bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cuprates: Back to the Fermi Surface
Authors: Newns D. M. , Tsuei C. C. , Pattnaik P. C. , Kane C. L. , Chi C. C. , Krishnamurthy H. R. , Daumling M. 
Published: March 2011

ABSTRACTThe cuprate superconductor problem is approached from the conventional metallic standpoint, valid at dopings near the Tc maximum and beyond. There is strong evidence that the Tc maximum corresponds to EF lying at a van Hove singularity, a special situation leading to Marginal Fermi Liquid behavior, and also to a minimum in the isotope shift, as observed. The superconducting properties are discussed in the light of phononic and electronic pairing models.
YBCO-Based Multilayer Structures on Large-Area Substrates
Authors: Gavaler J. R. , Talvacchio J. 
Published: March 2011

ABSTRACTWe have deposited YBa2Cu3O7 (YBCO) films on LaAlO3 substrates up to two inches in diameter using 90° off-axis magnetron sputtering from a single stoichiometric target. With this same method, epitaxial bilayers and trilayers of insulating SrTiO3, LaAlO3, MgO, metallic PrBa2Cu3O7 (PrBCO), or superconducting La2−xSrxCuO4 (LSCO) were deposited in combinations with YBCO. In the resulting structures with c-axis orientations, the YBCO had Tc's of 90K or higher over the entire surface area. Maximum resistivity values of 6 × 109 Ω-cm in YBCO/insulator/YBCO structures were obtained in vertical transport measurements with SrTiO3. An important cause for degraded electrical properties in the structures incorporating epitaxial insulators was the presence of copper oxide particles on the YBCO surface. Methods used to minimize the number of these particles are discussed.
Recrystallization of Amorphous or Nanocrystalline NdBa2Cu3O7−x and GdBa2Cu3O7−x
Authors: Folkerts T. J. , Yoo S. I. , Xu Youwen , Kramer M. J. , Dennis K. W. , Mccallum R. W. 
Published: March 2011

ABSTRACTUsing a novel melt-spinning technique, we have produced highly disordered NdBa2Cu3O7−x and GdBa2Cu3Oy−x materials. Samples which were melt-spun in an O2 environment consist of nanocrystals with the tetragonal REBa2Cu3O7−x structure: samples which were processed in an N2 environment consist of an amorphous matrix with small amounts of crystalline BaCu2O2, as shown by x-ray diffraction and electron microscopy. High temperature XRD studies indicate that the BaCu2O2 is eliminated during heating to 500°C in O2 and that the REBa2Cu3O7−x Phase recrystallizes directly from the amorphous matrix at temperatures below 800°C. Preliminary magnetization measurements show that higher temperature heat treatments are needed to restore superconductivity.
Anisotropic Electrical Resistivity of YBCO/PBCO Superlattice Films Grown on Miscut Substrates
Authors: Kerchner H. R. , Klabunde C. E. , Christen D. K. , Budai J. D. , Lowndes D. H. , Norton D. , Thomson J. O. 
Published: March 2011

ABSTRACTAnisotropie electrical resistivity is studied in epitaxial superlattice films of YBa2Cu3O7-δ/PrBa2Cu3O7-ε grown in situ by laser ablation on SrTiO3 surfaces aligned slightly away from the [100] direction. Layer thicknesses of each compound range from two to eight atomic cells. Electrical resistivity of these superlattice films always shows a peak at some cryogenic temperature that decreases with increasing PrBa2Cu3O7-ε layer thickness. Clear evidence is seen of vortex pinning or of supercurrent blocking by the step edges or by twin boundaries. The ratio of electrical resistivities for current directions parallel and perpendicular to these boundaries shows a large step-like change just above the superconductive critical temperature. The possibility is discussed that the Kosterlitz-Thouless transition explains this anisotropy change.
Deposition of Superconducting Tl-Ba-Ca-Cu-O Phases on Metal Foils by Metal-Organic Chemical Vapor Deposition
Authors: Schulzi D. L. , Hano B. , Neumayer D. , Hinds B. J. , Markst T. J. , Degroot D. C. , Schindler J. L. , Hogan T. , Kannewurf C. R. 
Published: March 2011

ABSTRACTThe synthesis of superconducting Tl-Ba-Ca-Cu-O thin films on metal foils (Au and Ag) by metal-organic chemical vapor deposition (MOCVD) has been investigated. Ba-Ca-Cu-O-(F) films are first prepared via MOCVD using fluorinated “second generation” metal-organic precursors. After an intermediate anneal with water vapor-saturated oxygen to promote removal of F, Tl is introduced by annealing in the presence of a mixture of oxides (Tl2O3, BaO, CaO, CuO) of a specific composition. Characterization of the thin films by scanning electron microscopy, EDX, x-ray diffraction, and variable temperature magnetization measurements has been carried out. High temperature superconductor (HTS) films of Tl2Ba2Ca1Cu2O8−x on Au foil exhibit a magnetically derived Tc = 80K and a high degree of texturing with the crystallite c-axes oriented perpendicular to the substrate surface as evidenced by enhanced (000 x-ray diffraction reflections. Thin film coverage on Ag foil becomes non-contiguous during the (Tl2O3, BaO, CaO, CuO) mixture anneal.
Critical Current Densities JC(H,T) and Current-Voltage Characteristics in Melt Processed Bi-2212 with and without Preferential Orientation
Authors: Paul W. , Heeb B. , Baumann Th. , Guidolin M. , Gauckler L. J. 
Published: March 2011

ABSTRACTIn contrast to sintered Bi2Sr2Ca1Cu2Oy (Bi-2212), melt processed material exhibits nonzero intergrain supercurrents at T < 77 K. By means of partial melting and long term annealing we achieved nonoriertted material with Jc(77) - 3500 A/cm2 (1μV/cm criterion) and Tc = 96 K. Zone melting leads to well textured bulk material with the c-axis of the crystallites oriented perpendicular to the pulling direction R, and thus to an anisotropie critical current density. The anisotropy factor is between 2 and 5. At low temperatures the melt textured ceramic exhibits higher critical currents than the nonoriented material. This is not true at high temperatures, since the latter has a higher critical temperature.At 77 K and small fields both oriented and nonoriented ceramics exhibit no transition in their current-voltage characteristics, but obey the power law E = Eo(j/jo(H)) α(H) over a large range in E (10”−3-10”−3 V/cm). Measurements on the textured ceramic with magnetic fields parallel and perpendicular to the pulling direction demonstrate that the superconducting properties of these materials are only affected by the field components parallel to the c-axes of the crystallites. For fields parallel to the pulling direction the measured values of α(H), Jo(H) and of the reversible magnetization Mrev can be attributed to the misorientation of the Bi-2212 platelets which is in average about 14°.
Microstructures at the Interface Between a-Axis Oriented YBa2Cu3O7−x and NdGaO3(110) Substrate
Authors: Takahashi Hiromi , Homma Norio , Okayama Satoru , Morishita Tadataka 
Published: March 2011

ABSTRACTThe interface between an a-axis oriented YBa2Cu3O7-x film and a NdGaO3(110) substrate has been investigated by cross-section transmission electron microscopy (TEM). The orientational relationship between the a-axis oriented film and substrate is YBa2Cu3O7-x[001] / NdGaO3[001]. This preferentially c-axis aligned direction of the YBa2Cu3O7-x film would be caused by a very small lattice mismatch (0.1%) between b(=a) lattice constant of YBa2Cu3O7-x and of the pseudo-cubic sub-lattices in NdGaO3 at a substrate temperature of 750°C. Two kinds of imperfections have been observed in the crystal lattice of YBa2Cu3O7-x near the interface; One is the deviation of YBa2Cu3O7-x [301] from NdGaO3 [111]. The other type is pair dislocations with a positive and negative Burgers vectors in the YBa2Cu3O7-x (103) planes. These two kinds of defects at the interface would be act to reduce the tensile stress within a distance of about l.lnm from the substrate interface.
Microstrucrure and Properties of In-Situ R. F. Sputtered YBa2Cu3O7−x Thin Films for Microwave Applications
Authors: Reagor David W. , Piza Margarita E. , Houlton Robert J. , Garzon Fernando H. , Hawley Marilyn , Raistrick Ian D. 
Published: March 2011

ABSTRACTThe residual surface resistance of a number of films of YBa2Cu3O7−x, prepared by off-axis sputtering onto MgO substrates, has been measured using a parallel-plate resonator technique. Deposition conditions were kept constant, apart from the substrate temperature. There is no correlation between surface resistance and other important microscopic parameters, such as Tc and c-axis lattice parameter. There is, however, a trend to higher Rs with increasing volume fraction of in-plane misoriented material, although the correlation is not perfect. Furthermore, we have found that most of the misoriented material is localized at the film substrate interface and, therefore, is probably not responsible for most of the RF losses. The data suggest that at higher deposition temperatures, there is an increasing tendency for 45° misoriented material to appear in the films, and a significant fraction of this material may be present closer to the free film surface. Scanning Tunneling Microscopy (STM) qualitatively supports this conclusion.
Current Controlled HTS Switches Fabricated by a Reactive Patterning Technique
Authors: Ma Q. Y. , Hardy W. N. , Laibowitz R. B. , Yang E. S. 
Published: March 2011

ABSTRACTA current controlled HTS switch (CCSS) has been fabricated using the Si-YBCO reactive patterning technique. The Si films were deposited on MgO substrates by e-beam evaporation and patterned via a lift-off process. The YBCO films were deposited thereafter by pulsed laser deposition to form micron-sized HTS strip lines with different widths and lengths. A typical line has a normal resistance ranging from 10 Ω to 100 KΩ. A CCSS was constructed using such a HTS line as a resistor in parallel with a load resistor. The operation of CCSS is similar to that of a current divider. Applications of CCSS includes HTS logic gates and circuit breakers.
Grain Boundary Structure and Properties of High-Tc Superconductors
Authors: Jagannadham K. , Narayan J. 
Published: March 2011

ABSTRACTWe have modelled the grain boundaries in high-Tc superconducting oxides and determined the critical current density. The tunneling of superconducting pairs across the coalesced regions is used to determine the boundary effects. The length of the coalesced regions, with continuity of the Cu-O planes maintained by relaxation of the atom positions, is determined by minimization of the energy of the configuration. The depression of the order parameter is evaluated using the continuity conditions at the boundary in the proximity effect formulation. The excess charge distribution at the core of the boundary, determined from the solution to the Poisson's equation, is used to determine the scattering of the superconducting pairs. The width of the boundary, evaluated from modelling, determines the transmission coefficient for tunnelingof superconducting pairs. The critical current density is expressed in terms of these four important factors associated with the grain boundary. All the experimental results are explained by the present modelling of the grain boundary effects.
Layered Structure in Melt-Processed BSCCO and YBCO Superconductors
Authors: Jin S. , Chen S. K. , Tiefel T. H. 
Published: March 2011

ABSTRACTBecause of the natural preference for crystal growth in the a-b direction, melt-processed YBCO as well as BSCCO tends to show a local texture with large parallel plates aligned in the direction of CuO2 planes. In YBCO, macroscopically layered and bi-axially textured material can be achieved over extended sample lengths through the use of temperature gradient during melt-texture processing. In BSCCO, a layered structure is relatively easily obtained by subjecting thin ribbon samples in contact with silver to a partial melt processing. While the nature and the mechanism of layer formation may not be the same, the layer configuration in both YBCO and BSCCO is essential for overcoming the grain boundary weak link problem and achieving high transport Jc. In this paper, the process and the mechanism of layer formation will be described, and the implications on superconductor properties will be discussed.
Correlation Between Nonlinear Charge Transfer and Behaviour of Tc in YBa2Cu3O7-y System
Authors: Zhao Y. , Liu H. K. , Dou S. X. 
Published: March 2011

ABSTRACTThe charge transfer in YBa2CU3O7-y system have been analysed by bond valence sum calculation. It is found that there exists an additional effective charge-transfer between the CuO2 planes and the CuO chain which varies nonlinearly with the oxygen stoichiometry and can be expressed as q = 0.151 exp(∼0.007/y4) + 0.35 exp(0.5 – 0.5/y4). This nonlinear charge-transfer is associated with the structural transitions of orthorhombic (I)-to-orthorhombic(II) and orthorhombic(II)-to-tetragonal symmetry, and thus related to the oxygen ordering in the CuO chains. A new relationship between the mobile hole number P(2) the localised hole number P(l) and the total hole number P has been established as P(2) = P - P(1), P(1) = 0.5 - y - q. The results also show that the 90 K and 60 K plateaus in Tc as a function of oxygen stoichiometry correspond to the plateaus in the curve of q versus y, indicating that both the nonlinear variations of Tc and the charge-transfer with the oxygen stoichiometry are intrinsically correlated.
Fabrication and Characterization of Nb/MgO/Bi2Sr2CaCu2Ox Tunnel Junctions Using a Single Crystal
Authors: Usuki T. , Yamano K. , Shimaoka K. , Takahashi K. , Yoshisato Y. , Nakano S. 
Published: March 2011

ABSTRACTNb/MgO/Bi2Sr2CaCu2Ox (BSCCO) tunnel junctions using both amorphous and crystalline MgO barriers were fabricated using a BSCCO single crystal in order to compare their superconducting states of interface. Both MgO thin films, 4–8 nm thick and with full coverage, were deposited onto BSCCO single crystals using the MBE method. The junctions using amorphous and crystalline MgO films were found to have gap opening structures at a bias voltage of about 38 mV and 25 mV at 5.2 K, respectively. The gap opening of the junction using an amorphous MgO barrier occurred below 86 K, corresponding very closely with the Tc for the BSCCO single crystal. Its characteristics showed a BCS-like temperature dependence.
Rheed Intensity Monitored Growth of Bi-Sr-Ca-Cu-O Superconductors
Authors: Sakai Shigeki , Kasai Yuji , Bodin Peter , Matsuhata Hirofumi 
Published: March 2011

ABSTRACTTo make Bi2Sr2CaCu2O8 superconducting films with top insulating SrTiO3, we use the molecular beam epitaxy technique (MBE) with in situ monitoring by reflection high-energy electron diffraction (RHEED). A new (RHEED)image enhancing technique, difference reflection high-energy electron diffraction (DRHEED) gave striking information on the growth process of each layer in the Bi:2212 compound as well as the rough and flat transition occurring during co-evaporated deposition of SrTi03.
Annealing Effects on Tc in the Tl-Ca-Ba-Cu-O System
Authors: Tsai M.-J. , Wu S. F. , Lu S. W. , Huang Y. T. 
Published: March 2011

ABSTRACTTl-2223 phase with a composition of Tl1.7Ca2.3Ba2Cu3O10 was prepared via a solid-state reaction route and systematically annealed under various conditions, including flowing oxygen, sealed quartz in vacuo, high oxygen pressures and hot isostatic press in an attempt to enhance the superconducting properties in the Tl-Ca-Ba-Cu-0 system. An almost monophasic sample was obtained by sintering at 910 °C for 3 hours in flowing oxygen. Most anneals enhance the Tc by 2 – 7 K, depending on the environment. When the sample is post-annealed at 820 °C for 16 hours in flowing oxygen it results in an optimal Tc of 127 K, as confirmed by magnetic susceptibility and electrical resistance measurements.
Observation of Macroscopic Quantum Effects in YBCO Thin Film Microbridge Rings
Authors: Huang Y. , Jiang H. , Widom A. , Vittoria C. 
Published: March 2011

ABSTRACTThin film rings with microbridge were constructed using high Tc Y-Ba-Cu-O super-conducting thin films which were made by laser ablation on the single crystal MgO(100) substrates. The thickness of the films is 5000 Å. The weak links were biased with an AC induced current. The resulting electron pair charges on the weak links were monitored by an output voltage. The charge stored on the link (as a function of the input bias voltage) is consistent with that of a “macroscopic quantum pendulum”
Microwave Absorption in YBCO/PrBCO Superlattices
Authors: Carlos W. E. , Kaplan R. , Lowndes D. H. , Norton D. P. 
Published: March 2011

ABSTRACTNon-resonant microwave absorption is employed to probe YBCO/PrBCO superlattices and compare the response to that of a YBCO film. Near the transition temperatures, the response of the superlattice samples and the YBCO film have similar amplitudes and orientation dependencies. At lower temperatures, the response of the superlattices is much stronger than that of the YBCO film and, while both responses are hysteretic at low temperatures, the widths of the hysteresis have opposite orientation dependencies, which we attribute to the role of the PrBCO layers.
YBa2Cu3O7−x Grain Boundary Weak Links on MgO Bicrystal
Authors: Lu H. B. , Tu S. L. , Wang J. J. , Lin J. , Huang T. W. , Yang S. J. , Hsu S. E. 
Published: March 2011

ABSTRACTThe characteristics of YBa2Cu3O7−x (YBCO) thin films by laser ablation on MgO bicrystals have been investigated. The bicrystals were fabricated by hot pressing two single crystals with the configuration of [001] tilt boundaries. The YBCO films were epitaxial grown with C-axis normal to the both adjacent grains of bicrystals. The FWHM about (005) reflection was 0.4–0.5 degree, indicating the high degree of the oriention for the film with small mosaic spread. Our preliminary study showed that the typical value of Jc on either side of the bicrystal boundary was 0.4–10×106 A/cm2 at 15K, while that across the 10° tilt boundaries was 0.3–9×105 A/cm2 at 15K. These results implied that the artificial grain boundaries effectively weakened the supercurrent, and therefore, the weak-link properties of artificial boundaries were more easily controllable than those of naturally occuring grain boundaries.
Effect of the Weak Links on the Surface Resistance of YBa2Cu3Ox Bulk Material
Authors: Wosik J. , Xie L. M. , Halbritter J. , Chau R. , Samaan A. , Wolfe J. C. , Selvamanickam V. , Saláma K. 
Published: March 2011

ABSTRACTDc magnetic field, temperature, and magnetic history dependencies of the millimeter-wave surface resistance have been measured in high quality grain-aligned and in polycrystalline YBa2Cu3Ox bulk material. The measurements were carried at 75 GHz using the endplate of the cavity replacement method. The data is interpreted in terms of the presence of intra- and inter-grain types of weak links. The values of characteristic critical fields of the bulk and the weak link junctions are determined and discussed.
Optical Energy Transfer and Photochromism in Doped Sol-Gel Glasses
Authors: L'Espérance Drew , Pelo John M. , Chronister Eric L. 
Published: March 2011

ABSTRACTOrganically doped sol-gel glasses are investigated by optical absorption and time-resolved fluorescence depolarization measurements. Silicate and aluminosilicate glasses have been doped with quinizarin (Q) and aluminum phthalocyanine chloride (CAP). The structure and bonding in these inorganic sol-gel solids is different from that in frozen liquids and organic polymers, and the unique dynamics of these systems are a motivation for this study. Both rotational dynamics and optical energy transfer of doped chromophores in sol-gel glasses are investigated by time-resolved fluorescence depolarization measurements. Since the dipole-dipole energy transfer rate is very sensitive to transfer distance, these measurements are used to probe the spatial distribution of dopant molecules within these solids. We also present photochromic results on aluminum phthalocyanine chloride doped silicate sol-gel glasses and discuss possible uses as an optical power limiting material.
Stressed In Situ X-Ray Diffraction Studies of a Ni-Ti Shape Memory Alloy
Authors: Hwang J. Y. , Yang C. F. 
Published: March 2011

ABSTRACTThe B2 ⌊ R ⌊ B19′ phase transformations in a Ni-50.7 at.% Ti alloy were investigated under a series of uniaxial tensile stresses. A custom-build X-ray sample holder with hot, cold and stressing stages was used for structure analysis at temperatures up to 140 °C under a variety of tensile stresses (up to 250 MPa). Reorientation and growth of favorably oriented variant domains of R phase and martensite under stress were observed. In the stress-assisted phase transformations, the favorable (020)M and (300)R planes are expected to align preferably parallel to (011)B2 planes, and the unfavorable (111)M and (112)R planes perpendicular to the (011)B2 planes. In addition, the results of semi-quantitative analyses of the relative amounts of parent phase and martensite formed under a specific stress and temperature condition, x=x(σ,T), are presented.
Electronic Determination of the Modulus of Elasticity and Intrinsic Stress of Thin Films using Capacitive Bridges
Authors: Wang Sha , Crary Selden , Najafi Khalil 
Published: March 2011

ABSTRACTWe extend the method of Najafi and Suzuki [1] for the electronic determination of the modulus of elasticity and intrinsic stress of thin films using capacitive bridge structures. New theoretical concepts are introduced. The extended method does not require that the test structures be exercised to the point of snap-action.
Materials Development of Thin Film TiNi Ferroelastic-Ferroelectric Heterostructures
Authors: Jardine A. Peter 
Published: March 2011

ABSTRACTActive and adaptive thin film materials for “smart” materials will likely be a heterostructure of several types of thin films. In this investigation, deposition and processing of thin film Shape Memory Effect TiNi and thin film ferroelectric BaTiO3 and SrTiO3 are discussed. Growth conditions as well as the thermodynamic conditions for thin films are described. It was found that amorphous thin films of TiNi and BaTiO3 can be crystallized simultaneously by air annealing at 600°C.
Analysis of Microfabricated Textured Multicrystalline Beams: I. Homogenization Approach
Authors: Mirfendereski Dariush , Ferrari Mauro , Der Kiureghian Armen 
Published: March 2011

ABSTRACTThis paper discusses a deterministic approach to the stress and deformation analysis of miniaturized structures. Analytical Voigt-Reuss-Hill averages for the elements of the fourth-ranked elasticity tensor representing a polycrystal are evaluated for a planar problem and the variations of elastic moduli with respect to the degree of anisotropy and the mean and coefficient of variation of the preferred orientation direction are studied. The applicability of the averaging methods to the characterization of materials used in micro-electro-mechanical systems are then assessed.
Analysis of Microfabricated Textured Multicrystalline Beams: II. Probabilistic Approach
Authors: Mirfendereski Dariush , Der Kiureghian Armen , Ferrari Mauro 
Published: March 2011

ABSTRACTThis paper reports on detailed approaches to the probabilistic modelling and analysis of multicrystalline microfabricated beams in the context of micro-electromechanical systems (mems) using simulation techniques. Random, textured multicrystalline beam structures are simulated and analyzed using the finite element method, employing randomly oriented orthotropic material properties to model each individual crystal grain.The simulation studies are used to assess the influence of size effects and texture on overall beam characteristics, such as stiffness. Results of these studies are then compared with the current approaches based on deterministic analysis and employing simplifying assumptions such as homogeneous, isotropic material properties, and with results obtained from the homogenization approach of Part I.