0001)s sapphire substrates. Cross-sectional specimens with thickness of <20 nm were prepared so that the Nb/A1203 interface could be investigated by high resolutionelectron microscopy (HREM). The orientation relationship between the metal film and the ceramic substrate was verified by selected area diffraction: (111)Nb ║(0001)S and [110]Nb║[2110]S. The atomistic structure of the interface was identified by HREM.
TEM Evaluation of CuAu-I Type Ordered Structures in MBE grown Ingaas Crystals on (110) Inp Substrates
Authors: Ueda O. , Nakata Y. , Nakamura T. , Fujii T.
Published: March 2011

CuAu-I type ordered structures in InGaAs grown on (110) InP substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. In the electron diffraction pattern from the InGaAs, superstructure spots associated withCuAu-I type ordered structure are found. When the tilting angle of the substrates increases, the ordering becomes stronger. The ordering is also stronger in crystals grown on substrates tilted toward the <001> or the <001> direction than those on substrates tilted toward the <110> direction. From these results, one can conclude that atomic steps on the growth surface play an important role in the formation of ordered structures. The ordering becomes stronger when the growth temperature increases in the range 360-485°C. In high resolution images of the crystal, doubling in periodicity of 220 and 200lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane.
Interface Stress in Artificial Multilayers
Authors: Ruud J.A. , Witvrouw A. , Spaepen F.
Published: March 2011

A new method for measuring interface stress is presented. The curvature of substrates coated with artificial multilayers is measured as a function of bilayer repeat length. The interface stress is determined from the slope of the curvature plotted versus inverse repeat length. As an example, the (111) Au/amorphous Al2O3 interface stress was determined to be 1.13±0.06 J/m2 (compressive) . X-ray and TEM observations allowed the possibility of interfacial phases to be ruled out as possible alternative sources of the stress.
Irradiation Defect Structures In YBa2Cu3O7-xand their Correlation with Superconducting Properties
Authors: Kirk Marquis A.
Published: March 2011

We review our work on irradiation effects in single crystal YBa2Cu3O7-x. Transmission electron microscopy has been employed to study the defect microstructures produced by irradiations with fast neutrons, MeV ions (Kr, Ne and p), and electrons. The atomic structure within defect cascades was investigated using 50 keV Kr and Xe ion irradiations to low doses. Evidence is shown for an amorphous structure with some incoherent recrystallization within individual cascades. Correlation with enhancements in critical current density produced by neutron irradiations suggest that this cascade structure effectively pins magnetic flux lines.

At sufficiently high fluences of fast neutrons or MeV Kr and Ne ions, a cellular microstructure is found. This structure consists of cells or microcrystallites of good crystalline and superconducting material (in the case of neutron irradiation), with cell walls of amorphous material. Full amorphization proceeds with the growth of cell wall volume. The formation of this microstructure coincides with a decrease in criticaltransportcurrent, but is not observed by magnetization measurements.

Increases in critical current density under proton irradiation, comparable to those produced by neutron irradiation, have been reported. The defect structure produced by proton irradiations is examined here and found to differ from that of neutron irradiations. The structure is suggested to be consistent with the clustering of mobile defects (at 300 K) produced by the lower energy recoils which dominate in proton irradiations. In both the proton and fast neutron irradiations, to fluences producing the maximum enhancements in critical current densities, the degradations in critical temperature are not severe, <10 K.

Our most recent measurements of changes in critical temperature and current density, and defect microstructure following electron irradiations will be described
Investigation Of YBa2Cu3O7-δ Films Grown on Vicinally-Polished MgOSubstrates
Authors: Streiffer S. K. , Lairson B. M. , Bravman J. C.
Published: March 2011

X-ray diffraction and transmission electron microscopy have been used to study the morphology and defect structure of YBa2Cu3O7-δ films on [001] MgO substrates polished away from the [001] crystallographic axis towards either [010] or [110] by angles ranging from 1° to 20°. On the [010] off-axis substrates it was found that growth of the YBCO film was highly influenced by the surface normal of the substrate with only very weak alignment to the substrate [001] direction. All [010]-angled samples maintained Tc's of 86K. Angles of 1°, 2.5°, and 5° toward [010] produced films with large mosaic spread parallel to the direction of the angle, as high as 4° FWHM for the 5° sample. Critical current densities of these films remained as high as those of films grown on on-axis substrates, e.g. 4.4×107 A/cm2 at 4.2 K and zero applied field. Larger off-axis angles led to samples with reduced mosaic spread but still alignment to the surface normal, and reduced Jc's of 2×107 A/cm2 and 1×l05 A/cm2 for 10° and 20° angles, respectively. TEM investigation and in-plane x-ray examination of the 5°, 10°, and 20° samples show good in-plane texture except for the 20° sample, and increased granularity with angle. Films on substrates polished off-axis towards [110] have degraded Tc's and Jc's for all angles.
Elastic After-Effect Due to Oxygen Relaxation in Yba2Cu3O7−δAbove Tc
Authors: Cost J. R. , Armstrong P. E. , Poeppel R. B. , Stanley J. T.
Published: March 2011

Isothermal elastic after-effect measurements to obtain relaxation times for the stress-induced motion of oxygen in YBa2Cu3O7−δ have been made from 50°C to 110°C. These results extend our previous internal friction measurements of the same oxygen relaxation to lower temperatures. The combined results, which cover nine orders of magnitude in relaxation time, show a classical Arrhenius temperature dependence, activation energy Q−1.13±0.01 eV and attempt frequency τ0−1.6×10−13 s (log τ0−.12.79±0.13). The mechanism of the relaxation is considered to be stress-induced ordering of oxygen atoms on theCuO basal plane. Diffusivities obtained from these results are compared with those from tracer diffusion of oxygen.
Several Important Problems in YBaCuO and Its Doped Systems
Authors: Zhang H. , Feng S.Q. , Feng Q.R. , Zhu X. , Gan Z.Z.
Published: March 2011

The orthorhombic-tetragonal transition, relationship between oxygen content and TC, electronic state of Cu and TC, lattice energy and TC in YBCO and its doped systems (Cu doped by Sn, Al, Fe, Zn, Ni; Ba by Sr, Ca; Y by Pr,Gd,Dy, respectively.) have been studied systematically. The experiments show that the O-T transition may not be the predominant factor governing superconductivity; there is no regular relationship between superconductivity and the oxygen content. In order to fully understand superconductivity, other defects must be considered; the valence of Cu has a strong correlation with oxygen content, but has no direct relationship with the TC value. The correlation among the electronic states of Ba, Cu and O are discovered, which is helpful to know the electfonic behavior of this material. Finally, we show that the lattice energy has a close relationship with the magnitude of TC. As the lattice energy is decreased, the TC is always depressed without any exception. The authors suggest that the lattice energy may be a probable predominant factor to superconductivity.
The Oxygen Defect Chemistry of La2−xSrxCuO4−x/2+δ
Authors: Opila Elizabeth J. , Tuller Harry L.
Published: March 2011

The equilibrium oxygen stoichiometry of La2−xSrxCuO4±y (x=O, 0.2, 0.4, and 1.0) has been determined by TGA at temperatures between 800 and 1050°C and oxygen partial pressures between 1 and 10−4 atmospheres. The changes in oxygen content with temperature, oxygen partial pressure, and strontium concentration are evaluated in terms of a defect model.
Microstructures in Y-Ba-Cu-O Thin Films Investigated by XAFS Techniques
Authors: Krol A. , Ming Z. H. , Lin C. S. , Soo Y. L. , Gu C. X. , Kao Y. H. , Narumi E. , Shaw D. T. , Smith G. C.
Published: March 2011

Superconducting films of YBa2Cu3O7−6 obtained by laser ablation on MgO and ZrO2 substrates were investigated by soft x-ray absorption fine structure technique (XAFS) at O K-edge. Local environment around oxygen atoms was probed and information on the distribution of the nearestneighbors was obtained. Much higher degree of local disorder than that in a bulk YBa2Cu3O7−δ sample was observed.
Volume Change in Ternary Zn-Al-Cu Alloy
Authors: Mykura N. , Murphy S. , Zhu Y.H.
Published: March 2011

The alloys of the ternary system Zn-Al-Cu are characterised by dimensional changes that occur on ageing in conjunction with certain phase transformations and changes in solid solubility [1]. The phase transformation that is suggested to be responsible is the four phase reaction

that occurs below 273°C [2]. The average density of the products of this reaction was hypothesised to be less than that of the reactants resulting in an increase in volume. Previous work [3] had indicated that the lattice parameters of the zinc structure cell varied considerably on ageing and this change was attributed to the change in solubility of substitutionally dissolved copper. On ageing it is hypothesised that copper tends to come out of solution in zinc, contributing to the total increase in volume. This copper may come out as ε-phase which may react to form T'-phase with a resulting change in volume.
Long-Period Structures of Al-Rich Al-Ti Alloys
Authors: Miida R. , Watanabe D.
Published: March 2011

Long-period one-dimensional antiphase structures with average domain sizes of non-integral multiples (M=1.33 and M=1.50−1.91) of the basic L12 cell, existing in the Al3-xTi1+x(00.33) alloys, were studied by electron diffraction, high-resolution electron microscopy and X-ray diffraction. The mode of mixing of M=1 and M=2 domains was revealed and the nature of lattice modulation associated with the antiphase structure was clarified. A new type of superstructure Al5Ti3 was also studied by highresolution electron microscopy and the structure model proposed previously was verified.
On Dark-Field High-Resolution Images Of Two-Dimensional Antiphase Structures
Authors: Terasaki O. , Wood G.J. , Watanabe D.
Published: March 2011

Dark-field images of two-dimensional antiphase domain structures with stepped boundaries have been simulated for imaging conditions corresponding to some current high resolution electron microscopes. The simulations reveal that the positions of the dots in the dark-field images do not give a true representation of atomic structure; thus, in contrast to the brightfield superstructure images, it is very misleading to say that bright dots in the dark-field image correspond exactly to the positions of the minority atoms.
Order-Disorder Transitions in Ternary Alloys A Study on the Microstructure of L10and L12Alloys
Authors: De Hosson J. Th. M.
Published: March 2011

The order-strengthening mechanism in the ternary alloy, Cu-Ni-Zn, is investigated by comparing stress-strain curves and electron micrographs of corresponding dislocation structure in disordered, partly ordered and ordered samples. Around the composition Cu2NiZn two different types of ordering are found experimentally: L10and L12. The degree of ordering is determined by measuring the equilibrium distance between superlattice dislocations and by single crystal neutron diffraction. The long-range zinc order parameter thus obtained appeared to be in agreement with calculations using the cluster variation method (CVM) in the tetrahedron approximation. Electron microscopic observations show that even in the disordered phase, when short range order exists, superlattice dislocations are created by Frank-Read sources, rather than the generation of single dislocations.
Ordered Structures on the BCC Lattice with First, Second, Third and Fifth Neighbour Interactions
Authors: Finel A. , Ducastelle F.
Published: March 2011

Using a method of linear inequalities similar to that introduced previously by Kanamori and others, we determine the ground state of the Ising model on the BCC lattice in the presence of first, second, thirdand fifth neighbour interactions. Thirteen new structures are found ; the C 11b (MoSi2)and B 11 (γ - TiCu) in particular are found to be stabilized by third and /for fifth neighbour interactions. Some regions of the phase diagram however are still not completely known.
Thermoelectroc Power for Phase Transformation Study in Metallic Alloys
Authors: Borrelly R. , Merle P. , Merlin J. , Pelletier J.M. , Vigier G.
Published: March 2011

Recent experiments have proved the efficiency of T.E.P. measurements in phase transformation studies. The main features of the technique are presented and two particular examples of application are given (influence of plastic deformation on short range ordering (S.R.O.) and study of dissolution of the equilibrium Θ phase in Al-Cu alloys).

Since the first studies [1] only very few attempts have been made to use thermoelectrical power measurements (T.E.P.) to characterize the evolution of an alloy during phase transformation. However, in spite of the complexity of the theoretical interpretations, T.E.P. measurements can give valuable informations on the microstructure of the material, sometimes with more easiness or more precision than with other techniques or even informations which would be impossible to obtain by another way.
Electronic Structure, Multiatom Interactions, Stability of Ordered Structures and Short Range Order in Binary Transition Metal Alloys
Authors: Bieber A. , GAUTIER F.
Published: March 2011

Mlultiatom interactions required in the statistical models used for the study of both the stability of ordered structures in the ground state and the chemical short range order, have been computed from the electronic structure for transition metal alloys. It is shown that : i) the most important interactions coming from “d” bands are those corresponding to self-retraced paths, the contributions of compact clusters being negligible ; ii) in general the results obtained using only second order pair interactions are valid provided that the concentration dependence of the pair interactions is taken into account. However in a few peculiar cases these results may be qualitatively modified.
Electronic Theory of Order-Disorder Transformations in Binary Alloys
Authors: Castillo-Alvarado F.L. , Moran-Lopez J.L. , Sanchez J.M.
Published: March 2011

A microscopic theory of order-disorder phase transitions in binary alloys is oresented. The internal energy of the system is calculated within the tight-binding Hamiltonian and long- and short-range order effects are included by solving the equations of motion for the Green's functions in the Be the lattice approximation. Results are presented for the electronic local density of states and for various values of the long- and short-range order parameters.
The Change of the Vibration Entropy Due to the Disordering of an Ordered Simple-Cubic Alloy
Authors: Waegmaekers A.A.H.J. , Bakker H.
Published: March 2011

Within a model of central and noncentral forces the exact change of the vibrational entropy, ΔS, is calculated, both as function of the degree of order and as a function of the diverse force constants. A linear relationship between ΔS and the short-range order parameter is found. Results of ΔS as a function of the force constants are compared with ΔS as calculated by an empirical formula based on a modified Einstein crystal model.
Electronic Structure and Stability of Vacancy-Ordered Compounds of Transition Metal Carbides and Nitrides
Authors: Landesman J.P. , Turchi P. , Ducastelle F. , Treglia G.
Published: March 2011

We make a connection, via the calculation of the band energy, between the stability of MX1−α, ordered phases (M being a transition metal, X being C or N, and α the vacancy concentration) and effective pair interactions on the metalloïd sublattice of these NaCl type compounds.
Electronic Properties and Stability of the TiAl3 and MoPt2 Type Ordered Structures in Binary Transition Metal Alloys
Authors: Kuentzler R. , Waterstrat R.M. , Turek P. , Bieber A.
Published: March 2011

In view of the recent constitution diagrams (for binary transition metal alloys) a systematic study of the electronic properties of all alloys which have either the TiAl3 or MoPt2 type of structure has been undertaken. Specific heat results are reported and briefly discussed in the frame of the theoretical calculations about band structure and stability of ordered alloys.
Application of a Solvation Shell Analysis to the Diffusivity of Interstitial Species in Binary Substitutional Solutions
Authors: Farkas D.
Published: March 2011

The problem of interstitial diffusion in substitutional lattices has been extensively studied due to the practical importance of carbon in ternary austenites, as well as H in alloys.
Shape of α'R. Zn Rich Precipitatesin Al Zn Alloys. Effect of an Uniaxial Stress on Decomposition
Authors: Livet F.
Published: March 2011

During the first stages of decomposition of Al Zn alloys, spherical GP zones are observed. On further ageing of the samples, the precipitates have the shape of flat ellipsoids, the small axis of which are in the various <111> directions.

We have followed such an evolution in single crystals by small angle neutron scattering. From the asymptotic behavior of the cross section, we have calculated the size (c) of the small semiaxis of the ellipsoids. We show that c is almost independent of the initial composition of our samples (5.3, 6.8, 12.1 at Zn %), independent of the other dimensions of the “α'R” precipitates and very sharply distributed around its mean value (c = 24.5 ± 2 Å at 293°C).

The strain field in the matrix must clearly be involved in the limitation of the c value. We have studied the effect of a uniaxial [110] compressive stress applied during ageing. Neutron small angle experiments, carried on an Al-12.1 at % Zn single crystal show that the c value remains the same. The scattering in the [111] and [11] directions is much higher than in the [111] and [111] directions. This is mainly due to the fact that the stress favors the number of [111] and [111] type of α'R precipitates.
Spinodal Decomposition in Fe-Cr-Co Alloys
Authors: Brenner S. S. , Camus P. P. , Miller M. K. , Soffa W. A.
Published: March 2011

Continuous phase separation or spinodal decomposition occurs within a miscibility gap through the selective amplification of long wavelength concentration waves to produce a two-phase modulated microstructure. To comprehensively study the formation of these modulated microstructures and the kinetics of continuous phase separation the behavior of the composition fluctuations in the decomposing material should be monitored directly. The atom probe field-ion microscope is an ideal instrument for this type of investigation of fine-scale microstructures because of its ultra-high spatial resolution and microchemical analysis capability.
Electronic Excess Energy in Modulated Positive-Background Model
Authors: Yahauchi H.
Published: March 2011

Electronic excess energy of a composition-modulated alloy system at absolute zero temperature is obtained using Hohenberg and Kohn's formula (for the ground-state energy of an inhomogeneous electron gas) in a modulated positive-background model. Dependence of the electronic excess energy on the modulation wavelength is studied. Two leading terms in the excess energy are examined to elucidate the limitation of this model.
Thermoelastic Martensitic Transformations and the Nature of the Shape Memory Effect
Authors: Wayman C. M.
Published: March 2011

Investigations of the shape memory effect in alloys forming thermoelastic martensites with various crystal structures (2H, 3R, 9R and 18R) reveal that universal behavior exists. A unified explanation of the martensite deformation processes and subsequent shape recovery is now in hand, even though the various martensites are both internally twinned and internally faulted and, in addition, have different crystal structures. In cases studied to date, an initial parent phase single crystal transforms into self-accommodating arrangements of martensite variants (plates) which are characterized by “plate groups.” Each group consists of four variants. The average shape deformation in a plate group is essentially zero.

Upon stressing below the Mf temperature the martensite undergoes deformation by detwinning (2H and 3R only), variant-variant coalescence and twinning processes, and further group-to-group coalescence. The deformed specimen eventually becomes a single crystal of martensite consisting of that particular habit plane variant whose shape deformation permits maximum extension in the direction of the applied stress. The deformed martensite persists after unloading has occurred; reverse rearrangements of twins and variants do not occur. Specimens deformed below Mf regain their initial shape characteristic of the initial parent phase upon heating from As to Af, during which the single crystal of martensite obtained by stressing the 24-variant configuration transforms back to the original parent phase single crystal in a unique manner, which is basically a simple “unshearing” process. The unshearing is the essence of the memory.

The two-way shape memory effect results after the initial martensitic transformation upon cooling is preprogrammed by the introduction of stresses which preferentially bias the transformation so that only a single variant of martensite forms upon cooling. The shape change of this single variant causes the characteristic spontaneous “bending” upon cooling. The characteristic “unbending upon heating is as with the conventional “one-way” shape memory effect.
Martensitic Transformation Cycling and the Phenomenon of Two-Way Shape Memory Training
Authors: Perkins J.
Published: March 2011

The character and mechanism of two-way shape memory (TWSM) “training” has been investigated in a Cu-Zn-Al alloy by means of detailed thermomechanical evaluation and TEM observations. The progressive effects of training on the TWSM behaviour, as well as an accompanying substructural evolution, have been established. The results indicate a relationship between the substructural effects of cyclic thermoelastic martensitic transformation and the ability to exhibit TWSM. Microscopic studies reveal that as the number of cycles of thermoelastic transformation under stress increases, specific physical features develop in the parent phase submicrostructure. These take the form of dislocation structures which evolve into “vestigial” martensite markinqs. These in turn assist in the nucleation and growth of a preferred martensite plate arrangement on cooling which is similar to that induced under stress during the training cycles.
Contribution of Martenistic Transformations to the Plastic Behavior and the Mechanical Properties of Cr, Ni Austenitic Stainless Steels
Authors: Chappuis G. , Najafi-Zadeh A. , Harmelin M. , Lehr P.
Published: March 2011

The aim of this paper is to study the contribution afforded by strain induced martensitic transformation to the plastic behavior under monotonic or cyclic loadings and the mechanical properties of Cr-Ni austenitic stainless steels. The study concerns namely the low carbon 18/10 steel, commonly used in various fields of technics and particularly in cryogenics (liquid gases storage or transportation).
Kinetic and Thermodynamic Aspects of the Bainite Reaction in a Silicon Steel
Authors: Papadimitriou G. , Genin J.M.R.
Published: March 2011

The bainite reaction in an Fe - 3.85 wt pct Si - 0.9 wt pct C steel is studied by several experimental techniques in the range of 250–450°C.

The high silicon content prevents the formation of cementite, so that the reaction is separated to two clearly distinct stages. In the primary stage ferrite forms alone, except at temperatures lower than 310°C where some carbides precipitate in it, and austenite becomes enriched in carbon. In the secondary stage occurring only above 400°C, the enriched austenite decomposes to ferrite and an unknown silicon carbide.

The microstructure, the enrichment of the austenite and the overall reaction kinetics of the two stages are studied and are found to be consistent with a displacive mechanism of the bainite reaction.

A tentative model, accounting for the competition of shear and diffusion, is proposed in order to fit our experimental data.
Microstructural Changes at Elevated Temperature of γ/γ′-α(Mo) Uds Eutectics
Authors: Dirnfeld S.F. , Schwam D.
Published: March 2011

Ni-Mo-Al eutectic alloys were subjected to a process of unidirectional solidification (UDS) by the Bridgman-Stockbarger technique with a view to a composite of ductile matrix containing ductile reinforcement of comparatively high strength. The microstructure after UDS consists of a γ/γ' matrix reinforced with Mo(α) fibers. The growth direction and the orientation relationships between the phases were determined by electron diffraction. In the present study, attention was focussed on phase stability after prolonged exposure at elevated temperature. Isothermal exposure of 90 min at 1250°C was followed by a mild water quench. Apart from the beneficial influence on the γ' morphology, partial transformation of the α(Mo) fibers into δ-NiMo intermetallic was observed. Replacement of the ductile α(Mo) fibers by the brittle δ-NiMo is accompanied by partial loss of facetting. Decisive evidence of this diffusion-controlled phase transformation is supplied by TEM micrographs.
Continuous Heat Treating of Sheet Steel
Authors: Lazaridis N.A. , Preban A.G. , Southwick P.D.
Published: March 2011

The continuous heat treatment of steel has been a widely used practice throughout the world for a considerable time. However, it is only in the past decade that the enormous potential of continuous annealing was recognized so that it is now possible to produce steels with a much wider variety of properties than is possible by batch annealing. These possibilities have been revealed not only by advances in controlling and configuring continuous annealing lines, but also in up-stream and downstream technology. These advances have made consistency the word which is synonymous with continuously annealed steel. This paper will review the fundamentals of continuous annealing and associated metallurgy, and the effect of processing variables on the product properties. The acceptable variation in processing to give an uniform product will be described.
Phase Transformations in Quench-Aged Zn-Al-Si Alloys
Authors: Zhu Y.H. , Savaskan T. , Murphy S.
Published: March 2011

Two zinc-aluminium based alloys with 30% Zn and 60% Zn and small additions of silicon have been quench-aged and the phase transformations studied in relation to the hardness. It was found that the peak hardness increase is due to the formation of αm″ and α″ phases and evidence has been obtained for the transformation of these to αm′ and α′. A cellular reaction αS′→αT′+η was observed in the first stage of ageing in the alloy with 60% Zn.