bluuebunny/crossref_metadata_2025 huggingface dataset:
Glass Films and Interfaces in Microelectronic Applications
Authors: Buchanan R. C. , Beck C. V.
Published: March 2011

Use of dielectric films is integral to most microelectronic packaging, as passive components for device insulation (interlayer dielectric, passivation, diffusion layer), as thin layer capacitive structures or as insulating coatings for thin film and thick film hybrid circuits. Depending on deposition technique, film composition may include SiO2, Al2O3, Si3N4, modified silicate or phosphate glasses as insulators. Compositions as well as methodologies for film preparation on Si, glass or metal substrate by spin coating (or spraying) are discussed, including film/substrate interface characteristics and properties related to dielectric film coatings.
Metallo-Organic Decomposition (MOD) Films for Electronic Packaging
Authors: Vest Geraldine M. , Cone V. P. , Herzfeld C. J. , Bhansali A. K.
Published: March 2011

A metallo-organic decomposition (MOD) film is one formed by thermal decomposition of a solution containing one or more metallo-organic compounds that were deposited onto a substrate. This process yields metal, glasses, or polycrystalline ceramic films directly without passing through the powder stage. Conductor films studied include a screen printable gold and a screen printable and ink jet printable silver. Dielectric films studied include a low K lead borosilicate glass and a variety of ferroelectric compositions.
Characterization of Surface Modified Carbon Fibers and Their Epoxy Composites by Small Angle X-Ray Scattering
Authors: Stoll Bernhard , Fellers J. F. , Lin J. S.
Published: March 2011

This paper correlates the interlaminar shear strength of 7 different carbon fiber/epoxy composite with structural characteristics determined by Small Angle X-ray Scattering (SAXS) measurements. The carbon fibers were all of the same type but had different surface treatments. The SAXS patterns of the fibers and of the composites showed a highly nonlinear Guinier region which could not be approximated by traditional linear regression. A new approach to the Guinier approximation was developed to treat this nonlinear curve using a polynomial of second order. The radius of gyration (RG) of the fibers, as determined by this new method, correlated clearly with both the extent of the surface treatment and the interlaminar shear strength of the composite. Also the difference in scattering between a dry fiber and a glycerine soaked fiber provides a way to characterize the changes obtained by surface treatments. These methods provide new ways to estimate the efficiency of a surface treatment and its effect on the interlaminar shear strength by analyzing the SAXS patterns of the fibers.
First Cumulant for Chains with Constraints
Authors: Akcasu A. Z , Hammouda B , Stockmayer W. H , Tanaka G.
Published: March 2011

The Fixman-Kovac formulation of chain dynamics with constraints is used to calculate the first cumulant Q(q) of the dynamic scattering function. This general formalism is applied to the case of freely jointed chains. It is shown that the large q limit (q being the scattering wavenumber) of Q(q) for a chain of N bonds in the absence of hydrodynamic interaction is proportional to the ratio (2N+3)/3(N+l) representing the fraction of unconstrained degrees of freedom of the chain. The inclusion of hydrodynamic interaction seems to enhance the apparent segmental diffusion. The use of constrained chain dynamics has no appreciable effects, however, on the behavior of Q(q) in the small and intermediate q regions for long enough chains. This formalism can be used to interpret neutron (spin echo) scattering experiments from semiflexible polymers in solution.
Scattering Studies of Cyrstallization in Highly Oriented Polymers
Authors: Schultz J. M.
Published: March 2011

The solidification of low molecular weight materials from their melts (in the absence of temperature fields) generally leads to a product with no preferred orientation, independent of the extent or rate of deformation of the melt. The solidification of polymers from a highly deformed melt or solution nearly always leads to a product with preferred molecular orientation. Further, the rate of solidification can be significantly increased by melt deformation. The change in rate, relative to that in a quiescent melt or solution, can be several orders of magnitude [1]. These differences, relative to small-molecule systems, arise from the degree to which orientation and local strain can be maintained in the melt. Due to the long-range connectivity within a polymer molecule, it is possible to impart large extensions to these molecules in the molten state, and significant time is often required for the molecules to relax back to their undistorted, coiled state. If crystallization or glass formation occurs before the chain can relax, an extended molecular configuration can be retained. Thus in the solidification of oriented polymers there exists a competition between the “freezing” of the molecular orientation and the relaxation (re-coiling) of the molecules.
Detailed Modeling of Structure and Deformation of Glassy Polymers
Authors: Theodorou Doros N. , Ludovice Peter J. , Suter Ulrich W.
Published: March 2011

The molecular structure of macromolecules determines to a very large extent the macroscopic properties of the polymers they make up, and delimits what variations in properties can potentially be effected by processing. It is, therefore, important to understand and to be able to reliably predict the relevant properties of polymers and the limits of these properties upon treatment from the knowledge of the molecular structure of the constituent chains. For many properties of amorphous polymeric glasses correlations have been introduced in the last decades; some of them have been very useful [1–3], but they lack basic understanding of the processes and mechanisms operative in the generation of the properties in question. Their application is, by definition, limited to interpolation in that part of “chemical structure space” used as basis for the correlation. Prediction implies the power of extrapolation and, consequently, some use of first-principle methods. Remarkably little such work [1, 4–6] has been done to date on amorphous polymeric glasses. We have recently begun to investigate the atomistic-level modeling of structure and properties of amorphous, “fully relaxed” polymeric glasses [7–9].
Neutron and Light Scattering Studies of Compatible Polymer Blends
Authors: Fischer E. W.
Published: March 2011

As it is well known the Flory-Huggins approach of the thermodynamic description of a mixture of two polymers A and B leads to an expression [1] for the Gibbs free energy of mixing ΔG
Scattering Studies on Mixtures of Poly(Ethylene Oxide) with Poly(Methyl Methacrylate)
Authors: Russell T. P. , Ito H. , Wignall G. D.
Published: March 2011

Molten and semi-crystalline mixtures of PEO and PMMA have been investigated by small angle neutron and X-ray scattering. It has been found that the Flory Huggins interaction parameter, evaluated from the intermolecular scattering function, is quite small and is apparently dominated by entropic contributions. Scattering profiles from the semi-crystalline mixtures clearly show that the PMMA is incorporated within the amorphous phase between the crystalline PEO lamellae.
A Molecular Orbital Model of Melting and Glass Formation
Authors: Eberhart M. E. , Johnnson K. H. , O'Handley R. C.
Published: March 2011

SCF-Xα-SW calculations have been performed on the glass forming crystal of Ni2B. The resulting molecular orbital topology near the fermi level is similar to that previously obtained by SCF-Xα-SW calculation on the glass forming crystals of Pd-Si and Cu-Zr. These similarties, it is conjectured, indicate melting is an electronically driven phase transition and that liquid and glass structures are more the result of electronic than kinetic factors. It is shown that the molecular orbital model of melting in transition metals will generate structures similar to those resulting from the dense random packing of hard spheres method, and the molecualr orbital mechanism admits, in a qualitative way, the explanation of a broad range of liquid and glass properties.
Rapid Solidification of Metastable Materials
Authors: Liebermann Howard , Walter John
Published: March 2011

There are numerous processing methods available for the fabrication of rapidly-solidified metastable alloys. Examples include splat quenching, melt-spinning, surface melting and quenching, melt atomization and solidification, and deposition by sputtering and evaporation. Experimental aspects of each of these fabrication methods will be discussed. These include solidification and quench rate, process control, and final product morphology and microstructure. Some properties of an amorphous alloy prepared by several of these processing methods will be discussed.
Rapid Solidification - Mechanisms, Morphology and Microstructure
Authors: Domingue J. A. , Boesch W. J. , Radavich J. F. , Yu K. O.
Published: March 2011

The cooling rates that accompany manufacture of gas turbine superalloy powders are sufficient to produce metastable structures and phase distributions. It is the aim of this investigation and report to develop some understanding of the relationships between powder manufacturing processes and powder structures by comparison of material made by two methods, and to describe some unusual experiments done to demonstrate structure solidification relationships.
Electronic Structure of CuZr and PdSi Metallic Glasses
Authors: Leon Francisco A. , Johnson Keith H.
Published: March 2011

The local electronic structures of representative amorphous alloys have been calculated using the SCF-Xα-SW cluster molecular orbital method. Prototype cluster models have been constructed for Cu-Zr and Pd-Si alloys which exemplify two major classes of binary (A-B) glass-forming systems, namely: (1) metallic glasses based on noble or transition elements (e.g., A=Cu) toward the right of the periodic table and transition elements (e.g., B=Zr) toward the left of the periodic table; (2) metalloid glasses based on transition elements (e.g., A=Pd) toward the middle of the periodic table and nonmetallic elements (e.g., B=Si) toward the right of the periodic table. The calculated electronic structures are in good quantitative agreement with, and provide an interpretation of, published photoelectron spectra for the above amorphous alloys.
The Effects of Ribbon Thickness and Annealing Temperature on the AC Magnetic Properties of the Fe81.5B14.5Si3C1 Alloy
Authors: Ihiuangp S.C. , Frischmann G. , Luborsky F.E. , Livingston J.D. , Mogro-Campero A.
Published: March 2011

The a.c. magnetic properties measured at 60 Hz are found to be strongly affected by ribbon thickness and annealing temperature. These magnetic results are further characterized by observations on magnetic domain structure, crystallization, stress relaxation, and ribbon surface finish.
Influence Of Cr, Mn, Co and Ni on the Crystallization Behaviour of (Fel−xMx)y Metalloid1−y Metallic Glasses
Authors: Bergmann H. W. , Brokmeier U.
Published: March 2011

The influence of Cr, Mn, Co and Ni on the thermodynamic properties (molar heat of fusion, heat of crystallization and melting temperature), crystallization behaviour and hardness was studied in (Fe1-xMx)83B17 as a function of the x content. The crystallization behaviour can be described by three parameters which enables an extrapolation to longer times.
Localized Shear Deformation of Amorphous Metals
Authors: Li J.C.M.
Published: March 2011

The characteristics of localized deformation in amorphous metals are reviewed. All the available evidences seem to suggest that dislocations are responsible for shear localization. These dislocations seem to require a stress concentration for their nucleation. Once nucleated, they are capable of producing both forward and reverse shear in a narrow band, much like the dislocations in crystalline materials.
The Effect of Hydrogen on an Iron Based Amorphous Alloy
Authors: Shahani H. , Soderhjelm H. , Nygren Mats
Published: March 2011

In this· investigation we have systematically studied the brittleness and the atomic structure in an Fe(SiBC) alloy. Different amounts of hydrogen have been dissolved in the alloy. It has then been studied at different cooling rates.

Hydrogen gas of different partial pressures was dissolved into the melt. The alloy was then rapidly quenched by a chill block melt spinning method. The cooling rates were changed by changing the velocity on the chilling roll. The brittleness and the atomic structure were examined by bending tests and x-ray diffraction.

X-ray diffractions showed that the ribbons were amorphous when the cooling rate was sufficient. Amorphous ribbons without any hydrogen were ductile, crystalline ribbons of this alloy were brittle. The ribbons with dissolved hydrogen and amorphous structure were brittle even at small amounts of hydrogen. At the highest cooling rates the ribbons with low hydrogen content were ductile. There seems to be a connection between the hydrogen content and the amorphous ribbons ductility. The hydrogen content only has a slight influence to amorphous structure.
Preferred Orientation in Splat-Quenched Materials
Authors: Blake N.W. , Rames F.A. , Smith R.W.
Published: March 2011

High purity, splat-quenched metal ribbons, produced by the melt spinning technique, were examined for preferred orientation using x-ray diffraction. Of the materials tested (Zn, Cd, Ag, Bi, Pb, Sb, Mg, Sn) all except Sn exhibited some degree of preferred orientation in the plane of the metal ribbon. the hcp metals Zn and Cd showed an extreme degree of preferred orientation with the 002 plane being closely parallel to the ribbon plane. The Zn ribbon was analysed more closely with a view to its use as a crystal monochromator for x-ray diffraction. The high purity Zn was found to have some instability of preferred orientation with increase in time and temperature. The orientation was found to be effectively stabilized by the intentional addition of impurities, or by the use of lower purity (99.99%) Zn. In this form, the Zn ribbon could be used as a crystal analyser for x-ray diffraction with both intensity and resolution comparable to that of the 1011 plane in Quartz.
Pseudo-Elastic Behaviour in Rapidly-Quenched Dilute Tin Alloys
Authors: Callernfault W.M. , Smith R.W.
Published: March 2011

Ribbons of pure tin (99.9999%) and dilute Sn-Ge alloys, prepared by melt spinning using a 4′ diameter copper cylinder, were strained in tension. Reversible strains of a few percent were recorded in the dilute alloys but not in the pure tin. X-ray diffraction examination suggests that this pseudoelasticity is due to twinning rather than a martensitic transformation.
Surface Melting of Cast Iron With a High Power Laser Beam
Authors: Nilsson Ylva
Published: March 2011

An investigation is done on partial surface hardening and alloying on cast iron by means of a high power laser beam. Samples of cast iron have been covered with alloying material i.e. Ti, Cr, Si, V and Nb respectively. The samples were irradiated with a 2.5 kW laser beam. A partial melting of the surface occured and the alloys were dissolved. The carbide structure in the resolidified part was governed by the alloy addition. The carbide structure was metallographicly analysed. The effect of different parameters as beam diameter, scanning rate, power and alloy content have been investigated and the crack frequency has been evaluated.
Transmission Electron Microscopy of RSP Fe/Cr/Mn/Mo/C Alloy
Authors: Rayment J. J. , Thomas G.
Published: March 2011

Rapid solidification processing (RSP) has been carried out on an Fe/Cr/Mn/Mo/C alloy using both electron-beam melting and piston-and-anvil techniques. Preliminary TEM results show RSP produces a refined duplex microstructure of ferrite and martensite, with a typical ferrite grain size of 0.50–3.0 microns. This RSP microstructure is significantly different from that observed in the conventionally austenitized and quenched alloys—a lath martensitic microstructure with thin films of retained interlath austenite. The morphological change produced by RSP is accompanied by an increase in hardness from 48Rc to 61Rc (^ 480 to 720 VHN). It is intended to use electron-beam specimens to examine the potential beneficial effect of RSP upon sliding wear resistance and, by careful TEM studies, it will be possible to characterize the microstructure and its role in the hardness and wear behavior of the RSP alloy.
Grazing Incidence X-ray Scattering Study of Defect Structures in MBE GaAs/Si Using Synchrotron Radiation
Authors: Laderman S. S. , Kortright J. , Scott M. , Fischer-Colbrie A.
Published: March 2011

Defect structures in thin, MBE grown, GaAs/Si(001) heteroepitaxial films were studied with grazing incidence x-ray scattering techniques. The diffuse scattering associated with GaAs having the predominant epitaxial orientation varied strongly with the penetration depth of the x-rays. Well directed streaks corresponding to planar faults were observed and easily distinguished from a broad and more randomly oriented background. Bragg peaks corresponding to twinned GaAs were also studied. The probability of twinning was seen to be much higher about the {111} planes whose normals, when projected onto the sample surface, lay parallel to the off-orientation direction than about the {111} planes whose normals, when projected onto the sample surface, lay perpendicular to the off-orientation direction. The intensity and breadth of the twin reflections were analyzed to estimate the corresponding defect density. The depth dependence of the twinning probability was seen to vary with growth parameters.
Characterization of GaAs and Ge Films on (100) Silicon
Authors: Baribeau J.-M. , Houghton D.C. , MaignÉ P. , Moore W.T. , Devine R.L.S. , Denhoff M.W. , Stoner R.J. , Mccaffrey J. , Jackman T.E.
Published: March 2011

A UHV MBE apparatus in which the deposition of both group IV and group III-V components is possible without breaking vacuum has been utilized to compare the growth of GaAs epilayers on non-polar Si(100) and Ge coated Si(100) substrates. In addition, a comparison of GaAs epilayers grown on substrates cleaned by ex-situ techniques and on substrates given all UHV in-situ surface preparation was made. Defect reduction by the incorporation of strained-layer superlattice dislocation filters and by post-growth rapid thermal anneal (RTA) thermal cycles was also investigated. Optical and material properties comparable to MBE grown GaAs/GaAs were obtained for GaAs grown on Ge coated Si(100) substrates.
Comparative Studies of the Structural, Electrical and Opto-Electronic Properties of Epitaxial GaAs Layers Grown On Either Si, Ge Or Ge Coated Si Substrates By Mocvd
Authors: Abdul Awai M. , Lee El Hang , Chan Eric Y. , Lum R.M. , Klingert J.K. , Sheng T.T. , Hopkins L.C. , Opila R.L.
Published: March 2011

We report the epitaxial growth of GaAs films on bulk Si, Ge and Ge coated Si substrates by MOCVD. This work is directed at comparing the structural, electrical, optical and optoelectronic properties of the GaAs films grown on these substrates. The quality of the GaAs films was evaluated by a number of techniques including X-ray, TEM, RBS, I-V and C-V. We have also obtained good photoresponse for Au-GaAs/Si, Au-GaAs/Ge and Au-GaAs/Ge/Si Schottky diodes at 0.87μm. We have observed significant differences in defect density, strain, crystalline quality, structural order, doping density depth-profile, dark current, diode ideality factor, photoresponse, inter-diffusion and interface structure among these three different structures. The GaAs/Ge structure exhibited the best structural and electrical characteristics of all. The GaAs/Ge/Si structure showed material properties and Schottky diode performance that are better than those of the GaAs/Si stucture. Although Ge and Si both out-diffuse into GaAs, that the out-diffusion of Si into GaAs appears to cause more degradation in the electrical and optoelectronic properties of GaAs.
Strain Measurements in Si/Si0.5Ge0.5 Superlattices by He Ion Channeling
Authors: Mantl S. , Kasper E. , Jorke H. J.
Published: March 2011

He ion channeling experiments have been performed on molecular beam grown Si/SiGe superlattices to determine the strain fields. Angular yield scans provide directly the tetragonal strains in the layers. In Si/Si0.5Ge0.5 superlattices grown on (100) Si only the SiGe layers are strained. Almost equal but opposite strains in the Si and SiGe layers have been found in a Si/Si0.5Ge0.5 superlattice deposited on a 230 nm thick SiO.71Ge0.29 buffer layer. Strain symmetrization yields the minimum elastic energy and thus to the most stable structure.
Epitaxial Ge Films on Si Substrates
Authors: Mccalmont J.S. , Robinson D. , Lakin K.M. , Shanks H.R.
Published: March 2011

Thin films of germanium have been prepared using an ultrahigh vacuum ionized-cluster beam (ICB) system. The dopant concentration of the films was varied by alloying the germanium source material with aluminum, a p-type dopant. X-ray diffraction analysis of the films has shown that an epitaxial (100) germanium film can be deposited on a (100) silicon substrate with a substrate temperature as low as 300°C. The results confirm that ICM deposition can be used to prepare epitaxial germanium films, but ionization of the clusters does not appear to affect the film growth.
Electrical Transport in Ultrathin Films of CoSi2 on Si(111)
Authors: Hensel J. C. , Phillips J. M. , Batstone J. L. , Augustyniak W. M. , Unterwald F. C.
Published: March 2011

We have performed electrical transport measurements on ultrathin films of epitaxial CoSi2 on Si(111) with film thickness ranging down to ∼10A. The resistivities exhibit temperature dependences characteristic of a metal and a thickness dependence which rises steeply with decreasing thickness suggestive of a quantum size effect. At the lowest temperatures (≲ 10K) the resistivities of the thinner films increase logarithmically with inverse temperature characteristic of transport in the weak localization regime as has been confirmed by magnetoresistance measurements. Hall effect measurements establish that carrier densities (holes) in the ultrathin films are essentially identical to those in bulk CoSi2, i.e. 26 × 1022 cm−3.
Preparation and Characterization of Epitaxial Yttrium Silicide on (111) Silicon
Authors: Gurvitch M. , Levi A. F. J. , Tung R. T. , Nakahara S.
Published: March 2011

Epitaxial YSi2-x films have been fabricated. The smooth ∼430 Å thick silicide films on Si(111) substrates were characterized by a Rutherford backscattering minimum channeling yield, Xmin = 8%. The best previously reported result, Xmin = 26%, was achieved using a relatively exotic e-beam heating method. By contrast we formed YSi2-x using a straightforward furnace annealing technique. We used improved Si surface cleaning procedures, sputter-deposited Y films, and performed two-stage anneals in a vacuum of ∼ 10−8 torr. The results of our work establish YSi2-x as one of the best epitaxial silicides. We describe our preparation technique as well as the evidence for epitaxy. Electrical measurements (Schottky barrier, temperature dependent resistivity, Hall effect) are also presented. Low temperature resistivity of YSi2-x is found to obey simple T5 Bloch's law. Based on resistivity data, YSi2-x appears to have a Debye temperature of 310 K. According to Hall measurements, it is an electronic conductor with n = 2.7 × 1022 cm−3 and the mean free path of electrons is ∼ 87 Å at 4.2 K. We measure a Schottky barrier height of 0.36 eV between YSi2-x, and n-type Si.
Residual Stress in GaAs Layer Grown on 4°-Off (100)Si by MBE
Authors: Yao T. , Okada Y. , Kawanami H. , Matsui S. , Imagawa A. , Ishida K.
Published: March 2011

Residual stress in molecular beam epitaxially (MBE) grown GaAs films on 4°-off (100)Si substrates is investigated with X-ray diffraction technique. It is experimentally confirmed that the GaAs lattice suffers tetragonal deformation with the c-axis being [100]. The GaAs lattice tilts by approximately 0.2° towards the tilted direction of the substrate. It is found that two-dimensional compressive stress dominates in GaAs films thinner than 0.3 μm in thickness, while two-dimensional tensile stress dominates in thicker films. The variation of the stress is understood in terms of a combination of misfit stress and thermal stress. The residual tensile stress is larger than 1 × 109 dyn/cm2 in the films thicker than I pm. The effect of the stress on the reliability of semiconductor laser diodes is discussed.
Analytical Electron Microscope Study of High- and Low-Coercivity SmCo 2:17 Magnets
Authors: Fidler Josef , Bernardi J. , Skalicky P.
Published: March 2011

Sintered, precipitation hardened SmCo 2:17 magnets contain a multiphase microstructure. Our electron microscopic investigations reveal that the size of the rhombic, cellular precipitation structure and the formation of cell interior and cell boundary phases is determined by the nominal composition of the alloy and the postsintering heat treatment conditions and primarily control the intrinsic coercivity of the magnet. Selected area electron diffraction together with high resolution electron microscopy showed a high density of basal stacking faults (microtwinning) of the cell interior phase of low coercivity (iHc < 700 kA/m) magnets with a (c/a)*- ratio of the basic structural unit of > 0.843. High coercivity magnets (iHc>) 1000 kA/m), containing a high density of the platelet phase perpendicular to the c-axis, exhibit cell diameters up to 200 nm with a (c/a)*-ratio of the basic structural unit of the cell interior phase of < 0.843.
Use of Permanent Magnets in Accelerator Technology: Present and Future
Authors: Halbach Klaus
Published: March 2011

Permanent magnet systems have some generic properties that, under some circumstances, make them not only mildly preferable over electromagnets, but make it possible to do things that can not be done with any other technology. After a general discussion of these generic advantages, some specific permanent magnet systems will be described. Special emphasis will be placed on systems that have now, or are likely to have in the future, a significant impact on how some materials research is conducted.
Static Devices with New Permanent Magnets
Authors: Chavanne J. , Laforest J. , Pauthenet R.
Published: March 2011

The high remanence and coercivity of the new permanent magnet materials are of special interest in the static applications. High ordering temperature and large uniaxial anisotropy at the origin of their good permanent magnet properties are obtained in rare earth-transition metal compounds. Binary SmCo5 and Sm2Co17 and ternary Nd2Fe14B compounds are the basis materials of the best permanent magnets. New concepts of calculations of static devices with these magnets can be applied : the magnetization can be considered as rigid, the density of the surface Amperian current is constant, the relative permeability is approximately 1 and the induction calculations are linear. Examples of hexapoles with Sm-Co and NdFeB magnets are described and the performances are compared. The problems of temperature behaviour and corrosion resistance are underlined.
High Temperature Superconductors in the La1+xBa2-xCu3Oy System
Authors: McCarron E. M. , Torardi C. C. , Attfield J. P. , Morrissey K. J. , Sleight A. W. , Cox D. E. , Bordia R. K. , Farneth W. E. , Flippen R. B. , Subramanian M. A. , Lopdrup E. , Poon S. J.
Published: March 2011

In the perovskite-related La/Ba/Cu oxide system, the lanthanum ions can substitute on the barium sites due to a close match in the ionic radius of the two. Thus it is possible to make a solid solution La1+xBa2-xCu3Oy where O ∼ x ≤ 0.5 and y ∼ 7. For the Ba-rich end member composition (x ∼ 0). the structure is orthorhombic. but as the La content increases and La begins to substitute on the Ba sites (disordered), the crystal symmetry changes from orthorhombic to tetragonal. In addition, the superconducting properties vary with increasing La content. In particular, the superconducting onset temperature is found to decrease linearly from 80 to 45 K over the compositional (x) range 0.0 → 0.375. In the La-rich limit (x = 0.5). 1/4 of the Ba atoms are replaced by La and superconductivity is lost. A correlation between oxygen ordering (annealing) and high Tc is observed for orthorhombic LaBa2Cu3Oy and inferred in the case of tetragonal La1.25Ba1.75Cu3Oy.
Oxygen Order, Stoichiometry and Magnetic Behavior of YBa2(Cu1−xFex)3O7+δ
Authors: Kimball C. W. , Matykiewicz J. L. , Giapintzakis John , Lee Hsun , Dunlap B. D. , Slaski M. , Fradin F. Y. , Segre C. , Jorgensen J. D.
Published: March 2011

Mössbauer effect and neutron diffraction measurements have been made as a function of composition for YBa2(Cu1−xFex)3O7+δ. A chemically driven disordering of the sublattices is observed with increasing Fe concentration which results in a transition from the orthorhombic to a tetragonal phase. However, as the occupancy of the oxygen site 0(1) in the chain is depleted and the site of the ordered vacancy 0(5) between the chains becomes occupied, the total oxygen content is not reduced but remains near seven in contrast to behavior observed in the quenched tetragonal phases. Mössbauer spectra for x =0.05 at temperatures below 15K show magnetic hyperfine splitting which is characteristic of a spin glass; i.e., a distribution of magnetic fields. It is inferred from Mössbauer results that Fe preferentially occupies the Cu(1) site.
High Critical-Current Density Ba2YCu3O7 Thin Films Produced by Coevaporation of Y, Cu, and BaF2
Authors: Mankiewich P. M. , Howard R. E. , Skocpol W. J. , Dayem A. H. , Ourmazd A. , Young M. G. , Good E.
Published: March 2011

High quality films of Ba2YCu3O7 have been made by coevaporation of Y, Cu, and BaF2 and subsequent annealing in oxygen. Addition of water vapor to the annealing gas at high temperatures has been found to greatly reduce the annealing time and, thus the substrate interaction. Transition temperatures (zero resistance) between 89–92 K are routinely obtained on SrTiO3 and cubic zirconia substrates. Critical current densities on SrTiO3 are as high as 106 A/cm2 at 81 K and routinely above 105 A/cm2 at 77 K. Transmission electron microscopy shows that on SrTiO3 the superconducting grains have an epitaxial orientation with respect to the substrate. Persistent current measurements in thin film rings demonstrate the absence of residual resistance in the superconducting state.
The n-p Transition in YBa2Cu3O6–5+x
Authors: Choi G. M. , Tuller H. L. , Tsai M.-J.
Published: March 2011

The role of annealing conditions on the equilibrium defect state of the material was investigated by computer controlled 4 probe d.c. conductivity and thermoelectric power measurements on dense homogeneous ceramics prepared from citrate precursors. At elevated temperatures, the conductivity first decreases and then increases exponentially with decreasing temperature with the conductivity minima shifting to lower temperatures with decreasing PO2. This unusual behavior is described as representing a transition from n-type to p-type conduction. The n-p transition is correlated with the corresponding stoichiometry shift upon cooling from oxygen deficient (Cu1, Cu2) to oxygen excess YBa3Cu3O6–5+x, (Cu2+, Cu3+). A preliminary defect model is proposed which provides a framework for understanding a number of the experimental observations.
High-TC Superconducting Oxide Films Produced from Solution Precursors
Authors: Cooper Emanuel I. , Frisch Margaret A. , Giess Edward A. , Gupta Arunava , Hussey Brian W. , O'Sullivan Eugene J.M. , Raider Stanley I. , Scilla Gerald J.
Published: March 2011

Superconducting films of Ba2RECu3O7−x were prepared from aqueous and aqueous-alcoholic mixed solutions of barium, rare earth (RE), and copper nitrates. The solutions were sprayed onto heated (100) orientated MgO, ZrO2 —9%Y2O3 and SrTiO3 substrates to form a dehydrated nitrate precursor; subsequent thermal treatment yielded the superconducting 2:1:3 compound. Earlier magnetic film studies with aqueous-alcoholic mixed solutions of rare-earth iron garnet precursors showed that alcohol improves the spreading and drying of solutions on substrates. Here, however, alcohol significantly lowers the solubility of Ba(NO3)2. Some compositions tend to phase segregate during film preparation. A key objective of this study was to understand reaction paths of the precursors in order to optimize the furnace annealing schedule. Film and substrate reactions complicate the process, especially for SrTiO3, which otherwise has a good lattice match with films. Analytical methods used were Knudsen effusion mass spectrometry, thermogravimetric analysis, x-ray diffraction, secondary ion mass spectroscopy, electron microscopy and temperature-dependent resistivity. The best samples showed a Tc of 95K and had zero resistivity below 89K. Advantages of this process include: simplicity of equipment, short deposition time; ease of making composition adjustments; and possible deposition on complex shapes.
Aligned Sintered Compacts of RBa2Cu3O7−x (R=Dy, Er, Eu, Gd, Ho, Y)
Authors: Arendt R. H. , Gaddipati A. R. , Garbauskas M. F. , Hall E. L. , Hart H. R. , Lay K. W. , Livingston J. D. , Luborsky F. E. , Schilling L. L.
Published: March 2011

Sintered compacts of magnetically aligned single-crystal particles have been studied by x-ray, microscopy, and magnetic measurements. Though significant alignment and very anisotropie magnetic hysteresis were obtained, the magnitude of the hysteresis indicates, through the critical state model, that the bulk critical current density remains low.
Defect Structures in YBa2Cu3O7−x Produced by Electron Irradiation
Authors: Kirk M. A. , Raker M. C. , Liu J. Z. , Lam D. J. , Weber H. W.
Published: March 2011

Defect structures in YBa2Cu3O7−x produced by electron irradiation at 300 K were investigated by transmission electron microscopy. Threshold energies for the production of visible defects were determined to be 152 keV and 131 keV (+ 7 keV) in directions near the a and b (b>a) axes (both perpendicular to c, the long axis in the orthorhombic structure), respectively. During above threshold irradiations in an electron flux of 3×1018 cm-2 s-1, extended defects were observed to form and grow to sizes of 10–50 nm over 1000 s in material thicknesses 20–200 nm. Such low electron threshold energies suggest oxygen atom displacements with recoil energies near 20 eV. The observation of movement of twin boundaries during irradiation just above threshold suggests movement of the basal plane oxygen atoms by direct displacement or defect migration processes. Crystals irradiated above threshold were observed after about 24 hours to have transformed to a structure heavily faulted on planes perpendicular to the c axis.
Transmission Electron Microscope Studies on Minor Phases and Imperfections in YBa2Cu3Ox Compounds
Authors: Ikeda Shozo , Kimura Kazuhiro , Matsushita Akiyuki , Aoki Haruyoshi , Hatano Takeshi , Matsumoto Takehiko , Ogawa Keiichi
Published: March 2011

We studied grain boundaries in calcined and sintered YBa2Cu3Ox transmission electron microscopy (TEM) and found complex Ba-Cu oxides. The complex oxide was polycrystalline and composed of grains smaller than 100 nm in diameter and it often included minor phases rich in Y. Some stoichiomet-ric oxides such as BaCuO2, CuO and BaO were also observed along grain boundaries.
Far-Infrared Properties of ab plane oriented YBa2Cu3O7-δ
Authors: Bonn D. A. , O'Reilly A. H. , Greedan J. E. , Stager C. V. , Timusk T. , Kamarás K. , Tanner D. B.
Published: March 2011

Polycrystalline samples of YBa2Cu2O7-δ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gap-like depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm−1 and at 155 cm−1 narrow in the superconducting state, in analogy with the effect of the electron phonon interaction in BCS superconductors. In the normal state the background conductivity is Drude like with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm−1. The extrapolated far-infrared conductivity agrees with the measured dc conductivity.
On the Twin Formation in Orthorhombic Y1Ba2Cu3O7-Y
Authors: Rios-Jara D. , Varea C. , Robledo A. , Huanosta A. , Dominguez J. M. , Omaña J. , Akachi T. , Escudero R.
Published: March 2011

Transmission and scanning electron microscopy were used to study some features of twins in the orthorhombic phase of Y1Ba2Cu3O7-Y compounds. A model that explains the formation and proliferation of thene defectr, is proposed. Some conclusions about the kinetics of formation of these defects are stated, which agree with observed changes in twin densities produced by different cooling rates. Electron energy loss spectrometry (EELS) was ucod to measure relative changes in oxygen, which give some information about the relative value and the stability of oxygen content in twinned regions. A Braggs-Williams model of the order-disorder transition, for oxygen occupancies in the Cu-O2 planes, predicts an enrichment of vacancies at the boundaries in these oxygen deficient perovskites. This could explain the observed deficiency in oxygen content with respect to the perfect Y1Ba2Cu3O7 stoichio-metry.
Sintering and Microstructure - Property Relations for YBa2Cu3Ox
Authors: Bordia R. K. , Horowitz H. S. , Subramanian M. A. , Michel J. B. , McCarron E. M. , Torardi C. C. , Bolt J. D. , Chowdhry U. , Lopdrup E. , Poon S. J.
Published: March 2011

The recent discovery of high temperature superconductivity in YBa2Cu3O7 has led to intense activity in the processing of these oxides. The earliest attempts to synthesize these materials were based on solid state routes. These routes do not produce highly sinterable powders. Solution routes can potentially produce much more sinterable powders. We have investigated several synthesis routes - both solid state and solution. The details of these will be presented elsewhere(1). Here, we contrast the physical properties and the densification behavior of powders made via solid state and solution routes. We also present preliminary results on the microstructural characterization and electrical properties of the sintered samples.
High TC Superconducting Films from Metallo-Organic Precursors
Authors: Davison W. W. , Shyu S. G. , Buchanan R. C.
Published: March 2011

High Tc superconducting films of heavy metal soaps (derived from carboxylic acid precursors) have been prepared on Si and other substrates. The precursors were synthesized and mixed in appropriate molar ratios to form the high Tc compound YBa2Cu3O7−x, using a high boiling point common solvent base. The precursor solution was deposited by a spin casting technique on the substrates. Film thicknesses of 0.1–1.0μm were achieved after heat treatment at 550°-850°C ≤4 hours. Films were analyzed as to orientation, appropriate phase, interfacial reaction and superconducting properties.
A Metal-Alloy Process for the Formation of Oxide Superconducting Films: Advantages, Problems Substrate Interactions, Buffer Layers
Authors: Gurvitch M. , Fiory A. T.
Published: March 2011

Most thin film processes developed for the formation of the new cuprate superconductors involve admixture of oxygen during film growth, followed by a subsequent anneal in O2 at high temperatures in order to form the correct phase. We completely separated the two processes by first depositing a metallic alloy of YBa2Cu3 by DC magnetron sputtering, taking full advantage of the ease of calibration and high rates of deposition typical of metals, and then performing a second oxidation and annealing step in an Oo furnace. A potential problem of the attack by ambient moisture on the highly reactive metallic alloy was handled by use of thin Y overlayers. We examined substrate interactions of our films and identified several favorable combinations of substrates and protective buffer layers, such as ZrO2 /Ag and MgO/Nb.
Spin-On thin films of YBa2Cu3O7-y and La2−xSrxCuO4-y from Citrate-Polymer Precursors
Authors: Chiang Yet-Ming , Forcone Sharon L. , Ikeda Jeri Ann S. , Rudman David A.
Published: March 2011

Thin films of La2−xSrxCuO4 and YBa2Cu3O7-y superconductors have been prepared from citrate-polymer precursors. By a simple spin-coating and pyrolysis process, films which are dense and continuous at greater than 0.5 μm thickness have been prepared. For YBa2Cu3O7-y films deposited on SrTiO3, a large degree of epitaxial orientation has been observed, with the a-b plane of the superconductor parallel to the (100) plane of the substrate. Microstructural characterization and electrical properties measurements of these films are presented.
Fabrication of high Tc Superconducting Films with Diffusion Barriers
Authors: Ghien C. T. , Xiao Gang , Cieplak M. Z. , Bakhshai A. , Gavrin A. , Streitz F. H. , Childress J.
Published: March 2011

Superconducting YBa2Cu3O; thin films have been prepared by magnetron sputtering onto [100] single crystal MgO with and without an Au buffer layer. All samples show high transition temperatures (82–87 K). The use of an Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106A/cm2 at 2 K and 3.5×104A/cm2 at T=77 K). The Au buffer layers remain metallic after high temperature annealing in an oxygen atmosphere, and may thus serve as effective current shunts.
Properties of Y-Ba-Cu-O Film Formed by the Spray Pyrolysis Method
Authors: Kawai Maki , Kawai Tomoji , Masuhira Hiromi , Takahasi Makoto
Published: March 2011

An oriented film of YBa2Cu3O7−x superconductor was formed by a spray pyrolysis method. The temperature dependence of resistance showed the Tc-onset at 95K and Tc-zero at 83K with the film on a cubic zirconia single crystal surface. The X-ray diffraction pattern showed that the structure of the film was pure orthorhombic phase. Effect of the substrates and the modification of the substrates surface to form superconductive films are presented.
High-Temperature Superconducting Y-Ba-Cu-O Thin Film by using Ionized Cluster Beam Method
Authors: Yamanishi K. , Yasunaga S. , Imada K. , Sato K. , Hashimoto Y.
Published: March 2011

High-temperature superconducting Y-Ba-Cu-O films were obtained for the first time by using the ionized cluster beam (ICB) method. It was confirmed that the films resulted in superconductor showing the zero resistance at the temperature above 7 7K.

Three ICB sources were used to control the composition of the film, where ionized each cluster of Y, Ba and Cu was ejected simultaneously from the sources to the MgO substrate in high vacuum. The grown film annealed at 930 °C in oxygen atmosphere showed superconducting behaviour in electrical resistance-temperature relationship. The transition temperature to a superconducting state depends on the voltage to accelerate ionized cluster beams and film thickness. The highest temperature obtained to date is 89K.
Superconducting Properties of Orthorhombic YBa2(Cu1−xZnx)3O7 and Tetragonal YBa2(Cu1−xGax)3O7
Authors: Xiao Gang , Cieplak M. Z. , Gavrin A. , Streitz F. H. , Bakhshai A. , Chien C. L.
Published: March 2011

We have used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to probe the YBa2Cu3O7 superconductor. A small doping of Ga induces an orthorhombic to tetragonal structural transition, but the values of Tc are as high as 81 K in the tetragonal phase. YBa2(Cu1−xZnx)3O7 retains the same orthorhombic structure as the parent compound, but with highly depressed Tc. The oxygen vacancy order, or the linear chain structure, is found to be not essential for the high Tc. Our data suggest that Ga and Zn preferentially substitute Cu(1) and Cu(2) sites, which leads to the conclusion that the most important feature of the high Tc oxide superconductors is the Cu—O2 planes.
Superconductivity of La(2-x)BaxCuO4
Authors: Moodenbaugh A. R. , Xu Y. , Suenaga M.
Published: March 2011

Superconductivity near 30 K in the La-Ba-Cu-O system, first observed by Bednorz and Müller [1], was soon found to be attributable to the K2NiF4-type (at room temperature) compound La(2-x)BxxCuO4 [2]. Substitution of Sr and Ca for Ba yielded superconducting systems, also with high superconducting transition temperature Tc. Replacement of La by Y led to the discovery of the 90 K superconductors.
Bulk Superconductivity in La2CuO4
Authors: Schirber J. E. , Venturini E. L. , Morosin B. , Kwak J. F. , Ginley D. S. , Baughman R. J.
Published: March 2011

There is considerable interest in the interplay, of superconductivity and magnetism in La2CuO4. Several groups [1–3] have noted signs of superconductivity in nominal La2CuO4, and antiferromagnetism has been reported[4] in La2CuO4-y with y>0. The superconductivity previously reported was of a filamentary nature because although resistance drops to near zero were observed, only small Meissner effects (∼10-3 to 10-4 of perfect diamagnetism) were observed. In this paper we describe our studies of. ceramic samples of La2CuO4-y, loaded with oxygen by high pressure. This technique results in substantial incorporation of O2 in the material (of the order of 0.3 to 0.4% by weight) and in gross changes in the bulk resistivity and magnetization as well as discernable changes in the lattice parameters of the material.
Short Range Order Structure Around Oxygen Atoms in the Superconductor Y-Ba-Cu-O
Authors: Woronick S. C. , Ng W. , Krol A. , Yang B. X. , Kao Y. H. , Meng R. L. , Hor P. H. , Chu C. W.
Published: March 2011

Spectra of the oxygen K-edge extended x-ray absorption fine structure (EXAFS) of the superconducting compound Y-Ba-Cu-O were obtained by measuring the total electron yield as a function of incident x-ray energy at temperatures between 77K and 300K. This technique affords a convenient way for probing the local environment around the oxygen atoms and soft modes in the lattice.
Electron Irradiation of YBa2Cu3O7 at low Temperatures
Authors: Stritzker B. , Zander W. , Dworschak F. , Poppe U. , Fischer K.
Published: March 2011

Bulk samples of YBa2Cu3O7−x have been homogenously irradiated with 3 MeV electrons at temperatures below 20 K. Whereas the superconducting transition temperature, Tc, drops dramatically with increasing dose the width of the transition remains unchanged (Δ Tc ≤ 1.5 K). The normal state resistance at 100 K increases substantially during the electron irradiation. Several irreproducible experiments can be interpreted with a radiation induced, unstable increase of Tc.
Rapid Solidification of YBa2Cu3O7−x, EuBa2Cu3O7−x, and GdBa2Cu3O7−x
Authors: Mckittrick J. , Mchenry M. E. , Standley P. , Heremans C. , Prasanna T. R. S. , Kalonn G. , O'handley R. C.
Published: March 2011

Rapid solidification of YBa2Cu3O7−x, EuBa2Cu3O7−x and GdBa2Cu3O7−x has resulted in the formation of amorphous materials with crystallization temperatures in the range of 730–750°C. Higher temperature anneals in oxygen result in the evolution of the orthorhombic phase. The peritectic decomposition temperature for MBa2Cu3O7−x→M2BaCuO7 + liquid (M=Y, Eu, Gd) is in the range of 1035–1085°C with the Eu and Gd compositions having the highest values.
Synthesis of Superconducting Oxides and Oxide/Metal Composites by Oxidation of Metallic Precursors
Authors: Yurek Gregory J. , Vander Sande John B. , Rudman David A.
Published: March 2011

One method for the synthesis of superconducting oxides is high temperature oxidation of a metallic alloy (a metallic precursor) that contains the metallic constituents of the oxide. In addition, a noble metal can be added to the precursor such that, after oxidation, a two phase, finely divided oxide/metal composite results. Superconducting oxides have been produced from Eu-Ba-Cu and Yb-Ba-Cu alloys by oxidizing the alloys at 300°C followed by an “oxygen anneal” at elevated temperatures. Similarly, a Eu1,Ba2Cu3O7−x /Au composite has been formed from a quaternary metallic precursor. each case an onset of superconductivity occurred at about 92K. This approach to producing superconducting oxides is felt to have a number of advantages associated with it, not the least of which is the improvement of the mechanical properties of the superconducting product.