bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization Relaxation in KDP-Isomorph Ferroelectrics
Authors: Homer Vicki , Edge Ronald
Published: March 2011

The two-dimensional position sensitive detector at IPNS was used to probe the splitting of a single Bragg peak of the ferroelectric KD2PO4 (DKDP) at temperatures below the Curie point. The (440) peak was split into four components as the crystal itself divided into four domains. When the crystal was subjected to electric fields of sufficient strength and duration, these peaks would change in relative intensity, thus displaying the rearrangement of the domain structure as the crystal changed its level of polarization. Even at temperatures 15–20K below the Curie point, the polarized crystal was observed to relax back to an almost completely unpolarized state upon removal of the applied electric field. This indicates that the true coercive field for the crystal at this temperature was much smaller than values previously reported [l]. Low frequency dielectric constant studies using a capacitance bridge have since been conducted, which confirm and expand on these results.
Neutron Powder Diffraction Study of the Structures of La1.9Ca1.1Cu2O6 and La1.9Sr1.1Cu2O6+δ
Authors: Santoro A. , Beech F. , Cava R. J.
Published: March 2011

The title compounds are structurally isomorphous and crystallize with the symmetry of space group 14/mmm. The lattice parameters are a = 3.8248(1), c = 19.4286(5)Å for La1.9Ca1.1Cu2O6 and a = 3.8601(1), c = 19.9994(5)Å for La1.9Sr1.1Cu2O6+δ. The structure can be easily derived from that of La2CuO4 by substituting the layers of composition CuO2 present in La2CuO4 with a block of three layers having composition and sequence (CuO2) - (R) - (CuO2), where R is Ca, Sr, and/or La. Although the general structural configuration is the same for the Ca and the Sr compounds, the distribution of the metal atoms is different in the two cases. More specifically, in La1.9Ca1.1Cu2O6 the perovskite-type layers form blocks with sequence (CuO2) - (Ca) - (CuO2), and are separated by rock-salt blocks of two layers (LaO) - (LaO). In La1.9Sr1.1Cu2O6+δ, on the other hand, the perovskite-type blocks have composition and sequence (CuO2) - (R) - (CuO2) and they are separated by blocks (NO) - (NO), where both R and N are about 65%La and 35%Sr.
The Advanced Neutron Source
Authors: Hayter John B.
Published: March 2011

The Advanced Neutron Source (ANS) is a new user experimental facility planned to be operational at Oak Ridge in the late 1990's. The centerpiece of the ANS will be a steady-state research reactor of unprecedented thermal neutron flux (φth ≍ 9·1019 m−2·s−1) accompanied by extensive and comprehensive equipment and facilities for neutron-based research.
Neutrons: The Kinder, Gentler Probe of Condensed Matter
Authors: Axe John D.
Published: March 2011

Neutrons play an increasingly important role in the characterization of advanced modern materials. They provide information that complements rather than competes with that provided by other scattering probes. Although neutrons require heroic efforts to produce, the techniques for using them are not particularly difficult, and with the advent of sufficient user friendly facilities, are becoming a routine tool in the arsenal of expanding numbers of materials scientists.
Neutron Depth Profiles of Boron Implanted Semiconductors
Authors: Bowman Robert C. , Knudsen John F. , Downing R. Gregory
Published: March 2011

The nondestructive neutron depth profile (NDP) technique has been used to measure boron (10B) distributions in Si and Hg0.7Cd0.3 Te after multiple energy ion implants. The NDP results are compared with simulations generated by TRIM and SUPREM computer codes. The influence of SiO2 films on the boron profiles was examined and the effects of thermal anneals are also described.
Neutron Scattering Study of Layered Silicates Pillared with Alkylandnonium Ions
Authors: Neumann D. A. , Nicol J. M. , Rush J. J. , Wada N. , Fan Y. B. , Kim H. , Solin S. A. , Pinnavaia T. J. , Trevino S. F.
Published: March 2011

Incoherent, inelastic neutron scattering has been used to study the vibrational spectra of tetramethylammonium montmorillonite and trimethylammonium vermiculite in the energy range 20–140 meV. For both systems peaks are observed due to the internal modes of the intercalate and to the excitations of the hydroxyl groups within the host layers. For the montmorillonite sample, it is found that the steric constraints imposed on the tetramethylammonium ion by the bounding clay layers contribute an additional 28 meV to the rotational barrier of the methyl groups. This additional barrier is shown to be strongly related to the volume that the tetramethylammonium ion occupies. For the trimethylammonium vermiculite sample normal mode analysis of the internal modes of the intercalated ion shows that the N-H bond is parallel to the c-axis of the host.
Analysis of Sans from Controlled Pore Glasses
Authors: Berk N. F. , Glinka C. J. , Haller W. , Sandert L. C.
Published: March 2011

Small angle neutron scattering measurements have been performed on several samples of silica controlled pore glasses with pore sizes ranging from roughly 7 to 30 nm. The scattering intensity is strongly peaked at small Q and shows approximate Porod law behavior at large Q. Contrast variation measurements have shown that the pore space in these samples is entirely interconnected and thus forms a bicontinuous microstructure. The scattering data have been analyzed using the leveled wave method based on an early scheme for representing two-phase microstructures resulting from spinodal decomposition. In this approach interfaces are modeled by the contours of a stochastic standing wave composed of plane wave components propagating in random directions with random phases and having wave numbers distributed according to a given probability density, P(k). We have determined model P(k) functions by fitting the SANS data with the leveled wave scattering function and then used these to construct leveled wave images of the corresponding porous structures. The average pore sizes obtained by measuring chord lengths in the computer models turn out to agree with the values determined for these glasses by mercury porosimetry.
Shear Induced Phase Behavior of Polymer Blends by Small Angle Neutron Scattering
Authors: Nakatani Alan I. , Kim Hongdoo , Han Charles C.
Published: March 2011

The phase behavior of polymer blends and solutions can be changed dramatically by a flow field using a variety of flow geometries. Unlike simple binary fluids which require extremely high shear rates to produce only small shifts in the phase boundary, polymer phase behavior may be influenced by as much as 10 degrees with the application of much lower shear rates. However, there is a large body of conflicting data concerning the nature of these shear effects in polymers.

Here we report on the effects of shear on the phase behavior of polymer blends by small angle neutron scattering (SANS). Experiments were conducted using a specially constructed, concentric cylinder apparatus for in situ studies of concentrated polymer solutions and melts. Two separate systems will be discussed: 1) a blend of polystyrene and polybutadiene. 2) a blend of polystyrene and poly(vinylmethylether). Both systems exhibit shifts in the phase behavior which indicate shear induced mixing in agreement with previous results obtained by other techniques. These results will be interpreted within the context of existing theories of shear induced phase behavior.
Fracture of Metal-Polymer Interfaces with Fine-Line Geometries
Authors: Chiu Shih-Liang , Jeng Y. H. , Acosta Raul E. , Ho Paul
Published: March 2011

The fracture behavior of metal-polymer line structures as a function of dimensions was investigated using a stretch-deformation technique. The effects of line orientation, line width and film thickness are reported in this paper. When the line orientation is parallel to the stretching direction, only formation of cracks normal to the lines is observed. However, when the line is perpendicular to the stretching direction, delamination becomes the dominant mode of fracture. Wide lines (16μm) exhibit larger shear stress at the edge of the metal-polymer interface, thus delaminate earlier than narrow lines (4μm). By decreasing the metal film thickness, the depth of stress penetration at the interface decreases, making the propagation of cracks more difficult in thin films than in thick films.

Finite element analysis was carried out to account for the experimental observations and good agreement was obtained. In the analysis, the plastic deformation characteristics of the metal and the polymer have been specifically taken into account. In comparison with a linear elastic analysis, the linear model predicts significantly higher stress levels and local concentrations than the nonlinear model.
Preparation of Al2 O3 -Coated Metal Substrate for High Density Electronic Assembly
Authors: Nakada K. , Ono M. , Kosuge S.
Published: March 2011

A study was conducted on the preparation of Al2 O3 -coated metal substrates for high density electronic assembly. Al2 O3 films of 3∼15μm thickness were deposited on metal substrates, such as aluminum, stainless steels and the like, at a deposition rate of 0.2∼5μm/min. They were examined in terms of chemical composition, microstructure, density, hardness, breakdown voltage, thermal conductivity and so on. It was found that the dense and stoichiometric films could be achieved by adjusting the process parameters, in particular, substrate temperature, deposition rate and distance between target and substrate. The results obtained led to the conclusion that this new Al2O3-coated metal substrate could be effective for high density electronic assembly.
The Fast Firing of the Ferroelectric Relaxor Pb(Mn1/3Nb2/3).02 (Mg1/2 W1/2 ).48 Zr.23 Ti.27O3
Authors: Mansfield Sean F. , Taylor Jenifer A.T. , Barus Aristianto M. , Landin Steven M.
Published: March 2011

The possibility of fast firing a relaxor dielectric to suppress grain growth, mitigate the lead loss and reduce the cost of sintering has been investigated. The relaxor Pb(Mn1/3 Nb2/3).02 (Mg1/2 W1/2 ).48 Zr.23 Ti.27 O3 [1] exhibits a highly desirable broad phase transistion range when the prbcessing procedures are carefully controlled and fired conventionally. When fast fired, this material's density, percentage of secondary phases, and dielectric constant were highly dependent on the sintering time. A sample fired for 6 minutes possessed a dielectric constant nearly equal to the same material conventionally fired for 16 hours.
Materials, Mechanical, and Thermal Considerations of High Density Multi-Chip Electronic Packages
Authors: Krusius J. Peter
Published: March 2011

Multi-chip packages (MCP) are analyzed for high density CMOS packaging using package system simulation, a new systematic methodology for design and trade-off studies of electronic packages. Technology parameters for a representative CMOS chip, multi-chip package, and printed wiring board technology are defined. The effect of these technology parameters on the characteristics of the MCP are examined. The MCP's are optimized using simulated annealing. A large set of optimum MCP's has been found. Based on this set, MCP technology parameters are ranked and their implications on future high density MCP's discussed.
On the Structure of Planar Defects in ALN
Authors: Mckernan Stuart , Carter C. Barry
Published: March 2011

Aluminum nitride has a great potential as a semiconductor substrate material. However, the defects which occur in this material are very detrimental to the material properties. ‘Domelike’ or ‘D’ defects, consisting of a flat basal fault joined to a curved planar fault, are examined by TEM. They are shown to be inversion domains, using a newly developed technique for polarity determination in the TEM. Structural models are proposed for the defects which incorporate a layer of alumina one unit cell thick into the basal fault of the defect.
Interfacial Failure In Ti/Sio2 and Ti/AIN System And Temperature Dependence Of Hardness Of AIN
Authors: Liu T. , Notis R. , Chou Y. T.
Published: March 2011

The load dependence of interracial failure induced by microindentation has been studied. It is demonstrated experimentally that substrate lateral defects induced by indentation contribute significantly to interracial failure. The microhardness of translucent AIN was measured at temperatures up to 1200°C. The hardness decreased from 10.6GPa at room temperature to 4.0GPa at 1200°C.
Electroless Plating of Copper Interconnections on Ion Beam Catalyzed Polyimide
Authors: Flottmann T. , Tulke A. , Esper E. , Lohmann W.
Published: March 2011

Decomposition of a palladium compound by ion irradiation has been used to catalyze electroless plating on polyimide. First, palladium-acetylacetonate or -acetate is spin-coated on a polyimide substrate. The thin resist film is then irradiated through a mask with He or Ar ions of 100 keV energy. After washing off the film parts which were not exposed to the ion beam, copper is deposited on the catalyzed polyimide substrate in an alkaline electroless plating bath. When using alkaline resistant polyimide, copper lines several microns thick can be plated. The chemical surface composition of the Pd-compounds after ion beam exposure has been investigated with ESCA. It has been found that the Pd is partially reduced. Pd-acetate is more effective to form catalytic sites than Pd-acetylacetonate.
The interdiffusion of Cu, Co and Au Thin Films at elevated temperatures
Authors: Madakson Peter , Liu Joyce C.
Published: March 2011

A detailed study of the interdiffusion and resistivity of Cu/Au, Cu/Co/ Co/Au and Cu/Co/Au thin film structures was carried out at temperatures ranging from 25 to 550°C1. Both Cu and Au, in the Cu/Au structure, intermix readily even at temperatures as low as 150°C and the interdiffusion is accompanied by rapid increase in resistivity. Very little interdiffusion occurs in the Cu/Co, Co/Au or Cu/Co/Au thin film structures up to about 400°C, after which the resistivity increases. The very rapid increase in resistivity observed at 250°C for the Cu/Au system and at 450°C for Cu/Co/Au, is associated with recrystallization of the films into large grains and the formation of AuCu, Cu3Au and Cu3Au2 compounds. The Cu/Co/Au structure recrystallizes at a higher temperature because of the time needed for Cu and Au to diffuse through the Co layer, which did not react significantly with either Au or Cu.
Oxidation Kinetics of (Pb-In) Single-Phase Alloys
Authors: Zhang M.-X. , Chang Y. A. , Marcotte V. C.
Published: March 2011

The solid state oxidation kinetics of Pb-In single-phase alloys were studied using AES (Auger Electron Spectroscopy) combined with sputter depth profiling. Samples containing 3, 30, 64 at% In were oxidized in air from room temperature up to 275 °C. At room temperature, the oxidation behavior for all three alloys was found to obey a direct logarithmic law. As the temperature is increased, the kinetics change from logarithmic to parabolic behavior. The transition between logarithmic and parabolic kinetics occurs between 150 °C and 175 °C for Pb-3 at% In alloy, and below 100 °C for Pb-30 at% In and Pb-64 at% In alloys. Using the solidius temperature as melting temperature of an alloy, the transition temperature for Pb-In alloys was observed to be approximately 70 – 75 % of the melting temperature.
Femtosecond Time Domain Techniques for Characterization of Linear and Nonlinear Optical Properties in GaAs Waveguides
Authors: Anderson K. K. , Lagasse M. J. , Haus H. A. , Fujimoto J. G.
Published: March 2011

Femtosecond time domain measurements can provide a powerful approach for characterizing both the nonlinear as well as linear optical properties of waveguide devices. We describe a new time division interferometry technique to perform direct measurements of the nonresonant nonlinear index of refraction in AIGaAs waveguides. In addition, femtosecond time of flight measurements permit linear properties such as absorption and dispersion to be characterized using time domain techniques. These techniques permit a comprehensive characterization of linear and nonlinear waveguide properties.
Mechanistic Aspects of the Deposition of thin Alumina Films Deposited by Mocvd
Authors: Morssinkhof R. W. J. , Fransen T. , Heusinkveld M. M. D. , Gellings P. J.
Published: March 2011

The object of this study is the decomposition mechanism of Aluminium-Tri- Isopropoxide and its influence on the deposition of A12O3 by MOCVD. DSC experiments reveal that the decomposition occurs in two steps: formation of aluminum hydroxide, followed by dehydration.

Deposition of A12O3 takes place by diffusion of AI(OH)3 to the substrate surface, followed by dehydration to Al2O3. This is supported by the insignificant amount of carbon found in the coating analyzed by XPS. A Langmuir type adsorption of the reactive components explains the change in reaction order of ATI from one at atmospheric pressure to two at 3 torr.
Selective Chemical Vapour Deposition of Tungsten Using SiH4/WF6 Chemistry
Authors: van der Jeugd C. A. , Verbruggen A. H. , Leusink G. J. , Janssen G. C. A. M. , Radelaar S.
Published: March 2011

The effect of deposition temperature and SiH4/WF6 flow ratio on the resistivity and impurity content of SiH4/WF6 tungsten films has been investigated. It is found that low deposition temperatures and high SiH4/WF6 ratios result in films with a high resistivity up to 150 μΩcm, whereas films deposited at high temperatures have a resistivity of 9 μΩcm. From Electron Probe Micro Analysis and Auger Electron Spectroscopy we conclude that the resistivity increase is due to silicon which is incorporated in the tungsten film during deposition. This results in a resistivity increase of 20 to 40 μΩcm per at% Si.
Identification of W20O58 Phase In CVD Tungsten Films
Authors: Lawrence M. , Dass A. , Sivaram Siva , Tracy Bryan
Published: March 2011

Thin films of tungsten grown in a CVD reactor by the reduction of hydrogen and silane consisted of a two phase microstructures; a matrix phase of bcc tungsten, and a second phase of W20O58. The second phase is uniformly distributed in the film and does not afeoct 5athe electrical resistivity of hydrogenreduced films (8 μohm-cm). However, dissolved oxygen in the silane-reduced film contributes to the observed higher electrical resistivity (13 μohm-cm) along with smaller grain size. The larger amount of oxide in the hydrogen-reduced film correlates with its slower growth rate when compared to the silane-reduced film which contained a smaller amount of oxide phase.
Investigation of CVD β-SiC Surfaces Produced VIA a “Novel” Surface Replication Process
Authors: Collins Aliki K. , Keeley Joseph T. , Pickering Michael A. , Taylor Raymond L.
Published: March 2011

A novel replication process for silicon carbide surfaces has been developed. A polished polycrystalline chemical vapor deposited (CVD) β-SiC surface was reproduced from a SiC substrate (mandrel) by a two-step pretreatment process followed by CVD of SiC. In this paper we describe the process and present characterization data for both the substrate and the replicated surfaces. Based on the characterization results, we have developed a model which describes the chemical reactions that occur during the replication process.
Application Of Ai Control To The Vls Sic Whisker Process
Authors: Shalek Peter D. , Parkinson W. J.
Published: March 2011

Silicon carbide whiskers have excellent mechanical and chemical properties, making them very desirable as a reinforcement for structural ceramic and other composite materials. Los Alamos has developed a laboratoryscale batch process for producing very high quality SiC whiskers by the vapor-liquid-solid (VLS) method which is an active candidate for technology transfer involving significant scale-up. The process, however, involves quite complex chemical/physical and parametric relationships and has not as yet lent itself successfully to modeling. An expert computer system was therefore developed to facilitate the transfer of this technology to industry. Optimum conditions were determined by relating the many process parameters to product results to establish a set of rules for running the process. These are incorporated in a two-phase expert system designed to guide inexperienced users. In Phase I, an expert consultant program provides the user with information that enables him to set up the run. This information is incorporated into the rule base that makes up Phase II- the control system. At present, the operator functions as the controller by responding to the decisions of the expert system; automation can be added later.
Laser Chemical Vapor Deposition Of Tin Films
Authors: Chen B. , Biunno N. , Singh R. K. , Narayan J.
Published: March 2011

We have investigated the pyrolytic deposition of TiN thin films on molybdenum and 304 stainless steel substrates by continuous wave (CW) and pulsed CO2 (λ=10.6 μm) laser radiation. A flow rate of NH3: TiCl4 of 5:1 was maintained during the deposition process. The substrate temperature was controlled by varying the intensity of the incident laser irradiation. The TiN films were characterized by Transmission Electron Microscopy (TEM), Auger Electron Spectroscopy (AES) and Rutherford Backscattering Spectrometry (RBS). TEM results showed that the films were polycrystalline of equiaxed nature with diffraction patterns containing the characteristic TiN rings. The films had a lattice parameter of 4.24Å. AES results showed a slight incorporation of oxygen.
A Low Temperature CVD Process for TiN Coatings
Authors: Aguero A. , Little D. , Lowden P.
Published: March 2011

A novel low temperature process for the chemical vapour deposition of titanium nitride films has been developed. Titanium sub-halides generated “in situ” by chlorination of titanium pellets are subsequently reacted with ammonia at reduced pressure and temperatures of 450–600° C. The coatings have excellent adhesion and wear resistance. A description of the process and the properties of the coatings produced by it will be presented.
Low Temperature MoCVD Routes to Thin Films from Transition Metal Precursors
Authors: Girolami Gregory S. , Gozum John E.
Published: March 2011

A review is presented of early and recent advances in the metal-organic chemical vapor deposition (MOCVD) of thin films from organotransition metal and related precursors. Routes to pure metals and alloys, metal carbides, metal borides, metal nitrides, metal silicides, and related materials will be summarized. Also included is a discussion of both the advantages and disadvantages of employing metal-organic precursors that contain transition elements.
Characterization of Mocvd Grown Epitaxial Ceramic Oxide Thin Films
Authors: Parker J. C. , Chang H. L. M. , Xu J. J. , Lam D. J.
Published: March 2011

Characterization of TiO2 films grown by the MOCVD technique was carried out using micro-Raman scattering. The effects of processing parameters on the film composition and morphology were investigated. The micro-Raman technique was shown to be a useful tool for characterizing oxide thin films grown by the MOCVD technique.
A Model for Chemical Vapor Infiltration of Fibrous Substrates
Authors: Melkote Rajesh R. , Jensen Klavs F.
Published: March 2011

A model is presented for CVI of a fibrous preform under isothermal and thermal gradient conditions. Transport and geometric properties during densification are calculated from a novel structural model, allowing prediction of deposition profiles and experimentally observed trends without the use of empiricism.
Anisotropy in the Far Infrared Conductivity of Magnetically-Oriented YBa2Cu3O7-δ Between 50–300K
Authors: Lu F. , Perry C.H. , Chen K. , Markiewicz R.S.
Published: March 2011

The far infrared reflectance of magnetically-oriented YBa2Cu3O7-δ has been measured from 30–600 cm-1 over the temperature range 300–50 K. A strongly temperature dependent optical anisotropy is observed in this region. The low energy Ē⊥c spectrum displays a high reflectivity associated with the dominant free carrier contribution. Peaks corresponding to phonons are present in the spectrum associated with the direction perpendicular to the high conductivity Cu - O planes. However the reflectivity for Ē∥c is not characteristic of an insulating material but rather shows a metallic-like rise with decreasing photon energy. The plasma frequencies for both polarizations, obtained from fits to the reflectance data, decrease with decreasing temperature. There is some evidence in the parallel conductivity data taken below Tc, for the onset of an energy gap that is substantially smaller than that deduced for the in-plane value; such a result suggests a large gap anisotropy. The parameters describing a number of low frequency phonon modes for Ē∥c have been determined from fits to the R∥ data. Most show a slight softening as Tc is traversed.
Physical Properties of Bi2sr2cuo6, the Semiconducting Phase, Structurally Distinct from the N=L Bi‐Cuprate Superconductor
Authors: Chakoumakos B. C. , Sonder Edward , Sales B. C.
Published: March 2011

The stable phase that forms near 2:2:1 in the Bi‐Sr‐Cu oxide system is now recognized as a semiconducting phase structurally distinct from the n = 1 Bi‐cuprate superconductor, whose actual composition (Bi2Sr2‐xCuO6‐y, x= 0.1‐0.25, y=0‐0.5) is deficient in Sr. The 2:2:1 phase forms by a slow solid‐state replacement of the superconducting phase for compositions near 2:2:1. It also can be grown from melt compositions involving several phase assemblages, but single‐phase products are not obtained, implying incongruent melting. Alumina and zirconia crucibles promote the growth of the superconducting phase by reacting with the melt to remove Sr, whereas Au crucibles promote the growth of the 2:2:1 phase. Owing to its fine‐grained, fibrous habit, structural characterization has been difficult. Of the unit cells proposed, the C‐centered monoclinic cell of Roth et al. provides the best fit to our x‐ray powder and single‐crystal precession data, a = 24.522(9), b = 5.426(2), c = 21.983(9) Å, β = 105.00(3)°. Perfect prismatic cleavages intersecting at ‐148° and ‐32° are indexed as {100} and {‐201} forms. Although, the superconducting n = 1 Bi‐cuprate exhibits variable Sr and O contents, the 2:2:1 phase appears to be a single composition with no oxygen exchange observed by TGA, although it may be somewhat deficient in Cu. The 2:2:1 phase is semiconducting as determined by electrical resistivity measurements, with an apparent activation energy of 0.013 eV. For a 2:2:1 stoichiometry, the measured density of ‐7.2. g/cm3 implies 16 formula units per cell.
Variation in Tc and Carrier Concentration Caused by Change of Oxygen Content in Tl-Based Superconductors
Authors: Shimakawa Y. , Kubo Y. , Manako T. , Igarashi H.
Published: March 2011

Tc variations observed in some Tl-based superconductors were studied. Clear correlations were found between Tc, carrier concentration, and c-axis length. In particular, for Tl2Ba2CuO6, a decrease in oxygen content of about 0.1 per formula unit, which corresponded to a decrease in hole concentration of about 0.2, increased Tc up to about 80K from a metallic non-superconductor, and elongated the c axis by about 0.4%. In addition, as Tc values increased systematic changes in metal-sheet separations were observed. Tc variations caused by a change in oxygen content were also observed in Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10. It was demonstrated that superconductivity appears in a certain appropriate range of carrier concentration similar to those observed in other high-Tc superconductors.
Ion-Irradiation Effects in Tl2Ca2Ba2Cu3010 Superconductors
Authors: Barbour J. C. , Kwak J. F. , Venturini E. L. , Ginley D. S. , Peercy P. S.
Published: March 2011

The effects of oxygen and helium ion irradiation on the superconducting properties of Tl2Ca2Ba2Cu3010 thin films were investigated. The transition temperature and width were monitored as a function of ion fluence using both magnetization and resistivity measurements. These data suggest that superconductivity is completely suppressed at 0.020 dpa for both He and 0 ion irradiation. Further, the rate of decrease in Tc as a function of deposited energy showed that the dominant mechanism causing damage-induced suppression of Tc in these films was from atomic collisions.
Magnetization Measurements of 5µm Ba0.6K0.4BiO3 Crystals: Approach to Intrinsic Behavior with Decreasing Size
Authors: Grader G. S. , Hebard A.F. , Schneemeyer L. F.
Published: March 2011

Magnetization measurements on cubic Ba0.6K0.4BiO3 crystals, approximately 5µm in radius, have been obtained using a recently-developed electrodynamic force balance technique. The onset of flux entry in an external filed H is marked by a pronounced deviation from a linear magnetization at a critical field H*c1 together with a noticeable reorientation of the crystal near H = 0, a reorientation caused by a field-induced torque on the remanent moment. The dependence of H*c1 on temperature is linear over the temperature range 7K≤T≤30K with a slope approximately a factor of three higher than published values. These higher values of H*c1 imply either intrinsically cleaner material with a reduced Ginzburg-Landau parameter K or higher surface critical fields. These results suggest that the intrinsic properties of high-Tc superconductors may be more accurately reflected in small crystals which are more likely to be of higher quality than larger crystals.
Anisotropic Thermal Conductivity of Superconducting Lanthanum Cuprate
Authors: Morelli D.T. , Doll G.L. , Heremans J.P. , Jenssen H.P. , Cassanho A. , Dresselhaus M.S.
Published: March 2011

The thermal conductivities of superconducting, Sr-doped lanthanum copper oxide single crystals have been measured from room temperature to below 100 mK parallel and perpendicular to the copper oxide planes. While the results indicate that the heat conduction is strongly anisotropic, the data have been analyzed in terms of a modified Bardeen-Rickhayzen-Tewordt theory of lattice thermal conductivity. It is shown that while electron scattering plays an important role in limiting the in-plane heat conductivity, this scattering channel is masked by other mechanisms for heat transport across the planes.
The Sputter Deposition and Characterisation of Epitaxial Magnesium Oxide Thin Films and Them Use as a Sappihre/YBCO Buffer Layer
Authors: Morris G W , Somekh R E , Barber Z H , Williams E J , Schmahl W W , Evetts J E
Published: March 2011

If useful electronic devices are to be fabricated from thin films of the high critical temperature oxide superconductors, such as yttrium barium copper oxide (YBCO), then films must be formed on substrates with dielectric properties which permit device operation at high frequencies, such as sapphire. It is, however, difficult to form high quality YBCO on sapphire because of reaction with the substrate and because epitaxy is not readily achieved.

We report the deposition of epitaxial thin films of magnesium oxide, by UHV reactive d.c. magnetron sputtering, on variously orientated substrates of sapphire, and the characterisation of the MgO/sapphire system by x-ray and TEM techniques.

Onto such films of MgO on sapphire we have deposited films of YBCO which were strongly textured with the c-axis perpendicular to the plane of the substrate and which were superconducting without the need for a high temperature post deposition anneal.
Effects of Low Magnetic Fields on Gold-YBCO Contacts
Authors: Tzeng Yonhua , Belser Mitchell A.
Published: March 2011

The effects of low magnetic field (0–40 Gauss) on electrical properties of gold-YBCO contacts are investigated. The contact resistance increases significantly with applied magnetic fields. For high magnetic field or when high current is flowing through the contact, the contact resistance decays after removing the magnetic field to a finite value greater than that is measured before the contact is exposed to the magnetic field and stays there for long time as long as the sample is kept below the superconductivity critical temperature.
Influence of the Partial Substitution of Small Rare Earths for Ca in the Superconductive Bi-Sr-Ca-Cu-O Compound
Authors: Casanove M. J. , Baules P. , Snoeck E. , Roucau C. , Millet P. , Enjalbert R. , Galy J.
Published: March 2011

Superconductive 2:2:1:2 phases of the type Bi2Sr2Ca1-yLnyCu2O8+x+y/2, where Ln stands for Yb or Er, have been synthesized and characterised by X-ray and electron diffraction. The small rare earth atoms prove to substitute preferentially in the Ca site. The electrical properties as well as the structural characteristics of these compounds are affected by the rare earth substitution rate. It is shown, in particular, that the long axis parameter of the subcell and the incommensurate period of the modulation decrease with increasing y. The substitution of trivalent cations for Ca requires the presence of additional oxygen atoms in the structure, the location of which is discussed.
Development of a Composite Tape Conductor of Y-Ba-Cu-O
Authors: Blaugher R.D. , Hazelton D.W. , Rice J.A. , Walker M.S.
Published: March 2011

Samples of a prototype composite tape conductor have been prepared consisting of a thick layer of Y Ba2 Cu3 O7 (123) on a metallic substrate. A thick coating of 123 precursor powder was applied to the substrate by a mechanical compaction process. A melt-quench-growth technique was then employed to effect a textured grain development and improved current density. The resulting melt processed structure showed a textured 123 orthorhombic matrix with a dispersion of the 211 phase. The orthorhombic 123 phase was highly developed with an onset temperature of 90K and current density near 104 A/cm2 at 4T and 50K measured by a steady-state magnetization method.
Influence of Silver Infiltration on the Microstructure and Transport Properties of YbacuO
Authors: Ryelandt L. , Cassart M. , Vandenbosch A. , Delannay F. , Issi J-P.
Published: March 2011

The results of measurements of the transport properties of high‐Tc superconductors containing different amounts of silver are reported. The Tc and Jc values were found to be similar to that of the single phase YBaCuO compound whereas the electrical and thermal conductivities above Tc were drastically increased. A very low contact resistance was observed.
Texture Formation and Improvement of Grain Boundary Weak‐Links in Tape Shaped Wire Prepared by the Unidirectional Solidification Technique.
Authors: Okada Michiya , Yuasa Toyotaka , Matsumoto Tosimi , Aihara Katuzo , Seido Masahiro , Matsuda. Sinpei
Published: March 2011

Au‐Sheathed Y‐Ba‐Cu‐O(YBCO) and Tl‐Ba/Sr‐Ca‐Cu‐O(TBSCCO) tapes were fabricated by the drawing‐rolling and subsequent unidirectional solidification. A typical microstructure of melt‐textured polycrystallite including fine particles of second phase(e.q. Y‐211) was observed. The Tl‐2223 tapes prepared at an optimized condition yielded Jc=15,300 A/cm2 at 77K in the absence of magnetic field, and l,100A/cm2 in a magnetic field of IT. The enhancement of Jc in a magnetic field is suggested to be due to the improvement of weak‐links in grain boundaries.
High Temperature Neutron Diffraction Study of the Formation Reaction of Bismuth Superconductors
Authors: Garbauskas Mary F. , Arendt Ronald H. , Jorgensen James D. , Hitterman Richard L.
Published: March 2011

High temperature neutron powder diffraction has been used to study the formation of the 110K transition temperature material, Bi2Ca2Sr2Cu3Ox (2223), both from synthetic reaction mixtures and after partial melting. The results indicate that the 80K transition temperature material, Bi2CaSr2Cu2Ox (2122), is the precursor to the (2223) material. The reaction to form the (2122) occurs rapidly at 860°C, while the conversion of this material to the (2223) is much slower.
Phase Development in Ag-Clad Bscco Wires
Authors: Ray II R.D. , Hellstrom E.E.
Published: March 2011

We have studied phase evolution in Ag‐clad BSCCO wires with nominal composition Bi2.4.8Sr2.05Ca0.95Cu2.27Oy‐ The wires were initially processed at 920°C where the oxide was partiaily moiten, then subsequently annealed at 840° C. The microstructure and composition of the phases present were studied at different points in the processing using optical and scanning electron microscopy, and electron probe microanalysis. The microstructure became simpler during the anneal resulting in two oxide phases and Ag. Ag from the cladding had dissolved into the melt at 920° C and subsequently precipitated in the core of the wire on cooling to the annealing temperature.
Some Theories of High Temperature Superconductivity
Authors: Cohen Marvin L.
Published: March 2011

A brief review is given of some historical aspects of theoretical research on superconductivity including a discussion of BCS theory and some theoretical proposals for mechanisms which can cause superconductivity at high temperatures.
Cation Disordering in the Tl-2122 Superconductors
Authors: Morosin B. , Ginley D. S. , Venturini E. L. , Baughman R. J. , Schirber J. E. , Tigges C. P.
Published: March 2011

We have examined several crystals belonging to the Tl‐2122 structure type (Tl2CaBa2Cu2O8 with c=29Å), and have shown that cation solid solution occurs. Such cation disorder appears to be responsible for the observed small differences in lattice parameters reported by various investigators and to contribute towards the substantial variation in the superconducting transition temperatures.
Superconducting and Structural Properties of the (Ba0.6K0.4) (Bi1-YSbY)O3 System
Authors: Dabrowski B. , Pei S. , Richards D.R. , Zheng Y. , Jorgensen J.D. , Hinks D.G. , Kimball C.D. , Mitchell A.W.
Published: March 2011

Single‐phase samples of (Ba1‐xKx)(Bi1‐xSby)O3 have been synthesized over a limited compositional range using a two‐step procedure: high‐temperature firing in a low oxygen partial pressure followed by low‐temperature oxygen annealing. For y=0 and 0.37<x<0.50, samples have a simple cubic structure and are bulk superconductors with Tc gradually decreasing from 30 to 22K as x increases to 0.50. For fixed x and y>0 samples are superconducting again with a simple cubic structure and with Tc gradually decreasing as y increases.
Oxygen Evolution from Yba2cu3o7‐δ Superconducting Powders Generated by Aerosol Routes
Authors: Biswas Pratim , Zhoul Derong , Grothaus Jeff , Boolchand Punit , McDaniel Darl
Published: March 2011

The oxygen desorption kinetics of the YBa2Cu3O7‐δ powders generated by an aerosol route was investigated and compared to that of solid state reacted powders. The oxygen content of the aerosol sample was determined using a thermogravimetric analyzer (at 990 C) and wet chemical methods, and δ was calculated to be ‐0.1. The activation energy and pre‐exponential factor were determined by regression for two peaks at 540 C and 850 C. Other activation parameters were also calculated. The calculated values of these parameters for aerosol samples and those reported for solid state reacted powders are in good agreement.
Ultrasonic Study of the Low Temperature Structural Phase Transition in Yba2Cu3O7-δ. and its Dependence on Oxygen Concentration
Authors: Toulouse J. , Wang X.Q. , Hong D.J.L.
Published: March 2011

Elastic and structural instability have been reported in YBa2Cu3O7‐δbetween 210K and 270K. We have carried out an ultrasonic study of these instabilities as a function of both oxygen concentration and annealing temperature. The results strongly indicate that an athermal (martensitic‐type) transition starts at a temperature Ts which decreases with decreasing oxygen concentration. A linear relationship between Ts and Tc suggests that the second phase formed is essential for the high Tc.
The Determination of the Oxygen Stoichiometry in High TC Superconducting Thin Films Using Nuclear Scattering of 3 Mev Protons
Authors: Jin H.-S. , Homma H. , Yan D. , Drehman A.J. , Wang G.-C.
Published: March 2011

The nuclear scattering of 3 MeV protons on oxygen is applied to determine the oxygen stoichiometry in high Tc superconducting (HTS) thin films. Their oxide substrates are used as reference standards. This is a nondestructive, absolute method, which is as simple as the traditional Rutherford Backscattering Spectrometry (RBS). However, the relative sensitivity to oxygen has been enhanced. To obtain the stoichiometry, one only needs the data on atomic stopping powers and the chemical composition of the substates.When the measurements on the thin film and on the substate are carried out simultaneously, the inaccuracy in charge integration can be avoided and the accuracy of the oxygen stoichiometry can be further improved.
The Effects of Metal Doping: Yba2(Cu1-XMX)3O7-δ (M=;Fe, Co, Ni, and Zn)
Authors: Yang C .Y. , Moodenbaugh A. R. , Wang Y. L. , Xu Youwen , Heald S. M. , Welch D. O. , Suenaga M. , Fischer D. A. , Kirkland J. P.
Published: March 2011

In this study, we describe X‐ray absorption measurements designed to determine the influence of subsitutents on the location of dopants, the valence of dopants, structural changes, and modifications of electronic densities of states. Several possible mechanisms are offered which may elucidate Tc suppression due to metal dopings.
Continuous Two-Dimensional Melting of Vortex-Solid in High Temperature Superconductors
Authors: Yeh N.-C.
Published: March 2011

A model of continuous two-dimensional melting in the mixed state of high temperature superconductors is proposed. Two-dimensional melting sets in at a cross-over temperature Tx(H) below the three-dimensinal phase transition Tx(H) due to finite size effects, and Tx(H) is a function of the sample thickness (lc), applied magnetic field (H), and k(= λ/ξ) For a given zero-field transition temperature Tc0 and material properties, (such as defect density), the onset temperature of 2D-melting (Tx(H)) decreases with decreasing sample thickness and increasing magnetic field. In transport studies, thermally induced melting is further complicated by the depinning effect of high current densities.
Control of Microstructures in the YBA2CU3O7‐σ system: 1. Reaction with CO2
Authors: Kingon Angus I. , Davis Cheryl D. , Hare Thomas M. , Palmour III Hayne , Koch Carl C. , Haase D.G.
Published: March 2011

Controlled reactions have been undertaken between CO2 and polycrystalline YBa2Cu3O7‐σ in the temperature range 500°‐700°C. Typical reaction products are Y2BaCu05, BaC03 and CuO. Subsequent processing in O2 (e.g. sintering) results in the formation of liquid phases(s) by peritectic reaction at temperatures of 935‐975°C, well below the incongruent melting point of YBa2Cu3O7‐σ (∼1010°C). This “low temperature” liquid phase is shown to have a dramatic influence on the sintering process, and the resulting microstructures. The reactions are difficult to reverse even after extended times at temperatures >900°C. The results give an indication of the effect of adsorbed CO2 into YBa2Cu3O7‐σ powders, albeit on a more localized scale.
Texturing Crystal Growth in Vertical Thermal Gradients
Authors: Tan N. X. , Bourdillon A. J. , Sawides N.
Published: March 2011

Texture growth in incongruently melting ceramic superconductor materials, such as YBa2Cu3O7‐χ can be combined with zone refinement in thermal gradients to increase critical current densities. In gravity aided texture growth (GATEG), a vertical thermal gradient is used with downward motion of the partially molten specimen (relative to the furnace) so that the molten phase recrystallizes with grain growth. The oxidation features of Y‐Ba‐Cu‐0 and Bi‐Sr‐Ca‐Cu‐0 can be explained by Madelung potentials.
Preparation of Bipbsrcacuo Superconductors by Laser Pedestal Growth Method
Authors: Hayashi K. , Nonoyama H. , Ueyama M. , Nagata M. , Hitotsuyanagi H.
Published: March 2011

Bi‐Pb‐Sr‐Ca‐Cu‐0 superconductors were prepared by the laser pedestal growth method. The high Tc phase was created only by post annealing. As the growing speed increased, the annealing time necessary to obtain a Tc above 100K decreased. When the low Tc phase was aligned with the growing direction, Tc was under 100K, but a Jc of 15B0A/cm2(77.3K, OT) was obtained. In this case, magnetic field dependence below 300 gauss was superior to that of Pb‐free materials.
Sandwich Excitons as the Mechanism of High-TC Superconductivity
Authors: Richert Brent A. , Schachinger Ewald , Allen Roland E.
Published: March 2011

One potential objection to virtual “sandwich excitons” as a pairing mechanism is that the transition densities may not be large enough to overcome the inherent disadvantage of a large energy denominator . In model calculations, we find that some of the transition densities and matrix elements can be large even if the dielectric constant is sizeable for, e.g., LaO excitons in La2‐xSrxCuO4
Solid State Formation of Superconducting Phases in the T1-Ca-Ba-Cu-O System
Authors: Huang T.W. , Hung M.P. , Chin T.S. , Ku H.C. , Yang S.C. , Hsu S.E.
Published: March 2011

Differential thermal analysis (DTA) and thermal gravitometry analysis (TG A) under flowing oxygen show that the formation temperatures of the high Tc T12Ca2Ba2Cu3Ox (2223) and the low Tc T12CaBa2Cu2Ox (2212) phases lie at around 910 °C and 840 °C, respectively. The activation energies are as low as 50 kcal/mole for the 2223 phase and 35 kcal/mole for the 2122 phase. Thus the time for the formation of these phases can be within 30 minutes.

Two preparation methods were tried, and the one with Ca3BaCu3O7 as a precursor was easier to attain pure high Tc 2223 phase than that prepared directly from component oxides and carbonates.
Microanalysis of Cuprate Superconductors Using the Color of Polarization
Authors: Hoff H.A. , Lechter W.L. , Osofsky M.S. , Candela G.A.
Published: March 2011

A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in a reflecting light optical microscope. Such colors are generally characteristic of particular phases. We have studied the presence of color in many superconducting cuprates and found a strong correlation between color and the existence of superconductivity. The change in color from insulator to superconductor facilitates the selection of grains for microanalysis. Color variations in a Tl-Sr-Ca-Cu-O material are investigated using quantitative energy dispersive x-ray spect-roscopy. Cation concentrations are found not to correlate with the changes in color. This apparent lack of correlation of color with composition is discussed.
Electronic Structure Calculations of the Copper Oxygen Planes in Yba2Cu3O6+δ, for 0 < δ < 1
Authors: Cogordan J. A.
Published: March 2011

Molecular ab initio seIf-consistent calculations on clusters simulating the
copper-oxygen layers in the Yba2Cu3O6;δ are reported. The electronic structure, of this layer, was computed for different sets of values of the lattice parameters (a,b,c), according to their dependence on the oxygen stiochiometry. For the molecular orbitals , two different electronic occupations are considered, a closed shell and an open shell. For the open shell, an electron has been excited to the first virtual molecular orbital. It is found that this excited state has lower energy than the closed shell configuration for 0 < δ < 1. Molecular energies an electronic population are reported.
Processing and Fabrication of YBa2Cu4O8 and YBa2Cu4O8/YBa2Cu3Ox Composites
Authors: Balachandran U. , Biznek M. E. , Goretta K. C. , Veal B. W. , Poeppel R. B.
Published: March 2011

Powders of YBa2Cu4O8 (“124”) were prepared via solid state reaction of Y2O3, BaCO3, and CuO. The mixed precursors were heated in flowing oxygen of reduced total pressure, followed by cooling and annealing at 750°C under ambient pressure oxygen. The procedure produced orthorhombic 124 as the main phase, with YBa2Cu3Ox (“123”) as a minor impurity phase. Phase purity improved, and nearly phase-pure 124 was obtained, upon annealing the as-calcined powder in flowing oxygen at 800°C.
Flux-Assisted Preparation of Powdered Bismuth Superconductors
Authors: Arendt R. H. , Garbauskas M. F. , Schilling L. L.
Published: March 2011

Results are presented on efforts to prepare both the 80K, Bi2CaSr2Cu2Oz (2122), and 11 OK, (Bi,Pb)2Ca2Sr2Cu3Oz (2223), transition temperature bismuth superconducting species in either phase pure or nearly phase pure, powdered form using either equimolar NaCI-KCI or NaBiOz as molten fluxes. Data are presented on the effects of variation of the reaction temperature and duration, solvent content, relative CaO and CuO contents, and of post-synthesis anneals of the product materials.