bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTLMTO-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.
Evidence of Forbidden Reflections in the Diffuse Scattering of Hg0.80Cd0.20Te Single Crystals
Authors: Quintana J. P. 
Published: March 2011

ABSTRACTThe 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

ABSTRACTStructural 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

AbstractThe 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.
Defects in the Structure of Σ=27 <110> Tilt Grain-Boundaries in Ge.
Authors: Mckernan Stuart , Barry Carter C. , Elgat Zvi 
Published: March 2011

ABSTRACTGeneral 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

ABSTRACTThe 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

ABSTRACTSingle 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

ABSTRACTCuAu-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

ABSTRACTA 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

ABSTRACTWe 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

ABSTRACTX-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

ABSTRACTIsothermal 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTSuperconducting 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 reactionthat 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

ABSTRACTLong-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(0<x>0.33) 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

ABSTRACTDark-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

ABSTRACTThe 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

ABSTRACTUsing 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

ABSTRACTRecent 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

ABSTRACTMlultiatom 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

ABSTRACTA 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

ABSTRACTWithin 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

ABSTRACTWe 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

ABSTRACTIn 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.