bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractEpitaxial 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

ABSTRACTResidual 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

ABSTRACTSintered, 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

ABSTRACTPermanent 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

ABSTRACTThe 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

ABSTRACTIn 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

ABSTRACTMössbauer 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

ABSTRACTHigh 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

ABSTRACTThe 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

ABSTRACTSuperconducting 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

ABSTRACTSintered 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

ABSTRACTDefect 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

ABSTRACTWe 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

ABSTRACTPolycrystalline 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

ABSTRACTTransmission 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.
High TC Superconducting Films from Metallo-Organic Precursors
Authors: Davison W. W. , Shyu S. G. , Buchanan R. C. 
Published: March 2011

ABSTRACTHigh 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

ABSTRACTMost 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

ABSTRACTThin 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.
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

ABSTRACTAn 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

ABSTRACTHigh-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

ABSTRACTWe 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.
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

ABSTRACTSpectra 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

ABSTRACTBulk 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

ABSTRACTRapid 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

ABSTRACTOne 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.
Annealing Effects on Properties of High Tc YBa2Cu3O7−x Ceramics
Authors: Shyu Shin-Guang , Louh R. F. , Buchanan R. C. 
Published: March 2011

ABSTRACTHigh Tc superconducting YBa2Cu3O7−x ceramics were prepared from the appropriate oxide constituents and heat treated under various conditions to determine the effects of annealing on superconducting properties. Sintered samples (900–920°C) were air cooled at 5°/min followed by annealing in oxygen or air at 500°C/12 hr. Resistance measurements, SQUID, SEM, and x-ray analysis were used to characterize the samples, which were of 38% porosity. Results showed all samples to be superconducting with TC(O) 84K. Superconducting properties of the air and oxygen annealed samples were equivalent but showed lower overall resistance and 30% higher superconducting phase (30 to 70 K) compared to the air cooled samples.