bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Temperature Mocvd of Silicon-Based Ceramic Films
Authors: Du Honghua , Bae Yongwoong , Gallois Bernard , Gonsalves Kenneth E.
Published: March 2011

A liquid methylsilazane compound, [CH3SiHNH]n, was used, with H2, NH3, and a 60%/40% mixture of NH3/H2, to deposit silicon-based ceramic films in a CVD reactor at 873–1073 K. Characterization of the films by ellipsometry, Fourier transform infrared spectrometry (FTIR) and Auger electron spectrometry (AES) showed that the methylsilazane was pyrolyzed to form silicon carbonitride in H2, and silicon nitride in both NH3and NH3/H2, with the incorporation of appreciable amounts of oxygen. The deposition rate increases and the activation energy decreases in order from NH3-, NH3/H2-, and H2-[CH3SiHNH]ngas mixtures. The temperature dependence of the structural density of the films increases in the same order.
Preparation, Structure and Properties of VOx and TiO2 Thin Films By Mocvd
Authors: Chang H. L. M. , Parker J. C. , You H. , xu J. J. , Lam D. J.
Published: March 2011

Titanium and vanadium oxide thin films have been prepared in a cold wall low pressure MOCVD system for the study of MOCVD processing of epitaxial oxide films. Films were deposited on Si(111) and sapphire (0001) and (1120) at temperatures from 400 to 800°C. Processing parameter-structureproperty relationship was examined in detail and the result is presented.
Low-temperature Chemical Vapor Deposition of Rhodium and Iridium thin Films
Authors: Smith David C. , Pattillo Steve G. , Elliott Norman E. , Zocco Thomas G. , Burns Carol J. , Laia Joseph R. , Sattelberger Alfred P.
Published: March 2011

Low-temperature chemical vapor deposition of M(allyl)3 (M = Rh, Ir; allyl = η3 -C3H5) in the presence of H• yields thin, crystalline metal films of greater than 97% metal composition. Depositions using H2 result in the formation of materials which are amorphous and contain a significant amount of residual carbon (14%). The composition of these materials does not differ significantly from that obtained from the vacuum thermal deposition of M(allyl)3.
Highly Resolved Gradient Patterns in Glass by means of Chemical Vapor Deposition
Authors: Wolkow E. , Gafney H. D. , Mendoza E. , Wong P. , Hanson A. L.
Published: March 2011

The impregnation of metallic oxides in ceramic bodies to convey information is as old as civilization itself. But unlike the potters of the past, whose purpose was mainly decorative, ours is to control the direction and the speed of traveling light. This may have practical uses with respect Optical waveguides, for integrated optic devices, and micro images for information storage. The ceramics we use are Porous Vycor Glass (PVG) and aerogels made from solgels, both composed mainly of SiO2.
Analytical Simulation of an Improved Cvi Process for Forming Highly Densified Ceramic Composites
Authors: Tai Nyan-Hwa , Chou Tsu-Wei
Published: March 2011

A model for chemical vapor infiltration (CVI) under pressure and temperature gradients is applied to the study of deposition of SiC from the pyrolysis of CH3SiCl3 within a 3-D woven fibrous preform. The model considers the infiltration of reactants into a preform with temperature gradients by applying a pressure gradient between the vapor inlet and outlet; it also takes into account the variation in concentration of the vapor precursor. A quasi-steady state approach has been adopted to simulate the matrix deposition in a 3-D unit cell. The density distribution, consolidation profile, and total fabrication period have been theoretically predicted.
Modelling Transport, Reaction, and Pore Structure Evolution During Densification of Cellular or Fibrous Structures
Authors: Sotirchos Stratis V. , Tomadakis Manolis M.
Published: March 2011

A mathematical model is developed to describe mass transport, reaction., and structure evolution during densification of porous media of initially fibrous or cellular structure. The use of Monte Carlo simulation procedures for determining the variation of the local (average) structural properties of the porous structure and of the effective diffusion coefficients in the porous medium with the porosity is also discussed, and results are presented for Knudsen diffusion in cellular or fibrous media. The model is used to theoretically study the transient behavior of the densification process during preparation of SiC/SiC ceramic matrix composites by chemical vapor infiltration (CVI) of porous preforms. Particular emphasis is placed on the investigation of the effects of pressure pulsing on the density gradients in the densifying structure.
Borazine Adsorption and Reaction on a Re(0001) Surface
Authors: He J.-W. , Goodman D. W.
Published: March 2011

The interaction of borazine (N3B3H6) with a Re(0001) surface has been studied by low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). It is shown that chemisorbed borazine dissociates into atomic N, B and H on Re(0001) at sample temperatures > 450K. However, borazine is found to decompose to a boron-nitrogen compound when irradiated with a 2 KeY e–beam.
Sn and Fe Mossbauer Spectra of Y Ba Cu (O, N)
Authors: DeMarco M. , Wang X. W. , Trbovich G. , Naughton M.J. , Chaparala M.
Published: March 2011

We report new results on 119 Sn and 57 Fe Mossbauer spectra of Y1 Ba2 Cu3-z (O, N)7-x, where M is either Sn or Fe, O denotes oxygen and N denotes ni trogen, 0 ≤ X ≤ 0.5, and z = 0.05, 0.1, 0.15, 0.2. The oxygen annealed samples were superconductors, but nitrogen annealed samples were not. The Mossbauer measurements indicate four quadrupole pairs in Y Ba2 (Cu, Fe)3 O7-x, but only three pairs in Y1 Ba2 (Cu, Fe)3 N6.5. In the Sn Mossbauer spectra, the quadrupole splittings of nitrogen annealed samples are larger than that of oxygen annealed samples. In both Fe and Sn spectra, the isomer shifts of oxygen annealed samples are different from that of nitrogen annealed samples. Our study provides some information about the Cu(1) and Cu(2) sites and their surrounding environment in the Y Ba Cu system.
Characterization of High-Temperature Superconducting Materials in Y-Ba-Cu-0 Systems
Authors: Kezuka Hiroshi , Masaki Tomomi
Published: March 2011

The Y-Ba-Cu-0 systems have been reported to be a high temprature superconductor with above 90K. Optical Study would give us useful informations as a characterization for Y-Ba-Cu-0 systems with an analysis of energy dispersive X-ray system EDS. Optical constants of superconducting Y-Ba-Cu-0 systems are n*=1.6 92-j0.403 for 99.99%(4N) with Y1.00 Bal.90 Cu2.87 and n*=1.604-j 0.441 for 99.99%+ (4N+) with Y1.00 Ba2.18 Cu3.12.
Transport and Diamagnetic Properties of 2:2:1:2 and 2:2:2:3 (Bi-Pb)-Sr-Ca-Cu-O Superconducting Materials
Authors: Ibanez R. , Sanchis M. J. , Sapina F. , Beltran D. , Beltran A. , De La Fuente G.F. , Rillo C. , Bartolome J. , Lera F. , Navarro R.
Published: March 2011

Bismuth superconducting oriented fibers of the compositions 2:2:1:2: and 2:2:2:3 have been grown by the Laser Floating Zone (LFZ) method. Growth conditions have been optimized in order to improve the superconducting properties. The 108 K onset in susceptibility measurements (associated to the 2:2:2:3 phase) only appears well defined when starting from Sr-defective precursors.
Field and Temperature Dependent Suspension Studies of High Temperature Superconductors
Authors: Huang Y. , Solin S.A.
Published: March 2011

We have employed a novel variable-temperature, variable-field/field-gradient cryogenic levitometer, previously used in levitation experiments, to study the suspension properties of the thallium-based high temperature superconductors. Our results are compared and contrasted with the levitation studies and the singular features of the suspension properties are noted.
Expansion of Pb2Sr2Y1-xCaxCu3O8+δ and Ba2YCu3O6+δ
Authors: O'Bryan H. M. , Gallagher P. K.
Published: March 2011

The expansions of Pb2Sr2Y1-xCaxO8+δ for x=0, 0.2 and 0.4 and Ba2YCu3O6+δ have been determined during heating to 700°C. Thermal and compositional components of the expansion have been identified by using different atmospheres. In N2 only thermal expansion with a CTE~13 ppm/*C is noted, while in O2 compositional effects are domina nt. At 550* the incorporation of 1.2 atoms of oxygen by Pb2Sr2YCu3O8 produces an expansion -0.4%. This behavior contrasts to the -0.2% shrinkage which occurs for Ba2YCu3O6.2 when -0.6 atom of oxygen is added. The different expansion behaviors of the two compounds are explained in terms of their structures and the position of the removable oxygen.
Anomaly in Thermal Expansion of YB2Cu307-y Around 250K
Authors: Ramadass G.A. , Ramcahdnran V. , Srinivasan R.
Published: March 2011

The linear thermal expansion coefficient of YBa2Cu307 as a function of temperature has been studied. An anomaly is observed at 250K. This temperature is found to be dependent on oxygen deficiency.
High Speed Infrared Detectors Using Y-Ba-Cu-O Thin Films
Authors: Zheng J.P. , Ying Q.Y. , Kwok H.S.
Published: March 2011

Y-Ba-Cu-O thin films were used for CO2 laser detection. Operation of the Y-Ba-Cu-O detector in both the bolometric and nonbolometric modes were studied. It was found that the detectivity of the superconducting detector was competitive with conventional detectors. The speed was within the instrument resolution of 10 ns. The superconducting film quality is critical to the performance of these detectors.
In-Situ Preparation and Characterization of Superconducting Thin Films and Related Materials by Mocvd for the Development of Three Terminal Switching Devices
Authors: Singh R. , Sinha S. , Narayan J.
Published: March 2011

Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a major technique for the fabrication of high temperature superconductor devices. In this paper, we present preliminary results of in-situ deposition of Y-Ba-Cu-0 thin films (Tc = 79K) by rapid isothermal processing assisted MOCVD on BaF2/silicon substrates.
Measurements of the Surface Resistance of Hts Thin Films From 0.5 to 40Ghz
Authors: Steinueck J. , Oates D.E. , Anderson A.C.
Published: March 2011

We have measured the surface resistance R, in polycrystalline films of YBCO and BSCCO deposited in our laboratory as well as oriented films made by other laboratories by codepostion techniques. The R, of YBCO and BSCCO has been measured in the frequency range between 0.5 and 40 GHz using a stripline resonator technique. R, for the films is nearly proportional to the square of the applied frequency over the entire measurement range. The magnitude of R, is, however, strongly dependent on the film microstructure. Our measurements at 1 GHz and 4 K show that randomly oriented films have R, ~ 10~3 Ω (close to Cu) while oriented large-grain films have markedly lower R, ~ 2 x 10-6 Ω, approaching the R, of superconducting Nb. The magnitude of R, rises to ~ 2 Ω and ~ 10-3 Ω at 40 GHz for the randomly oriented and preferentially oriented films, respectively. An effective penetration depth, λeff, has been determined from R, using local electrodynamics. We find that λeff is dependent on film microstructure and is ~ 5 µm for high-R, films, decreasing to ~ 5000 Å for low-R, films. The smaller values of Ωeff calculated for oriented films are of similar magnitude to values of the YBCO penetration depth (~ 2000 Å) reported in the literature. The use of the stripline resonator technique for temperature and magnetic field dependent i Measurements of R, will also be discussed.
Laser Interferometric Temperature Measurement of Heated Substrates Used for High Tc Superconductor Deposition
Authors: Saenger K. L. , Roy R. A. , Gupta J. , Doyle J. P. , Cuomo J.J.
Published: March 2011

Substrate temperature during film growth is an important processing parameter for vapor deposited films of the high Tc superconductors. In this paper we describe a novel, non-contact optical thermometry technique in which the temperature of a transparent substrate or “temperature sensor” is determined from its thermal expansion and refractive index change measured by laser interferometry. The technique is easy to implement and extremely accurate. Temperatures measured with this technique are reported for MgO substrates in varying degrees of thermal contact with a heated backing plate and compared to those measured conventionally by optical pyrometry or thermocouples in close proximity to the sample. The effect of the deposited film on the temperature of radiatively heated substrates will also be discussed.
Reactions at Ceramic Superconductor/Metal Interfaces
Authors: Oh Min-Seok , Notis Michael R.
Published: March 2011

Joining technology for ceramic superconductors is currently a major problem. The possible reactions which occur at ceramic superconductors/metal interfaces are discussed and examples are shown of interfaces between YBa2Cu3Ox and Nd1.85Ce0.15CuO4-x vs. a series of metals (Ag, Ni, Fe) now being considered for joining and cladding applications. Various characterization techniques, including EPMA and x-ray mapping, are utilized for analyzing the spatial distribution of reaction products. In a composite configuration, Ag interlayer is found to promote interfacial reactions.
Preparation of High Tc Oxide Superconducting Tape by Rf Magnetron Sputtering
Authors: Fukutomi M. , Tanaka Y. , Asano T. , Maeda H. , Takahara H.
Published: March 2011

The feasibility of preparing YBaCuO films on metallic substrates is discussed in an attempt to fabricate a superconducting tape. Deposition method employed was an rf magnetron sputtering. An amorphous MgO thin layer was found to be a promising buffer layer. The highest zero resistance temperature was 84.0 K in its as grown state, and a critical current density was 4.8x10 A/cm2 at zero field and 77.4 K. Preliminary experiments using laser ablation technique were also carried out to obtain YBaCuO films at a rather high deposition rate.
High Density Bulk Shape Rapid Consolidation of the Yba2Cu307-X Superconductor
Authors: Rele S. V. , Raman R. V. , Meeks H. S. , Anderson R. L. , Shelton R. N. , Lan M. D.
Published: March 2011

A novel rapid densification technique for fabrication of bulk shape YBa2Cu307–xsuperconductor is presented. The Ceracon process is a one‐step, quasi‐isostatic consolidation route utilizing conventional P/M equipment and set‐up. The Ceracon technology has enabled successful fabrication of bulk, shapes such as discs, cylinders, hollow cylinders and spheres along with significant increases in the density up to 95‐98% of the theorertical. The superconducting volume fraction is preserved due to short hold times at the operating temperatures and avoidance of high processing temperatures. Results based on densities, microstructure, susceptibility measurements, X‐ray diffraction patterns and TGA measurements are discussed.
High-Temperature Deformation of Yba2Cu307-8 With Ag Additions
Authors: Routbort J.L. , Goretta K.C. , Singh J.P.
Published: March 2011

The steady‐state flow stress of YBa2Cu3O7‐δ containing 15 to 30 vol.% Ag has been measured in air at nearly constant compressive strain rates between 5 x 10‐6 and 1 x 10‐4 s‐1 from 830 to 900°C. Addition of Ag dramatically decreases the flow stress compared to that of the pure superconductor, but the stress exponents and the activation energy for deformation remain unchanged.
Crystallite Orientation in Ybco Ceramic Layers Sintered on Silver Substrates
Authors: Schüler Claus Chr. , Greuter Felix , Kluge-Weiss Petra
Published: March 2011

Strongly c‐axis textured layers of YiBa2Cu307_xwere prepared by sintering a precursor powder on Ag‐foils. Critical current densities of layers with a few (Am thickness are presently jc∼ 5000‐8000 A/cm2(77 K, H = 0) over a few centimeters length.
The Fabrication and Magnetic Shielding Properties of Melt Cast Bi‐Sr‐Ca‐Cu‐O
Authors: Rayne R.J. , Toth L.E. , Bender B.A. , Lawrence S.H. , Soulen R.J. , Miller M.M. , Candella G.
Published: March 2011

Magnetic shields for SQUID applications were successfully fabricated using high Tc superconducting BSCCO. To produce shields with appropriate superconducting properties and close dimensional control, it was necessary to develop new processing techniques. Shields were produced by casting liquid BSCCO into molds, heat treating and machining. This technique is applicable to fabricating other types of superconducting devices requiring bulk superconductors with complex shapes and close dimensional control.
Magnet Replica by High Tc Superconductors
Authors: Weinstein R. , Chen In-Gann , Liu J. , Parks D.
Published: March 2011

A study of magnetic field trapping phenomenon in oriented grain YBa2Cu3O7‐x samples produced by liquid phase processing has been conducted. The magnetic field reproduced from the parent magnetic field allows the production of “magnet replicas”, which can be used in various instruments when large magnetic field is needed constant in time. This paper reports the magnetic field trapping capability and uniformity observed in these oriented grain samples. The feasibility of building large and uniform magnetic field by assembling small SC specimens has also been explored.
High Resolution Neutron Powder Diffraction Study of the Tubular Phase Bi4Sr8Cu5O19+x
Authors: Caldés M.T. , Navarro J.M. , Fuertes A. , Obradors X. , Miravitlles C. , Rodriguez - Carvajal J. , Vallet M. , Gonzâlez-Calbet J.
Published: March 2011

A high resolution neutron powder diffraction experiment has been performed on Bi4Sr8Cu5O19+x. The structure is well described in the space group Fmmm with the oxygen atoms in the bismuth planes appearing disordered in intermediate positions between NaCl and bridging sites as occurs in the superconductors Bi2Sr2Can‐1CunO4n+2. Temperature dependence study of powder neutron diffraction patterns between 1.5K and 998K does not show any relevant structural change neither evidence of antiferromagnetic ordering in this sample.
Renormalization from Density Functional Theory to Strong Coupling Models for the Electronic Structure of La2CuO4
Authors: Hybertsen Mark S. , Schluter Michael , Stechel E.B. , Jennison D.R.
Published: March 2011

Strong coupling models for the electronic structure of La2CuO4 are derived in two successive stages of renormalization. First, a three-band Hubbard model is derived using a constrained density functional approach. Second, exact diagonalization studies of finite clusters within the three band Hubbard model are used to select and map the low energy spectra onto effective one-band Hamiltonians. At each stage, some observables are calculated and found to be in quantitative agreement with experiment. The final results suggest the following models to be adequate descriptions of the low energy scale dynamics: (1) a spin 1/2 Heisenberg model for the insulating case with nearest neighbor J≈130 meV; (2) a "t–t'–J" model with nearly identical parameters for the electron and hole doped cases.
Oxidation and Reduction of Bi2Sr1.85Cuo6-Y Crystals
Authors: Sonder Edward , Chakoumakos B. C. , Sales B. C.
Published: March 2011

The effects of oxidizing and reducing atmospheres on the oxygen contents and electrical properties of Bi2Sr1.85CuO6‐y single crystals were investigated. As‐grown crystals were normally semiconducting but became metallic and superconducting after heating the crystals for several hours in oxygen at temperatures between 500 and 800°C Previously superconducting crystals were made semiconducting by heat treatments in helium at temperatures between 700 and 780°C. Changes in the oxygen content of the crystals as well as the oxidation and reduction kinetics during the various heat treatments were monitored using standard thermogravimetric techniques. A good correlation was found between the annealing temperatures in oxygen (helium) at which there was an uptake (loss) of oxygen by the crystals, 500°C (700°C), and the onset (loss) of metallic behavior and superconductivity. From isothermal measurents of the weight change as a function of time, it was found that the apparent activation energies for oxidation and reduction were about 0.5 eV and 2.7 eV, respectively. A partial decomposition of the crystals during the various heat treatments, however, precluded a quantitative analysis of the kinetic data.
A Systematic Study of the Effects of Metal Substitutions for Cu in Yba2(Cu1-XMX)3O7-δ, M=Fe, Co, Al, Ga, Cr, Ni, and Zn
Authors: Xu Youwen , Moodenbaugh A. R. , Wang Y. L. , Suenaga M. , Sabatini R. L.
Published: March 2011

A series of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (1:2:3) samples with a typical grain size > 10μm was prepared using well controlled and reproducible precedures. This relatively large grain size allowed microprobe studies of individual grains to determine M content of the 1:2:3 phase. Solubility limits of substitutions for Cu in these samples are estimated. Superconducting transition temperatures and lattice parameters are presented. In the case of Ga, microprobe studies show no evidence for Ga content of 1:2:3 above x=0.01. Preliminary studies show no evidence for solid solution above x=0.01 when substituting Mn, Cr, Zr, and Ti for Cu in 1:2:3.
Conversion of 124 into 123 + CuO: microstructure and phase diagram
Authors: Morris Donald E. , Nickel Janice H. , Markelz Andrea G. , Gronsky Ronald , Fendorf Mark , Burmester Christopher P.
Published: March 2011

Conversion of 124 into 123 + CuO is interesting because it can produce non‐superconducting CuO islands and highly strained local regions, both of which may act as flux pinning centers. Microstructural studies (TEM) show localized regions with high strain fields resulting from the lattice mismatch between 124 and 123 along the c axis. Enhanced Tc (95 K) was found in partly converted samples. The partial pressure of oxygen necessary for conversion from YBa2Cu4O8 (124) to YBa2Cu307 (123) decreases with decreasing temperatures, and below 850°C the boundary between 123 and 124 phase regions is found to fall approximately as log ρ(θ2) = 19.3 ‐22000/T. The phase diagram of the Y‐Ba‐Cu‐O system is given as a function of temperature and partial pressure of oxygen over the range between 500°C and 1000°C and 10‐6< P[O2] < 102 bar.
Two Fluid superconductors
Authors: Bar-Yam Y.
Published: March 2011

An approach to the theory of high‐Tc superconductivity is discused in which the semiconductor‐like layers between the copper‐oxide planes are more active participants in the superconductivity. Two types of states appear in the theory, a lattice of negative‐U sites and single particle (positive‐U) dispersive states. The negative‐U sites originate in oxygen vacancies and the single particle states in the copper‐oxide planes. The coupling between these two types of states lead to a two‐fluid superconductivity where the negative‐U sites give rise to a charged Bosonic fluid and the single particle states are a Cooper‐paired superconductor. The coupled Fermion‐Boson model for superconductivity is related both to theories of superconductivity in semiconductor‐metal eutectic alloys, and recent suggestions of s‐channel superconductivity of R. Freidberg and T. D. Lee. Basic aspects of general phenomenology are described. The breakdown of Fermi liquid theory in the normal state results from mixing of Fermions and Bosons at the Fermi energy. When the two‐particle states are filled, anti‐ferromagnetism arises from the positive‐U of the single particle states with a contribution from virtual excitation of two‐particle states. Prediction is made of a large class of superconducting materials based on metal‐semiconductor layering.
Preparation of High Tc Bi‐Pb‐Sr‐Ca‐Cu‐O Superconducting Fibers by Laser Heated Pedestal Growth Method
Authors: Tomomatsu K. , Kume A. , Tominaga H.
Published: March 2011

Highly oriented Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting fibers have been prepared by the laser heated pedestal growth method. The annealed fiber showed both the high Tc (≃K) phase's and the low Tc (≃80K) phase's superconducting transition. The fiber grown at 2mm/h had the Jc value as high as l.0x103A/cm2. The misalignment of the high Tc phase's a‐b plane was measured by XRD less than ± 2°. It was found that the high Tc phase formed during the annealing was highly oriented as well as the low Tc phase.
Preparation of Fibrous Bi(Pb)-Sr-Ca-Cu-O Crystals Containing the High-Tc Phase
Authors: Matsubara I. , Tanigawa H. , Ogura T. , Yamashita H. , Kinoshita M. , Kawai T.
Published: March 2011

Fibrous crystals containing the high-Tc phase (2223 phase) of the Bi(Pb)-Sr-Ca-Cu-O superconductor have been prepared by heating a glassy melt-quenched plate in a stream of oxygen gas. Each fiber is composed of several platelike single crystals which are stacked in a layered structure. The fibers show two stepdrops in resistance at 105K and 73K, and a zero-resistance state around 70K. From the results of SQUID measurements, the volume fraction of the high-T phase is found to be about 0.6%. The high-Tc phase is also detected with a microarea X-ray diffractometer, and it is stacked in the interlayer between the low-Tc platelike crystals. For the fibrous Bi-Sr-Ca-Cu-Li-O crystals, the volume fraction of the high-Tc phase increases to 1.5% and a zero resistance state is achieved at 81K. The Jc value of the Li doped fiber is 30,000A/cm2 at 77K and 300,000A/cm2 at 66K in a zero magnetic field.
The Effects of Seeding on the Formation of High-Tc Bi-Pb-Sr-Ca-Cu-O Compounds
Authors: Kim Cheol J. , DeGuire Mark R. , Bansal Narottam P.
Published: March 2011

The effect of adding of Bi1.80Pb1.33Sr1.87Ca2Cu3O2 seeds(the 37Å phase) to the polycrystalline and glassy Bi-(Pb)-Sr-Ca-Cu-O materials was studied using XRD and SEM. The seeding effect was observed at 835 °C, 855 °C, and 870 °C in several compositions. Adding pre-synthesized 37Å phase powder to a mixture of unreacted starting materials accelerates the formation of additional 37Å phase.
Comparison of Barium Carbonate and Nitrate Used in the Preparation of YBa2Cu3O7-x Superconductors
Authors: Wahlbeck Phillip G. , Myers Dwight L. , Ronald Richards R.
Published: March 2011

Samples of YBa2Cu3O7-x were prepared by the solid state reaction method using Y2O3, CuO, and either BaCO3 or Ba(NO3)2. The samples were studied using DTA-TGA, Knudsen cell mass spectrometry, and SEM-EDAX. The results indicated that C was more abundant in samples prepared from the carbonate than from the nitrate. In both samples, C was more abundant than N which was at low levels in both samples. Knudsen cell mass spectrometry has proven to be an experimental technique which is sensitive to volatile impurities at low levels.
Electronic Structures of Ga- and Zn- Substituted Yba2Cu3O7 Superconductors
Authors: Xu Yong-Nian , Ching W.Y. , Wong K.W.
Published: March 2011

The band structures of YBa2Cu307 superconductors in which one of the Cu atoms was replaced by Ga or Zn have been studied by the first‐principles orthogonalized LCAO method. Substitutions involving Cu on the chain site and Cu on the plane site were investigated. Results show significant modifications in the electronic structure due to the dopant‐specific and site‐specific substitutions. These results are discussed in light of some recent experimental observations.
Superconducting High TC Thin Films Prepared by Laser Deposition: Comparison of Laser Sources
Authors: Lynds L. , Weinberger B. R. , Lindsay M. P. , Potrepka D. M.
Published: March 2011

A comparison of the energetics and stoichiometry of effluents from YBa2CU307‐x targets ablated by Nd:YAG (1064 nm) and excimer (248 nm) lasers is presented. NdrYAG ablative processes are characterized by specularly directed neutral atom/cluster formation with translational energies in the range of 2 ‐ 20 eV. In sharp contrast, excimer ablation leads mainly to highly forward directed atomic ions with centroid energies between 200 and 400 eV. Analysis of the energetics indicates that different mechanisms are at play but both processes are non‐equilibrium in nature.
In-Situ Pulsed Laser Deposition of High-TC Yba2Cu3O7 Superconducting Thin Films on (100) LaAlO3 Substrates
Authors: Tiwari P. , Sharan S. , Singh R. K. , Holland O. W. , Narayan J.
Published: March 2011

The formation of superconducting thin films on lanthanum aluminate substrates is very important for high‐frequency applications. In this paper, we discuss the fabrication of epitaxial superconducting YBa2Cu3O7 thin films on (100)LaAlO3 substrates, which exhibit excellent dielectric properties required for high frequency applications. The films were deposited by the biased pulsed laser evaporation technique (PLE) at substrate temperatures between 500‐650°C and exhibit excellent crystallinity with best minimum ion channeling yields corresponding to approximately 3%. The superconducting transition temperatures varied from 88‐92 K with critical current densities at 77K and zero magnetic field greater than 4 ‐ 5 x 106 Amps/cm2.
Grain Boundaries in Yba2 Cu3O7-δ Thin Films
Authors: Norton M. Grant , Tietz Lisa A. , Carter C. Barry , Russek Stephen E , Moeckly Brian H. , Buhrman Robert A
Published: March 2011

Grain boundaries in YBa2Cu3O7-δ thin films deposited on (001)-MgO by pulsed laser ablation have been characterized using selected area diffraction. In addition to twin boundaries, the presence of both low-angle and high-angle grain boundaries were characteristic of the film's microstructure. The presence of certain grain boundaries may be responsible for the weak-link Josephson behavior observed in small constrictions formed in superconducting films on MgO.
Preparation of Superconducting Y‐Ba‐Cu‐O Thin Films by Mo‐Cvd
Authors: Ohnishi Hiroshi , Kusakabe Yoshihiko , Kobayashi Minoru , Hoshinouchi Susumu , Harima Hiroshi , Tachibana Kunihide
Published: March 2011

High‐Tc superconducting Y‐Ba‐Cu‐O films were prepared on Mg0(100) substrate by MO‐CVD technique without post annealing. The highest Tc obtained was 85K. The film was made up of dense matrix and dispersed fine particles. The Y‐Ba‐Cu composition of matrix was nearly equal to the 1:2:3 superconducting phase. The film was highly oriented with c‐axis perpendicular to the substrate. The lattice constant of the film was 11.68A.
Low Temperature Preparation of Y‐Ba‐Cu‐0 High Tc Superconducting Thin Films by Plasma‐Enhanced Organometallic Chemical Vapor Deposition
Authors: Zhao Jing , Marcy Henry O. , Tonge Lauren M. , Wessels Bruce W. , Marks Tobin J. , Kannewurf Carl R.
Published: March 2011

We report here a plasma‐enhanced organometallic chemical vapor deposition process for the preparation of YBa2Cu3O7‐x thin films using two rf plasma coupling configurations. For the films grown under a direct plasma glow, the YBa2Cu3O7‐x phase is not found in the as‐deposited state. However, by employing plasma‐activated nitrous oxide as the reactant gas, superconducting YBa2Cu3O7‐x films having a low carbon content and a mirror‐like surface have been prepared in‐situ at a substrate temperature of 610°C using an organometallic chemical vapor deposition process.
Superconducting yba2cu3o7‐x Thin Film on Metal Substrate by Chemical Vapor Deposition Process.
Authors: Yamaguchi T. , Aoki S. , Sadakata N. , Kohno O.
Published: March 2011

Superconducting YBa2Cu307_x thin films were prepared by chemical vapor deposition using beta‐diketonate chelates on various oxide substrates and metal substrates. According to X‐ray diffraction patterns, the existence of a well‐oriented orthorhombic YBagCUgO^x structure has been confirmed in all specimens. The temperature of complete superconducting transition were observed at 89K on single‐crystalline oxide substrate, and 84K on metal substrate. Reduced critical current density of the film on single‐crystalline substrate in magnetic fields up to 600mT at 77K remained one or two order of magnitude higher than that of the film on metal substrate.
High‐Tc Undoped and Pb‐Doped BI‐SR‐CA‐CU‐O thin Films Prepared by Organometallic Chemical Vapor Deposition
Authors: Zhang J. M. , Marcy H. O , Tonge L .M. , Wessels B. W. , Marks T. J. , Kannewurf C. R.
Published: March 2011

Films of the high‐Tc undoped and Pb‐doped Bi‐Sr‐Ca‐Cu‐O (BSCCO) superconductors have been prepared by low pressure organometallic chemical vapor deposition (OMCVD) using the volatile metal‐organic precursors Cu(acetylacetonate)2, Sr(dipivaloylmethanate)2, Ca(dipivaloylmethanate)2, and triphenyl bismuth. Factors which influence texture and morphology of the OMCVD‐derived films have been investigated, including the effects of annealing, doping, and substrates.
Preparation of Bi‐Sr‐Ca‐Cu‐0 Superconducting Thin Films by Mocvd
Authors: Gohda Shinji , Maeda Yasuhiro
Published: March 2011

Bi‐Sr‐Ca‐Cu‐0 superconducting thin films have been prepared on MgO substrates by a Metalorganic Chemical Vapor Deposition technique using an infrared lamp. It was found in this study that the film composition ratio could be precisely controlled by using this technique. A zero resistance at 81K was obtained for Bi1Sr1.3Ca0.9Cu1.8Ox film grown at 850°C. The critical current density of this film was 1.0xl03A/cm2 at 77K.
Preparation of Yba2Cu3O7-X. Superconducting Thin Films by Means of Single Target Rf-Sputtering+
Authors: Weyten Herman D.L. , Batist R. De , Nagels P. , Cornelis J.
Published: March 2011

High Tc superconducting thin films have been deposited on sapphire by means of RF‐sputtering from a single stoichiometric target of YBa2Cu3O7‐x composition. The YBa2Cu3O7‐x films were deposited in an argon‐oxygen atmosphere on a substrate which reached a temperature of s 400°C during deposition. The study of stoichiometry and homogeneity of the as‐deposited films, by means of electromicroprobe analysis (EMPA), was used to optimize the sputtering parameters of the system. To achieve superconductivity, with an onset of s 90 K, a high‐temperature, post‐deposition thermal treatment in oxygen was necessary. Resistivity measurements show that, with respect to the bulk samples, zero resistivity is lowered as a result of substrate interaction. The use of buffer layers can improve the quality of the superconducting thin films.
Partial Reduction/Re-Oxidation Processing of Y-Ba-Cu-O Sputtered Thin Films
Authors: Garzon F.H. , Beery J. G. , Wilde D. K. , Raistrick I. D.
Published: March 2011

Thin films of Y‐Ba‐Cu‐O were produced by RF sputtering of YBa2Cu3O7‐x ceramic targets, using a variety of plasma compositions, RF power levels, and substrate temperatures. Post annealing of these films in oxygen produced superconducting films with Tc values between 40‐60 K, broad transition widths and semiconductor‐like electrical behavior above Tc. Subsequent annealing at 850°C in an inert gas with a residual oxygen partial pressure of ≤10 ppm followed by an oxygen anneal produced high quality thin films: Tc> 85 K with narrow transition widths. The structure and morphology of these films during reduction‐oxidation processing were monitored using X‐ray diffraction and electron microscopy.
X-Ray Line Broadening Analysis of Ybacuo Superconducting Thin Films
Authors: Ece M. , Vook R.W. , Allen John P.
Published: March 2011

Thin films of YBaCuO were prepared on MgO and SrTi03/Al2 03 substrates by rf magnetron sputtering. The SrTi03 was deposited onto AI2O3 by flash evaporation. The as‐deposited films on both substrates had an (001) orientation and were superconductors. Annealing the films in O2 improved their crystal 1inity and raised their critical temperatures (Tc). A detailed X‐ray diffraction study of the YBaCuO films was carried out. Values for the particle sizes and nonuniform strains along the c axis were obtained from broadened diffraction lines by using an integral breadth method. It was found that the broadening was mainly caused by nonuniform strain. It was also observed that nonuniform strain decreased as the films were annealed at various temperatures. The Tc's of the films were very sensitive to changes in nonuniform strain.
The Use of BaF2 Buffer Layers for the Sputter-Deposition of Ticabacuo Thin-Film Superconductors
Authors: Hubbard K.M. , Arendt P.N. , Brown D.R. , Cooke D.W. , Elliott N.E. , Fan J.D. , Nastasi M. , Ott K.C. , Peterson E.J. , Reeves G.A.
Published: March 2011

Thin films of the Tl‐based superconductors often have relatively poor properties because of film/substrate interdiffusion which occurs during the anneal. We have therefore investigated the use of BaF2 as a diffusion barrier. TICaBaCuO thin films were deposited by dc magnetron sputtering onto MgO <100> substrates, both with and without an evaporation‐deposited BaF2 buffer layer, and post‐annealed in a Tl over‐pressure. Electrical properties of the films were determined by four‐point probe analysis, and compositions were measured by ion‐backscattering spectroscopy. Structural analysis was performed by X‐ray diffraction and scanning electron microscopy. The BaF2 buffer layers were found to significantly improve the properties of the TICaBaCuO thin films.
Characterization of Epitaxial Superconducting YBacuO Thin Films with Three Different Orientations
Authors: Wang X.K. , Li D.X. , Song S.N. , Zheng J.Q. , Chang R.P.H. , Ketterson J.B.
Published: March 2011

Epitaxial thin films of YBaCuO were prepared by multilayer deposition from Y, Cu, and BaF2 sources with: (1) the a‐axis perpendicular to (100)SrTiO3; (2) the c‐axis perpendicular to (100)SrTiO3; and (3) the [110] axis perpendicular to (110)SrTiO3. XRD patterns as well as SEM and HREM images confirm that the films are highly oriented, essentially epitaxial. Both the a‐axis oriented and the c‐axis oriented films exhibit zero resistance at 91K. The [110] oriented film shows the sharpest transiton with a transition width of IK and zero resistance at 85K. The zero field critical current density, Jc, determined magnetically, is in excess of 107A/cm2 at 4.4K and 1.04 x 106A/cm2 at 77K for the c‐axis oriented film; for the a‐axis oriented film we obtained 6.7 x 106A/cm2 at 4.4K and 1.2 x 105A/cm2 at 77K. The orientation dependence of the critical current density in the basal plane of the a‐axis oriented film was studied. The largest Jc's occur along the in‐plane <100> axes of the substrate.
Annealing Behavior of Ba2Ycu3+XO7+Y Thin Films
Authors: Siegrist T. , Coleman E.
Published: March 2011

The annealing behavior of Ba2YCu3+xO7+y films grown by coevaporation of BaF2, Y and Cu on SrTiO3 has been studied as a function of temperature. Upon annealing at temperatures below 800°C, the phase forming first is Ba2YCu4O8, independent of the starting stoichiometry. Higher temperatures, above approximately 825 ° C are needed for Ba2YCu3O7 to crystallize.
Microstructures of Y123 Films on Srtio3, Lagao3 and Laaio3
Authors: Roy T. , Raistrick I. D. , Mitchell T. E.
Published: March 2011

Transmission electron microscopy(TEM) and scanning electron microscopy (SEM) have been used to study the microstructural features of YBa2Cu3O7 (hereafter referred to as Y123) films grown on various single crystal substrates by electron beam deposition. The films are all of high quality with the best observed Jc value being 10 A.cm‐2 at 7K. Cross‐sectional views in TEM have shown that the morphology of the film depends on its thickness. Thinner films (2500 Å) have a single layer of Y123 oriented with its c‐axis perpendicular to the substrate while thicker films(8000 Å) have this same c‐axis perpendicular layer closest to the interface with a c‐axis parallel layer above it. The interface between the film and the substrate is well defined in all cases with no amorphous region at the interface. Chemical analysis shows evidence of interdiffusion between the film and substrate.
Critical Current Density and Microstructure of Yba2Cu3O7-X Films as a Function of Film Thickness
Authors: Mogro-Campero A. , Turner L.G. , Hall E.L. , Lewis N.
Published: March 2011

Thin films of nominal composition YBa2Cu3O7‐x (YBCO) were produced on (100) SrTiO3 substrates by coevaporation and furnace annealing. Film thicknesses in the range of 0.2 to 2.4/μm were analyzed. Microstructural investigations by cross sectional transmission electron microscopy (TEM) reveal a continuous layer of about 0.4 μm thickness adjacent to the substrate with c‐axis normal to the substrate plane. In thicker films the remaining top portion has the c‐axis in the film plane. The critical current density (J ) at 77 K decreases with increasing thickness in the thickness range exceeding 0.4 μm, qualitatively consistent with the microstructural observations, but quantitatively inconsistent with a simple model based on the microstructural data.
High Tc Superconductor Films Grown by the Liquid Phase Epitaxial Technique
Authors: Yang C. S. , Yue A. S.
Published: March 2011

High Tc superconducting YBa2Cu3O7 films have been prepared by the Liquid Phase Epitaxial (LPE) technique. The x‐ray diffraction patterns displayed a high degree of (00l) preferred orientations with c‐axes perpendicular to the film surfaces. The in‐situ grown YBa2Cu3O7 films showed zero‐resistivity at 76*K. Examination of the film cross sections by SEM revealed a growth mechanism.
A Crucibleless Liquid Phase Growth Method of Preparing the Y‐Ba‐Cu‐0 Superconducting Films
Authors: Chen K.C. , Perng L.H. , Lin C.H. , Perng T.P. , Wu T.B. , Wu J.M. , Chin T.S.
Published: March 2011

Superconducting Y‐Ba‐Cu‐0 film can be prepared by a liquid phase growth method without crucible on 96 % and 99 % alumina substrates. A buffer layer of sputtered gold or platinum was necessary for the formation of Yba2Cu3Ox phase. The flux of Ba2Cu3O10. was appropriate for this purpose. For a film of 10 mm x 20 mm x 10 micron, 0.6 to 0.8 gm initial weight was optimal, the optimum melting temperature was 1090 to 1110 °C for 20 ‐ 30 minutes. In order to obtain films with superconducting transition, an additional Y2BaCuO5‐underlayer was necessary. The resultant optimal films had Tc‐onset of above 80 % and Tc ‐zero of typically around 60 K.
Spray Pyrolysis Technique for the Deposition of Superconducting Films
Authors: Soller Marc , Moy Larry P. , Squillante Michael R. , Marzik James
Published: March 2011

Research has been performed on the use of chemical spray pyrolysis for depositing films of YBCO. The effects of reagent concentration, deposition rate, substrate temperature and substrate type were investigated. Films from less than 2 to more than 10 microns thick were deposited on single crystal strontium titanate, polycrystalline alumina and type 304 stainless steel.
A Novel Spray Pyrolysis System for the Deposition of High Tc Superconductors
Authors: Cumberbatch Toby J. , Deane Stephen , Barden Paul E. , Yu R.
Published: March 2011

A spray pyrolysis system has been developed in which the use of airless atomisation and optical heating permits the deposition of thin film superconductors at growth surface temperatures exceeding 650*C. A comparison between centrifugal and hydrodynamic atomisation techniques shows that each possesses advantages and disadvantages for the deposition of thin films by this technique. The presence of a corona discharge has been found to be an essential ingredient for growth at high substrate temperatures.
Direct Imaging of the Atomic Structure and Chemistry of Defects and Interfaces by Z-Contrast Stem
Authors: Pennycook S. J. , Chisholm M. F. , Jesson D. E. , Norton D. P. , Mccamy J. W. , Lowndes D. H.
Published: March 2011

Z-contrast scanning transmission electron microscopy (STEM) is a fundamentally new approach to high-resolution imaging which provides unambiguous, compositionally sensitive images on the atomic scale. Such images are intuitively interpretable, even in thick regions of the sample, tremendously simplifying determination of the structure and chemistry of defects and interfaces. To illustrate this, examples are presented of commonly observed planar defects in laser-ablated thin films of YBa2Cu3O7-x. Film/substrate interfaces are shown to be chemically diffuse on the atomic scale and steps or undulations in the substrate need not result in defects in the film. Low-angle grain boundaries are found to be chemically clean, the drastic reductions in critical currents with tilt angle being due to the array of intrinsic structural defects comprising the boundary.
Mechanism of Twin Formation During the Tetragonal to Orthorhombic Transformation In Yba2Cu3O7-X
Authors: Sarikaya Mehmet , Aksay Ilhan A. , Kikuchi Ryoichl
Published: March 2011

The formation of twins in the YBa2Cu3O7‐x system has been studied theoretically on the basis of transmission electron microscopy observations. The shape of the lips of the twinned domains is determined from two elastic strains, one associated with the twin boundary and the other with the lattice distortion at the lip region. The tangent of the angle at the tip which was calculated from the model agrees with experimental observations sufficiently well. The growth mechanism of the twinned domains is analyzed with an energy minimization approach. The similarities of transformation characteristics in this system to those of other systems are briefly discussed.
On the Resistive State of High Temperature Superconductors in Magnetic Field
Authors: Iye Y. , Nakamura S. , Tamegai T. , Terashima T. , Bando Y.
Published: March 2011

Experimental studies of the resistive state of high temperature superconductors in the mixed state were carried out on thin film samples of YBa2Cu3O7‐y and Bi2Sr2CaCu2Os+y. Precise angular dependence measurements on Yba2Cu3O7‐y epitaxial film have revealed not only the critical field anisotropy with respect to the a, b, and c‐axes but also a feature associated with twin boundaries. Dependence on the angle between the transport current and the magnetic field is investigated and discussed in terms of flux dynamics in highly anisotropic layered superconductors. Peculiar behavior of the Hall effect in the resistive state is reported.
Critical Current Densities in Bi2Sr2Cacu2O8+D
Authors: Nomura Shunji , Yamada Yutaka , Yamashita Tomohisa , Yoneda Eriko , Yoshino Hisashi , Ando Ken
Published: March 2011

Critical current densities and upper critical fields were measured for a single crystal of the high Tc oxide superconductor, Bi2Sr2CaCu2O8+d, within the ab basal plane and along the c axis. The anisotropy in critical current densities was observed to be Jc⊥/Jc//=10 in agreement with the anisotropy in resistivity for the normal state. The magnetic field dependence of the critical current densities can be interpreted by the anisotropy in the upper critical fields. The scaling of the critical current density with the magnetic field was found. The critical current density scaled to zero at fields Bc2 in the ab plane and along the c axis which were in good agreement with the upper critical fields measured by transport.

The anisotropy in flux pinning force density along the b axis, Fp//b, and along the a axis, Fp//a, was found to be Fp//b/Fp//a=3. The data provided strong evidence for flux pinning by the modulated structure in this system.
Comparison of Flux Dynamics in Two Samples of YBa2Cu3O7 with Different Pinning
Authors: Turchinskaya M. , Bennett L.H. , Swartzendruber L.J. , Roitburd A. , Chiang C.K. , Hill M. , Blendell J.E. , Sawano K.
Published: March 2011

The kinetics of magnetization in two samples of YBa2Cu3O7 prepared by different methods, are studied. Magnetization vs. time data were obtained at various temperatures for a number of applied fields. The data display (after some short period of time) logarithmic behavior and (after a sufficiently long time) exponential behavior. The pinning parameter “activation volume” was determined from the experimental data for both samples.
Transport Critical Current of Sintered YBa2Cu3Ox in Time-Varying Magnetic Fields
Authors: Hambourger P. D. , DiCillo J. , Gibberman M. , Marino J. , Valek L. P. , Centanni Michael A.
Published: March 2011

The transport critical current of bulk sintered YBa2Cu3Ox has been measured at 77 K in the presence of static and sinusoidally-time-dependent (10–100 Hz) magnetic fields. In all cases, the field required for a given reduction of critical current density was independent of frequency to within ~10%.