WorldWideScience

Sample records for bicrystals

  1. Shot noise in YBCO bicrystal Josephson junctions

    DEFF Research Database (Denmark)

    Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.; Mygind, Jesper; Pedersen, Niels Falsig

    2003-01-01

    We measured spectral noise density in YBCO symmetric bicrystal Josephson junctions on sapphire substrates at bias voltages up to 100 mV and T 4.2 K. Normal state resistance of the Josephson junctions, R-N = 20-90 Omega and ICRN up to 2.2 mV have been observed in the experimental samples. Noise me...

  2. Molecular dynamics study of thermal disorder in a bicrystal model

    International Nuclear Information System (INIS)

    This paper studies a (310) θ = 36.86 degrees left-angle 001 right-angle symmetrical-tilt bicrystal model using an Embedded Atom Method aluminum potential. Based on explicit results obtained from the simulations regarding structural order, energy, and mobility, the authors find that their bicrystal model shows no evidence of pre-melting. Both the surface and the grain-boundary interface exhibit thermal disorder at temperatures below Tm, with complete melting occurring only at, or very near, Tm. Concerning the details of the onset of melting, the data show considerable disordering in the interfacial region starting at about 0.93 Tm. The interfaces exhibit metastable behavior in this temperature range, and the temperature variation of the interfacial thickness suggests that the disordering induced by the interface is a continuous transition, a behavior that has been predicted by a theoretical analysis

  3. GRAIN BOUNDARY CORROSION, STRUCTURE AND SEGREGATION IN NICKEL BICRYSTALS

    OpenAIRE

    Vignaud, C.; Beaunier, L.; Biscondi, M.

    1990-01-01

    Nickel bicrystals with tilt boundaries are used to study the influence of the structure of the grain boundaries on the intergranular corrosion. An electrochemical test allows to obtain the evolution of the corrosion versus the misorientation of grains and the repartition of elements segregated during the elaboration and / or heat treatment at 800°C. Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) on intergranular fracture surfaces allows a corrosion-segregation-struc...

  4. Atomic simulation of grain boundary sliding in Co/Cu two-phase bicrystals

    International Nuclear Information System (INIS)

    Molecular dynamic simulations of grain boundary sliding were performed on Cu/Cu one-phase bicrystal and Co/Cu two-phase bicrystal models. The grain boundary sliding and migration behaviors of the Co/Cu bicrystals were different from those of the Cu/Cu bicrystals, and the Co/Cu sliding behavior was less related to the free volume, than that of Cu/Cu. In the Co/Cu(2 2 1) grain boundary model, the pore structure units were formed on the Cu side very near the Co/Cu interface, not just at the interface. The onset of grain boundary sliding in the Co/Cu bicrystals was due to the uncorrelated atomic shuffling induced by the pore structure units.

  5. A TEM and DLTS study of a near. Sigma. 25 CdTe bicrystal

    Energy Technology Data Exchange (ETDEWEB)

    Wang, N.; Haasen, P. (Inst. fuer Metallphysik, Univ. Goettingen (Germany))

    1991-11-16

    Cadmium precipitates are observed at the grain boundary (GB) of a CdTe bicrystal by means of transmission electron microscopy (TEM). In a simple model based on the theory of electron hopping, electrons can be excited by thermal activation and flow from boundary states to precipitates in the boundary. This model gives, in particular, a simple explanation for the emission properties of the precipitates, as determined by deep-level-transient spectroscopy (DLTS) on the bicrystal. (orig.).

  6. Intergranular precipitation in aluminium-copper oriented bi-crystals

    International Nuclear Information System (INIS)

    In the first part of this research thesis, the author addresses the fabrication of aluminium-copper oriented bi-crystals by discussing the specific problems raised by this fabrication, and by describing the aspect after a thermal treatment chosen to reach a defined objective: the visibility of precipitates in all grain boundaries, and a secondary role of kinetic parameters. The second part addresses the density of intergranular precipitates by reporting and commenting the results of precipitate numbering in symmetric and asymmetric boundaries performed by using optic microscopy. The third part addresses the dimensions and shapes of intergranular precipitates. The author there reports the study of the average dimensions of precipitates with respect to boundary nature. Some additional remarks are made regarding their shape and crystallographic nature. Numerical results are obtained from measurements performed on photographs of carbon replicates taken by using an electronic microscope. The author then reports the study of the width of the area of low precipitation density at the edge of boundaries. A copper assessment in the intergranular band is performed which shows the type of relationship which seems to exist between previously studied phenomena. Finally, the author reports the study of the relationship between boundary atomic structure and intergranular precipitation. A grain boundary model has been developed and allows a definition of intergranular germination sites to be obtained

  7. Influence of Grain Boundary on Fatigue Behavior of Ni-base Bicrystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The influence of the grain boundary on the fatigue behavior was studied by two three-point-bending (TPB) specimens.One TPB specimen was named Bicrystal 1, whose pre-crack was along the grain boundary and the applied loadparalleled to pre-crack direction, while the other TPB specimen was named Bicrystal 2, whose the pre-crack wasperpendicular to the grain boundary and the applied load paralleled also to the pre-crack. It was found that the rateof the fatigue crack growth of Bicrystal 1 was about a tenfold higher than that of Bicrystal 2. The fatigue behaviorof Bicrystal 2 specimens was dependent on the distance between the crack tip and grain boundary. The crack growthrate was highest when the crack tip was at a critical distance to the grain boundary, while the rate was the lowestwhen the crack tip reached grain boundary. After the crack was over the grain boundary, the crack growth rateincreased. The crystallographic finite element method was applied to analyze the stress and strain structure aheadof the crack, in order to reveal the above characteristics of the fatigue behavior. It is the grain boundary-inducedredistribution of stresses near the crack tip that induces the difference of fatigue behavior.

  8. The 0 and pi contact array model of bicrystal junctions and interferometers

    DEFF Research Database (Denmark)

    Kornev, Victor K.; Soloviev, Igor I.; Klenov, Nikolai V.; Pedersen, Niels Falsig; Borisenko, Igor V.; Mozhaev, Peter B.; Ovsyannikov, Gennady A.

    2003-01-01

    The array model of the faceted bicrystal Josephson junctions has been developed more comprehensively. The facet size and the facet critical current dependence on. magnetic field are taken in to consideration. The model can be successfully used with high-performance software meant for numerical si...

  9. Study of deformation mechanisms of zinc bicrystals by thermal cycling (1963)

    International Nuclear Information System (INIS)

    The thermal cycling of zinc bicrystals has been studied in order to precise the thermal cycling growth mechanism, proposed by Burke and TURKALO, specially the dependence of 'equi-cohesive' temperature of grains on their mutual orientation and the parameters of the thermal cycle. Dilatometric studies showed that a bicrystal had no equi-cohesive temperature and that the grain-boundary develops stress at all temperatures. The creep of single and bicrystal have been studied on a dilatometer with stress below the Yield-stress. At constant temperature secondary creep appears after a transient period, at cycled temperature creep stays transient for strains of about 10-4 to 10-3 when the crystal is plastically hard. Micrographic investigations show that grain-boundary migration accompanies the grain boundary shearing and that cycles produce a strong polygonisation, corroborating the fact that the grain boundary remains a stress-generator and that creep occurs in the volume of grains. The discussion of results shows that the transient creep of hard grain in a bicrystal makes the thermal cycling irreversible and allows on elongation at each cycle if that have the lower expansion coefficient. (author)

  10. Low voltage excess noise and shot noise in YBCO bicrystal junctions

    DEFF Research Database (Denmark)

    Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;

    2002-01-01

    The spectral density of background noise emitted by symmetric bicrystal YBaCuO Josephson junctions on sapphire substrates have been measured by a low noise cooled HEMT amplifier for bias voltages up to V approximate to 50 mV. At relatively low voltages V <4 mV a noticeable noise rise has been...

  11. Preparation and photocatalytic activity of bicrystal phase TiO2 nanotubes containing TiO2-B and anatase

    Science.gov (United States)

    Huang, Chuanxi; Zhu, Kerong; Qi, Mengyao; Zhuang, Yonglong; Cheng, Chao

    2012-06-01

    Bicrystal phase TiO2 nanotubes (NTS) containing monoclinic TiO2-B and anatase were prepared by the hydrothermal reaction of anatase nanoparticles with NaOH aqueous solution and a heat treatment. Their structure was characterized by XRD, TEM and Raman spectra. The results showed that the bicrystal phase TiO2 NTS were formed after calcining H2Ti4O9·H2O NTS at 573 K. The bicrystal phase TiO2 NTS exhibit significantly higher photocatalytic activity than the single phase anatase NTS and Dessuga P-25 nanoparticles in the degradation of Methyl Orange aqueous solution under ultraviolet light irradiation, which is attributed to the large surface and interface areas of the bicrystal phase TiO2 NTS.

  12. Resistive memory devices with high switching endurance through single filaments in Bi-crystal CuO nanowires

    International Nuclear Information System (INIS)

    Highlights: • We investigate the influence of microstructure on the resistive switching behavior. • A simple system via bi-crystal CuO nanowires is proposed and discussed in this work. • The endurance of memory resistive switching of bi-crystal CuO nanowires is at least 1000 cycles. - Abstract: We propose a simple system to investigate the influence of microstructure on the resistive switching behavior via bi-crystal CuO nanowires. CuO nanowires are prepared by thermally oxidizing transmission electron microscopy copper grids in air. Single-crystal and bi-crystal CuO nanowires can be selectively obtained by adjusting the temperature. The devices made of single-crystal nanowires follow Ohm’s law, with a high resistance, within the sweeping voltage range of 0–4 V, whereas those made of bi-crystal nanowires exhibit threshold and memory resistive switching behaviors, which are due to the enrichment of copper ions in the grain boundaries of bi-crystal CuO nanowires providing sources for the formation of conductive filaments. Moreover, the bi-crystal nanowires with higher defect densities in grain boundaries result in lower threshold voltages of switching from high to low resistance states. The threshold resistive switching behavior can be turned into memory resistive switching behavior by increasing the thickness of the device electrodes or reducing the compliance current. The endurance of memory resistive switching through the pre-defined conduction paths in the single grain boundaries of bi-crystal CuO nanowires is at least 1000 cycles without any performance deterioration. This high reliability is ascribed to the single conductive filaments

  13. Study of the creep of germanium bi-crystals by X ray topography and electronic microscopy

    International Nuclear Information System (INIS)

    This research thesis addresses the study of the microscopic as well as macroscopic aspect of the role of grain boundary during deformation, by studying the creep of Germanium bi-crystals. The objective was to observe interactions of network dislocations with the boundary as well as the evolution of dislocations in each grain. During the first stages of deformation, samples have been examined by X ray topography, a technique which suits well the observation of low deformed samples, provided their initial dislocation density is very low. At higher deformation, more conventional techniques of observation of sliding systems and electronic microscopy have been used. After some general recalls, the definition of twin boundaries and of their structure in terms of dislocation, a look at germanium deformation, and an overview of works performed on bi-crystals deformation, the author presents the experimental methods and apparatuses. He reports and discusses the obtained results at the beginning of deformation as well as during next phases

  14. Grain boundary structure and solute segregation in titanium-doped sapphire bicrystals

    OpenAIRE

    Taylor, Seth T.

    2002-01-01

    Solute segregation to ceramic grain boundaries governs material processing and microstructure evolution, and can strongly influence material properties critical to engineering performance. Understanding the evolution and implications of grain boundary chemistry is a vital component in the greater effort to engineer ceramics with controlled microstructures. This study examines solute segregation to engineered grain boundaries in titanium-doped sapphire (Al2O3) bicrystals, and explores re...

  15. Internal and external stresses: In situ TEM compression of Cu bicrystals containing a twin boundary

    International Nuclear Information System (INIS)

    Uniaxial compression experiments on single- and twinned bicrystalline Cu samples using conventional and scanning in situ transmission electron microscopy reveal no increase in flow stress for the bicrystals. Dislocation curvature and dislocation source size analysis combined with indenter force measurements show agreement between local internal stresses acting on the dislocations and external stresses imposed by the indenter, indicating no stress concentrations due to the twin boundary. Furthermore, the dislocation density evolution shows stochastic variations but never a complete dislocation starvation

  16. HYDROGEN EMBRITTLEMENT IN GRAIN BOUNDARIES STUDIED BY FATIGUE CRACK PROPAGATION IN Al-Zn-Mg BICRYSTALS

    OpenAIRE

    Niegel, A.; Gudladt, H.-J.; Gerold, V.

    1988-01-01

    High cycle fatigue crack propagation in grain boundaries was studied in precipitation hardened Al-Zn-Mg specimens containing a single grain boundary (gb) perpendicular to the load axis. In peak-aged bicrystals tested in wet nitrogen atmospheres, cracks propagated in an intercrystalline manner. Under cyclic loading conditions two different mechanisms contribute to crack propagation which are termed stress corrosion cracking (SCC) and intergranular corrosion fatigue (CF). In both cases, it is w...

  17. Grain boundary migration in Fe-3mass%Si alloy bicrystals under a magnetic field

    Czech Academy of Sciences Publication Activity Database

    Tsurekawa, S.; Inoue, K.; Lejček, Pavel

    2010-01-01

    Roč. 50, č. 4 (2010), 591-595. ISSN 0915-1559 R&D Projects: GA ČR GA106/08/0369 Grant ostatní: JSPS(JP) 19106013 Institutional research plan: CEZ:AV0Z10100520 Keywords : grain boundary migration * magnetic field * grain boundary character * Fe-Si alloy * bicrystals Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.742, year: 2010

  18. Grain boundary complexion transitions in WO3- and CuO-doped TiO2 bicrystals

    International Nuclear Information System (INIS)

    Several grain boundary complexions (grain boundary interfacial phases) have been identified in TiO2 bicrystals by high-resolution transmission electron microscopy (TEM) and aberration-corrected scanning TEM (STEM). An intrinsic grain boundary with no apparent impurity segregation was observed in an undoped TiO2 bicrystal. In a WO3-doped TiO2 bicrystal, WO3 second-phase particles formed along the boundary, with a nominally clean, intrinsic-type grain boundary in between the particles. In a CuO-doped bicrystal, a remarkable series of three distinct grain boundary complexions with abrupt structural transitions was discovered coexisting at the grain boundary, and the existence of a fourth equilibrium complexion at the annealing temperature was implied. Thus, the WO3- and CuO-doped TiO2 bicrystals exhibit dramatically different solute partitioning behavior which can be understood in terms of the relative interphase boundary energies of these two systems. STEM–electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy analysis of the nanoscale lens-shaped films of amorphous material in the CuO-doped TiO2 bicrystal demonstrated an excess of CuO, as expected, yet also revealed the unintentional presence of SiOx. The multiple grain boundary complexions in CuO-doped TiO2 offer an explanation for the CuO-enhanced grain growth and sintering of TiO2 that has been reported in the literature. Conversely, the intrinsic grain boundary complexion observed in WO3-doped TiO2 is consistent with previous work showing that WO3 has no effect on grain boundary mobility in TiO2. A phenomenological thermodynamic model is proposed to explain the physical origin of these observed grain boundary complexions and the abrupt, first-order complexion transitions that are believed to occur upon cooling of the CuO-doped TiO2 bicrystal

  19. Computation of LACBED images from bi-crystals using reciprocity. Part 1 Rigid-body displacements between parallel crystals

    International Nuclear Information System (INIS)

    A new method for the rapid generation of high resolution bicrystal LACBED images is described, which uses reciprocity to generate the second-crystal transmission function for a specific doubly-transmitted beam. As a result, sets of bright-field or specific dark-field LACBED images can readily be generated for sets inter-crystal displacements, to allow comparison with experimental results. In Part I we describe results obtained for pure translations between bi-crystals pairs, while in Part II we describe the method for bi-crystals incorporating relative rotations as well as translations. It is envisaged that this technique will be useful for the body semi-conductor crystal pair interfaces, and metal-alloy grain boundaries, in particular. (authors). 16 refs., 6 figs

  20. X-ray characterization of a SrTiO3 bicrystal interface

    DEFF Research Database (Denmark)

    Kazimirov, A.; Zegenhagen, J.; Denk, I.; Maier, J.; Smilgies, D.-M.; Feidenhans'l, R.

    1996-01-01

    We studied a SrTiO3 bicrystal with X-ray diffraction. It was prepared by fusing two iron doped crystals, with 18.4 degrees miscut from the (001) direction along the [100] azimuth, at elevated pressure and temperature. This miscut corresponds to a (103) orientation of the interface and surface. One...... of the crystals has been polished to a thickness of 10 mu m to make the interface accessible to the synchrotron X-ray beams. Crystal truncation rod scattering was used to study the structure of the interface. Our results show a very narrow interface region with a thickness of about 11 Angstrom and a...

  1. Superconducting vortex dynamics on arrays with bicrystal-like structures: matching and rectifier effects

    International Nuclear Information System (INIS)

    Hybrid nanostructures of magnetic Ni dots embedded in superconducting Nb films have been fabricated. The dot arrays show bicrystal-like structures with an interface which separates two different dot arrangements in the same array. Vortex lattice dynamics is studied on these particular bi-arrays using magnetotransport measurements. Commensurability and rectifier (ratchet) effects have been observed. Matching between the vortex lattice and the pinning bi-array is only governed by the interplay between the densities of vortices and pinning centers. In bi-arrays with dissimilar pinning densities, for vortex flow parallel to the boundary, the highest pinning center density governs the matching effects. Hybrid samples with only half of the array with asymmetric potentials show a ratchet effect; that is input ac currents yield a net flow of vortices. (paper)

  2. Flux-line pinning by the grain boundary in niobium bicrystals

    International Nuclear Information System (INIS)

    Flux-line pinning by the grain boundary in niobium bicrystals was investigated by making four-terminal measurements of the critical current and neutron diffraction measurements of the flux-line bending. The elementary pinning interaction is estimated from the critical current data by using an approximate theory of the current distribution on the grain boundary. The data reported here are mainly for a sample in which the applied magnetic field is parallel to the [111] and the [001] crystal directions in the two grains when it is in the plane of the boundary and perpendicular to the current direction. Evidence is seen of grain boundary faceting and of a flux-flow rectification effect that peaks as a function of temperature below 30K. The scale of the grain-boundary pinning is consistent with the quasiparticle-scattering theory

  3. Properties of submicron [001] tilt symmetric and asymmetric 450 bicrystal grain boundary junctions

    International Nuclear Information System (INIS)

    We have fabricated submicron YBa2Cu3O7-x [001] tilt bicrystal grain boundary junctions by a focused ion beam process. The reduction of the junction width, leading to more homogeneous grain boundary interfaces, has been proved to be very important for the study of many fundamental properties of high critical temperature superconducting junctions. In particular, experiments on 450 symmetric junctions have shown a clear evidence of midgap states, with a 0- to π- junction transition in the case of small barrier transparency; moreover, in 450 asymmetric junctions we have observed a transition from an unconventional to a Fraunhofer-like magnetic field dependence of the critical current, sign of the reduced influence of faceting on the junction properties

  4. Mechanism and dynamics of shrinking island grains in mazed bicrystal thin films of Au

    International Nuclear Information System (INIS)

    This work investigates the mechanism and dynamics of grain boundary migration driven by capillary forces via in situ electron microscopy, complemented by molecular-dynamics simulations. Using thin films of Au with the mazed bicrystal geometry, the shrinkage of island grains with 90°〈1 1 0〉 tilt grain boundaries was observed by diffraction contrast and high-resolution imaging. The grains remained cylindrical throughout the shrinkage, and there was no measurable grain rotation even at very small sizes. The rate of shrinkage was found to be erratic and inconsistent with parabolic kinetics, accelerating before complete disappearance. Residual defects were found immediately after complete shrinkage, although the type and magnitude of the defects varied from grain to grain. Measurement of the grain boundary shape anisotropy showed a preference for facets on low-index planes of the crystals, including the mirror-symmetry planes of the bicrystal. These facets were also found directly on individual images extracted from high-resolution video recordings of shrinking grains at ∼300 °C. The dynamics of boundary motion were found to be limited by nucleation and propagation of steps on these facets. The cylindrical geometry and size of the experimentally observed island grains allow direct comparison with molecular-dynamics simulations on the same length scale, which reproduced many of the experimentally observed features, including non-parabolic shrinkage, absence of systematic grain rotation, step-controlled migration and dislocation debris after complete grain shrinkage. Differences between model and experiment are discussed in terms of the possible role of impurities, surfaces and interfacial steps.

  5. Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

    Indian Academy of Sciences (India)

    Neeraj Khare; A K Gupta; U P Moharil; A K Raychaudhuri; S P Pai; R Pinto

    2002-05-01

    La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a $36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature > 175 K. At low temperature, - characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance–voltage characteristics of the bicrystal grain boundary indicates that at low temperatures ( < 175$ K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures ( > 175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.

  6. Grain boundary structure and solute segregation in titanium-doped sapphire bicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Seth T.

    2002-05-17

    Solute segregation to ceramic grain boundaries governs material processing and microstructure evolution, and can strongly influence material properties critical to engineering performance. Understanding the evolution and implications of grain boundary chemistry is a vital component in the greater effort to engineer ceramics with controlled microstructures. This study examines solute segregation to engineered grain boundaries in titanium-doped sapphire (Al2O3) bicrystals, and explores relationships between grain boundary structure and chemistry at the nanometer scale using spectroscopic and imaging techniques in the transmission electron microscope (TEM). Results demonstrate dramatic changes in solute segregation stemming from small fluctuations in grain boundary plane and structure. Titanium and silicon solute species exhibit strong tendencies to segregate to non-basal and basal grain boundary planes, respectively. Evidence suggests that grain boundary faceting occurs in low-angle twis t boundaries to accommodate nonequilibrium solute segregation related to slow specimen cooling rates, while faceting of tilt grain boundaries often occurs to expose special planes of the coincidence site lattice (CSL). Moreover, quantitative analysis of grain boundary chemistry indicates preferential segregation of charged defects to grain boundary dislocations. These results offer direct proof that static dislocations in ionic materials can assume a net charge, and emphasize the importance of interactions between charged point, line, and planar defects in ionic materials. Efforts to understand grain boundary chemistry in terms of space charge theory, elastic misfit and nonequilibrium segregation are discussed for the Al2O3 system.

  7. Experimental study of noise and Josephson oscillation linewidths in bicrystal YBCO junctions

    DEFF Research Database (Denmark)

    Constatinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.;

    2001-01-01

    which may take place in the d-wave superconducting junctions. Experimental results on noise performance are also compared with the qualitatively similar dependences of the current noise, known for the s-superconducting ballistic point-like or diffusive-type SNS junctions, where the excess low......The intensities of the noise in a bicrystal high-T-c (HTS) Josephson junction have been precision-measured at 1-2 GHz frequency band at bias voltages up to 50 mV at T = 4.2 K. At large bias voltages, V > 30 mV, the dependence of current noise density was found exactly coinciding with the Schottky...... shot noise asymptote 2eI. At relatively low voltages, V <4 mV, a noticeable noise rise has been registered. The broadening of Josephson oscillation linewidths fJ over the values Deltaf(RSJ) predicted by the RSJ model has been experimentally studied at different frequencies in the nim and submm wave...

  8. Submicron YBa2Cu3O7-x bicrystal grain boundary junctions by focused ion beam

    International Nuclear Information System (INIS)

    Submicron YBa2Cu3O7-x bicrystal grain boundary junctions have been fabricated, for the first time, by a focused ion beam process. Although such a process has always been considered detrimental to the YBa2Cu3O7-x because of gallium contamination, high quality 24 deg. [001] tilt junctions characterized by RSJ current-voltage characteristics, ICRN products of the order of 1-4 x 104 A cm-2 at 77 K and Fraunhofer-like modulation patterns have been obtained. No significant degradation has been observed over more than 3 months. The critical current density JC and the characteristic voltage ICRN show a clear maximum for widths of the order of the Josephson penetration depth. The asymptotic normal resistance shows a typical (width)-1 dependence, indicating that the FIB process does not increase the grain boundary resistivity of submicron junctions. Experimental results clearly show that FIB is a very powerful tool for the fabrication of high critical temperature superconducting circuits, requiring a small number of submicron Josephson junctions, and for fundamental physics analysis. It also allow the final tuning or repair of superconducting or more complex integrated superconducting-semiconducting devices

  9. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

    Science.gov (United States)

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

    2016-01-01

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis. PMID:27255415

  10. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface.

    Science.gov (United States)

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K Y; Klie, Robert F; Kim, Moon J

    2016-01-01

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1-10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis. PMID:27255415

  11. Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

    Science.gov (United States)

    Sun, Ce; Paulauskas, Tadas; Sen, Fatih G.; Lian, Guoda; Wang, Jinguo; Buurma, Christopher; Chan, Maria K. Y.; Klie, Robert F.; Kim, Moon J.

    2016-06-01

    Extended defects are of considerable importance in determining the electronic properties of semiconductors, especially in photovoltaics (PVs), due to their effects on electron-hole recombination. We employ model systems to study the effects of dislocations in CdTe by constructing grain boundaries using wafer bonding. Atomic-resolution scanning transmission electron microscopy (STEM) of a [1–10]/(110) 4.8° tilt grain boundary reveals that the interface is composed of three distinct types of Lomer dislocations. Geometrical phase analysis is used to map strain fields, while STEM and density functional theory (DFT) modeling determine the atomic structure at the interface. The electronic structure of the dislocation cores calculated using DFT shows significant mid-gap states and different charge-channeling tendencies. Cl-doping is shown to reduce the midgap states, while maintaining the charge separation effects. This report offers novel avenues for exploring grain boundary effects in CdTe-based solar cells by fabricating controlled bicrystal interfaces and systematic atomic-scale analysis.

  12. Electromagnetic characterization of YBa2Cu3O7-δ thin films with calcium doping for bi-crystal grain boundary conductivity enhancement

    International Nuclear Information System (INIS)

    The objective of this study was to examine the transport properties of two YBa2Cu3O7-δ thin films with (Y0.9Ca0.1)2BaCuO5 additions deposited on vicinal SrTiO3 60 bi-crystal substrates and to investigate the possible correlations between spatial calcium distribution and local electromagnetic properties across bi-crystal grain boundaries using evanescent microwave microscopy (EMM) and atomic force microscopy (AFM). The samples under consideration differed in transport critical current measurements by a factor of two although they were deposited on the same type of bi-crystal substrate. A near-field evanescent microwave microscope based on a coaxial transmission line resonator with an end-wall aperture was used to measure changes in conductivity local to the bi-crystal boundary of YBa2Cu3O7-δ thin films below (79.2 K) and above (room temperature) the superconducting transition temperature. Atomic concentration measurements by electron microprobe analysis were performed in the same regions, and a clear correlation between calcium distribution and conductivity at 79.2 K (as represented by the change in quality factor) was found. Surface potential imaging (SPI) and quality factor scans in the area of the bi-crystal grain boundaries were performed at room temperature using AFM and EMM, respectively, to evaluate local electromagnetic properties in the normal state and investigate their correlation with superconducting properties

  13. Grain boundary character dependence of oxygen grain boundary diffusion in α-Al2O3 bicrystals

    International Nuclear Information System (INIS)

    We measured oxygen diffusion coefficients (Dgb) along five grain boundaries (GBs) in alumina bicrystals by tracing 18O by secondary ion mass spectrometry. Although all boundaries are classified as coincident site lattice boundaries with relatively ordered structures, Dgb varied up to 103 times among them. On the other hand, the boundaries with identical boundary planes had relatively similar diffusivities as well as similar structures, regardless of Σ values. These results suggest that Dgb are related to GB atomic structures and hence the GB character, especially GB planes.

  14. Study of the grain boundary of stainless steel bicrystals, by creep tests and by transmission electron microscopy observations

    International Nuclear Information System (INIS)

    Symmetric tilt bicrystals of stainless steel 17 per cent Cr - 13 per cent Ni, have been grown. Misorientation is 10-30-40-50-53-60-70 deg. around the tilt axis [001]. We study the deformation of these bicrystals by creep tests under high temperature (900-1200 deg. C) and low stresses (50-350 g/mm2). Sliding of several dozen microns occurs after a few hours along the grain boundary. The creep/time curves have a parabolic shape; sliding is thermally activated, the activation energy being of the order of 30 kcal/mole; the influence of misorientation is important for low angles and for twin positions such as (012). For this reason, the structure of the grain boundary is studied before creep, by T.E.M. observations. These observations show a network of intergranular dislocations, which appear in the form of zig-zag lines parallel to [001] common axis. The Burgers' vector of these dislocations is of the a/2 type. They are due to the non coincidence of the [001] axes of the two crystals. A theoretical model, based on Bollmann's theory, explains the different observations and gives for an eventual creep theory, a description of high angle grain boundary in terms of dislocations. (author)

  15. Effect of twin boundary on nanoimprint process of bicrystal Al thin film studied by molecular dynamics simulation

    Institute of Scientific and Technical Information of China (English)

    谢月红; 徐建刚; 宋海洋; 张云光

    2015-01-01

    The effects of twin boundary (TB) on the mechanical properties of two types of bicrystal Al thin films during the nanoimprint process are investigated by using molecular dynamics simulations. The results indicate that for the TB direction parallel to the imprinting direction, the yield stress reaches the maximum for the initial dislocation nucleation when the mould directly imprints to the TB, and the yield stress first decreases with the increase of the marker interval and then increases. However, for the TB direction perpendicular to the imprinting direction, the effect of the TB location to the imprinting forces is very small, and the yield stress is greater than that with the TB direction parallel to the imprinting direction. The results also demonstrate that the direction of the slip dislocations and the deformation of the thin film caused by spring-back are different due to various positions and directions of the TB.

  16. Critical current density behaviors across a grain boundary inclined to current with different angles in YBa2Cu3O7‑δ bicrystal junctions

    Science.gov (United States)

    Tao, Hua; Wei-Wei, Xu; Zheng-Ming, Ji; Da-Yuan, Guo; Qing-Yun, Wang; Xiang-Rong, Ma; Rui-Yu, Liang

    2016-06-01

    The critical current density behaviors across a bicrystal grain boundary (GB) inclined to the current direction with different angles in YBa2Cu3O7‑δ bicrystal junctions in magnetic fields are investigated. There are two main reasons for the difference in critical current density in junctions at different GB inclined angles in the same magnetic field: (i) the GB plane area determines the current carrying cross section; (ii) the vortex motion dynamics at the GB affects the critical current value when the vortex starts to move along the GB by Lorentz force. Furthermore, the vortex motion in a bicrystal GB is studied by investigating transverse (Hall) and longitudinal current–voltage characteristics (I–V xx and I–V xy ). It is found that the I–V xx curve diverges from linearity at a high driving current, while the I–V xy curve keeps nearly linear, which indicates the vortices inside the GB break out of the GB by Lorentz force. Project supported by the National Natural Science Foundation of China (Grant Nos. 61501222, 61371036, and 61571219) and the School Scientific Research Fund of Nanjing Institute of Technology, China (Grant Nos. YKJ201418).

  17. Study of deformation mechanisms of zinc bicrystals by thermal cycling (1963); Etude des mecanismes de deformation par cyclage thermique de bicristaux de zinc (1963)

    Energy Technology Data Exchange (ETDEWEB)

    Mondon, J. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

    1963-06-15

    The thermal cycling of zinc bicrystals has been studied in order to precise the thermal cycling growth mechanism, proposed by Burke and TURKALO, specially the dependence of 'equi-cohesive' temperature of grains on their mutual orientation and the parameters of the thermal cycle. Dilatometric studies showed that a bicrystal had no equi-cohesive temperature and that the grain-boundary develops stress at all temperatures. The creep of single and bicrystal have been studied on a dilatometer with stress below the Yield-stress. At constant temperature secondary creep appears after a transient period, at cycled temperature creep stays transient for strains of about 10{sup -4} to 10{sup -3} when the crystal is plastically hard. Micrographic investigations show that grain-boundary migration accompanies the grain boundary shearing and that cycles produce a strong polygonisation, corroborating the fact that the grain boundary remains a stress-generator and that creep occurs in the volume of grains. The discussion of results shows that the transient creep of hard grain in a bicrystal makes the thermal cycling irreversible and allows on elongation at each cycle if that have the lower expansion coefficient. (author) [French] Le cyclage thermique de bicristaux de zinc a ete etudie pour preciser le mecanisme de la croissance au cyclage thermique propose par BURKE et TURKALO, notamment la temperature d' 'equicohesion' des grains en fonction de leur orientation mutuelle et du regime de cyclage impose. Des essais dilatometriques ont montre qu'un bicristal ne presentait pas de temperature d'equicohesion et que le joint exercait des contraintes quelle que soit la temperature superieure du cycle. Le fluage de monocristaux et de bicristaux a ete etudie sur un dilatometre avec des contraintes inferieures a la limite elastique. A temperature constante le fluage secondaire apparait apres une periode transitoire, a temperature cyclee le fluage reste

  18. Explanation of low critical currents in flat, bulk versus meandering, thin-film [001] tilt bicrystal grain boundaries in YBa2Cu3O7

    International Nuclear Information System (INIS)

    Thin-film and bulk [001] tilt, bicrystal grain boundaries in YBa2Cu3O7 exhibit a strong dependence of critical current density on misorientation angle. What is particularly difficult to understand is its thirty times lower magnitude in bulk grain boundaries which are microscopically more perfect, i.e., flatter, minimally faceted, and free of impurity phases. A plausible explanation, based on differences of the pinning of Josephson vortices in these grain boundary types, is proposed here. copyright 1998 The American Physical Society

  19. Large Tc depression at low angle [100] tilt grain boundaries in bulk Bi2Sr2CaCu2O8+δ bicrystals

    International Nuclear Information System (INIS)

    Large depression of Tc at 7 degree [100] tilt grain boundaries was observed in bulk Bi2Sr2CaCu2O8+δ (Bi2212) bicrystals by measuring the zero-field electrical transport properties of the grain boundaries and the constituent single crystals over an extended range of currents and voltages. The Tc-depressed region was determined to be around 20 nm, comparable to the width of the strain field associated with the observed array of grain-boundary dislocations. Superconducting coupling of the grain boundaries increases sharply as temperature decreases below the grain-boundary Tc congruent 68 K. copyright 1997 American Institute of Physics

  20. Molecular dynamics study on the atomic mechanisms of coupling motion of [0 0 1] symmetric tilt grain boundaries in copper bicrystal

    International Nuclear Information System (INIS)

    Recent research has revealed that some grain boundaries (GBs) can migrate coupled to applied shear stress. In this paper, molecular dynamics (MD) simulations were performed on sixteen [0 0 1] symmetric tilt GBs of bicrystal Cu to identify atomic-scale GB migration mechanisms and investigate their dependence on GB structure. The misorientation angles (θ) of the sixteen GBs cover the interval from 0° to 90° and a wide range of Σ values. A general method was proposed to explore the possible GB structures for each misorientation angle. Molecular statics simulation at a temperature of 0 K was carried out first to determine the equilibrium and some possible metastable structures of the sixteen investigated [0 0 1] GBs. MD simulations were then conducted on the bicrystal models at equilibrium by applying a shear strain parallel to the GB plane. Shear deformation caused the tangential translation of the grain and induced normal motion of the GBs. This boundary coupling motion was present in the entire range of misorientation angles. Different mechanisms of coupled boundary motion at atomic scale were carefully examined in this work. The common feature of these mechanisms can be regarded as the displacement of local atoms and rotation of certain structure unit. Structure phase transformation of GB was found during the migration of Σ17 (4 1 0) and Σ73 (8 3 0) GBs. (papers)

  1. Magneto-optical study of flux penetration and critical current densities in [001] tilt YBa2Cu3O7-δ thin-film bicrystals

    International Nuclear Information System (INIS)

    Magneto-optical (MO) imaging has been used to visualize and calculate magnetic flux and current distributions at temperatures T ranging from 7 to 80 K in thin-film [001] tilt YBa2Cu3O7-δ bicrystals with misorientation angles 3 degree ≤θ≤10 degree. A characteristic cusp in the flux distribution Bz(x,y) was observed for 5 degree ≤θ≤7 degree, which is shown to indicate that the critical current density Jb across the boundary is smaller than the intragrain Jc. We use the Bean model for thin-film superconductors to calculate the observed features of the Bz(x,y) distribution and to separate both the intragrain Jc and intergrain Jb(θ) independently from the MO data. The study of angular and temperature dependencies of Jb(T,θ) in bicrystals with different θ shows that Jb(θ) strongly decreases with θ above θ≅5 degree. The decrease of Jb(T,θ) with temperature becomes weaker as the misorientation angle θ is increased, so the substantial difference in Jb for 5 degree and 7 degree boundaries at low T turns out to be less pronounced at liquid-nitrogen temperatures. In addition, the ratio Jb(θ,T)/Jc(T) for low-angle grain boundaries is shown to exhibit an anomalous increase with T, thus indicating that the grain boundaries can provide additional flux pinning. This is plausibly associated with the grain boundary dislocations that accommodate the misorientation of the grains. copyright 1996 The American Physical Society

  2. Characterization of three-dimensional grain boundary topography in a YBa2Cu3O7-d thin film bicrystal grown on a SrTiO3 substrate

    International Nuclear Information System (INIS)

    The topography and crystallography of YBa2Cu3O7-d (YBCO) bicrystal films grown epitaxially on oriented SrTiO3 (STO) bicrystals have been characterized by scanning and transmission electron microscopies (SEM and TEM) and atomic force microscopy (AFM). The YBCO films were formed by laser ablation on melt-grown Σ13 STO bicrystals with a misorientation of 24 degree around the left-angle 001 right-angle tilt axis. In agreement with previous reports, TEM analysis revealed that the grain boundary in the film did not always follow the planar substrate grain boundary faithfully, but undulated about the average boundary plane. High resolution electron microscopy observations of the apparently complex undulating boundary structures could be explained as a result of an overlap between different orientation variants of the orthorhombic YBCO film. Cross correlation between SEM, AFM, and TEM imaging gave a clear evidence that an island growth mechanism is responsible for the observed grain boundary structure and morphology for which a schematic model is presented. It is seen that meandering of the YBCO grain boundary (GB) is necessarily coupled to a wide range of inclination of the GB plane in the z direction. The implications of this interfacial structure for the behavior of GB based Josephson junctions are discussed and compared to models proposed in the literature. It is also seen that inclination of the GB may be responsible for the poor correlation usually found in the literature between calculations and experimental curves of current density Jc versus the GB angle since the most elaborate models proposed up to now take into account only pure tilt GB plane facets, that is to say facets in the zone of the tilt axis. Moreover, such a GB structure may affect the interpretation of recent phase sensitive experiments done on bicrystal or tricrystal high Tc superconductors to determine the symmetry of the order parameter. copyright 1998 American Institute of Physics

  3. 硅双晶结高温超导直流量子干涉器件%High Tc DC-SQUIDs with silicon bicrystal junctions

    Institute of Scientific and Technical Information of China (English)

    漆汉宏; 魏艳君; 王天生; 田永君

    2001-01-01

    The preparation and properties of high-Tc YBCO DC-SQUIDs on silicon bicrystal substrate are studied.YSZ and CeO2 buffer layers,YBCO superconducting thin film and non-superconducting YBCO passivation layer are in-situ deposited on substrate by pulsed laser deposition technique. The critical temperature of the superconducting film is about 88?K. The prepared bicrystal junction using laser technique is of the typical RSJ-like characteristics with its IcRN products of 150?μV at 77 K and Fraunhofer-diffraction-like Ic(H) characteristics. The realized DC-SQUIDs have the voltage-flux transfer function of 4.835?938?GV/Wb and noise of 136.478 16 zWb/Hz1/2 at white noise region and 299.838?39?zWb/Hz1/2 at 1?Hz respectively.%研究了在硅双晶基片上制备高临界温度(Tc),YBa2Cu3O7 (YBCO)直流量子干涉器件(DC-SQUID)工艺及其特性。采用脉冲激光沉积技术在Si (100)双晶基片上原位制备钇稳定氧化锆(YSZ)、CeO2隔离层、YBCO超导薄膜及非超导YBCO钝化层,超导薄膜临界温度为88?K。采用激光技术直接成型的硅双晶结符合典型电阻分路结RSJ模型,其IcRN 值在77?K下可达到150?μV,具有Fraunhofer衍射状的Ic(H)特性。所实现的DC-SQUID器件电压-磁通传输函数达4.835?938?GV/Wb,白噪声区及1?Hz下的噪声水平达136.478?16?zWb/Hz1/2和299.838?39?zWb/Hz1/2。

  4. Inductive measurement of in-field critical current density of YBCO thin film on a SrTiO3 bicrystal substrate using the third harmonic voltage method

    International Nuclear Information System (INIS)

    The spatial distribution and the magnetic field dependence of the critical current density Jc for a YBa2Cu3Oy (YBCO) thin film deposited on a SrTiO3 (STO) bicrystal substrate have been investigated using the third harmonic voltage method. When a pick-up coil is mounted on the area without a crystal grain-boundary, the third harmonic voltage V3 increases monotonically with increasing coil current I0 over a certain threshold value. On the other hand, when the pick-up coil is mounted on the area with a crystal grain-boundary, the V3–I0 curve shows a strange behavior. However, the V3–I0 curves show a monotonic increase when a magnetic field over 0.07 T is applied to the YBCO thin film, because the shielding current hardly flows across the crystal grain-boundary in the large magnetic field. The magnetic field dependence of Jc is also measured using the four-probe method to clarify the strange behavior of the V3–I0 curve in the third harmonic voltage method.

  5. Optimization of electrical and structural parameters of YBa2Cu3O7−x thin-film bicrystal Josephson junctions with chemical and thermal treatments of substrates

    International Nuclear Information System (INIS)

    The [100]-tilt high-Tc Josephson junctions are characterized by high characteristic voltages IcRn but their current range is limited by low critical currents Icf of the thin-film electrodes with tilted c-axes. The impact of chemical and thermal treatments of NdGaO3 substrates on morphology and IV curves of the YBa2Cu3O7−x thin films and the bicrystal thin-film junctions have been studied. It was found that IV curves of the films above a critical current Icf are described by a power-law dependence V = V0(I/Icf – 1)n, where Icf, V0 and n are dependent on the c-axis tilt of the film and treatment of the substrate. Critical current densities jc(78 K) up to 1.4107 A/cm2 have been reached in 1.7°-tilt YBa2Cu3O7−x films perpendicular to the tilt. Bicrystal junctions have been fabricated with optimized YBa2Cu3O7−x thin films, and RSJ-like IV-curves in the current ranges from Ic up to 5 Ic with IcRn (78 K)-values of 1 mV have been achieved.

  6. Electric characterization of grain boundaries in ionic conductors by impedance spectroscopy measurements in a bicrystal; Caracterizacion electrica de fronteras de grano en conductores ionicos mediante medidas de espectroscopia de impedancias en un bicristal

    Energy Technology Data Exchange (ETDEWEB)

    Frechero, M. A.; Rocci Riner Schmidt, M.; Diaz-Guillen, M.; Doaz-Guillen, M. R.; Dura, O.; Rivera-Calzada, A.; Santamaria, J.; Leon, C.

    2012-07-01

    Here we show impedance spectroscopy measurements on a bicrystal of the ionically conducting Yttria stabilized zirconia (YSZ). By using micrometer sized electrodes it is possible to measure ionic transport perpendicular to a single grain boundary, and characterize its electrical properties. We are thus able to obtain the microscopic parameters that determine the charge distribution at the grain boundary and the ionic transport through it, as the potential energy barrier {delta}{phi} = 0.35{+-}0.01 V at 275 degree centigrade, and the space charge layer thickness {lambda} = 5{+-}1 A. These values are significantly different from those previously obtained in polycrystalline ceramic samples of the same material, and show much better agreement with the values predicted by the Mott-Schottky model for the charge distribution and ionic transport through the grain boundary. (Author) 31 refs.

  7. Low voltage excess noise and shot noise in YBCO bicrystal junctions

    DEFF Research Database (Denmark)

    Constantinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.; Mygind, Jesper; Pedersen, Niels Falsig

    registered. At large bias voltages V > 30 mV a clear dependence of noise power. exactly coinciding to the asymptote of the Schottky shot noise function, has been observed for the first time. Experimental results are discussed in terms of multiple Andreev reflections which may take place in d...

  8. INFLUENCE OF HYDROGEN ON THE INTERFACE STRUCTURE AND PROPERTIES OF FATIGUED Al-Zn-Mg-BICRYSTALS

    OpenAIRE

    Wunderlich, W.; Niegel, A.; Gudladt, H.

    1990-01-01

    Hydrogen enrichment at grain boundaries has a strong influence on the mechanical properties of Al-Zn-Mg-alloys. Under moisture crack propagation in fatigue experiments is accelerated drastically. If hydrogen is enriched at the grain boundary region, local embrittlement of the grain boundary takes place leading to intergranular crack initiation and propagation. As can be seen by HREM-micrographs the hydrogen affected precipitates have planar and facetted interfaces, while the as recieved speci...

  9. Experimental study of noise and Josephson oscillation linewidths in bicrystal YBCO junctions

    DEFF Research Database (Denmark)

    Constatinian, K.Y.; Ovsyannikov, G.A.; Borisenko, I.V.; Pogosyan, N.G.; Hakuhoumian, A.A.; Yagoubov, P.; Mygind, J.; Pedersen, Niels Falsig

    range up to voltages V = 2 mV in connection with low-voltage noise rise. Both the features observed, the linewidth broadening and the excess noise over the noise level of thermal fluctuations, are discussed in terms of multiple Andreev reflection, giving rise to a nonequilibrium shot noise-the case...... which may take place in the d-wave superconducting junctions. Experimental results on noise performance are also compared with the qualitatively similar dependences of the current noise, known for the s-superconducting ballistic point-like or diffusive-type SNS junctions, where the excess low......-voltage noise is manifested due to multiple Andreev reflections. Increasing the operating temperature, the thermal (equilibrium) fluctuations were found to predominate, resulting in a decrease of ratio Deltaf(J)/Deltaf(RSJ). The characteristics of the ac Josephson effect in FITS junctions measured at submm...

  10. The effect of surface contact conditions on grain boundary interdiffusion in a semi-infinite bicrystal

    Czech Academy of Sciences Publication Activity Database

    Svoboda, Jiří; Fischer, F. D.; Klinger, L.; Rabkin, E.

    2014-01-01

    Roč. 94, č. 30 (2014), s. 3398-3412. ISSN 1478-6435 Institutional support: RVO:68081723 Keywords : grain boundary diffusion * liquid metals * stress analysis * interfacial thermodynamics Subject RIV: BJ - Thermodynamics Impact factor: 1.825, year: 2014

  11. Observation of distinct, temperature dependent flux noise near bicrystal grain boundaries in YBa2Cu3O7-x films

    DEFF Research Database (Denmark)

    Bukh, K. R.; Jacobsen, Claus Schelde; Hansen, Jørn Bindslev; Shen, Y. Q.; Holst, T.

    The characteristics of the magnetic flux noise in high temperature superconducting thin-films of yttrium-barium-copper-oxide (YBa2Cu3O7) in the vicinity of artificial grain boundaries have been studied by means of a low critical temperature superconducting quantum interference device (SQUID...

  12. Comparison of effective noise temperatures in YBa2BCu3O7-δ junctions

    DEFF Research Database (Denmark)

    Fischer, Gerd Michael; Mygind, Jesper; Pedersen, Niels Falsig

    1997-01-01

    The dc voltage response to 70 GHz radiation was measured for YBCO bicrystal junctions, step edge junctions and ramp edge junctions at temperatures from 4 K to 90 K. Employing the RSJ-model and assuming thermal noise, the Josephson radiation is about equal to the voltage difference of the voltage...... response to the small signal microwave irradiation. In the presence of excess noise, an effective noise temperature can be defined and is used as a figure of merit. In bicrystal grain boundary junctions with zero magnetic field the effective noise temperature was determined to be equal to the physical...... temperature within experimental error. Bicrystal grain boundary junctions with non-zero magnetic field, step edge junctions and ramp edge junctions showed excess noise. The scaling of the noise temperature is compared with the width of the junction in units of the Josephson penetration depth...

  13. Characteristics of Off-Chip Millimeter-Wave Radiation from Serial Josephson Junction Arrays

    Institute of Scientific and Technical Information of China (English)

    WANG Zheng; FAN Bin; ZHAO Xin-Jie; YUE Hong-Wei; HE Ming; JI Lu; YAN Shao-Lin; FANG Lan; Klushin A. M.

    2011-01-01

    @@ We investigate the self-emissions from serial high-temperature superconductor bicrystal Josephson junction ar- rays embedded in a quasi-optical resonator.A bicrystal substrate is used as a dielectric resonator antenna, which increases the coupling strength between the junction array and the electromagnetic (EM) wave.Both three-dimension (3D) electromagnetic simulations and experiments are performed.Strong ofT-chip radiations axe measured from the junction array at 78 GHz and 78 K.The proposed method and the experimental results are important for millimeter wave applications in junction arrays.

  14. Fraunhofer regime of operation for superconducting quantum interference filters

    DEFF Research Database (Denmark)

    Shadrin, A.V.; Constantinian, K.Y.; Ovsyannikov, G.A.;

    2008-01-01

    Series arrays of superconducting quantum interference devices (SQUIDs) with incommensurate loop areas, so-called superconducting quantum interference filters (SQIFs), are investigated in the kilohertz and the gigahertz frequency range. In SQIFs made of high-T-c bicrystal junctions the flux...

  15. Anisotropy of grain boundary migration observed in situ by synchrotron radiation

    Czech Academy of Sciences Publication Activity Database

    Paidar, Václav; Lejček, Pavel; Polcarová, Milena; Brádler, Jaroslav; Jacques, A.

    467-470, - (2004), s. 911-916. ISSN 0255-5476 R&D Projects: GA ČR GA202/02/0916 Institutional research plan: CEZ:AV0Z1010914 Keywords : bicrystals * grain boundary motion * synchrotron radiation * X-ray topography Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.498, year: 2004

  16. HTS dc SQUID based rf amplifier: development concept

    DEFF Research Database (Denmark)

    Prokopenko, G.V.; Shitov, S.V.; Borisenko, I.V.; Mygind, Jesper

    We present a concept of a rf amplifier based on a directly coupled dc SQUID with bicrystal junctions, which have high saturation power and can be used with SIS mixers or possibly for satellite and cellular phone communications. A novel input resonant circuit is proposed using single layer of HTS...

  17. Sozdanije ob'emnych p-n perechodov v poluprovodnikovych bikristallach metodom tverdofaznogo sraščivanija

    Czech Academy of Sciences Publication Activity Database

    Lomov, A. A.; Stepancov, A. E.; Kacerovský, Pavel

    Moskva : Institut kristallografii imeni A. V. Šubnikova Rossijskoj Akademii Nauk, 2004. s. 154. [Nacional'naja konferencija po rostu kristallov NKRK -2004 /11./. 14.12.2004-17.12.2004, Moskva] R&D Projects: GA AV ČR(CZ) KSK1010104 Keywords : bicrystals * p-n junctions * X-ray diffraction Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  18. HTS dc SQUID based rf amplifier: development concept

    DEFF Research Database (Denmark)

    Prokopenko, G.V.; Shitov, S.V.; Borisenko, I.V.;

    2002-01-01

    We present a concept of a rf amplifier based on a directly coupled dc SQUID with bicrystal junctions, which have high saturation power and can be used with SIS mixers or possibly for satellite and cellular phone communications. A novel input resonant circuit is proposed using single layer of HTS...

  19. Growth of metallic crystals by floating zone technique with optical heating

    Czech Academy of Sciences Publication Activity Database

    Lejček, Pavel; Kopeček, Jaromír

    567-568, - (2007), s. 277-280. ISSN 0255-5476 R&D Projects: GA AV ČR IAA1010414 Institutional research plan: CEZ:AV0Z10100520 Keywords : single crystals * bicrystals * tricrystals * melt growth * optical floating zone * metals Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.399, year: 2005

  20. Grain-boundary melting: A Monte Carlo study

    DEFF Research Database (Denmark)

    Besold, Gerhard; Mouritsen, Ole G.

    1994-01-01

    Grain-boundary melting in a lattice-gas model of a bicrystal is studied by Monte Carlo simulation using the grand canonical ensemble. Well below the bulk melting temperature T(m), a disordered liquidlike layer gradually emerges at the grain boundary. Complete interfacial wetting can be observed...

  1. Grain dependent electrochemical investigations on pure iron in acetate buffer pH 6.0

    International Nuclear Information System (INIS)

    The influence of grain orientation on the electrochemical behaviour of iron in acetate buffer pH 6.0 was analyzed using a capillary microcell. Cyclic voltammetry and simultaneous capacity measurements were performed on the two crystal faces of an iron (1 0 0)/(1 1 1) bi-crystal, on the grain boundary between these two orientations and on several single grains of a coarse grain iron sample. The combination with electron back scattered diffraction (EBSD) yields the surface orientation of the analyzed grains and makes it possible to perform orientation dependent experiments on the polycrystalline metal. Clear differences in the electrochemical behaviour, e.g. in corrosion tendency and oxide formation rate were found between the orientations (1 0 0) and (1 1 1) of the iron bi-crystal and between several grain orientations of the polycrystalline sample

  2. First principles modeling of grain boundaries in CdTe

    Science.gov (United States)

    Chan, Maria K. Y.; Sen, Fatih; Buurma, Christopher; Paulauskas, Tadas; Sun, Ce; Kim, Moon; Klie, Robert

    The role of extended defects is of significant interest for semiconductors, especially photovoltaics since energy conversion efficiencies are often affected by such defects. In particular, grain boundaries in CdTe photovoltaics are enigmatic since the achievable efficiencies of CdTe photovoltaics are higher in polycrystalline devices as compared to single crystalline devices. Yet, despite recent advances, the efficiency of poly-CdTe devices are still substantially below the theoretical maximum. We carry out an atomistic-level study using Scanning Transmission Electron Microscopy (STEM), together with first principles density functional theory (DFT) modeling, in order to understand the properties of specific bicrystals, i.e. artificial grain boundaries, constructed using wafer bonding. We discuss examples of bicrystals, including some involving large scale DFT calculations, and trends in defect and electronic properties. This work was funded by DOE SunShot BRIDGE program.

  3. A class of high-Tc Y Ba2Cu3O7-x grain boundary junctions with high-IcRn products

    International Nuclear Information System (INIS)

    The properties of symmetric 240 and asymmetric 45 deg. [100] tilt Y Ba2Cu3O7-x bicrystal grain boundary junctions (GBJs) have been extensively investigated. A large number of junctions, with dimensions ranging from 2 to 20 μm, have been fabricated and characterized at 4.2 K. Experimental data have been compared with [001] tilt bicrystal and [100] tilt biepitaxial Y Ba2Cu3O7-x junctions. [100] GBJs show high IcRn products in the range 5-10 mV at T = 4.2 K, these being slightly sensitive to the critical current density values. A direct tunnelling mechanism for both Cooper pair and quasiparticles has been evidenced. The reduced IcRn values of asymmetric 45 deg. with respect to symmetric 24 deg. [100] tilt GBJs have been accounted for by considering a d-wave symmetry of the order parameter using the Sigrist-Rice equation. (rapid communication)

  4. NANOSIZE EFFECT IN GRAIN BOUNDARY MIGRATION OF COPPER

    Institute of Scientific and Technical Information of China (English)

    L. Zhou; X.Q. Wei; N.G. Zhou; D.G. Li

    2004-01-01

    Molecular dynamics simulations of high temperature annealing of copper bicrystals have been carried out. The bicrystals have planar grain boundaries, and the gain size varies in nano range. An EAM (embedded atom method) potential of FS type is used for calculating the interatomic forces. The results show that in nanocrystalline copper, GB migration driven by inter-GB reaction can take place. A critical grain size is identified, below which the inter-GB reaction becomes strong enough to trigger GB motion, which accelerates rapidly and leads to annihilation of the grain boundaries. The critical size is found to be 16 atomic radii. A "through intermediate grain mechanism" is identified for the nano-grain boundary motion observed, which is never reported for GB migrations of conventional polycrystalline metals.

  5. The influence of vortex pinning and grain boundary structure on critical currents across grain boundaries in YBa2Cu3Ox

    International Nuclear Information System (INIS)

    We have used studies of single grain boundaries in YBCO thin films and bulk bicrystals to study the influence of vortex pinning along a grain boundary on dissipation. The critical current density for transport across grain boundaries in thin films is typically more than an order of magnitude larger than that measured for transport across grain boundaries in bulk samples. For low disorientation angles, the difference in critical current density within the grains that form the boundary can contribute to the substantial differences in current density measured across the boundary. However, substantial differences exist in the critical current density across boundaries in thin film compared to bulk bicrystals even in the higher angle regime in which grain boundary dissipation dominates. The differences in critical current density in this regime can be understood on the basis of vortex pinning along the boundary

  6. Shock-induced spall in copper: the effects of anisotropy, temperature, loading pulse and defect

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Shengnian [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory; An, Qi [Los Alamos National Laboratory; Han, Li - Bo [USTC

    2009-07-28

    Shock-induced spall in Cu is investigated with molecular dynamics simulations. We examine spallation in initially perfect crystals and defective solids with grain boundaries (columnar bicrystals), stacking faults or vacancies, as well as the effect of temperature and loading pulses. Spall in single crystal Cu is anisotropic, and defects and high temperature may reduce the spall strength. Taylor-wave (triangular shock-release wave) loading is explored in comparison with square wave shock loading.

  7. Influence of inductance induced noise in an YBa2Cu3O7 dc-SQUID at high operation temperatures

    DEFF Research Database (Denmark)

    Nilsson, P. Å.; Claeson, T.; Hansen, J. B.; Kyhle, Anders

    1994-01-01

    The voltage modulation depth of a high T(c) dc-SQUID was measured at temperatures close to T(c) and compared to a model by Enpuku et al. where the flux noise from the SQUID inductance is taken into account. The device was an YBa2Cu3O7 dc-SQUID made on a bicrystal substrate of SrTiO3. The design was...

  8. Extraordinary diffusion in Co/Cu grain boundaries

    International Nuclear Information System (INIS)

    Usually, Cu atoms hardly diffuse in Co because of the very low solid solubility limit. However, this letter shows by transmission electron microscopy that extraordinary diffusion of Cu in the Co phase occurred in Co/Cu bicrystal fabricated by diffusion joining and that many dislocations were found in the Co phase. First-principles calculations suggested that the extraordinary diffusion of Cu in Co is related to the movement of dislocations which Cu atoms adhere to

  9. Dynamics of pi-junction interferometer circuits

    DEFF Research Database (Denmark)

    Kornkev, V.K.; Mozhaev, P.B.; Borisenko, I.V.; Ovsyannikov, G.A.; Pedersen, Niels Falsig

    The pi-junction superconducting circuit dynamics was studied by means of numerical simulation technique. Parallel arrays consisting of Josephson junctions of both 0- and pi-type were studied as a model of high-T-c grain-boundary Josephson junction. The array dynamics and the critical current...... dependence on magnetic field are discussed. Experimental results for dc interferometers with 0 and pi high-T-c bi-crystal Josephson junctions are reported and discussed in comparison with numerical simulation....

  10. Study of twist boundaries in aluminium. Structure and intergranular diffusion

    International Nuclear Information System (INIS)

    This research thesis addresses the study of grain boundaries in oriented crystals, and more particularly the systematic calculation of intergranular structures and energies of twist boundaries of <001> axis in aluminium, the determination of intergranular diffusion coefficients of zinc in a set of twist bi-crystals of same axis encompassing a whole range of disorientations, and the search for a correlation between these experimental results and calculated structures

  11. In situ observation of grain boundary migration by synchrotron radiation topography

    International Nuclear Information System (INIS)

    The application of in situ synchrotron radiation (SR) transmission topography to the study of grain boundary migration in bicrystals of an Fe-6 at.%Si alloy is described. The details on experimental arrangement of the high-temperature in situ observations of dynamic processes in material are given. The pertinence of this method is documented by comparison of the data on migration of {130} grain boundary measured this way and by optical method after heating and cooling cycles

  12. Magnetic properties of bi-, tri- and multicrystals of 3D topological insulator Bi1−x–Sbx(0.06⩽x⩽0.2)

    International Nuclear Information System (INIS)

    The magnetic properties of bi-, tri- and multicrystals of 3D topological insulator Bi1−xSbx(0.06c for one superconducting phase changes considerably, from 8.3 to 36 K, while for another superconducting phase, Tc remains within the range 3.7–4.6 K. In tricrystals and bicrystals with high contents of structural disorder and topological defects, ferromagnetic hysteresis loops and magnetic field expulsion have been observed simultaneously.

  13. Non-uniform Stress Field and Stress Concentration Induced by Grain Boundary and Triple Junction of Tricrystal

    Institute of Scientific and Technical Information of China (English)

    Jiansong WAN; Zhufeng YUE

    2003-01-01

    The stress characteristics in the anisotropic bicrystal and tricrystal specimens were analyzed using the anisotropic elastic model, orthotropic Hill's model and rate-dependent crystallographic model. The finite element analysis results show that non-uniform stresses are induced by the grain boundary. For bicrystal specimens in different crystallographic orientations, there exist stress concentrations and high stress gradients nearby the boundaries. The activation and slipping of the slip systems are dependent on the crystallographic orientations of the grains and also on the relative crystallographic orientations of the two adjoining grains. For the tricrystal specimens, there is not always any stress concentrations in the triple junction, and the concentration degree depends on the relative crystallographic orientations of the three grains. Different from the bicrystal specimens, there may be or no stress concentration in the vicinity of grain boundaries for the tricrystal specimens, which depends on the relative crystallographic orientations of the three grains. The stress concentration near to the grain boundaries and triple junction can be high enough for the local plastic deformation, damage and voiding or cracking even when the whole specimen is still under the elastic state.It can be further concluded that homogeneous assumption for polycrystalline materials is not suitable to study the detailed meso- or micro-mechanisms for damaging and fracturing.

  14. The role of disconnections in deformation-coupled grain boundary migration

    International Nuclear Information System (INIS)

    Grain boundary (GB) migration under stress has been recognized in recent years as an important plastic deformation mechanism especially in small-grained materials. It is believed to occur via the motion of disconnections along the interface. However, the origin of these disconnections is a key point for a deeper understanding of this mechanism. In this paper, we consider that GB migration under stress can occur both due to the motion of pre-existing disconnections and due to disconnections resulting from decomposition of lattice dislocations interacting with the GB. High-resolution transmission electron microscopy experiments carried out on an aluminum bicrystal with a Σ41〈001〉{540} GB indeed confirm the existence of different kinds of disconnections and pure steps prior to deformation. In situ straining experiments performed in the same bicrystal at room and high temperatures reveal the rapid decomposition of lattice dislocations in the GB plane. Theoretical investigation of the possible decomposition reactions shows that different types of disconnections with Burgers vector having both glide and climb components, i.e. parallel and perpendicular to the GB plane, can be produced. Disconnections with a small climb component are likely to move along the GB under stress and induce deformation parallel and perpendicular to the GB plane. Concomitant motion of disconnections with Burgers vectors at right angles to the GB plane is believed to produce GB migration coupled with grain rotation. It is also shown that disconnection interactions in the GB lead preferentially to purely glissile disconnections producing a coupling factor in agreement with the observed coupling factor measured in experiments on macroscopic bicrystals. The idea that shear-coupled GB migration can occur by the continuous feeding of lattice dislocations decomposing in the GB during the migration is also investigated. This process is thought to play a role during recrystallization

  15. Computer modeling of the process of self-propagating high-temperature synthesis in thin system Ni-Al

    International Nuclear Information System (INIS)

    Full text: The process of synthesis of thermal phases of the system Ni-Al is studied through the method of molecular dynamics. As the object of investigation was chosen two-dimensional crystal, that corresponds to atomic packing laying at the plane of volumetric fcc crystal. Clean Ni was taken as a matrix crystal. A particle of clean Al is packed in the center of matrix block. Beyond the bounds of calculated block crystal packing is repeated with the help of periodical border conditions. The interaction between different pairs of atoms is set by pair potential function of Morse, considering interatomic bonding of the point of the sixth coordinate sphere. The allocation of speeds of atomic function in the system is set through the Boltzmann factor, depending the temperature. When the bicrystal is represented by the ideal atom packing and there are no vacancies , the process of structural adjustment is only observed at the temperature, that is higher than melting point. At that, structural adjustment is observed in circular mechanism of atom allocation, also through the border between phases of clean Ni and Al. As a result, Al particle is transformed, at the border between metals, fields of positional disorder and embryos of intermetallide phases NiAl2, Ni2Al, Ni3Al. The introduction of of free volume through the creation of vacancies significantly lowers the temperature of the beginning of the synthesis process of intermetallide phases. The greatest decrease in temperature to the point of 300 K happens, when the vacancies are located in Ni field of bicrystal, the beginning of the thermo-activation is directly connected with the distance from interphase borders. As the process of thermo-activation continues, vacancies located in Ni matrix right up to seventh neighborhood relatively the border bicrystal. During thermo-activation Al particles enter the field and activate the synthesis process

  16. High-Tc SQUID magnetometers for use in moderatemagnetically-shielded room

    OpenAIRE

    MATSUDA, Mizushi; Ono, S.; Kato, K.; Matsuura, T.; Oyama, H; Hayashi, A; Hirano, S.; Kuriki, S; YOKOSAWA, K.

    2001-01-01

    We have fabricated and characterized high-Tc planar SQUID magnetometers and first derivative gradiometers with directly-coupled pickup loops. The devices were made from single layer of YBa2Cu3O7-δ thin film on LSAT bicrystal substrate with 30° or 24° misorientation angle. Magnetic properties were investigated by applying a magnetic field B0 for the SQUID magnetometer patterned with holes to reduce the maximum structural width. We found an increasing low frequency noise with cooling fields B0 ...

  17. Optimum high temperature strength of two-dimensional nanocomposites

    Directory of Open Access Journals (Sweden)

    M. A. Monclús

    2013-11-01

    Full Text Available High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

  18. Optimum high temperature strength of two-dimensional nanocomposites

    International Nuclear Information System (INIS)

    High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures

  19. Optimum high temperature strength of two-dimensional nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Monclús, M. A.; Molina-Aldareguía, J. M., E-mail: jon.molina@imdea.org [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Zheng, S. J.; Mayeur, J. R.; Beyerlein, I. J.; Mara, N. A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Polcar, T. [Czech Technical University in Prague, Technická 2, Prague 6 (Czech Republic); Llorca, J. [IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid (Spain); Department of Materials Science, Polytechnic University of Madrid, E. T. S. de Ingenieros de Caminos, 28040 Madrid (Spain)

    2013-11-01

    High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

  20. Influence of substrate on coupling of high temperature superconducting Josephson junction arrays

    International Nuclear Information System (INIS)

    High temperature superconducting (HTS) Josephson junction arrays (JJAs) fabricated on bicrystal substrate were embedded in a Fabry-Pérot (F-P) resonator. We detected the radiation from the JJAs at about 74.08 GHz. By investigating the Current-Voltage (I-V) characteristics of the JJAs, the influence of the substrate on height of the Shapiro steps was studied. The result showed that the JJAs located at different positions of the substrate had different coupling strength. Also, the influence of the substrate was explored by presenting the comparison of radiation at different frequencies. Electromagnetic simulation was used to explain the experiment results.

  1. Influence of substrate on coupling of high temperature superconducting Josephson junction arrays

    Energy Technology Data Exchange (ETDEWEB)

    Wang, P. [Department of Electronics, Nankai University, Tianjin 300071 (China); Wang, Zh. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Fan, B. [Department of Electronics, Nankai University, Tianjin 300071 (China); Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48823 (United States); Xie, W.; Liu, W.; Zhao, X.J.; Zhang, X. [Department of Electronics, Nankai University, Tianjin 300071 (China); Ji, L., E-mail: luji@nankai.edu.cn [Department of Electronics, Nankai University, Tianjin 300071 (China); He, M.; Fang, L.; Yan, S.L. [Department of Electronics, Nankai University, Tianjin 300071 (China)

    2012-12-14

    High temperature superconducting (HTS) Josephson junction arrays (JJAs) fabricated on bicrystal substrate were embedded in a Fabry-Perot (F-P) resonator. We detected the radiation from the JJAs at about 74.08 GHz. By investigating the Current-Voltage (I-V) characteristics of the JJAs, the influence of the substrate on height of the Shapiro steps was studied. The result showed that the JJAs located at different positions of the substrate had different coupling strength. Also, the influence of the substrate was explored by presenting the comparison of radiation at different frequencies. Electromagnetic simulation was used to explain the experiment results.

  2. High performance dc SQUID magnetometers with single layer YBa2Cu3O7-x flux transformers

    International Nuclear Information System (INIS)

    We have fabricated high-transition temperature superconducting magnetometers involving a flux transformer patterned in a single film of YBa2Cu3O7-x (YBCO) on a 50-mm-diam substrate. This transformer is inductively coupled to a loop that in turn is directly coupled to a dc superconducting quantum interference device, patterned in a single layer of YBCO deposited on a SrTiO3 bicrystal. At 77 K, the lowest magnetic field noise achieved is 31 fT Hz-1/2 at frequencies above 5 Hz, increasing to 39 fT Hz-1/2 at 1 Hz

  3. Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors

    KAUST Repository

    Wang, Lei

    2011-06-01

    We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystallineSr0.6K0.4Fe2As2superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale crystallites sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.

  4. Direct correlations between fracture toughness and grain boundary segregation behavior in ytterbium-doped magnesium aluminate spinel

    International Nuclear Information System (INIS)

    The effect of ytterbium (Yb) on magnesium aluminate spinel (MgAl2O4) grain boundary structure and strength has been evaluated using mechanical testing and electron microscopy. Bicrystal specimens were prepared by hot pressing. Certain interfaces were doped with Yb prior to bonding. Interfaces were characterized using atomic-resolution high-angle annular dark-field imaging. Interface fracture toughness was determined using a microscale cantilever beam test. A 30% increase in fracture toughness was found to correlate with grain boundary Yb segregation

  5. Molecular dynamics simulation of Ga penetration along grain boundaries in Al: a dislocation climb mechanism.

    Science.gov (United States)

    Nam, Ho-Seok; Srolovitz, David J

    2007-07-13

    Many systems where a liquid metal is in contact with a polycrystalline solid exhibit deep liquid grooves where the grain boundary meets the solid-liquid interface. For example, liquid Ga quickly penetrates deep into grain boundaries in Al, leading to intergranular fracture under very small stresses. We report on a series of molecular dynamics simulations of liquid Ga in contact with an Al bicrystal. We identify the mechanism for liquid metal embrittlement, develop a new model for it, and show that is in excellent agreement with both simulation and experimental data. PMID:17678231

  6. Elementary Mechanisms of Shear-Coupled Grain Boundary Migration

    Science.gov (United States)

    Rajabzadeh, A.; Mompiou, F.; Legros, M.; Combe, N.

    2013-06-01

    A detailed theoretical study of the elementary mechanisms occurring during the shear-coupled grain boundary (GB) migration at low temperature is performed focusing on both the energetic and structural characteristics. The migration of a Σ13(320) GB in a copper bicrystal in response to external shear displacements is simulated using a semiempirical potential. The minimum energy path of the shear-coupled GB migration is computed using the nudge elastic band method. The GB migration occurs through the nucleation and motion of GB steps identified as disconnections. Energy barriers for the GB and disconnection migrations are evaluated.

  7. Microwave testing of high-Tc based direct current to a single flux quantum converter

    DEFF Research Database (Denmark)

    Kaplunenko, V. K.; Fischer, Gerd Michael; Ivanov, Z. G.;

    1994-01-01

    Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain...... boundary of a 0°–32° asymmetric Y-ZrO2 bicrystal substrate. The performance of such converters is important for the development of the fast Josephson samplers required for testing of high-Tc rapid single flux quantum circuits in high-speed digital superconducting electronics. Journal of Applied Physics is...

  8. Grain boundary tunnel spectroscopy of the electron-doped cuprate superconductor La2-xCexCuO4

    International Nuclear Information System (INIS)

    The electron doped superconductor La2-xCexCuO4 (LCCO) has been investigated by electric transport measurements at low temperatures T down to 5 K and high magnetic fields up to 16 T. For this purpose LCCO thin film tunnel junctions have been prepared on bicrystal substrates by molecular beam epitaxy and micro structuring. The samples were characterised by measuring the thin film resistivity and the tunnel conductance of quasi particles across the grain boundary. By these measurements an unconventional symmetry of the order parameter could be revealed for La2-xCexCuO4. Furthermore it was shown, that the tunnel conductance can be used as a probe for the upper critical field Bc2(T). By using this method a value of Bc2∝24 T has been found for La2-xCexCuO4, a value roughly three times bigger than previously known. By this observation it was shown that the superconducting phase covers a larger region in the B-T-phase diagram. In addition it was concluded, that the pseudogap phase in La2-xCexCuO4 is either not existent at all or covers only a small temperature region. Besides quasiparticle tunneling also the tunneling of Cooper pairs in small magnetic fields has been investigated. It was shown that the critical current across the grain boundary depends on the supplier of the bicrystal substrate. (orig.)

  9. Local and bulk melting of Cu at grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Shengnian [Los Alamos National Laboratory; Han, Li - Bo [USTC; An, Qi [USTC/CALTECH; Fu, Rong - Shan [USTC; Zheng, Lianqing [FSU

    2008-01-01

    We investigate gain boundary (GB) melting using molecular dynamics simulations on face-centered-cubic Cu bicrystals with symmetric {l_angle}110{r_angle} tilt grain boundaries. Two representative types of GBs are explored: {Sigma} = 11/(113)/50.48{sup o} (low GB energy) and {Sigma} = 27/(552)/148.41{sup o} (high GB energy). The temperature and temporal evolutions of the Cu bicrystals under stepped heating are characterized in terms of order parameters and diffusion coefficients, as ell as the nucleation and growth of melt. Within the GB region, continuous local melting precedes discontinuous bulk melting, while continuous solid state disordering may precede local melting. Premelting may occur for local melting but not for bulk melting. For {Sigma} = 11/(113)/50.48{sup o}, premelting of the GB region is negligible, and local melting occurs near the thermodynamic melting temperature. The GB region as a whole is superheated by about 13% before its bulk melting. In the case of {Sigma} = 27/(552)/148.41, considerable premelting is observed for local melting, while the bulk melting occurs with negligible superheating. The exact melting behavior of a general GB depends on the GB energy, but is likely bracketed within these two cases.

  10. A predictive model for transferability of plastic deformation through grain boundaries

    Directory of Open Access Journals (Sweden)

    T. Tsuru

    2016-01-01

    Full Text Available The material strengths of polycrystalline metals have been widely predicted according to the grain size, where yield stress is governed by slip transfer through the grain boundary (GB. The transferability of a dislocation across a GB is enormously important in the deformation process as well as the interaction between a dislocation and GB. This paper proposes a new criterion for the transferability of dislocations through a GB that considers both the intergranular crystallographic orientation of slip systems and the applied stress condition. Atomistic simulations were carried out to investigate the slip transfer event of simple bicrystals composed of Σ 3 ( 1 ̄ 12 GB than Σ 3 ( 1 ̄ 11 GBs under uniaxial deformation and to illustrate the availability of this criterion. As a result, in contrast to the predictions of conventional criteria such as the M-value, dislocations propagated more easily across the Σ 3 ( 1 ̄ 11 and Σ 3 ( 1 ̄ 12 GB under given stress states, reflecting a larger L′-value of Σ3 bicrystal associated with higher transferability.

  11. Development and investigation of novel single-layer gradiometers using highly balanced gradiometric SQUIDs

    International Nuclear Information System (INIS)

    The sensitivity of galvanically coupled single-layer gradiometers on bicrystal substrates for homogeneous magnetic fields can be minimized by an increase of the balance, which is the ratio of the effective area of the antennas and the effective area of the SQUID. In this paper, we describe possible realizations of new gradiometric SQUIDs (G-SQUIDs) on 10x10 mm2 STO-bicrystal substrates, which minimize the effective area of the SQUID, and therefore the parasitic area of the gradiometer, to 34 μm2. We integrate these gradiometric SQUIDs in well-defined gradiometer antennas. The G-SQUID layouts with coupling inductances between 20 pH and 100 pH do not show any dependence of the parasitic area from the SQUID inductance. With a gradient field resolution of 1.6 pT(cm√Hz)-1 (white, unshielded) at 24 pH and 1.8 pT(cm√Hz)-1 at 55 pH, these gradiometers possess outstanding noise characteristics. So the balance of comparable conventional gradiometers, which show values of about 100, can be increased by more than an order of magnitude to 1070 with the new layouts. (author)

  12. X-Ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals

    International Nuclear Information System (INIS)

    The deformation behavior of BCC metals is being investigated by x-ray microdiffraction measurements (mu XRD) for the purpose of characterizing the dislocation structure that results from uniaxial compression experiments. The high brilliance synchrotron source at the Advanced Light Source (Lawrence Berkeley National Lab) and the micron resolution of the focusing optics allow for the mapping of Laue diffraction patterns across a sample. These measurements are then analyzed in order to map the distribution of residual stresses in the crystal. An important finding is the observation of Laue spot ''streaking'', which indicates localized rotations in the lattice. These may represent an accumulation of same-sign dislocations. Theoretical modeling of the diffraction response for various slip systems is presented, and compared to experimental data. Preliminary results include orientation maps from a highly strained Ta bicrystal and a less highly strained Mo single crystal. The orientation maps of the bicrystal indicate a cell-like structure of dense dislocation walls. This deformation structure is consistent with previous OIM studies of the same crystal. The results suggest that mu XRD may be a particularly useful tool for microscale studies of deformation patterns in a multi-scale investigation of the mechanisms of deformation that ranges from macroscopic deformation tests to high resolution TEM studies of dislocation structures

  13. Interpreting the stress–strain response of Al micropillars through gradient plasticity

    International Nuclear Information System (INIS)

    Micropillar compression has fascinated the materials and mechanics communities for over a decade, due to the unique stochastic effects and slip zones that dictate their stress–strain curves and microstructure. Although plethora studies exist that capture experimentally the mechanical response of various types of micropillars, limited theoretical models can interpret the observed behavior. Particularly, single crystal micropillars exhibit multiple serrations in their stress–strain response, indicating the activation of slip zones, while bi-crystal pillars, in which the grain boundary lies parallel to the pillar axis, do not display such serrations, but rather a distinct “knee”, which indicates dislocation pileups at the grain boundary. In-situ synchrotron microdiffraction experiments have illustrated that not only dislocations, but also significant plastic strain gradients develop during micropillar compression. In the present study, therefore, appropriate gradient plasticity models that can account for the pillar microstructure, are successfully used to capture the stress–strain response of single- and bi-crystal Al pillars

  14. Molecular dynamics simulation of thin film interfacial strength dependency on lattice mismatch

    International Nuclear Information System (INIS)

    Laser-induced thin film spallation experiments have been previously developed to characterize the intrinsic interfacial strength of thin films. In order to gain insights of atomic level thin film debonding processes and the interfacial strength dependence on film/substrate lattice structures, in this study, molecular dynamics simulations of thin film interfacial failure under laser-induced stress waves were performed. Various loading amplitudes and pulse durations were employed to identify the optimum simulation condition. Stress propagation as a function of time was revealed in conjunction with the interface structures. Parametric studies confirmed that while the interfacial strength between a thin film and a substrate does not depend on the film thickness and the duration of the laser pulse, a thicker film and a shorter duration do provide advantage to effectively load the interface to failure. With the optimized simulation condition, further studies were focused on bulk Au/Au bi-crystals with mismatched orientations, and Ni/Al, Cu/Al, Cu/Ag and Cu/Au bi-crystals with mismatched lattices. The interfacial strength was found to decrease with increasing orientation mismatch and lattice mismatch but more significantly dominated by the bonding elements' atomic structure and valence electron occupancy. - Highlights: • Molecular dynamics simulation was done on stress wave induced thin film spallation. • Atomic structure was found to be a primary strength determining factor. • Lattice mismatch was found to be a secondary strength determining factor

  15. Temperature influence on the faceting of Σ3 and Σ9 grain boundaries in Cu

    International Nuclear Information System (INIS)

    The faceting of a tube-like tilt grain boundary (GB) in Cu bicrystals has been studied in the temperature interval from 0.5 to 0.95 of the melting temperature T m (T m = 1356 K). The grains of the bicrystals form the coincidence site lattice (CSL) with inverse density of coincidence sites Σ = 3 and Σ = 9. No rounded edges between facets were observed up to 0.95T m. With decreasing temperature new facets of increasingly higher CSL indices appear. At 0.5T m six crystallographically different Σ = 3 facets exist simultaneously. The appearance of high-index CSL facets can be explained by the roughening phase transition of a Kosterlitz-Thouless type. The ratio of GB energy σ GB and surface energy σ sur of the specimen was measured by applying atomic force microscopy to the profile of the GB thermal groove formed upon additional annealing. The Wulff-Herring diagrams were constructed using measured σ GB/σ sur values

  16. High temperature superconducting thin films and quantum interference devices (SQUIDs) for gradiometers

    International Nuclear Information System (INIS)

    This thesis describes several aspects of the development of gradiometers using high temperature Superconducting Quantum Interference Devices (SQUID). The pulsed laser deposition of thin films of YBa2Cu3O7-δ (YBCO) on SrTiO3 substrates was analysed using the method of 'Experimental Design'. Optimised YBCO films had a critical temperature of 90.5K and a critical current density of 3.6MAcm-2. As a result of the 3D screw dislocation mediated growth mode of YBCO, all films showed a considerable surface roughness, between 5-17nm. In a second study, the pulsed laser deposition of NdBa2Cu3O7-δ (NBCO) on SrTiO3 substrates was investigated. The highest critical temperature was 90K. but the properties of the used NBCO bulk targets resulted in degraded properties after thin film patterning. Compared to YBCO, optimised NBCO films required a larger target-substrate separation during deposition and showed smoother surfaces with a roughness of at most 2nm. Both observations were attributed to a 2D layer-by-layer growth mode. dc-SQUIDs were fabricated and characterised from thin films of both materials incorporating bicrystal and step-edge junctions. The lowest white flux noise was 5μΦ0/√Hz for a 50pH YBCO device on a SrTiO3 bicrystal with a 24 deg misorientation angle. First order SQUID gradiometers were fabricated from single layers of YBCO. The baseline of these devices was 4mm and the best balance and gradient sensitivity at 1kHz were 3x10-3 and 222fT/(cm√Hz))) respectively. The measured spatial response to a current carrying wire was in good agreement with a theoretical model. A significant performance improvement was obtained with the development of a single layer gradiometer with 13mm baseline, fabricated on 30x10mm2 bicrystals. For such a device, the gradient sensitivity at 1kHz was 50fT/(cm√Hz)) and the gradiometer was used successfully for unshielded magnetocardiography. A parasitic effective area compensation scheme was employed with two neighbouring SQUIDs

  17. High temperature superconducting thin films and quantum interference devices (SQUIDs) for gradiometers

    Energy Technology Data Exchange (ETDEWEB)

    Graf zu Eulenburg, A

    1999-07-01

    This thesis describes several aspects of the development of gradiometers using high temperature Superconducting Quantum Interference Devices (SQUID). The pulsed laser deposition of thin films of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) on SrTiO{sub 3} substrates was analysed using the method of 'Experimental Design'. Optimised YBCO films had a critical temperature of 90.5K and a critical current density of 3.6MAcm{sup -2}. As a result of the 3D screw dislocation mediated growth mode of YBCO, all films showed a considerable surface roughness, between 5-17nm. In a second study, the pulsed laser deposition of NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NBCO) on SrTiO{sub 3} substrates was investigated. The highest critical temperature was 90K. but the properties of the used NBCO bulk targets resulted in degraded properties after thin film patterning. Compared to YBCO, optimised NBCO films required a larger target-substrate separation during deposition and showed smoother surfaces with a roughness of at most 2nm. Both observations were attributed to a 2D layer-by-layer growth mode. dc-SQUIDs were fabricated and characterised from thin films of both materials incorporating bicrystal and step-edge junctions. The lowest white flux noise was 5{mu}{phi}{sub 0}/{radical}Hz for a 50pH YBCO device on a SrTiO{sub 3} bicrystal with a 24 deg misorientation angle. First order SQUID gradiometers were fabricated from single layers of YBCO. The baseline of these devices was 4mm and the best balance and gradient sensitivity at 1kHz were 3x10{sup -3} and 222fT/(cm{radical}Hz))) respectively. The measured spatial response to a current carrying wire was in good agreement with a theoretical model. A significant performance improvement was obtained with the development of a single layer gradiometer with 13mm baseline, fabricated on 30x10mm{sup 2} bicrystals. For such a device, the gradient sensitivity at 1kHz was 50fT/(cm{radical}Hz)) and the gradiometer was used successfully for

  18. Foundations for quantitative microstructural models to track evolution of the metallurgical state during high purity Nb cavity fabrication

    Energy Technology Data Exchange (ETDEWEB)

    Bieler, Thomas R [Michigan State University; Wright, Neil T [Michigan State University; Compton, Chris C [Facility for Rare Isotope Beams

    2014-03-15

    The goal of the Materials Science SRF Cavity Group of Michigan State University and the National Superconducting Cyclotron has been (and continues to be) to understand quantitatively the effects of process history on functional properties. These relationships were assessed via studies on Nb samples and cavity parts, which had various combinations of forming processes, welding, heat treatments, and surface preparation. A primary focus was on large-grain cavity building strategies. Effects of processing operations and exposure to hydrogen on the thermal conductivity has been identified in single and bi-crystal samples, showing that the thermal conductivity can be altered by a factor of 5 depending on process history. Characterization of single crystal tensile samples show a strong effect of crystal orientation on deformation resistance and shape changes. Large grain half cells were examined to characterize defect content and surface damage effects, which provided quantitative information about the depth damage layers from forming.

  19. Physics of Negative Refraction and Negative Index Materials Optical and Electronic Aspects and Diversified Approaches

    CERN Document Server

    Krowne, Clifford M

    2007-01-01

    This book deals with the subject of optical and electronic negative refraction (NR) and negative index materials NIM). Diverse approaches for achieving NR and NIM are covered, such as using photonic crystals, phononic crystals, split-ring resonators (SRRs) and continuous media, focusing of waves, guided-wave behavior, and nonlinear effects. Specific topics treated are polariton theory for LHMs (left handed materials), focusing of waves, guided-wave behavior, nonlinear optical effects, magnetic LHM composites, SRR-rod realizations, low-loss guided-wave bands using SRR-rods unit cells as LHMs, NR of electromagnetic and electronic waves in uniform media, field distributions in LHM guided-wave structures, dielectric and ferroelectric NR bicrystal heterostructures, LH metamaterial photonic-crystal lenses, subwavelength focusing of LHM/NR photonic crystals, focusing of sound with NR and NIMs, and LHM quasi-crystal materials for focusing.

  20. Arrays and the combinatorics of Young tableaux

    International Nuclear Information System (INIS)

    The classical theory of Young tableaux is presented in the rather new and non-traditional language of arrays. With the usual operations (or algorithms) of insertion and jeu de taquin as a starting point, more elementary operations on arrays are introduced. The set of arrays equipped with these operations forms an object which can be referred to as a bicrystal. This formalism is presented in the first part of the paper, and its exposition is based on the theorem that the vertical and horizontal operators commute. In the second part the apparatus of arrays is used to present some topics in the theory of Young tableaux, namely, the plactic monoid, Littlewood-Richardson rule, Robinson-Schensted-Knuth correspondence, dual tableaux, plane partitions, and so on

  1. Operation of a high-T C SQUID gradiometer with a two-stage MEMS-based Joule–Thomson micro-cooler

    Science.gov (United States)

    Kalabukhov, Alexey; de Hoon, Erik-Jan; Kuit, Kristiaan; Lerou, Pieter-Paul P. P. M.; Chukharkin, Maxim; Schneiderman, Justin F.; Sepehri, Sobhan; Sanz-Velasco, Anke; Jesorka, Aldo; Winkler, Dag

    2016-09-01

    Practical applications of high-T C superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule–Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-T C SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-T C SQUIDs in practical applications such as magnetic bioassays.

  2. Tunneling transport properties in (La,Sr)2CuO4 grain boundary Josephson junctions

    International Nuclear Information System (INIS)

    We investigate tunneling transport properties in thin film grain boundary Josephson junctions (GBJ's) of epitaxially grown (La,Sr)2CuO4 (LSCO) on bicrystal substrates. These optimally doped LSCO films were made by molecular beam epitaxy producing a very smooth film at the grain boundary. Measurements of the critical current Ic at low magnetic fields B (mT range) are used to characterize the quality of the junctions. Deviations from the ideal Ic(B) pattern enable us to indicate the homogeneity of the GBJ. Measurements of the differential conductance in high magnetic fields (T range) are used to investigate quasiparticle tunneling across the grain boundary. Results are compared to theoretical predictions

  3. Geometry of polycrystals and microstructure

    Directory of Open Access Journals (Sweden)

    Ball John M.

    2015-01-01

    Full Text Available We investigate the geometry of polycrystals, showing that for polycrystals formed of convex grains the interior grains are polyhedral, while for polycrystals with general grain geometry the set of triple points is small. Then we investigate possible martensitic morphologies resulting from intergrain contact. For cubic-totetragonal transformations we show that homogeneous zero-energy microstructures matching a pure dilatation on a grain boundary necessarily involve more than four deformation gradients. We discuss the relevance of this result for observations of microstructures involving second and third-order laminates in various materials. Finally we consider the more specialized situation of bicrystals formed from materials having two martensitic energy wells (such as for orthorhombic to monoclinic transformations, but without any restrictions on the possible microstructure, showing how a generalization of the Hadamard jump condition can be applied at the intergrain boundary to show that a pure phase in either grain is impossible at minimum energy.

  4. Training of polycrystalline NiMnGa alloys

    Energy Technology Data Exchange (ETDEWEB)

    Chulist, Robert; Oertel, Carl-Georg; Skrotzki, Werner [Institut fuer Strukturphysik, Technische Universitaet Dresden (Germany); Poetschke, Martin [Institut fuer Metallische Werkstoffe, Leibniz-Institut fuer Festkoerper- und Werkstoffforschung, Dresden (Germany); Boehm, Andrea [Fraunhofer-Institut fuer Werkzeugmaschinen und Umformtechnik, Dresden (Germany); Rybacki, Erik [GeoForschungsZentrum Potsdam (Germany)

    2010-07-01

    In order to achieve magnetic field induced strain in NiMnGa alloys a training process is applied. This process consists of successively compressing the sample along two or three axes. As a result the twinning stress is reduced and the strain is maximized. To study the effect of training, two samples with 5M modulated structure were used: bi-crystal and polycrystal deformed by high pressure torsion. Within the individual parent austenitic grains the initial orientation is characterized by three different martensitic variants separated by twin boundaries. Compression of the samples results in the motion of the twin boundaries changing the volume fraction of particular variants. Local orientation measurements by electron backscatter diffraction directly confirm twin boundary motion. The training process finally leading to a single variant state will be discussed with respect to initial microstructure and number of martensitic variants.

  5. Diffusion-controlled intergranular penetration and embrittlement of copper by liquid bismuth between 300 and 600 Celsius degrees

    International Nuclear Information System (INIS)

    Hybrid reactors are a new concept for energy production and nuclear waste treatment. Among other requirements, structural materials have to withstand liquid metal embrittlement. This thesis aimed therefore to identify the controlling mechanism for the intergranular embrittlement of copper in contact with liquid bismuth. Scanning electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy have been used to analyze fracture surfaces of both copper polycrystals and a copper bicrystal (symmetric tilt boundary 50 degrees ). These analyses reveal both parabolic intergranular penetration kinetics and a maximal intergranular bismuth concentration that is less than two monolayers equivalent. These two results allow us to identify grain boundary diffusion as the controlling mechanism for the intergranular penetration of copper by liquid bismuth between 300 and 600 Celsius degrees, showing the absence of perfect grain boundary wetting. (author)

  6. Single crystal plasticity with bend-twist modes

    Science.gov (United States)

    Elkhodary, Khalil I.; Bakr, Mohamed A.

    2015-06-01

    In this work a formulation is proposed and computationally implemented for rate dependent single crystal plasticity, which incorporates plastic bend-twist modes that arise from dislocation density based poly-slip mechanisms. The formulation makes use of higher order continuum theory and may be viewed as a generalized micromechanics model. The formulation is then linked to the burgers and Nye tensors, showing how their material rates are derivable from a newly proposed third-rank tensor Λp, which incorporates a crystallographic description of bend-twist plasticity through selectable slip-system level constitutive laws. A simple three-dimensional explicit finite element implementation is outlined and employed in three simulations: (a) bi-crystal bending; (b) tension on a notched single crystal; and (c) the large compression of a microstructure to induce the plastic buckling of secondary phases. All simulation are transient, for computational expediency. The results shed light on the physics resulting from dynamic inhomogeneous plastic deformation.

  7. Limits of Line VISAR data interpretation with large spatial velocity variations.

    Science.gov (United States)

    Furnish, Michael

    2015-06-01

    Line-imaging velocimetry provides information on position dependence of velocity histories, and in turn on grain anisotropies, texture, variability, and nonplanar material motion. In recent experiments on copper bicrystals, strong position dependence of motion created complicated fringe patterns not amenable to conventional analysis methods (mock quadrature or FFT). The data were initially interpreted by hand. Subsequently, a Matlab-based program was prepared to reduce such records by a fringe-trace method, as well as to extract precise wave-transit time information. Limits and capabilities of such analyses will be discussed and set in the context of other methods, using experimental and synthetic data. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  8. Two channel model as a possible microscopic configuration of the open-quotes barrierclose quotes in high-Tc grain boundary junctions

    International Nuclear Information System (INIS)

    High-Tc superconductors are intensively studied for applications such as biomagnetism, but the great difficulties in making integrated dc SQUIDs have slowed down applications in the biomedical field. Moreover, magnetic noise and energy resolution are not always low enough to permit measurements of human body magnetic signals. Noise in bicrystal and biepitaxial grain boundary junctions has been extensively analyzed, and both structures showed similar 1/f noise behaviors. In order to account for the experimental results, different models describing grain boundary junctions have been made, each able to explain some aspects of the phenomenology. In this work we suggest that the open-quotes barrierclose quotes is constituted by a large number of microscopic weak links in parallel, and we analyze the effects of such a model on noise properties and the temperature dependences of the critical current, finding a good agreement with most experiments carried out on grain boundary junctions. 15 refs., 1 fig

  9. Size effects in crystal plasticity

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    growth and interaction between neighboring voids, and on a comparison between the developed strain gradient crystal plasticity theory and a discrete dislocation plasticity theory. Furthermore, voids and rigid inclusions in isotropic materials have been studied using a strain gradient plasticity theory......Numerical analyses of plasticity size effects have been carried out for different problems using a developed strain gradient crystal plasticiy theory. The theory employs higher order stresses as work conjugates to slip gradients and uses higher order boundary conditions. Problems on localization...... of plastic flow in a single crystal, grain boundary effects in a bicrystal, and grain size effects in a polycrystal are studied. Single crystals containing micro-scale voids have also been analyzed at different loading conditions with focus on the stress and deformation fields around the voids, on void...

  10. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals

    Science.gov (United States)

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-03-01

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship.

  11. Magneto-cardiogram measurement using a high-Tc SQUID magnetometer

    International Nuclear Information System (INIS)

    We made Superconducting Quantum Interference Devices (SQUIDs) coupled with large pick-up loops (directly coupled SQUIDs) by using single-layer YBCO thin films on SrTiO3 bicrystal substrates. The I-V characteristics of the SQUIDs showed Resistively Shunted Junction type (RSJ-type) behavior, and the measured IcRn values were in the 100∼300 μV range. The rms field resolution of a directly coupled SQUID measured in liquid nitrogen was 0.9 pT/Hz at 1 Hz and 0.1 pT/Hz at 1 kHz. Using this directly coupled SQUID, we have developed a SQUID magnetometer system operating in liquid nitroge, and we used that system in a magnetically shielded environment to measure biomagnetic signals from human heart

  12. Fabrication of HTS SQUID Sensors for the Application to a High S/N Ratio Magnetocardiograph System

    International Nuclear Information System (INIS)

    YBCO do superconducting quantum interference device (SQUID) magnetometers based on bicrystal Josephson junctions on 10 mm x 10 mm SrTiO3 substrates have been fabricated. The pickup coil of the device was designed to have 16 parallel loops with 50-fm-wide lines. We could obtain optimised direct coupled YBCO SQUID magnetometer design with field sensitivity BNφ/ of 4.5 nT/φ0 and magnetic field noise BN of about 22 fT/Hz12/ with an I/f corner frequency of 2 Hz measured inside a magnetically shielded room. Preliminary results of magnetocardiograph measurement using the HTS SQUID magnetometers show signal to noise ratio of about 110, which is comparable to the quality of a commercial MCG system based on Nb-SQUIDs.

  13. A thermal-mechanical constitutive model for b-HMX single crystal and cohesive interface under dynamic high pressure loading

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Due to the significant thermal-mechanical effects during hot spot formation in PBX explosives,a thermodynamic constitutive model has been constructed for HMX anisotropic single crystal subjected to dynamic impact loading. The crystal plasticity model based on dislocation dynamics theory was employed to describe the anisotropic plastic behavior along the preferential slip systems. A modified equation of state (EOS) was introduced into the constitutive equations through the decomposing stress tensor and the nonlinear elasticity for materials was taken into account. The one-dimensional strain impact simulations for HMX single crystal and quasi-bicrystal were performed respectively,in which the cohesive elements were inserted over the interface areas for the latter. The predicted particle velocities for the single crystal sample agreed well with the experimental results in the literature. Furthermore,the effects of crystal orientations,interface,misorientations on localized strain,stress and temperature distributions were predicted and discussed.

  14. Stabilizing nanocrystalline materials with dopants

    International Nuclear Information System (INIS)

    The enhancement of material properties caused by extremely small grain sizes in metals and ceramics is attractive for many technological applications including protective coatings, electronic interconnects and microelectromechanical systems (MEMS) devices. However, the large driving force for grain growth caused by the abundance of grain boundaries remains a critical complication in the synthesis and functionality of nanocrystalline materials. Here we present atomistic simulations that illuminate the stabilizing effect of interfacially segregated, oversized dopants in face-centered cubic (fcc) copper. Using a bicrystal configuration, the calculated grain boundary energy is reduced to zero with systematically increasing dopant coverage and atomic radius mismatch. We then extend this result to a nanocrystalline network and determine the critical dopant concentration required to eliminate grain growth in bulk and thin film structures. The results of this investigation are intended to guide future experimental efforts to design appropriately doped, stable nanocrystalline materials

  15. Production of nickel oxide thin films by magnetron sputtering

    International Nuclear Information System (INIS)

    Discrepancies between short-circuit diffusion data derived from nickel oxide bicrystals and specimens produced by the oxidation of nickel has led to a requirement for thin film nickel oxide specimens of controlled microstructure and impurity level that can be produced independently of the oxidation process. RF magnetron sputtering of nickel oxide has been used to produce thin films intended for this application. The as-deposited films contain excess oxygen compared to stoichiometric nickel oxide and exhibit strong preferred orientation. Annealing in argon leads to oxygen deficient films. The reduction in porosity which accompanies the annealing leads to the formation of through-thickness cracks in the films. Subsequent oxygen tracer studies demonstrate that the cracks give rise to excessive oxygen transport through the films compared to that expected for thermally oxidised scales. The microstructural anomalies produced by the annealing process mean that the required microstructures were not achieved and these films are not useful analogues of thermal nickel oxide scales. (author)

  16. Computational study of the impurity induced reduction of grain boundary energies in nano- and bi-crystalline Al-Pb alloys

    International Nuclear Information System (INIS)

    Segregation of impurities with limited solubilities to grain boundaries can slow or even eliminate grain growth in nanocrystalline materials. Due to a very limited miscibility Pb is a potential candidate for thermodynamically stabilizing nanocrystalline Al. To investigate this we have used atomic modeling to characterize the structure and energy of substitutional Pb defects in bulk Al, in Al bi-crystals and in an Al nanocrystal. Monte Carlo simulations using a modified embedded-atom method (MEAM) potential fit to the results of density functional theory (DFT) calculations predict the formation of Pb clusters, in agreement with prior experiments. In addition, the simulations show strong segregation of Pb atoms to grain boundaries, a result that supports prior suggestions that Pb is distributed along grain boundaries in nanocrystals created by ball milling. Analysis of the enthalpies for Pb defects using MEAM and DFT calculations suggests that Pb impurities can help stabilize nanocrystalline Al against grain growth.

  17. Partial dislocation configurations in a low-angle boundary in α-Al2O3

    International Nuclear Information System (INIS)

    The dislocation structures of a low-angle tilt grain boundary in alumina bicrystal were investigated by transmission electron microscopy. The grain boundary was found to consist of two regions: an area with pairs of partial dislocations and an area with groups of odd numbered partial dislocations (multiple-partial-structure). Eight kinds of multiple-partial-structures were found in the fabricated grain boundary. The Burgers vectors of each partial dislocation in the grain boundary can be distinguished by dark-field imaging, and thus the arrangement of partial dislocations in the multiple-partial-structures are determined. It is concluded that a slight twist component of the boundary is the origin of the characteristic multiple-partial-structures

  18. Diffusion-controlled intergranular penetration and embrittlement of copper by liquid bismuth between 300 and 600 Celsius degrees; Penetration intergranulaire fragilisante du cuivre par le bismuth liquide: identification de la cinetique et du mecanisme de type diffusionnel entre 300 et 600 deg

    Energy Technology Data Exchange (ETDEWEB)

    Laporte, V

    2005-02-15

    Hybrid reactors are a new concept for energy production and nuclear waste treatment. Among other requirements, structural materials have to withstand liquid metal embrittlement. This thesis aimed therefore to identify the controlling mechanism for the intergranular embrittlement of copper in contact with liquid bismuth. Scanning electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy have been used to analyze fracture surfaces of both copper polycrystals and a copper bicrystal (symmetric tilt boundary 50 degrees <100>). These analyses reveal both parabolic intergranular penetration kinetics and a maximal intergranular bismuth concentration that is less than two monolayers equivalent. These two results allow us to identify grain boundary diffusion as the controlling mechanism for the intergranular penetration of copper by liquid bismuth between 300 and 600 Celsius degrees, showing the absence of perfect grain boundary wetting. (author)

  19. Tests of operating conditions for metrological application of HTS Josephson arrays

    International Nuclear Information System (INIS)

    We report on an experimental study of metrological properties of High Temperature Superconductor arrays, made of shunted bicrystal YBCO Josephson junctions, to assess their accuracy. A detailed analysis of measurement errors is presented, mainly based on a direct comparison of an HTS array against a low temperature array. Owing to the high sensitivity of the comparison, we were able to measure the changes in the HTS array voltage on a step at nanovolt level. A precise estimate of the dependence of the HTS array step width on operating conditions was obtained. Differences were observed with respect to the results provided by the usual, low sensitivity, techniques, confirming that the method we adopted is necessary in the study of HTS arrays for metrology. The high sensitivity analysis was applied in the derivation of the temperature dependence of the critical current as well, providing some insights on the behaviour of the HTS array

  20. Study and operating conditions of HTS Josephson arrays for metrological application

    International Nuclear Information System (INIS)

    We report an experimental study of metrological properties of high-temperature superconductor arrays, made of shunted bicrystal YBCO Josephson junctions. The work is mainly based on a direct comparison against a low temperature array. Owing to the high sensitivity of the measurements, we observed at nanovolt level the changes in the HTS array voltage on a step. A precise estimate of the dependence of the HTS array step width on operating conditions was obtained. Differences were observed with respect to the results of low sensitivity techniques, confirming that our method is necessary in the study of HTS arrays for metrology. The high sensitivity analysis was also applied in the derivation of the temperature dependence of the critical current, providing insights on the behavior of the HTS array

  1. Josephson spectroscopy on submillimeter waves

    International Nuclear Information System (INIS)

    The Josephson high-temperature superconducting submillimeter spectrometer is developed, made and experimentally investigated. The integral receiving structure of the spectrometer comprises the YBCO Josephson junction on the bicrystal boundary, the two-gap (or logo-periodic) antenna and the low-inductive resistive shunt. The selective detector response and the response on the intermediate frequency 1.4 GHz are measured at the action of signals in the frequency range 350-1250 GHz. Th new spectroscopy method based on the mode of the mixer with self-pumping is proposed. The technique for the separation of the studied signal spectrum from the measured HF response is presented. This spectroscopy method with using the Josephson mixer with self-pumping at the high intermediate frequency allows one to improve the sensitivity, the spectral resolution and the dynamic range of the Josephson spectrometer

  2. Evidence for Nonlocal Electrodynamics in Planar Josephson Junctions

    Science.gov (United States)

    Boris, A. A.; Rydh, A.; Golod, T.; Motzkau, H.; Klushin, A. M.; Krasnov, V. M.

    2013-09-01

    We study the temperature dependence of the critical current modulation Ic(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O7-δ bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the Ic(H) modulation field ΔH becomes almost T independent and neither ΔH nor the critical field for the penetration of Josephson vortices vanish at Tc. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth λ from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when λ(T) becomes larger than the electrode thickness.

  3. Study of some properties of point defects in grain boundaries

    International Nuclear Information System (INIS)

    With the aim of deducing simple informations on the grain boundary core structure, we investigated self diffusion under hydrostatic pressure, impurity diffusion (In and Au), electromigration (Sb) along certain types of grain boundaries in Ag bicrystals, and the Moessbauer effect of 57Co located in the grain boundaries of polycrystalline Be. Our results lead to the following conclusions: the formation of a vacancy like defects is necessary to grain boundary diffusion; solute atoms may release most of their elastic energy of dissolution as they segregate at the boundary; in an electrical field, the drift of Sb ions parallel to the boundary takes place toward the anode as in the bulk. The force on the grain boundary ions is larger than in the bulk; Moessbauer spectroscopy revealed the formation of Co-rich aggregates, which may proves important in the study of early stages of grain boundary precipitation. (author)

  4. Capturing recrystallization of metals with a multi-scale materials model

    Energy Technology Data Exchange (ETDEWEB)

    D. A. Hughes; D. J. Bammann; A. Godfrey; V. C. Prantil; E. A. Holm; M. A. Miodownik; D. C. Chrzan; M. T. Lusk

    2000-04-01

    The final report for a Laboratory Directed Research and Development project entitled, ``Capturing Recrystallization of Metals in a Multiscale Materials Model'' is presented. In this project, deformation and recrystallization processes have been followed experimentally and theoretically in order to incorporate essential mechanisms from the defect (dislocation) and grain size length scales. A nonlinear rotational gradient theory has been developed which enables the incorporation of microstructural parameters. The evolution of these parameters during deformation and recrystallization has been characterized qualitatively and quantitatively, applying various electron optic techniques ranging over several length scales. The theoretical and experimental framework developed is general. It has been exemplified by an application to recrystallization in single crystals and bicrystals of aluminum. The recrystallization process has been modeled using a 3-D model for the changes in key structural parameters during recrystallization.

  5. A study of diffusion and grain boundaries in ionic compounds by the molecular dynamic method; Etude par dynamique moleculaire de la diffusion et des joints de grains dans les composes ioniques

    Energy Technology Data Exchange (ETDEWEB)

    Karakasidis, T.

    1995-11-13

    In the first part, we present a model of variable cationic charges based on a rigid ion potential. In order to implement the model we performed static and dynamic simulations in calcium fluoride. The structural properties do not depend on the way the model is adjusted but the anion diffusion and the high frequency dielectric constant do. These results allowed to specify the criteria to adjust the variable charge model. As indicated by the behaviour of optical phonons this model introduced a supplementary polarisation mechanism to the rigid ion model. In the second part of this work, we studied the structural and diffusional behaviour of a high angle tilt grain boundary in NiO by molecular dynamics, using a usual rigid ion model. We examined structures with and without point defects between 0 K and 2500 K. The structure without defects presents always the lowest potential energy. In the others structures the defects can cluster and sometimes cause local changes in the boundary. Computer simulated images of high resolution electron microscopy, produced using these structures, present a similarity with the experimental ones. We calculated in the same boundary the diffusion coefficient of a doubly charged nickel vacancy between 2250 k and 2650 K. The atomic trajectories reveal the existence of preferential migration paths for the vacancy. The grain boundary diffusion is slightly anisotropic which is in agreement with an extrapolation of experimental results. A similar study in the volume reveals a migration energy higher than in the grain boundary. The calculated quantities allow for an estimation of the nickel diffusion acceleration due to the boundary. This acceleration is significant, but lower than the one measured by certain authors in polycrystalline, NiO; other authors studying bicrystals have not observed any certain authors in polycrystalline, NiO; other authors studying bicrystals have not observed any acceleration. (author) 118 refs.

  6. Critical current density and grain boundary property of BaFe2(As,P)2 thin films

    International Nuclear Information System (INIS)

    Highlights: •Jc and grain boundary property of BaFe2(As,P)2 thin films were investigated. •We found a correlation of Jc with the Fe/Ba composition ratio. •A very large Jc of 1.2 × 107 A/cm2 was observed with a Fe rich thin film. •A grain boundary junction having a misorientation angle of 24° was fabricated. •Jc across the grain boundary (θGB = 24°) recorded 106 A/cm2. -- Abstract: We have investigated the critical current density (Jc) and the grain boundary property of BaFe2(As,P)2 thin films grown on MgO single crystal or bicrystal substrates by molecular beam epitaxy. We found a strong correlation between Jc and the Fe/Ba composition ratio, and a very large self-field Jc of 1.2 × 107 A/cm2 at 4.2 K with a thin film for which the Fe/Ba ratio was 2.4. A grain boundary junction was fabricated by growing a thin film on a MgO bicrystal substrate having a misorientation angle of 24°. The inter-grain Jc at 4.0 K recorded 106 A/cm2, which is higher than that of YBa2Cu3Oy. These results demonstrate the high potential of BaFe2(As,P)2 in practical applications and indicate that the necessary condition for in-plane alignment is less severe than YBa2Cu3Oy

  7. Grain boundary tunnel spectroscopy of the electron-doped cuprate superconductor La{sub 2-x}Ce{sub x}CuO{sub 4}; Korngrenzen-Tunnelspektroskopie am elektronendotierten Kupratsupraleiter La{sub 2-x}Ce{sub x}CuO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Wagenknecht, Michael

    2008-07-01

    The electron doped superconductor La{sub 2-x}Ce{sub x}CuO{sub 4} (LCCO) has been investigated by electric transport measurements at low temperatures T down to 5 K and high magnetic fields up to 16 T. For this purpose LCCO thin film tunnel junctions have been prepared on bicrystal substrates by molecular beam epitaxy and micro structuring. The samples were characterised by measuring the thin film resistivity and the tunnel conductance of quasi particles across the grain boundary. By these measurements an unconventional symmetry of the order parameter could be revealed for La{sub 2-x}Ce{sub x}CuO{sub 4}. Furthermore it was shown, that the tunnel conductance can be used as a probe for the upper critical field B{sub c2}(T). By using this method a value of B{sub c2}{proportional_to}24 T has been found for La{sub 2-x}Ce{sub x}CuO{sub 4}, a value roughly three times bigger than previously known. By this observation it was shown that the superconducting phase covers a larger region in the B-T-phase diagram. In addition it was concluded, that the pseudogap phase in La{sub 2-x}Ce{sub x}CuO{sub 4} is either not existent at all or covers only a small temperature region. Besides quasiparticle tunneling also the tunneling of Cooper pairs in small magnetic fields has been investigated. It was shown that the critical current across the grain boundary depends on the supplier of the bicrystal substrate. (orig.)

  8. Critical properties of the high-energy electron-beam-irradiated superconductor weak links

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sung Hoon; Lee, Soon Gul [Korea University, Sejong (Korea, Republic of)

    2014-11-15

    We have studied the effects of high-energy electron-beam irradiation on the superconducting transition properties of an YBCO bicrystal junction, a focused ion-beam (FIB)-patterned YBCO nanobridge, a MgB{sub 2} intergrain nanobridge, and a BaKFeAs multigrain microbridge. We used one sample for each junction type and repeated the irradiation-and-measurement process at 6 accumulated-dose steps: 0, 3 x 10{sup 14}, 10{sup 15}, 3 x 10{sup 15}, 10{sup 16}, and 10{sup 17} e/cm{sup 2}. A uniform electron beam with a 1-MeV kinetic energy was irradiated indiscrimately over the samples. We measured the resistive transition temperature, the normal-state resistance, and the critical current. The irradiation effect was significant for all the samples except the BaKFeAs microbridge. The critical current data for the YBCO bicrystal junction and the MgB{sub 2} intergrain nanobridge had a maximum at 3 x 10{sup 15} e/cm{sup 2}, and the YBCO nanobridge showed a monotonic decrease. For all the samples, the normal state resistance increased monotonically with increasing dose by up to ∼20% at 10{sup 16} e/cm{sup 2}, and the change in T{sub c} was negligible. The results showed that the YBCO and MgB{sub 2} weak links were susceptive to irradiation, indicating the possibility of controlling the critical current of those junctions by using high-energy electron-beam irradiation.

  9. Characteristics of an HTS-SQUID gradiometer with ramp-edge Josephson junctions and its application on robot-based 3D-mobile compact SQUID NDE system

    International Nuclear Information System (INIS)

    We investigated behavior of HTS-dc-SQUID gradiometers with ramp-edge Josephson junctions (JJs) in ac and dc magnetic fields. In the both fields, the gradiometers show higher durability against entry of flux vortices than SQUIDs with bicrystal JJs. A robot-based SQUID NDE system utilizing the gradiometer was developed in an unshielded environment. Detectability of the system to detect non-through cracks in double-layer structures was demonstrated. A new excitation coil was applied to detect cracks that oriented vertical and parallel to the baseline of the gradiometer. In this paper, we investigated detailed behavior of novel HTS-dc-SQUID gradiometers with ramp-edge Josephson junctions (JJs) in both an ac magnetic field and a dc magnetic field. In the both fields, the novel gradiometers shows the superior performance to the conventional YBa2Cu3O7-x (YBCO) HTS-dc-SQUID gradiometer and a bare HTS-dc-SQUID ring with bicrystal JJs concerning durability against entry and hopping of flux vortices, probably due to their differential pickup coils without a grain boundary and multilayer structure of the ramp-edge JJs. A robot-based compact HTS-SQUID NDE system utilizing the novel gradiometer was reviewed, and detectability of the system to detect non-through cracks in a carbon fiber reinforced plastic (CFRP)/Al double-layer structure was demonstrated. A new excitation coil in which the supplied currents flowed in the orthogonal directions was applied to detect cracks that oriented vertical and parallel to the baseline of the gradiometer.

  10. Behaviour and damage of aged austenitic-ferritic steels: a micro-mechanical approach; Comportement et endommagement des aciers austeno-ferritiques vieillis: une approche micromecanique

    Energy Technology Data Exchange (ETDEWEB)

    Bugat, St

    2000-12-15

    The austenitic-ferritic steels are used in the PWR primary cooling system. At the running temperature (320 C), they are submitted to a slow aging, which leads to the embrittlement of the ferritic phase. This embrittlement leads to a decrease of the mechanical properties, in particular of the crack resistance of the austenitic-ferritic steels. The damage and rupture of the austenitic-ferritic steels have been approached at the ENSMP by the works of P. Joly (1992) and of L. Devilliers-Guerville (1998). These works have allowed to reveal a damage heterogeneity which induces a strong dispersion on the ductilities and the toughnesses as well as on the scale effects. Modeling including the damage growth kinetics measured experimentally, have allowed to verify these effects. Nevertheless, they do not consider the two-phase character of the material and do not include a physical model of the cleavage cracks growth which appear in the embrittled ferrite. In this study, is proposed a description of the material allowing to treat these aspects while authorizing the structure calculation. In a first part, the material is studied. The use of the ESBD allows to specify the complex morphology of these steels and crystal orientation relations between the two phases. Moreover, it is shown that the two phases keep the same crystal orientation in the zones, called bicrystals, whose size varies between 500 {mu}m and 1 mm. The study of the sliding lines, coupled to the ESBD, allows to specify too the deformation modes of the two phases. At last, tensile and tensile-compression tests at various deformation range are carried out to characterize the macroscopic mechanical behaviour of these materials. Then, a micro-mechanical modeling of the material behaviour is proposed. This one takes into account the three scales identified at the preceding chapter. The first scale, corresponding to the laths is described as a monocrystal whose behaviour includes both an isotropic and a kinematic

  11. Behaviour and damage of aged austenitic-ferritic steels: a micro-mechanical approach

    International Nuclear Information System (INIS)

    The austenitic-ferritic steels are used in the PWR primary cooling system. At the running temperature (320 C), they are submitted to a slow aging, which leads to the embrittlement of the ferritic phase. This embrittlement leads to a decrease of the mechanical properties, in particular of the crack resistance of the austenitic-ferritic steels. The damage and rupture of the austenitic-ferritic steels have been approached at the ENSMP by the works of P. Joly (1992) and of L. Devilliers-Guerville (1998). These works have allowed to reveal a damage heterogeneity which induces a strong dispersion on the ductilities and the toughnesses as well as on the scale effects. Modeling including the damage growth kinetics measured experimentally, have allowed to verify these effects. Nevertheless, they do not consider the two-phase character of the material and do not include a physical model of the cleavage cracks growth which appear in the embrittled ferrite. In this study, is proposed a description of the material allowing to treat these aspects while authorizing the structure calculation. In a first part, the material is studied. The use of the ESBD allows to specify the complex morphology of these steels and crystal orientation relations between the two phases. Moreover, it is shown that the two phases keep the same crystal orientation in the zones, called bicrystals, whose size varies between 500 μm and 1 mm. The study of the sliding lines, coupled to the ESBD, allows to specify too the deformation modes of the two phases. At last, tensile and tensile-compression tests at various deformation range are carried out to characterize the macroscopic mechanical behaviour of these materials. Then, a micro-mechanical modeling of the material behaviour is proposed. This one takes into account the three scales identified at the preceding chapter. The first scale, corresponding to the laths is described as a monocrystal whose behaviour includes both an isotropic and a kinematic strain

  12. Interaction between phase transformations and dislocations at the nanoscale. Part 2: Phase field simulation examples

    Science.gov (United States)

    Javanbakht, Mahdi; Levitas, Valery I.

    2015-09-01

    The complete system of phase field equations for coupled martensitic phase transformations (PTs), dislocation evolution, and mechanics at large strains is presented. Finite element method (FEM) is utilized to solve this system for two important problems. The first one is related to the simulation of shear strain-induced PT at the evolving dislocation pile-ups in a nanosized bicrystal. Plasticity plays a dual part in the interaction with PT. Dislocation pile-ups produce strong stress tensor concentrators that lead to barrierless martensite (M) nucleation. On the other hand, plasticity in the transforming grain relaxes these stress concentrators suppressing PT. The final stationary M morphology is governed by the local thermodynamic equilibrium, either at the interfaces or in terms of stresses averaged over the martensitic region or the entire grain. This is very surprising because of strong heterogeneity of stress fields and is in contrast to previous statements that phase equilibrium conditions do not enter the description of strain-induced PTs. The second problem is devoted to martensitic plate propagation through a bicrystal during temperature-induced PT. For elastic growth (without dislocations) and a large thermal driving force, a complex transformation path with plate branching and direct and reverse PTs is observed, which still ends with the same stationary nanostructure as for a smaller driving force and a traditional transformation path. Sharp grain boundary arrests plate growth at a relatively small driving force, exhibiting an athermal friction. For elastoplastic growth, the generation of dislocations produces athermal friction and arrests the plate below some critical driving force, leading to a morphological transition from plate to lath M. The width of the martensitic plate increases in comparison with elastic growth due to internal stress relaxation. Plate growth is accompanied by the nucleation of dislocations within M and remaining in M, the

  13. Synthesis of Uniformly Distributed Single- and Double-sided Zinc Oxide (ZnO) Nanocombs

    Energy Technology Data Exchange (ETDEWEB)

    Petford-Long, Amanda K.; Liu, Yuzi; Altintas Yildirim, Ozlem

    2015-11-15

    Uniformly distributed single- and double-sided zinc oxide (ZnO) nanocomb structures have been prepared by a vapor-liquid-solid technique from a mixture of ZnO nanoparticles and graphene nanoplatelets. The ZnO seed nanoparticles were synthesized via a simple precipitation method. The structure of the ZnO nanocombs could easily be controlled by tuning the carrier-gas flow rate during growth. Higher flow rate resulted in the formation of uniformly-distributed single-sided comb structures with nanonail-shaped teeth, as a result of the self-catalysis effect of the catalytically active Zn-terminated polar (0001) surface. Lower gas flow rate was favorable for production of double-sided comb structures with the two sets of teeth at an angle of similar to 110 degrees to each other along the comb ribbon, which was attributed to the formation of a bicrystal nanocomb ribbon. The formation of such a double-sided structure with nanonail-shaped teeth has not previously been reported.

  14. Dislocation transmission through a Σ=3 grain boundary in Fe 6 at.% Si: In situ experiments in compression specimen

    International Nuclear Information System (INIS)

    Fe 6 at.% Si bicrystals were observed by in situ X-ray Topography with a monochromatic beam during a compression test by surface reflection. The primary slip system was the same in both grains. As the specimen contains subgrain boundaries (GBs), it had to be rocked during exposure to ensure imaging of the whole gauge length. Images were recorded both on X-ray films (rocking with the specimen) and using a fixed X-ray camera. The distortions of the images were used to investigate stress repartition in the whole specimen and local stress concentrations at points where slip bands met the GB. In the present case, slip transfer through the GB was apparently easy. However, a careful analysis of stresses within the specimen shows it was not the case. In Fe 6% Si, the creation and motion of slip bands is very sensitive to local stress. Transmission occurs on the most stressed surface, at the tip of slip bands containing a few hundred dislocations. The transmitted slip bands then propagate through the bulk of the specimen to less stressed areas. A careful analysis using all available experimental data is, thus, necessary to avoid misinterpretation

  15. Spatially resolved analytical electron microscopy at grain boundaries of {alpha}-Al{sub 2}O{sub 3}; Ortsaufgeloeste analytische Elektronenmikroskopie an Korngrenzen in {alpha}Al{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Nufer, S.

    2001-10-01

    Aluminum oxide, {alpha}-Al{sub 2}O{sub 3}, is a common structural ceramic material. The most technologically important properties are either determined or strongly influenced by the polycrystalline microstructure. For instance, the grain boundaries control the mechanical behavior (e.g. plasticity, creep, and fracture) or various transport phenomena (e.g. ion diffusion, segregation, and electrical resistivity). In order to understand the structure-properties relationships, it is therefore important to characterize the structure and chemistry of grain boundaries, both experimentally and theoretically. In this work the electronic structure of the basal and rhombohedral twin grain boundaries and the impurity excess at different tilt grain boundaries in bicrystals were investigated, using electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). The electronic structure of the rhombohedral twin grain boundary was determined by comparing spatially resolved EELS measurements of the O-K ionisation edge with the theoretical density of states (DOS), obtained from local density functional theory (LDFT) calculations. The interface excess of impurities was quantitatively analysed at grain boundaries with and without Y-doping. (orig.)

  16. Dual flux-to-voltage response of YBa2Cu3O7−δ asymmetric parallel arrays of Josephson junctions

    International Nuclear Information System (INIS)

    We fabricated a parallel array of 440 YBa2Cu3O7−δ bicrystal grain boundary Josephson junctions having an inductive asymmetric loop configuration within the array. Families of current–voltage characteristics (IVCs) have been measured in the temperature range (4.7–92) K for various values of a magnetic flux applied via a control current Ictrl. For both positive and negative current biases, I current-driven chains of magnetic vortices are propagating along the array producing flux-flow current resonances on the IVCs. However, at 77 K and above, due to the system’s inductive asymmetry the flux flow is suppressed (enhanced) for negative (positive) I. Consequently, the system shows a dual flux-to-voltage response. For negative I it operates like a flux-interferometer having a rather sinusoidal V (Ictrl) response. In contrast, for positive I the device’s response V (Ictrl) remains periodic but highly non-sinusoidal due to the interplay between multiple flux-flow modes. Below 60 K such a dual behaviour is far less pronounced as a result of flux-flow modes being suppressed due to a decrease of the dissipation coefficient with temperature. (paper)

  17. YBa2Cu3O7-δ dc SQUID array for multichannel magnetometry and multichannel flip-chip current sensors

    International Nuclear Information System (INIS)

    We have prepared arrays of single-layer washer-type dc superconducting quantum interference devices (SQUIDs) on 10 mm 10 mm bicrystal substrates. Each SQUID in the array is equipped with its own modulation loop, which makes a separate operation of them possible. Arrays containing nine or 11 dc SQUIDs have been tested and the crosstalk between neighbouring channels has been found to be 5%. The field sensitivity of the SQUIDs is 85 nT Φ0-1 and 105 nT Φ0-1 for the nine- and 11-device array, respectively. The equivalent flux noise is typically ≤ 20 μΦ0 Hz-1/2 down to 1 Hz with ac bias reversal. A field resolution of less than 2.1 pT Hz-1/2 has been obtained for at least eight channels on a chip. By using multiturn YBa2Cu3O7-δ input coils and mounting them in a flip-chip configuration together with the single-layer dc SQUIDs we have been able to build three-channel current sensors. The current sensitivity equals 3-3.5 μA Φ0-1 depending on the alignment of the flip-chip configuration. The current resolution of the devices is -1/2. We show the possibility of building sensitive magnetometers by connecting the input coil of these current sensors to a normal-conducting pickup antenna. (author)

  18. A two-dimensional study of coupled grain boundary motion using the level set method

    International Nuclear Information System (INIS)

    The coupled motion of a closed non-circular grain boundary (GB) in a bicrystal, with both isotropic and anisotropic GB energies, is studied using the level set method. The kinetic relations, obtained within the framework of linear irreversible thermodynamics, govern the overall dynamics, including normal motion (migration) of the GB, viscous sliding along the GB and tangential motion of the grains which is geometrically coupled with the migration. The shape accommodation necessary to maintain coherency of relatively rotating and non-deforming grains is accomplished by allowing for diffusion along the GB. We solve the governing equations for the coupled motion in order to determine the shape and the misorientation evolution of an isolated GB under various constitutive assumptions. First, assuming both GB energy and kinetic coefficients to be isotropic, we study the interplay between kinetic coefficients for initially circular, near-circular and non-circular GBs, as well as the impact of stress and initial conditions on the GB dynamics. Next, we study the influence of anisotropy in the GB energy, mobility and geometric coupling for various combinations of parameters and initial conditions. Allowing for geometric coupling can in fact lead to shapes distinctly different to those that are usually predicted on the basis of migration alone. Our numerical scheme provides a general framework in which to study these and other related problems of GB motion. (paper)

  19. Grain boundary engineering with gold nanoparticles

    International Nuclear Information System (INIS)

    We investigated high-TC grain boundary Josephson junctions with and without incorporated gold nanoparticles. Pulsed laser deposition was used for the deposition of YBa2Cu3O7−δ thin films on SrTiO3 bicrystal substrates with different grain boundary angles. During the deposition process, single-crystalline nanoparticles self-assembled from a thin gold layer which was sputtered on the substrate before the YBCO deposition. The interaction between nanoparticles and thin film growth significantly influences the quality of the YBCO films [1]. The critical current density and the critical temperature of the superconducting films can be increased in a defined manner. Furthermore, the nanoparticles influence the growth conditions in the region of the grain boundary and thus the properties of the later patterned Josephson junctions. The comparison between Josephson junctions with and without nanoparticles on the same substrate shows a reduction of the critical current IC and an increase of the normal state resistance RN for all investigated types of grain boundaries in the areas with gold nanoparticles. In some cases we even found an increase of the resulting ICRN product. We present the influence of light irradiation on the properties of the Josephson junctions.

  20. Preparation and properties of two types of submicron high-Tc Josephson junctions

    International Nuclear Information System (INIS)

    There is a variety of different types of high-Tc Josephson junctions corresponding to the short coherence length, high anisotropy and some interface problems of the oxide superconductors. Using submicron technologies nanobridges and bridges modified by ion beams in a hundred nanometer region can be fabricated. Depending on preparation parameters the ion beam influence causes implantation, sputtering or a modification of the lattice changing the superconducting properties. The case of modification is discussed in details. It is shown how parameters of the preparation process influence the physical properties of these junctions. The application of such junctions is shown for DC-SQUIDs and gradiometers including a comparison to other junction types like bicrystal or step-edge junctions. Submicron technology is useful for preparation of intrinsic stacked junctions out of thin films. In this case the single junction dimension is determined by the coupling of two copper oxide planes in an atomic scale. A mesa structure acts as a series connection of a number of single junctions corresponding to the stack height. Preparation and physical properties of these types of junction arrays are given in detail. The possible application of such new kind of devices as radiation sources or voltage standard will be discussed

  1. Use of tracer techniques for studying the influence of addition elements and crystallographic parameters on intergranular diffusion in austenitic stainless steels

    International Nuclear Information System (INIS)

    16% chromium, 14% nickel stainless steel, austenitic at all temperatures, covers a wide field of industrial use. Its behavior was studied in order to find out more about how impurities affect the three basic elements forming the solid solution. After a review of some general properties (segregation, precipitation, migration, structure and energy of boundaries) the physico-chemical aspect of the grain boundaries was investigated. The atomic diffusion rates of the three basic elements forming the solid-solution were compared in order to evaluate their mutual kinetics and the effects of impurities such as C, Si or addition elements such as Ni were studied. The radiotracer technique was used (59Fe, 51Cr, 63Ni). The structural aspect of the grain boundaries of this type of steel was then examined by analyzing the self-diffusion of iron in preoriented bicrystals and considering the properties of the boundaries parallel with and perpendicular to the (001) bending axis. A study was devoted to the effect of a new structural parameter, asymmetry of the grain boundaries, little analyzed in diffusion

  2. Resonant behavior of the barrier of YBa2Cu3O7 grain boundary Josephson junctions fabricated on bicrystalline substrates with different geometries

    International Nuclear Information System (INIS)

    We have analyzed a resonant behavior in the dielectric constant associated to the barrier of YBa2Cu3O7 (YBCO) grain boundary Josephson junctions (GBJJs) fabricated on a wide variety of bicrystalline substrates: 12° [0 0 1] tilt asymmetric, 24° [0 0 1] tilt asymmetric, 24° [0 0 1] tilt symmetric, 24° [1 0 0] tilt asymmetric, 45° [1 0 0] tilt asymmetric and 24° [0 0 1] tilt symmetric +45° [1 0 0] tilt asymmetric bicrystals. The resonance analysis allows us to estimate a more appropriate value of the relative dielectric constant, and so a more adequate value for the length L of the normal N region assuming a SNINS model for the barrier. In this work, the L dependence on the critical current density Jc has been investigated. This analysis makes possible a single representation for all the substrate geometries independently on around which axes the rotation is produced to generate the grain boundary. On the other hand, no clear evidences exist on the origin of the resonance. The resonance frequency is in the order of 1011 Hz, pointing to a phonon dynamic influence on the resonance mechanism. Besides, its position is affected by the oxygen content of the barrier: a shift at low frequencies is observed when the misorientation angle increases.

  3. Structure of screw dislocations in a (0 0 0 1)/[0 0 0 1] low-angle twist grain boundary of alumina (α-Al2O3)

    International Nuclear Information System (INIS)

    An alumina (α-Al2O3) bicrystal with a (0 0 0 1)/[0 0 0 1] low-angle twist grain boundary was fabricated by bonding two (0 0 0 1) substrates at 1500 °C in air. Dislocation structures in the resultant grain boundary were extensively observed in plan view and cross-sectional direction by transmission electron microscopy (TEM). The grain boundary consisted of a hexagonal dislocation network of 1/3〈12¯10〉 basal screw dislocations and wavy belt structures. The atomic core structure of the screw dislocations was analyzed in end-on view by high-resolution TEM. It was evident that the 1/3〈12¯10〉 basal screw dislocation does not dissociate into partial dislocations, which is in contrast to the 1/3〈12¯10〉 basal edge dislocation that dissociates into 1/3〈11¯00〉 and 1/3〈01¯10〉 partial dislocations. Also, TEM observation revealed that the wavy belt structures correspond to planar voids. From the morphology of the planar voids, it is considered that they accommodate a slight tilt component of the boundary.

  4. Optimization of a 115 GHz waveguide mixer based on an HTS Josephson junction

    International Nuclear Information System (INIS)

    A waveguide mixer based on a Josephson junction made from a high-temperature superconductor (HTS) has been analysed at frequencies of 90 GHz and 115 GHz. The mixer consisted of a single-grain-boundary bicrystal junction which was integrated with a bow-tie antenna and a microstrip filter structure fabricated on an MgO substrate. Two different designs of mixer block were tested. Using the first design the best noise performance was measured at a local oscillator (LO) frequency of about 90 GHz. At the projected LO frequency of 115 GHz significant deterioration of performance was observed. A computer simulation of the mixer chip and substrate channel structure was performed using the 3D simulation program HFSS. Sufficient RF signal rejection by the filter structure was confirmed at 90 GHz. After a simulation cycle at 115 GHz the substrate channel in the mixer block was modified. Using this second design we measured a double-sideband mixer noise temperature of 1090 K at 10 K operating temperature which is the best performance of an HTS Josephson mixer to date obtained at this frequency and temperature. (author)

  5. Properties of the quantum Hall effect of the two-dimensional electron gas in the n-inversion layer of InSb grain boundaries under high hydrostatic pressure

    International Nuclear Information System (INIS)

    The magnetotransport properties of the two-dimensional electron gas (2DEG) confined at the interface of the grain boundary in p-type InSb bicrystals are investigated. Under high hydrostatic pressures and in high magnetic fields (B > 5 T) the integral quantum Hall regime is reached, where the Hall resistance ρxy is quantized to h/e2j (j is the number of filled Landau levels of the 2DEG). In this high field regime detailed measurements are given of the resistivity ρxx and the Hall resistance ρxy as function of temperature T and current density jx. An unexpected high accuracy of the Hall resistance ρxy at magnetic field values close to a fully occupied Landau level is found, despite the high value of the diagonal resistivity ρxx. At high current densities jx in the quantum Hall regime (j = 1) a sudden breakdown of the quantized resistance value associated with a jump-like switching to the next lower quantized value h/2e2 is observed. A simple macroscopic picture is proposed to account for these novel transport properties associated with the quantum Hall effect. (author)

  6. Development of a neutron irradiation device with a cooled crystal filter: Radiation physical properties and applications in in vivo irradiations

    International Nuclear Information System (INIS)

    The radiation-physical and geometrical properties of a neutron-beam, collimated with a Bi-crystal filter were investigated at the reactor BER II. The influence of the crystal temperature as well as the actions of a reflector and a collimator on neutron flux-density and neutron field of the thermal neutrons were investigated. The dose contributions of the thermal, epithermal and fast neutrons as well as γ-radiation was determined by activation of the sample respective with TLD-measurements. The influence of irradiation and measurement geometry on the sensitivity and detection probability was investigated by means of phantom irradiations. The method prooved to be suitable, to detect changes of the Ca-content in a rat hind leg by about 10%. In investigations on animal groups of about 10 animals a threshold of detectability for changes of the ca-content is to be expected by about 4%. In a further group experiment it was found, that even in the case of multiple radiation the procedure of irradiation and measurement was not followed by a significant change in the Ca-content of the hind legs of the testing animals. (orig.)

  7. A scanning SQUID microscope with 200 MHz bandwidth

    International Nuclear Information System (INIS)

    We developed a scanning DC SQUID microscope with novel readout electronics capable of wideband sensing of RF magnetic fields from 50 to 200 MHz and simultaneously providing closed-loop response at kHz frequencies. To overcome the 20 MHz bandwidth limitation of traditional closed-loop SQUIDs, a flux-modulated closed-loop simultaneously locks the SQUID quasi-static flux and flux-biases the SQUID for amplification of the RF flux up to Φ0/4 in amplitude. Demodulating the SQUID voltage with a double lock-in technique yields a signal representative of both the amplitude and phase of the RF flux. This provides 80 dB of a linear dynamic range with a flux noise density of 4 μΦ0 Hz−1/2 at 200 MHz for a Y Ba2Cu3O7 bi-crystal SQUID at 77 K. We describe the electronics’ performance and present images for RF magnetic field of the travelling wave in a coplanar waveguide, the standing wave in an open-circuited microstrip, and a surface mounted device antenna. (paper)

  8. Characterization of directly coupled YBa2Cu3O7-x SQUID magnetometers

    International Nuclear Information System (INIS)

    Superconducting Quantum Interference Devices (SQUIDs) can be employed as highly sensitive magnetic field sensors in a variety of applications such as magnetoencephalography or magnetic nanoparticle detection. We fabricated SQUIDs from the high-Tc superconductor YBa2Cu3O7-x on symmetric SrTiO3-bicrystal substrates by pulsed laser deposition and argon ion etching. The layout consists of two directly coupled magnetometers on one chip which are attached to a rectangular pickup loop. The measurements were carried out in a liquid nitrogen container using a variable temperature insert. The temperature at the magnetically shielded sample holder can be adjusted between 77 K and 100 K. Here, we present measurements of the I-V-curves under the influence of a magnetic field for different sample temperatures. Also, the influence of the temperature and the influence of the bias current on the V-Φ-curves were investigated. From these measurements, parameters of the SQUID were calculated and compared to the theoretical estimations. Additionally, noise spectra were recorded for different bias reversal frequencies by using a direct-coupled flux-locked loop electronics from Magnicon GmbH.

  9. Influence of point defects on grain boundary diffusion in oxides. Final technical report, July 1, 1990--June 30, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Stubican, V.S.

    1993-11-01

    Grain boundary diffusion coefficients of {sup 57}Co and {sup 59}Co in polycrys. NiO, NiO bicrystal, and polycrys. Fe{sub 3}O{sub 4} were determined at various oxygen pressures at 750 C. For NiO, the low oxygen pressure region (<10{sup {minus}10} MPa) displayed constant grain boundary diffusion coefficients as the oxygen pressure decreased, indicating an extrinsic region in which the impurity-induced defects dominated the intrinsic defects. At greater oxygen pressures, the intrinsic defects (Ni vacancies) dominated the extrinsic defects, causing the diffusion to increase with pressure. For Fe{sub 3}O{sub 4}, at low oxygen pressures (<10{sup {minus}16} MPa), the grain boundary diffusion coefficient increased when the pressure decreased, owing to interstitial type diffusion; at >10{sup {minus}15} MPa, the diffusion increased with pressure, owing to vacancy type diffusion. D{sub gb} of Co ions in Fe{sub 3}O{sub 4} is proportional to pO{sub 2}{sup {minus}2/3} in the low pressure region and to pO{sub 2}{sup 2/3} in the high pressure region, indicating similar mechanisms in the grain boundary diffusion and volume diffusion. Ratio of D{sub gb}/D was about 10{sup 3}.

  10. NiFe epitaxial films with hcp and fcc structures prepared on bcc-Cr underlayers

    Energy Technology Data Exchange (ETDEWEB)

    Higuchi, Jumpei, E-mail: higuchi@futamoto.elect.chuo-u.ac.jp [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan); Ohtake, Mitsuru; Sato, Yoichi [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan); Kirino, Fumiyoshi [Graduate School of Fine Arts, Tokyo National University of Fine Arts and Music, 12-8 Ueno-koen, Taito-ku, Tokyo 110-8714 (Japan); Futamoto, Masaaki [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan)

    2011-09-30

    NiFe epitaxial films are prepared on Cr(211){sub bcc} and Cr(100){sub bcc} underlayers grown hetero-epitaxially on MgO single-crystal substrates by ultra-high vacuum rf magnetron sputtering. The film growth behavior and the crystallographic properties are studied by reflection high energy electron diffraction and pole figure X-ray diffraction. Metastable hcp-NiFe(11-bar 00) and hcp-NiFe(112-bar 0) crystals respectively nucleate on Cr(211){sub bcc} and Cr(100){sub bcc} underlayers, where the hcp-NiFe crystals are stabilized through hetero-epitaxial growth. The hcp-NiFe(11-bar 00) crystal is a single-crystal with the c-axis parallel to the substrate surface, whereas the hcp-NiFe(112-bar 0) crystal is a bi-crystal with the respective c-axes lying in plane and perpendicular each other. With increasing the film thickness, the hcp structure in the NiFe films starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001) close packed plane. The resulting films consist of hcp and fcc crystals.

  11. NiFe epitaxial films with hcp and fcc structures prepared on bcc-Cr underlayers

    International Nuclear Information System (INIS)

    NiFe epitaxial films are prepared on Cr(211)bcc and Cr(100)bcc underlayers grown hetero-epitaxially on MgO single-crystal substrates by ultra-high vacuum rf magnetron sputtering. The film growth behavior and the crystallographic properties are studied by reflection high energy electron diffraction and pole figure X-ray diffraction. Metastable hcp-NiFe(11-bar 00) and hcp-NiFe(112-bar 0) crystals respectively nucleate on Cr(211)bcc and Cr(100)bcc underlayers, where the hcp-NiFe crystals are stabilized through hetero-epitaxial growth. The hcp-NiFe(11-bar 00) crystal is a single-crystal with the c-axis parallel to the substrate surface, whereas the hcp-NiFe(112-bar 0) crystal is a bi-crystal with the respective c-axes lying in plane and perpendicular each other. With increasing the film thickness, the hcp structure in the NiFe films starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001) close packed plane. The resulting films consist of hcp and fcc crystals.

  12. Epitaxy of semiconductor-superconductor nanowires

    Science.gov (United States)

    Krogstrup, P.; Ziino, N. L. B.; Chang, W.; Albrecht, S. M.; Madsen, M. H.; Johnson, E.; Nygård, J.; Marcus, C. M.; Jespersen, T. S.

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures.

  13. A New Generation of the HTS Multilayer DC-SQUID Magnetometers and Gradiometers

    International Nuclear Information System (INIS)

    We have optimized the preparation of submicrometer wide symmetric 200 bicrystal Josephson junctions on the basis of YBa2Cu3O7-x (YBCO) films and integrated them in SQUID magnetometers and gradiometers with multilayer flux transformers. The achieved reduction of the curvature of the grain boundary leads to an improvement of the homogeneity of the current flow in the junction due to the d-wave symmetry of the order parameter in YBCO. The junctions have typical normal resistance Rn above 10 Ω and a IcRn product of about 0.4 mV at 77.4 K. The high resistance of the junctions has required an extensive use of low pass filters, rf-shields and microwave absorbers to protect the junctions from increased interference of high frequency electromagnetic fields. Integration of such junctions in SQUID magnetometers with a square 16-mm multilayer flux transformer allowed us for the first time to reach a field resolution of about 3.5 fT/√Hz at frequencies above 10 Hz and about 7 fT/√Hz at 1 Hz at an operation temperature of 77.4 K. SQUID gradiometers with a 10 mm base length of the planar multilayer flux transformer have achieved resolutions of about 15 fT/cm√Hz at frequencies above 10 Hz and about 30 fT/cm√Hz at 1 Hz and temperature 77.4 K

  14. Resonant behavior of the barrier of YBa{sub 2}Cu{sub 3}O{sub 7} grain boundary Josephson junctions fabricated on bicrystalline substrates with different geometries

    Energy Technology Data Exchange (ETDEWEB)

    Navacerrada, M.A., E-mail: mdelosangeles.navacerrada@upm.es [Grupo de Acustica Arquitectonica, Escuela Tecnica Superior de Arquitectura, Universidad Politecnica de Madrid, Avenida Juan de Herrera 4, 28040 Madrid (Spain); Lucia, M.L.; Sanchez-Quesada, F. [Departamento Fisica Aplicada III (Electricidad y Electronica), Facultad de Cc. Fisicas, Universidad Complutense, Avenida Complutense s/n, 28040 Madrid (Spain)

    2012-12-14

    We have analyzed a resonant behavior in the dielectric constant associated to the barrier of YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) grain boundary Josephson junctions (GBJJs) fabricated on a wide variety of bicrystalline substrates: 12 Degree-Sign [0 0 1] tilt asymmetric, 24 Degree-Sign [0 0 1] tilt asymmetric, 24 Degree-Sign [0 0 1] tilt symmetric, 24 Degree-Sign [1 0 0] tilt asymmetric, 45 Degree-Sign [1 0 0] tilt asymmetric and 24 Degree-Sign [0 0 1] tilt symmetric +45 Degree-Sign [1 0 0] tilt asymmetric bicrystals. The resonance analysis allows us to estimate a more appropriate value of the relative dielectric constant, and so a more adequate value for the length L of the normal N region assuming a SNINS model for the barrier. In this work, the L dependence on the critical current density Jc has been investigated. This analysis makes possible a single representation for all the substrate geometries independently on around which axes the rotation is produced to generate the grain boundary. On the other hand, no clear evidences exist on the origin of the resonance. The resonance frequency is in the order of 10{sup 11} Hz, pointing to a phonon dynamic influence on the resonance mechanism. Besides, its position is affected by the oxygen content of the barrier: a shift at low frequencies is observed when the misorientation angle increases.

  15. Miniaturization of Micro-Solder Bumps and Effect of IMC on Stress Distribution

    Science.gov (United States)

    Choudhury, Soud Farhan; Ladani, Leila

    2016-04-01

    As the joints become smaller in more advanced packages and devices, intermetallic (IMCs) volume ratio increases, which significantly impacts the overall mechanical behavior of joints. The existence of only a few grains of Sn (Tin) and IMC materials results in anisotropic elastic and plastic behavior which is not detectable using conventional finite element (FE) simulation with average properties for polycrystalline material. In this study, crystal plasticity finite element (CPFE) simulation is used to model the whole joint including copper, Sn solder and Cu6Sn5 IMC material. Experimental lap-shear test results for solder joints from the literature were used to validate the models. A comparative analysis between traditional FE, CPFE and experiments was conducted. The CPFE model was able to correlate the experiments more closely compared to traditional FE analysis because of its ability to capture micro-mechanical anisotropic behavior. Further analysis was conducted to evaluate the effect of IMC thickness on stress distribution in micro-bumps using a systematic numerical experiment with IMC thickness ranging from 0% to 80%. The analysis was conducted on micro-bumps with single crystal Sn and bicrystal Sn. The overall stress distribution and shear deformation changes as the IMC thickness increases. The model with higher IMC thickness shows a stiffer shear response, and provides a higher shear yield strength.

  16. High temperature superconducting thin films and quantum interference devices (SQUIDs) for gradiometers

    CERN Document Server

    Graf zu Eulenburg, A

    1999-01-01

    the best balance and gradient sensitivity at 1kHz were 3x10 sup - sup 3 and 222fT/(cm sq root Hz))) respectively. The measured spatial response to a current carrying wire was in good agreement with a theoretical model. A significant performance improvement was obtained with the development of a single layer gradiometer with 13mm baseline, fabricated on 30x10mm sup 2 bicrystals. For such a device, the gradient sensitivity at 1kHz was 50fT/(cm sq root Hz)) and the gradiometer was used successfully for unshielded magnetocardiography. A parasitic effective area compensation scheme was employed with two neighbouring SQUIDs coupled in an opposite sense to the same gradiometer loop. This improved the balance from the intrinsic value of 10 sup - sup 3 to 3x10 sup - sup 5. This thesis describes several aspects of the development of gradiometers using high temperature Superconducting Quantum Interference Devices (SQUID). The pulsed laser deposition of thin films of YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (YBCO) on Sr...

  17. A simple and inclusive method to determine the habit plane in transmission electron microscope based on accurate measurement of foil thickness

    International Nuclear Information System (INIS)

    A simple and inclusive method is proposed for accurate determination of the habit plane between bicrystals in transmission electron microscope. Whilst this method can be regarded as a variant of surface trace analysis, the major innovation lies in the improved accuracy and efficiency of foil thickness measurement, which involves a simple tilt of the thin foil about a permanent tilting axis of the specimen holder, rather than cumbersome tilt about the surface trace of the habit plane. Experimental study has been done to validate this proposed method in determining the habit plane between lamellar α2 plates and γ matrix in a Ti–Al–Nb alloy. Both high accuracy (± 1°) and high precision (± 1°) have been achieved by using the new method. The source of the experimental errors as well as the applicability of this method is discussed. Some tips to minimise the experimental errors are also suggested. - Highlights: • An improved algorithm is formulated to measure the foil thickness. • Habit plane can be determined with a single tilt holder based on the new algorithm. • Better accuracy and precision within ± 1° are achievable using the proposed method. • The data for multi-facet determination can be collected simultaneously

  18. Epitaxy of semiconductor-superconductor nanowires.

    Science.gov (United States)

    Krogstrup, P; Ziino, N L B; Chang, W; Albrecht, S M; Madsen, M H; Johnson, E; Nygård, J; Marcus, C M; Jespersen, T S

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures. PMID:25581626

  19. Interaction of shear-coupled grain boundary motion with crack: Crack healing, grain boundary decohesion, and sub-grain formation

    Science.gov (United States)

    Aramfard, Mohammad; Deng, Chuang

    2016-02-01

    Stress-driven grain boundary motion is one of the main mechanisms responsible for microstructural evolution in polycrystalline metals during deformation. In this research, the interaction of shear-coupled grain boundary motion (SCGBM) in face-centered cubic metals with crack, which is a common type of structural defects in engineering materials, has been studied by using molecular dynamics simulations in simple bicrystal models. The influences of different parameters such as metal type, temperature, grain boundary structure, and crack geometry have been examined systematically. Three types of microstructural evolution have been identified under different circumstances, namely, crack healing, grain boundary decohesion, and sub-grain formation. The underlying atomistic mechanisms for each type of SCGBM-crack interaction, particularly grain boundary decohesion and crack healing, have also been examined. It is found that crack healing is generally favoured during the SCGBM-crack interaction at relatively high temperature in metals with relatively low stacking fault energy and grain boundary structure with relatively low misorientation angles. The results of this work may open up new opportunities for healing severely damaged materials.

  20. UHV-cluster-tool for fabrication of thin film structures and transport- and noise properties of YBa2Cu3O7-δ grain boundary-SQUIDs

    International Nuclear Information System (INIS)

    A UHV-thin-film-deposition system for the fabrication of thin film structures of metals and oxides was designed and optimized. For oxide materials, Pulsed Laser Deposition (PLD) was implemented. Epitaxial thin film growth can be analyzed during the PLD process by high-pressure RHEED (Reflection High-Energy Electron Diffraction). Furthermore layer-by-layer growth can be triggered by Pulsed Laser Intervall Deposition (PLiD). Heteroepitaxial multilayers can be fabricated automatically. Metal thin films can be grown by planar magnetron sputtering and by electron beam evaporation. Furthermore the system contains an rf-plasma source for surface cleaning and Ion Beam Etching (IBE). The three different deposition techniques are located in separate vacuum chambers which are connected by a central handling chamber allowing to combine all these processes in-situ. Furthermore superconducting quantum interference devices (SQUIDs) were fabricated out of epitaxially grown high-temperature superconducting YBa2Cu3O7-films on bicrystals. The SQUIDs were structured using a combined process of ion milling and chemical wet etching. By this combined etching process, edge signals that appear during imaging of flux quanta by low temperature scanning microscopy can be avoided. The transport- and noise properties of the SQUIDs were investigated. (orig.)

  1. The structure and properties of grain boundaries in Ni3Al

    International Nuclear Information System (INIS)

    This paper reports that the mechanical behavior of polycrystalline intermetallic compounds are often strongly influenced by the properties of the interfaces present. A classic example of this is the intergranular fracture exhibited by polycrystalline Ni3Al, and the dramatic increase in ductility upon the addition of small amounts of boron. It has been proposed that boron may promote the transmission of slip across grain boundaries by inducing the formation of a local region of compositional disorder. The results of experimental efforts to characterize the effect of boron on the structure and chemistry of these grain boundaries are summarized. Recent high resolution transmission electron miroscopy studies using oriented bicrystals are described which indicate that there is no apparent change in the compositional ordering to within 0.5 nm from the boundary. These experimental results are compared with the results of atomistic calculations which have been used to examine the effect of stoichiometry and boron content on the energy and degree of ordering of these boundaries. The proposed mechanisms of intergranular fracture in Ni3Al are discussed based on the experimental and theoretical work

  2. Simulations of thermal conductance across tilt grain boundaries in graphene

    Institute of Scientific and Technical Information of China (English)

    Peng Wang; Bo Gong; Qiong Feng; Hong-Tao Wang

    2012-01-01

    Non-equilibrium molecular dynamics (MD) method was performed to simulate the thermal transportation process in graphene nanoribbons (GNRs).A convenient way was conceived to introduce tilt grain boundaries (GBs) into the graphene lattice by repetitive removing C atom rows along certain directions.Comprehensive MD simulations reveal that larger-angle GBs are effective thermal barriers and substantially reduce the average thermal conductivity of GNRs.The GB thermal conductivity is ~ 10 W.m-1·K-1 for a bicrystal GNR with a misorientation of 21.8°,which is ~97% less than that of a prefect GNR with the same size.The total thermal resistance has a monotonic dependence on the density of the 5-7 defects along the GBs.A theoretical model is proposed to capture this relation and resolve the contributions by both the reduction in the phonon mean free path and the defect-induced thermal resistance.

  3. Simulation on Grain Boundary Sliding during Superplastic Deformation Using Molecular Dynamics Method

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Grain growth and grain boundary sliding are the two main superplastic deformation mechanisms. In the paper,simulation work is focused on the sliding of a ∑3 (111) symmetric twist coincidence grain boundary, a ∑13 (110)asymmetric tilt coincidence grain boundary, and a ∑3 (110) symmetric tilt coincidence grain boundary in Al, and the energies of grain boundary for each of equilibrium configurations are computed. An embedded atom method (EAM) potential was used to simulate the atomic interactions in a bicrystal containing more than 2000 atoms. At 0 K, the relationships between total potential energy and time steps for ∑3 (111) symmetric twist coincidence grain boundary and ∑3 (110) symmetric tilt coincidence grain boundary during sliding at 2 m/s represent the periodic characteristic. However, the relationship between total potential energy and time steps for ∑13 (110) asymmetric tilt coincidence grain boundary represents the damp surge characteristic. It is found that grain boundary sliding for ∑ 3 (110) symmetric tilt coincidence grain boundary is coupled with apparent grain boundary migration.

  4. Liquid metal embrittlement studies on model systems with respect to the spallation target technology: the importance of nano-metre-thick films

    International Nuclear Information System (INIS)

    Liquid metal embrittlement (LME) is illustrated on the Cu-Bi and Cu-PbBi systems at 300 deg C using either constant strain-rate tests at 10-4 s-1 or constant load tests at 25% of yield stress. Intergranular penetration was studied in the Ni-Bi system at 700 deg C and was shown to result in the formation of slowly growing micro-metre-thick and rapidly growing nano-metre-thick films. Both induce very strong intergranular brittleness but only micro-metre-thick films are visible by SEM on polished cross-sections. Nano-metre-thick films were analysed by Auger electron spectroscopy after 'in situ' fractures within the spectrometer; in particular, a series of analyses on an Ni bicrystal proved the constant thickness of this film over several hundreds of microns. The severity of embrittlement due to bismuth penetration was confirmed in the analysis of the Ni-PbBi system. Based on these results, il is underlined that technological systems like T 91 steel / Pb or T91 / PbBi should work at temperatures below the wetting transition temperature (Tw), i. e. in the temperature range where intergranular films can't form. If it is not the case, nano-metre-thick films should be taken into account, both in the evaluation of the kinetics of embrittlement and in the modelling of intergranular penetration and LME. (authors)

  5. Grain boundary diffusion and wetting in the analysis of intergranular penetration

    Energy Technology Data Exchange (ETDEWEB)

    Wolski, K. [Centre SMS, Ecole des Mines de St-Etienne, CNRS UMR 5546 PECM, 158, cours Fauriel, 42 023 Saint Etienne (France)], E-mail: wolski@emse.fr; Laporte, V. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratoire de Metallurgie Mecanique, IMX STI LMM - Station 12, CH-1015 Lausanne (Switzerland)

    2008-11-15

    Intergranular penetration of liquid bismuth has been analysed in two pure metals, Cu at 500 deg. C and Ni at 700 deg. C, used either as polycrystals or as oriented bicrystals. At the liquid/solid interface, large grooves have developed in Cu-Bi, while micrometer-thick films were observed in Ni-Bi. The bismuth concentration measurements obtained by Auger electron spectroscopy indicate a zone of monolayer Bi segregation followed by a diffusion-type profile over a distance of the order of 100 {mu}m for Cu-Bi and a nanometer-thick film followed by similar diffusion-type profile for Ni-Bi. In both cases the kinetics of intergranular penetration and embrittlement has been shown to be parabolic. It is concluded that no wetting occurs in Cu-Bi system at 500 deg. C while Bi wets Ni at 700 deg. C. It is postulated that the mechanism of intergranular penetration operates at a very tip of the penetration front, as opposed to the tip of liquid Bi film observed by scanning electron microscopy, and must be based on diffusion rather than wetting phenomena. Some suggestions are formulated for the future research in the area of intergranular penetration that can be split in two phenomena: grain boundary wetting above the wetting transition temperature and grain boundary diffusion below.

  6. Molecular dynamics study on the grain boundary dislocation source in nanocrystalline copper under tensile loading

    Science.gov (United States)

    Zhang, Liang; Lu, Cheng; Tieu, Kiet; Pei, Linqing; Zhao, Xing; Cheng, Kuiyu

    2015-03-01

    Grain boundary (GB) is the interface between different oriented crystals of the same material, and it can have a significant effect on the many properties of materials. When the average or entire range of grain size is reduced to less than 100 nm, the conventional plastic deformation mechanisms dominated by dislocation processes become difficult and GB mediated deformation mechanisms become increasingly important. One of the mechanisms that can play a profound role in the strength and plasticity of metallic polycrystalline materials is the heterogeneous nucleation and emission of dislocations from GB. In this study, we conducted molecular dynamics simulations to study the dislocation nucleation from copper bicrystal with a number of tilt GBs that covered a wide range of misorientation angles (θ). We will show from this analysis that the mechanic behavior of GBs and the energy barrier of dislocation nucleation from GBs are closely related to the lattice crystallographic orientation, GB energy, and the intrinsic GB structures. An atomistic analysis of the nucleation mechanisms provided details of this nucleation and emission process that can help us to better understand the dislocation source in GB.

  7. Solidification in a Supercomputer: From Crystal Nuclei to Dendrite Assemblages

    Science.gov (United States)

    Shibuta, Yasushi; Ohno, Munekazu; Takaki, Tomohiro

    2015-08-01

    Thanks to the recent progress in high-performance computational environments, the range of applications of computational metallurgy is expanding rapidly. In this paper, cutting-edge simulations of solidification from atomic to microstructural levels performed on a graphics processing unit (GPU) architecture are introduced with a brief introduction to advances in computational studies on solidification. In particular, million-atom molecular dynamics simulations captured the spontaneous evolution of anisotropy in a solid nucleus in an undercooled melt and homogeneous nucleation without any inducing factor, which is followed by grain growth. At the microstructural level, the quantitative phase-field model has been gaining importance as a powerful tool for predicting solidification microstructures. In this paper, the convergence behavior of simulation results obtained with this model is discussed, in detail. Such convergence ensures the reliability of results of phase-field simulations. Using the quantitative phase-field model, the competitive growth of dendrite assemblages during the directional solidification of a binary alloy bicrystal at the millimeter scale is examined by performing two- and three-dimensional large-scale simulations by multi-GPU computation on the supercomputer, TSUBAME2.5. This cutting-edge approach using a GPU supercomputer is opening a new phase in computational metallurgy.

  8. A simple and inclusive method to determine the habit plane in transmission electron microscope based on accurate measurement of foil thickness

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Dong, E-mail: d.qiu@uq.edu.au; Zhang, Mingxing

    2014-08-15

    A simple and inclusive method is proposed for accurate determination of the habit plane between bicrystals in transmission electron microscope. Whilst this method can be regarded as a variant of surface trace analysis, the major innovation lies in the improved accuracy and efficiency of foil thickness measurement, which involves a simple tilt of the thin foil about a permanent tilting axis of the specimen holder, rather than cumbersome tilt about the surface trace of the habit plane. Experimental study has been done to validate this proposed method in determining the habit plane between lamellar α{sub 2} plates and γ matrix in a Ti–Al–Nb alloy. Both high accuracy (± 1°) and high precision (± 1°) have been achieved by using the new method. The source of the experimental errors as well as the applicability of this method is discussed. Some tips to minimise the experimental errors are also suggested. - Highlights: • An improved algorithm is formulated to measure the foil thickness. • Habit plane can be determined with a single tilt holder based on the new algorithm. • Better accuracy and precision within ± 1° are achievable using the proposed method. • The data for multi-facet determination can be collected simultaneously.

  9. Disconnections kinks and competing modes in shear-coupled grain boundary migration

    Science.gov (United States)

    Combe, N.; Mompiou, F.; Legros, M.

    2016-01-01

    The response of small-grained metals to mechanical stress is investigated by a theoretical study of the elementary mechanisms occurring during the shear-coupled migration of grain boundaries (GB). Investigating a model Σ 17 (410 ) GB in a copper bicrystal, both and GB migration modes are studied focusing on both the structural and energetic characteristics. The minimum energy paths of these shear-coupled GB migrations are computed using the nudge elastic band method. For both modes, the GB migration occurs through the nucleation and motion of disconnections. However, the atomic mechanisms of both modes qualitatively differ: While the mode presents no metastable state, the mode shows multiple metastable states, some of them evidencing some kinks along the disconnection lines. Disconnection kinks nucleation and motion activation energies are evaluated. Besides, the activation energies of the mode are smaller than those of the one except for very high stresses. These results significantly improve our knowledge of the GB migration mechanisms and the conditions under which they occur.

  10. Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

    Energy Technology Data Exchange (ETDEWEB)

    Sung, Zu-Hawn, E-mail: ZSung@uss.com [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); Now at US-Steel, Pittsburgh, US (United States); Lee, Peter J., E-mail: lee@asc.magnet.fsu.edu; Polyanskii, Anatolii, E-mail: polyanskii@asc.magnet.fsu.edu; Balachandran, Shreyas, E-mail: shreyasb@asc.magnet.fsu.edu; Chetri, Santosh, E-mail: sc13ad@my.fsu.edu [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); Larbalestier, David C., E-mail: larbalestier@asc.magnet.fsu.edu [The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States); FSU/FAMU College of Engineering (United States); Wang, Mingmin, E-mail: wangmi22@msu.edu; Compton, Christopher, E-mail: compton@nscl.msu.edu; Bieler, Thomas R., E-mail: bieler@egr.msu.edu [Michigan State University, US (United States)

    2015-12-04

    High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.

  11. Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

    Science.gov (United States)

    Sung, Zu-Hawn; Lee, Peter J.; Polyanskii, Anatolii; Balachandran, Shreyas; Chetri, Santosh; Larbalestier, David C.; Wang, Mingmin; Compton, Christopher; Bieler, Thomas R.

    2015-12-01

    High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.

  12. A method of coupling discrete dislocation plasticity to the crystal plasticity finite element method

    Science.gov (United States)

    Xu, Y.; Balint, D. S.; Dini, D.

    2016-05-01

    A method of concurrent coupling of planar discrete dislocation plasticity (DDP) and a crystal plasticity finite element (CPFE) method was devised for simulating plastic deformation in large polycrystals with discrete dislocation resolution in a single grain or cluster of grains for computational efficiency; computation time using the coupling method can be reduced by an order of magnitude compared to DDP. The method is based on an iterative scheme initiated by a sub-model calculation, which ensures displacement and traction compatibility at all nodes at the interface between the DDP and CPFE domains. The proposed coupling approach is demonstrated using two plane strain problems: (i) uniaxial tension of a bi-crystal film and (ii) indentation of a thin film on a substrate. The latter was also used to demonstrate that the rigid substrate assumption used in earlier DDP studies is inadequate for indentation depths that are large compared to the film thickness, i.e. the effect of the plastic substrate modelled using CPFE becomes important. The coupling method can be used to study a wider range of indentation depths than previously possible using DDP alone, without sacrificing the indentation size effect regime captured by DDP. The method is general and can be applied to any problem where finer resolution of dislocation mediated plasticity is required to study the mechanical response of polycrystalline materials, e.g. to capture size effects locally within a larger elastic/plastic boundary value problem.

  13. Atomistically derived cohesive zone model of intergranular fracture in polycrystalline graphene

    Science.gov (United States)

    Guin, Laurent; Raphanel, Jean L.; Kysar, Jeffrey W.

    2016-06-01

    Pristine single crystal graphene is the strongest known two-dimensional material, and its nonlinear anisotropic mechanical properties are well understood from the atomic length scale up to a continuum description. However, experiments indicate that grain boundaries in the polycrystalline form reduce the mechanical behavior of polycrystalline graphene. Herein, we perform atomistic-scale molecular dynamics simulations of the deformation and fracture of graphene grain boundaries and express the results as continuum cohesive zone models (CZMs) that embed notions of the grain boundary ultimate strength and fracture toughness. To facilitate energy balance, we employ a new methodology that simulates a quasi-static controlled crack propagation which renders the kinetic energy contribution to the total energy negligible. We verify good agreement between Griffith's critical energy release rate and the work of separation of the CZM, and we note that the energy of crack edges and fracture toughness differs by about 35%, which is attributed to the phenomenon of bond trapping. This justifies the implementation of the CZM within the context of the finite element method (FEM). To enhance computational efficiency in the FEM implementation, we discuss the use of scaled traction-separation laws (TSLs) for larger element sizes. As a final result, we have established that the failure characteristics of pristine graphene and high tilt angle bicrystals differ by less than 10%. This result suggests that one could use a unique or a few typical TSLs as a good approximation for the CZMs associated with the mechanical simulations of the polycrystalline graphene.

  14. Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces

    Science.gov (United States)

    Frechero, M. A.; Rocci, M.; Sánchez-Santolino, G.; Kumar, Amit; Salafranca, J.; Schmidt, Rainer; Díaz-Guillén, M. R.; Durá, O. J.; Rivera-Calzada, A.; Mishra, R.; Jesse, Stephen; Pantelides, S. T.; Kalinin, Sergei V.; Varela, M.; Pennycook, S. J.; Santamaria, J.; Leon, C.

    2015-12-01

    The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5 nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary.

  15. Miniaturization of Micro-Solder Bumps and Effect of IMC on Stress Distribution

    Science.gov (United States)

    Choudhury, Soud Farhan; Ladani, Leila

    2016-07-01

    As the joints become smaller in more advanced packages and devices, intermetallic (IMCs) volume ratio increases, which significantly impacts the overall mechanical behavior of joints. The existence of only a few grains of Sn (Tin) and IMC materials results in anisotropic elastic and plastic behavior which is not detectable using conventional finite element (FE) simulation with average properties for polycrystalline material. In this study, crystal plasticity finite element (CPFE) simulation is used to model the whole joint including copper, Sn solder and Cu6Sn5 IMC material. Experimental lap-shear test results for solder joints from the literature were used to validate the models. A comparative analysis between traditional FE, CPFE and experiments was conducted. The CPFE model was able to correlate the experiments more closely compared to traditional FE analysis because of its ability to capture micro-mechanical anisotropic behavior. Further analysis was conducted to evaluate the effect of IMC thickness on stress distribution in micro-bumps using a systematic numerical experiment with IMC thickness ranging from 0% to 80%. The analysis was conducted on micro-bumps with single crystal Sn and bicrystal Sn. The overall stress distribution and shear deformation changes as the IMC thickness increases. The model with higher IMC thickness shows a stiffer shear response, and provides a higher shear yield strength.

  16. Study of the annealing of defects introduced in silver by cold-working (1962)

    International Nuclear Information System (INIS)

    The tempering and the recrystallisation of silver (99.99 per cent purity) following cold-working is studied by means of density (Δd / d ≅ 5.10-6) and microhardness measurements, and of X-ray diagrams. The results depend in particular on the type and the conditions of the cold-working. For a rolling of 200 per cent carried out at temperatures under 80 deg. C, the recrystallisation occurs already at room temperature. By means of isothermal annealings it has been possible to measure the self-diffusion energy (1.90 eV). For a rolling of 200 per cent carried out at room temperature, there occurs already at 25 deg. C an increase in the density corresponding to an elimination of vacancies. For a bicrystal subjected to a 200 per cent rolling, the tempering is accompanied, from 65 to 90 deg. C, by a decrease in the density due probably to the evaporation of vacancy-impurity complexes formed during the cold-working, the impurity is very likely oxygen. At high temperature, after recrystallisation, a new and big decrease in the density let on a swelling of the silver due no doubt to slightly soluble oxygen. The density of the dislocations formed is evaluated for the different types of cold working. (author)

  17. Intergranular fracture in UO2: derivation of traction-separation law from atomistic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Yongfeng Zhang; Paul C Millett; Michael R Tonks; Xian-Ming Bai; S Bulent Biner

    2013-10-01

    In this study, the intergranular fracture behavior of UO2 was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt E5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at the propagating crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior.

  18. Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

    International Nuclear Information System (INIS)

    High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques

  19. LLE review, Volume 77. Quarterly report, October--December 1998

    Energy Technology Data Exchange (ETDEWEB)

    Regan, S.P. [ed.

    1998-12-31

    This volume of the LLE Review, covering the period October--December 1998, includes two articles addressing issues applicable to direct-drive ICF on the National Ignition Facility (NIF): laser-plasma interactions and laser-irradiation uniformity. Additional highlights of the research presented in this issue are: (1) P.B. Radha and S. Skupsky present a novel charged-particle diagnostic that performs simultaneous {rho}R measurements of the fuel, shell, and ablator regions of a compressed ICF target, consisting of an inner DT fuel region, a plastic (CH) shell, and an ablator (CD), by measuring the knock-on deuteron spectrum. (2) F. Dahmani, S. Burns, J. Lambropoulos, S. Papernov, and A. Schmid report results from stress-inhibited laser-driven crack propagation and stress-delayed damage-initiation experiments in fused silica at 351 nm. Research is underway presently to determine the ramifications of these findings for large-aperture systems, such as OMEGA. (3) V. Goncharov presents an analytic theory of the ablative Richtmyer-Meshkov instability, which shows that the main stabilizing mechanism of the ablation-front perturbations is the dynamic overpressure of the blowoff plasma with respect to the target material. The perturbation evolution during the shock transit time is studied to determine the initial conditions for the Rayleigh-Taylor phase of the instability and to analyze the level of laser imprint on ICF direct-drive targets. (4) J.M. Larkin, W.R. Donaldson, T.H. Foster, and R.S. Knox examine the triplet state of rose bengal, a dye used in photodynamic therapy, that is produced by 1,064-nm excitation of T{sub 1}. (5) R. Adam, M. Currie, R. Sobolewski, O. Harnack, and M. Darula report measurements of the picosecond photoresponse of a current-biased YBCO microbridge coupled to a bicrystal YBCO Josephson junction.

  20. Transport and microwave properties of YBa2Cu3O7-x superconducting films

    International Nuclear Information System (INIS)

    High quality YBCO c-axis oriented films were made by a laser ablation technique. Josephson weak links were fabricated on a modified microbridge by using bicrystal YBCO films. Shapiro steps were observed on modified microbridge weak links. Vortex ring nucleation by thermal activation and quantum tunneling processes in high Tc superconductors is discussed. The nonlinear resistance scales as e-(Jv/J)v. Thermal activation yields a critical index of v = 1, while quantum tunneling (without normal current dissipation) yields v = 2. I-V characteristics were measured on both disordered (low Jc), ordered (high Jc) YBCO films and microbridges below Tc. The data were examined in terms of both thermal activation and quantum tunneling models. Intrinsic critical current densities in high Tc superconducting films are discussed. The enhancement of the quantum electrodynamic tunneling process due to normal current dissipation is proposed to explain the measured Jc results for YBCO films. The limitation of Jc appears to be due to vortex ring creation. Studying Jc of bridge constrictions was a way to approach the depairing current limit. A novel microwave self-resonant (MSR) technique was developed to measure surface resistance, R8, of YBCO superconducting films directly and surface reactance, X8, indirectly. R8 at 21 GHz decreased by about three orders of magnitude as the temperature decreased from 90K to 80K. The smallest surface resistance was 2.7 x 10-4Ω at 21 GHz and at 15K, and the surface reactance was 0.031Ω. Using the MSR technique, the authors measured the London penetration depth and coherence length, and found that both λ and ξ were anisotropic, their values depended on the direction of the microwave electric field relative to the c-axis

  1. High transition-temperature SQUID magnetometers and practical applications

    Energy Technology Data Exchange (ETDEWEB)

    Dantsker, E [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) are described. Essential to the achieving high magnetic field resolution at low frequencies is the elimination of 1/f flux noise due to thermally activated hopping of flux vortices between pinning sites in the superconducting films. Through improvements in processing, 1/f noise in single layer YBCO thin films and YBCO-SrTiO{sub 3}-YBCO trilayers was systematically reduced to allow fabrication of sensitive SQUID magnetometers. Both single-layer directly coupled SQUID magnetometers and multilayer magnetometers were fabricated, based on the dc SQUID with bicrystal grain boundary Josephson junctions. Multilayer magnetometers had a lower magnetic field noise for a given physical size due to greater effective sensing areas. A magnetometer consisting of a SQUID inductively coupled to the multiturn input coil of a flux transformer in a flip-chip arrangement had a field noise of 27 fT Hz{sup {minus}1/2} at 1 Hz and 8.5 fT Hz{sup {minus}1/2} at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz{sup {minus}1/2} at 1 Hz and 18 fT Hz{sup {minus}1/2} at 1 kHz. A three-axis SQUID magnetometer for geophysical applications was constructed and operated in the field in the presence of 60 Hz and radiofrequency noise. Clinical quality magnetocardiograms were measured using multilayer SQUID magnetometers in a magnetically shielded room.

  2. YBa2Cu3O7- dc SQUID array for multichannel magnetometry and multichannel flip-chip current sensors

    Science.gov (United States)

    Ramos, J.; Zakosarenko, V.; IJsselsteijn, R.; Stolz, R.; Schultze, V.; Chwala, A.; Hoenig, H. E.; Meyer, H.-G.

    1999-09-01

    We have prepared arrays of single-layer washer-type dc superconducting quantum interference devices (SQUIDs) on 10 mm × 10 mm bicrystal substrates. Each SQUID in the array is equipped with its own modulation loop, which makes a separate operation of them possible. Arrays containing nine or 11 dc SQUIDs have been tested and the crosstalk between neighbouring channels has been found to be 5%. The field sensitivity of the SQUIDs is 85 nT icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/>0-1 and 105 nT icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/>0-1 for the nine- and 11-device array, respectively. The equivalent flux noise is typically icons/Journals/Common/le" ALT="le" ALIGN="TOP"/> 20 icons/Journals/Common/mu" ALT="mu" ALIGN="TOP"/>icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/>0 Hz-1/2 down to 1 Hz with ac bias reversal. A field resolution of less than 2.1 pT Hz-1/2 has been obtained for at least eight channels on a chip. By using multiturn YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> input coils and mounting them in a flip-chip configuration together with the single-layer dc SQUIDs we have been able to build three-channel current sensors. The current sensitivity equals 3-3.5 icons/Journals/Common/mu" ALT="mu" ALIGN="TOP"/>A icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/>0-1 depending on the alignment of the flip-chip configuration. The current resolution of the devices is coil of these current sensors to a normal-conducting pickup antenna.

  3. Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

    2012-05-30

    Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas

  4. The material point method and simulation of wave propagation in heterogeneous media

    International Nuclear Information System (INIS)

    The mechanical response of polycrystalline materials, particularly under shock loading, is of significant interest in a variety of munitions and industrial applications. Homogeneous continuum models have been developed to describe material response, including Equation of State, strength, and reactive burn models. These models provide good estimates of bulk material response. However, there is little connection to underlying physics and, consequently, they cannot be applied far from their calibrated regime with confidence. Both explosives and metals have important structure at the (energetic or single crystal) grain scale. The anisotropic properties of the individual grains and the presence of interfaces result in the localization of energy during deformation. In explosives energy localization can lead to initiation under weak shock loading, and in metals to material ejecta under strong shock loading. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain-scale material response.Numerical simulations are performed to gain insight into grain-scale material response. The Generalized Interpolation Material Point Method family of numerical algorithms, selected for their robust treatment of large deformation problems and convenient framework for implementing material interface models, are reviewed. A three-dimensional simulation of wave propagation through a granular material indicates the scale and complexity of a representative grain-scale computation. Verification and validation calculations on model bimaterial systems indicate the minimum numerical algorithm complexity required for accurate simulation of wave propagation across material interfaces and demonstrate the importance of interfacial decohesion. Preliminary results are presented which predict energy localization at the grain boundary in a metallic bicrystal

  5. Surface film effects on drop tube undercooling studies

    Science.gov (United States)

    Ethridge, E. C.; Kaukler, W. F.

    1986-01-01

    The effects of various gaseous atmospheric constituents on drop-tube solidified samples of elemental metals were examined from a microstructural standpoint. All specimens were prepared from the purest available elements, so effects of impurities should not account for the observed effects. The drop-tube gas has a definite effect on the sample microstructure. Most dramatically, the sample cooling rate is effected. Some samples receive sufficient cooling to solidify in free fall while others do not, splating at the end of the drop tube in the sample catcher. Gases are selectively absorbed into the sample. Upon solidification gas can become less soluble and as a result forms voids within the sample. The general oxidation/reduction characteristics of the gas also affect sample microstructures. In general, under the more favorable experimental conditions including reducing atmospheric conditions and superheatings, examination of sample microstructures indicates that nucleation has been suppressed. This is indicated by underlying uniform dendrite spacings throughout the sample and with a single dendrite orientation through most of the sample. The samples were annealed yielding a few large grains and single or bi-crystal samples were commonly formed. This was especially true of samples that were inadvertently greatly superheated. This is in contrast with results from a previous study in which surface oxides were stable and contained numerous sites of nucleation. The number of nucleation events depends upon the surface state of the specimen as determined by the atmosphere and is consistent with theoretical expectations based upon the thermodynamic stability of surface oxide films. Oxide-free specimens are characterized by shiny surfaces, with no observable features under the scanning electron microscope at 5000X.

  6. High transition-temperature SQUID magnetometers and practical applications

    International Nuclear Information System (INIS)

    The design, fabrication and performance of SQUID magnetometers based on thin films of the high-transition temperature superconductor YBa2Cu3O7-x (YBCO) are described. Essential to the achieving high magnetic field resolution at low frequencies is the elimination of 1/f flux noise due to thermally activated hopping of flux vortices between pinning sites in the superconducting films. Through improvements in processing, 1/f noise in single layer YBCO thin films and YBCO-SrTiO3-YBCO trilayers was systematically reduced to allow fabrication of sensitive SQUID magnetometers. Both single-layer directly coupled SQUID magnetometers and multilayer magnetometers were fabricated, based on the dc SQUID with bicrystal grain boundary Josephson junctions. Multilayer magnetometers had a lower magnetic field noise for a given physical size due to greater effective sensing areas. A magnetometer consisting of a SQUID inductively coupled to the multiturn input coil of a flux transformer in a flip-chip arrangement had a field noise of 27 fT Hz-1/2 at 1 Hz and 8.5 fT Hz-1/2 at 1 kHz. A multiloop multilayer SQUID magnetometer had a field noise of 37 fT Hz-1/2 at 1 Hz and 18 fT Hz-1/2 at 1 kHz. A three-axis SQUID magnetometer for geophysical applications was constructed and operated in the field in the presence of 60 Hz and radiofrequency noise. Clinical quality magnetocardiograms were measured using multilayer SQUID magnetometers in a magnetically shielded room

  7. Shear responses of [ 1-bar 1 0]-tilt {1 1 5}/{1 1 1} asymmetric tilt grain boundaries in fcc metals by atomistic simulations

    International Nuclear Information System (INIS)

    The shear response of the ∑3[ 1-bar 1 0]-tilt {1-bar 1-bar 5}/{1 1 1} and ∑9[ 1-bar 1 0]-tilt {1 1 5}/{1 1 1} asymmetric tilt grain boundaries (GBs) in fcc metals Cu and Al has been studied by atomistic simulation methods with the embedded atom method interatomic potentials and with a bicrystal model. It is found that the structure of the GBs studied can be well described by the coincidence site lattice (CSL) theory. Shear of these GBs at room temperature along eight different directions within the GB plane shows that these two types of GBs can transform between each other by the formation of a coherent twin boundary. The structure transformation of the GBs can also take the form of GB sliding, GB sliding–migration coupled motion, GB faceting, GB 9R structure formation, etc, depending on the shear directions adopted and the material involved (Cu or Al). The detailed structure transformation mechanisms have been analyzed with the aid of the CSL–DSC (displacement shift complete) theory. Several structure transformation paths adherent to these two types of GBs have been identified for the activation of the GB sliding–migration coupled motion. It is concluded that, although CSL–DSC theory can be applied to describe the sliding–migration coupled motion of the GBs studied, some other effects such as the shear direction within the GB plane and the bonding characteristics of the materials should also play a significant role in the shear response of these GBs. (paper)

  8. Simulations of dislocation pile-ups at assymetric tilt boundaries in aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Valone, Steven [Los Alamos National Laboratory; Wang, Jian M [Los Alamos National Laboratory; Hoagland, Richard C [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory

    2011-01-21

    Materials deformation processes are increasingly approachable through the both conventional and accelerated molecular dynamics. In one deformation process, dislocation pile-up at a grain boundary, a greater understanding is required as to how dislocations transmit through grain boundaries, causing plastic deformation, or reflect and reconstruct the grain boundary, but with no macroscopic deformation. Here dislocation pile-ups in an alwninum bicrystal with an asymmetric tilt grain boundary are simulated atomistically, introducing effects of dislocation interactions beyond linear elastic ones. The observed responses as functions of the number of explicitly modeled dislocations and the magnitude of the applied stress are discussed. Typical conditions for the simulations consist of thermal relaxation room temperature, five active dislocations inserted within a 6.5-million-atom cell, and an additional fourteen dislocations represented within the atomistic simulation by their elastic strain fields. The dislocations are initially distributed according to linear elastic estimates of their positions in a double-ended pile-up from a chosen far-field stress. The whole cell is allowed to relax according to a procedure to be described. In the ensuing simulations, the system is propagated for some substantial period of time (lOs of ps), followed by small increments of strain. After a number of such increments, we observe all of the anticipated events. Usually several of the closest dislocations are absorbed into the grain boundary, resulting in varying amounts of reconstruction. Reflections from the boundary are common and show a strong dependence on sample thickness. Transmission events are seen on both slip systems in the other grain. The particulars of these events will be described as well.

  9. Low-frequency noise in high-{Tc} superconductor Josephson junctions, SQUIDs, and magnetometers

    Energy Technology Data Exchange (ETDEWEB)

    Miklich, A.H.

    1994-05-01

    Design and performance of high-T{sub c} dc superconducting quantum interference devices (SQUEDs), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDS; this suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5{times}10{sup {minus}30} J Hz{sup {minus}1} at 1 Hz is reported. Magnetometers in which a (9 mm){sup 2} pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz{sup {minus}1/2} down to frequencies below I Hz, improving to 39 fT Hz{sup {minus}1/2} at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz{sup {minus}1/2} in the white noise region is reported with a (10 mm){sup 2} pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz{sup {minus}1/2}. High-T{sub c} SQUIDs exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10--20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV.Hz{sup {minus}1/2} at 10 Hz (24 pV Hz{sup {minus}1/2} at 1 Hz) is described.

  10. Some Bristol-Prague explorations in x-ray topography

    International Nuclear Information System (INIS)

    lightly-deformed Fe-Si bicrystals. A very different enterprise was the Bristol method of producing x-ray moire patterns by superposing one crystal plate upon another, achieved in 1967. This project gained from Czech collaboration through the skilful participation of J Bradler, on leave from Prague

  11. Micro-mechanical investigation for effects of helium on grain boundary fracture of austenitic stainless steel

    International Nuclear Information System (INIS)

    Highlights: • We investigate effects of helium on grain boundary fracture of stainless steel. • We conduct micro-tensile tests on helium ion-implanted type 316 stainless steel. • Brittle fracture occur on grain boundaries on which small bubbles formed densely. • Formation of bubbles both on grain boundary and in matrix promotes brittle fracture. • Grain boundary segregated helium atoms may have a role in grain boundary fracture. - Abstract: Effects of helium (He) on grain boundary (GB) fracture of austenitic stainless steel were investigated by micro-tensile tests. Micro-bicrystal tensile specimens were fabricated for non-coincidence site lattice boundaries of He ion-irradiated 316 stainless steel by focused ion beam (FIB) micro-processing. Micro-tensile tests were conducted in a vacuum at room temperature in the FIB system. Specimens containing more than 2 at.% He fractured at GBs. The criteria for brittle fracture occurrence on GBs were: (1) He concentrations higher than 2 at.%; (2) formation of He bubbles on the GBs with less than a 5 nm spacing; and (3) matrix hardening to more than 4.6 GPa (nano-indentation hardness). The fracture stress of GB brittle fracture was lower for a specimen with higher He concentration while the size and areal density of the GB He bubbles were the same. The specimens that contained 10 at.% He and had been annealed at 923 K after irradiation fractured at the GB nominally in a brittle manner; however the inter-bubble matrix at the GB experienced ductile fracture. The annealing caused He bubbles to grow but decreased the areal density so that the spacing of the GB He bubbles widened and the hardness decreased, therefore the fracture mode changed from brittle to ductile. The findings revealed that He promotes GB fracture by weakening the GB strength and hardening the matrix due to the formation of He bubbles both on GBs and in the matrix. In addition, the findings suggested that GB segregated He atoms may have a role in GB

  12. Low-Frequency Noise in High-T Superconductor Josephson Junctions, Squids, and Magnetometers.

    Science.gov (United States)

    Miklich, Andrew Hostetler

    The design and performance of high-T_ {rm c} dc superconducting quantum interference devices (SQUIDs), the junctions that comprise them, and magnetometers made from them are described, with special attention paid to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDs. This noise suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions, in contrast, have levels of critical current noise that are controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5times 10^{-30} J Hz^ {-1} at 1 Hz is reported. Magnetometers in which a (9 mm)^2 pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz^{-1/2} down to frequencies below 1 Hz, improving to 39 fT Hz^{-1/2} at 1 Hz with the addition of a 50 mm-diameter single-turn flux transformer. Although the performance of these devices is sufficient for single -channel biomagnetometry or geophysical studies, their relatively poor coupling to the pickup loop makes it difficult to satisfy the competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz^{-1/2} in the white noise region is reported with a (10 mm) ^2 pickup loop. However, additional 1/f noise from the processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz^ {-1/2}. High-T_{ rm c} SQUIDs are shown to exhibit additional 1/f noise when they are cooled in a nonzero static magnetic field because of the additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10-20 in a field of 0.05 mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution

  13. Low-frequency noise in high-(Tc) superconductor Josephson junctions, SQUIDs, and magnetometers

    Science.gov (United States)

    Miklich, A. H.

    1994-05-01

    Design and performance of high-T(sub c) dc superconducting quantum interference devices (SQUID's), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUID's; this suggests a poorly connected interface at the grain boundary junction. SQUID's from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5 x 10(exp -30) J Hz(exp -1) at 1 Hz is reported. Magnetometers in which a (9 mm)(exp 2) pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz(exp -1/2) down to frequencies below 1 Hz, improving to 39 fT Hz(exp -1/2) at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz(exp -1/2) in the white noise region is reported with a (10 mm)(exp 2) pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz(exp -1/2). High-T(sub c) SQUID's exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10-20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV Hz(exp -1/2) at 10 Hz (24 pV Hz(exp -1/2) at 1 Hz) is described.

  14. The critical current density of yttrium barium copper oxide coated conductors

    Science.gov (United States)

    Kim, Sang Il

    The critical current density Jc of YBa 2Cu3O7-x (YBCO) coated conductors is determined by the connectivity of the polycrystalline grain network and by vortex pinning. The aim of this work is to explore these two key scientific issues. Current obstruction effects of the grain boundary network were first studied by measuring variable width tracks in variously-textured ex situ coated conductors. We found that the global texture exercises a significant effect on Jc especially in low fields. We then grew low angle [001]-tilt bicrystal YBCO films with controlled doping so as to study the influence that variable size and charge segregants would have on the inter-grain Jc. The beneficial effects of Ca doping was already proven, but here we were able to show that the optimum doping of low angle grain boundaries was obtained with the smaller substitutions of 15% Ca for Y, rather than the 30% previously employed. We then studied Ca-doping in the small rare-earth (RE) ion Yb variant of the RE-123 structure, YbBa2Cu3O7-x, and the influence of substitutions for Y of the large RE ion Nd in YBa2Cu3O7-x. We found that strain- and charge-driven segregation to the grain boundary was consistent with the segregation model of Gurevich. Very interestingly, the 6° Nd-doped YBCO grain boundaries exhibited no degradation of intergrain Jc compared to the intragrain Jc without significant Tc reduction. Then, the vortex pinning was studied by sequential ion milling of YBCO films with various vortex pinning microstructures. YBCO films without strong pins exhibited two-dimensional collective pinning behavior and thermal fluctuation depinning effect, and thus Jc fell off fast with increasing thickness, magnetic field and temperature. In contrast, a YBCO film with dense, insulating, nanoscale pins exhibited strong three-dimensional pinning behavior and a high and uniform Jc through thickness. Analysis of the through-thickness properties of ex situ high Jc coated conductors showed them to be well

  15. Surface polishing of niobium for superconducting radio frequency (SRF) cavity applications

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Liang [College of William and Mary, Williamsburg, VA (United States)

    2014-08-01

    Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by

  16. The hierarchical characterization of deformation heterogeneities in compressed metal single crystals

    Science.gov (United States)

    Magid, Karen Ruth

    Plastic deformation is an inherently heterogeneous process whose understanding is still incomplete after more than 50 years of study. The traditional methods of analysis look at both bulk material deformation and properties and the microscale features which comprise the inherent deformation processes. A large amount of information occurring on the mesoscale, from 1 to 100 microns, has not been analyzed. Here we present the results from an x-ray diffraction technique with submicron spatial resolution used to analyze compressed metal single crystals. The mesoscopic structure of the inhomogeneous macroscopic deformation pattern was explored with selected area diffraction, using a focused synchrotron radiation polychromatic beam with a resolution of 1-3 mum. Single crystals of copper, molybdenum, and zinc were oriented for single slip tested to ˜2-14% strain in nearly uniaxial compression, using a specifically designed 6 degree of freedom compressive test device. The macroscopic strain field was monitored during the test by optical image correlation methods that mapped the strain field with a spatial resolution of about 100 mum. The copper and molybdenum crystals deformed unexpectedly, exhibiting significant amounts of secondary slip activity alongside the primary slip. Areas of interest from adjacent faces were identified from the image correlation and mapped for their orientation, excess defect density, and shear stress. The mesoscopic defect structure in the copper specimens consisted of broad, somewhat irregular primary bands that lay nominally parallel to (111), in an almost periodic distribution with a period of about 30 mum. These primary bands were dominant even in the region of conjugate strain. There were also broad conjugate defect bands, almost precisely perpendicular to the primary bands that tended to bridge primary bands and terminate at them. In addition, a tantalum bicrystal, previously compressed and characterized using electron back

  17. Josephson effectss in bicrystalline Bi2Sr2CaCu2O8+δ thin films

    International Nuclear Information System (INIS)

    A pulsed laser deposition process is developed for preparing high quality thin films of Bi2Sr2CaCu2Ox on different substrates. Both microstructural and electrical properties of the superconducting films are well characterized, e.g. by SEM, TEM and AFM. The high reproducability of the thin film quality facilitated a detailed study of Josephson effects in bicrystalline grain boundary junctions (GBJs). Thin films are deposited on commercially available (001) SrTiO3 bicrystalls and patterned by standard photolithography using wet-etching or Ar+-ion milling. The width of the micobridges ranges from 2 to 111 μm. The critical current densities across grain boundaries of thin film bicrystals have been measured as a function of the tilt angle Θ. For Θ=0 to 45 , the ratio of the grain boundary critical current density to the bulk critical current density decreases exponentially with increasing tilt angle. Microstructure investigations show a rough grain boundary of the superconductor (roughness 100 nm-1 μm) which is not determined by the roughness of the substrate grain boundary (1-3 nm) but by the island-plus-layer growth of the twin domains. The electrical properties are well described by the resistively shunted junction (RSJ) model. The IcRn-product reaches values of 2.2 mV at 4.2 K and 60 μV at 77 K. An optimized design for dc SQUIDs (Θ=24 ) is developed relating to the results of single GBJs. The values of the transfer function (∂V/∂Φ) run up to 74 μV/Φo. The equivalent flux noise which is measured in a flux-locked loop mode amounts 4.5 to 25 μPhio Hz in the white noise region for Φ≥25-50 Hz and 13 to 150 μΦo Hz at 1 Hz. In conclusion, microstructural as well as electrical properties of bicrystalline Bi2Sr2CaCu2Ox and YBa2Cu3Oy GBJs are more or less equal. (orig.)

  18. Low-temperature silicon thin films for large-area electronics: Device fabrication using soft lithography and laser-crystallization by sequential lateral solidification

    Science.gov (United States)

    Jin, Hyun-Chul

    resistance and current spreading. We discuss the future use of these electrical characterization techniques to analyze the properties of individual grain boundaries in thin film Si bicrystals formed by SLS.

  19. Progress in the Investigations of Grain Boundary Internal Friction%晶界内耗研究的进展

    Institute of Scientific and Technical Information of China (English)

    孔庆平; 方前锋; 蒋卫斌; 崔平

    2016-01-01

    . Previously, the GB internal friction was mostly studied with polycrystalline materials, in which mixed contributions of different types of GBs are involved. Since the microstructures and behaviors of different types of GBs are different, such internal friction can only reveal the general behaviors of GBs, while the detailed mechanism of the GB peak in polycryatals is hardly clarified. From the beginning of the 21th century, the internal friction in bicrystals (each has a single boundary) has been systematically investigated. The results indicate that the internal friction can be used to distinguish the individual behavior of different types of GBs and applied to the practice of “GB design and control” (or “GB engineering”). Moreover,the coupling effect and compensation effect involved in GB relaxation has been recently revealed and explained. These findings improve the understanding of the mechanism of GB internal friction. The present paper attempts to give a comprehensive review to the investigations of GB internal friction in polycrystals, bamboo-crystals and bicrystals. The microscopic mechanisms and the further applications of GB internal friction are discussed and prospected.

  20. Discovering the Role of Grain Boundary Complexions in Materials

    Energy Technology Data Exchange (ETDEWEB)

    Harmer, Martin P. [Lehigh Univ., Bethlehem, PA (United States)

    2015-03-19

    in a range of materials systems, and to characterize their structures, range of stability and selected physical properties. First, an Au-based bilayer interfacial phase was discovered at a bicrystal boundary in the Si-Au system. This bilayer transitioned abruptly to an intrinsic (“clean”) grain boundary phase, suggesting first-order phase behavior. This study represents the discovery of grain boundary complexions in a completely new system, i.e., a semiconductor-metal system, giving further support to the expectation that grain boundary complexions are a general phenomenon not limited to any particular class of materials. The TiO2-CuO system exhibited four grain boundary interfacial phases: a monolayer, disordered bilayer, disordered trilayer, and non-wetting nanoscale amorphous drop (which likely resulted from dewetting of a nanoscale IGF). SiO2 contamination was discovered in the TiO2-CuO samples, and we hypothesize that this impurity may have caused an “order-disorder” transition to occur. In other words, we expect that pure TiO2-CuO may have a higher tendency to exhibit ordered bilayer and trilayer complexions, which may also exhibit a well-defined order-disorder transition temperature. In this effort we have also identified unique complexion transitions in yttria and strontium titanate.

  1. Realizing Controllable Quantum States

    Science.gov (United States)

    Takayanagi, Hideaki; Nitta, Junsaku

    -- 4. Mesoscopic superconductivity with unconventional superconductor or ferromagnet. Ultraefficient microrefrigerators realized with ferromagnet-superconductor junctions / F. Giazotto et al. Anomalous charge transport in triplet superconductor junctions by the synergy effect of the proximity effect and the mid gap Andreev resonant states / Y. Tanaka and S. Kashiwaya. Paramagnetic and glass states in superconductive YBa[symbol]Cu[symbol]O[symbol] ceramics of sub-micron scale grains / H. Deguchi et al. Quantum properties of single-domain triplet superconductors / A. M. Gulian and K. S. Wood. A numerical study of Josephson current in p wave superconducting junctions / Y. Asano et al. Tilted bi-crystal sapphire substrates improve properties of grain boundary YBa[symbol]Cu[symbol]O[symbol] junctions and extend their Josephson response to THZ frequencies / E. Stepantsov et al. Circuit theory analysis of AB-plane tunnel junctions of unconventional superconductor Bi[symbol]Sr[symbol]Ca[symbol]Cu[symbol]O[symbol] / I. Shigeta et al. Transport properties of normal metal/anisotropic superconductor junctions in the eutectic system Sr[symbol]RuO[symbol]Ru / M. Kawamura et al. Macroscopic quantum tunneling in d-wave superconductor Josephson / S. Kawabata et al. Quasiparticle states of high-T[symbol] oxides observed by a Zeeman magnetic field response / S. Kashiwaya et al. Experimentally realizable devices for controlling the motion of magnetic flux quanta in anisotropic superconductors: vortex lenses, vortex diodes and vortex pumps / S. Savel'ev and F. Nori. Stability of vortex-antivortex "molecules" in mesoscopic superconducting triangles / V. R. Misko et al. Superconducting network with magnetic decoration - Hofstadter butterfly in spatially modulated magnetic field / Y. Iye et al. Observation of paramagnetic supercurrent in mesoscopic superconducting rings and disks using multiple-small-tunnel-junction method / A. Kanda et al. Guidance of vortices in high

  2. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    Science.gov (United States)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    A, Gonzalez E M and Vicent J L 2012 Superconducting vortex dynamics on arrays with bicrystal-like structures: matching and rectifier effects Supercond. Sci. Technol. 25 124006 [7]Lehtinen J S and Arutyunov K Yu 2012 The quantum phase slip phenomenon in superconducting nanowires with a low-Ohmic environment Supercond. Sci. Technol. 25 124007

  3. The Dependence of Electrical Properties on Miscut Orientation in Direct Bonded III-V Solar Cell Layers

    Science.gov (United States)

    Seal, Mark

    cm 2 for GaAs//GaAs structures, from 0.00824 O˙cm2 to 0.0161 O˙cm2 for GaAs//InP structures and only from 0.0063 O˙cm2 to 0.0089 O˙cm 2 for InP//InP structures. The electronic behavior at the interface was modeled using the Seager-Pike theoretical model for electron tunneling between adjacent semiconductor bicrystals. In accordance with this model the zero-bias conductance was used to estimate the conduction barrier height at the bonded interface. The zero-bias conductance taken at temperatures from 90 to 340 K reveals an increase in potential barrier height across all wafer combinations as the degree of surface misorientation is increased, from 0.26 eV to 0.305 eV for InP//InP structures, from 0.32 eV to 0.39 eV for GaAs//InP structures, and from 0.54 eV to 1.0 eV for GaAs//GaAs structures. For all material combinations studied, structures with zero relative misorientation displayed equivalent electrical performance to nominal on-axis substrates, demonstrating that relative surface misorientation rather than substrate miscut is responsible for changes in electrical resistivity. The large increase in potential barrier height for GaAs//GaAs structures indicates that the degree of relative misorientation between GaAs//GaAs wafer bonded pairs has a significant impact on interface electrical properties, and is consistent with previous GaAs//GaAs studies. However for GaAs//InP wafer bonded pairs, the relative misorientation across the bonded interface plays a less significant role, and the impact of relative misorientation is least significant for InP/.InP bonded structures. This is illustrated by the increase in potential barrier of 0.04 eV for InP//InP structures, 0.06 eV for GaAs//InP structures, and 0.47 eV for GaAs//GaAs structures as relative misorientation is increased from 0° to 8°. High resolution transmission electron microscopy and high-angle annular dark field are used to confirm the misorientation of GaAs//InP and InP//InP bonded samples and determine the

  4. Preface

    Science.gov (United States)

    Gorse, D.; Boutard, J.-L.

    2002-09-01

    propagation kinetics can now be followed at ESRF (Grenoble) using synchrotron radiation imaging techniques. It is now possible to follow the propagation, structure and chemistry of the embrittling phase in the crack, at microscopic and at nanometric scale. It is also possible, in principle, to take into account the role of defects in grain-boundaries (GB) on the penetration of the embrittling species and conversely to investigate the role of the defects produced by wetting on the GB microstructure. We do hope that these techniques open a new and attractive field of research to improve the understanding of LME. The HRTEM study carried out by A. Charai et al. enlightens the importance of crystallography on wetting. Two exemplary couples are thoroughly investigated: the Mo/Ni couple giving rise to an interfacial nanometer thick interface for one type of Mo bicrystal wetted by nickel and the Ni/Pb couple pointing out the role of the GB plane on wetting. Y. Brechet et al. investigated not only the microstructure effects on “LM" penetration into cracks (cracks kinetics and morphologies), but also the plasticity effects ahead of the crack tip, studying a variant of the mythic Al/Ga couple, say the 7010 Aluminum alloy in contact with Gallium, allowing for modifications of the precipitation state at the GBs by applying various heat treatments. Y. Brechet et al. conclude in favour of a step by step penetration process, quasi at atomic scale and give an estimate of crack propagation velocity, of the order of a few micrometers per second, in good agreement with experimental observations. The author stresses the importance of defects in the GBs (precipitates...) at different scales which can explain discrepancies between the experimental crack velocity and the one calculated using a continuum elastic model. The paper presented by W. Ludwig et al. concentrates on two synchrotron radiation imaging techniques (X-ray micro-radiography and micro-fluorescence) available at ESRF (Grenoble) in