bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and Magnetic Properties of RBa2Cu2NbO8(R = La, Pr, Nd)
Authors: Radousky H. B. , C. O'Brien J. , Bennahmias M. , Klavins P. , Smith C. A. , Link J. M. , Goodwin T. J. , Shelton R. N. 
Published: March 2011

ABSTRACTPrBa2Cu2NbO8(PrBCNO) is an insulating analog to the YB2CU3O7(YBCO) system, which is interesting as a thin film buffer layer in YBCO/PrBCNO/YBCO tunnel junctions as well as a potential high Tcsuperconductor if proper doping could be achieved. PrBCNO has a similar structure to PrBCO, with NbO2planes replacing the CuO chains. Single phase polycrystalline samples of RBCNO have been synthesized with R = La, Pr and Nd. Attempts to synthesize this structure with the smaller ions Y and Gd have been unsuccessful. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12 K. No such magnetic phase transition is observed down to 2 K in the NdBCNO material.
Effect of O2 Partial Pressure on Post Annealed Ba2YCU3O7-δ Thin Films
Authors: PhUlips Julia M. , Siegal M. P. , Hou S. Y. , Tiefel T. H. , Marshall J. H. 
Published: March 2011

ABSTRACTEpitaxial films of Ba2YCu3O7-δ (BYCO) as thin as 250 å A and with Jc's approaching those of the best in situ grown films can be formed by co-evaporating BaF2, Y, and Cu followed by a two-stage anneal. These results extend the work on films > 2000 Å thick by R. Feenstra et al. [J. Appl. Phys. 69, 6569 (1991)]. High quality films of these thicknesses become possible if low oxygen partial pressure [p(O2) = 4.3 Torr] is used during the high temperature portion cf the anneal (Ta). The BYCO melt line is the upper limit for Ta. The use of low p(O2) shifts the window for stable BYCO film growth to lower temperature, which allows the formation of smooth films with greater microstructural disorder than is found in films grown in p(O2) = 740 Torr at higher Ta. The best films annealed in p(O2)=4.3 Torr have Jc values a factor of four higher than do comparable films annealed in P2=740 Torr. The relationship between the T required to grow films with the strongest pinning force and p(O2) is log independent of growth method (in situ or situ) over a range of five orders of magnitude of P(O2).
Thermoelectric and Thermomagnetic Effects in High-Temperature Superconductors
Authors: Huebener R. P. , Ri H. -C. , Gross R. , Kober F. 
Published: March 2011

ABSTRACTIn the mixed state of high-temperature superconductors the dominant part of the Seebeck and Nernst effect is due to the thermal diffusion of quasiparticles and vortices, respectively. Our understanding of the Seebeck effect is based on the two-fluid counterflow model of Ginzburg and its extension to the mixed state with the presence of vortices. From the Nernst effect the transport entropy of the vortices is obtained. We summarize the recent thermoelectric and thermomagnetic experiments, paying also attention to the role of the Magnus force (Hall effect) and to the thermal fluctuation effects near TC.
YBa2Cu3O7 Thin Films on Polycrystalline Diamond Films with Buffer Layers
Authors: Cui G. , Beetz C. P. , Lincoln B. A. , Kirlin P. S. 
Published: March 2011

ABSTRACTThe deposition of in-situ YBa2CU3O7-δ Superconducting films on polycrystalline diamond thin films has been demonstrated for the first time. Three different composite buffer layer systems have been explored for this purpose: (1) Diamond/Zr/YSZ/YBCO, (2) Diamond/Si3N4/YSZ/YBCO, and (3) Diamond/SiO2/YSZ/YBCO. The Zr was deposited by dc sputtering on the diamond films at 450 to 820 °C. The YSZ was deposited by reactive on-axis rf sputtering at 680 to 750 °C. The Si3N4 and SiO2 were also deposited by on-axis rf sputtering at 400 to 700 °C. YBCO films were grown on the buffer layers by off-axis rf sputtering at substrate temperatures between 690 °C and 750 °C. In all cases, the as-deposited YBCO films were superconducting above 77 K. This demonstration enables the fabrication of low heat capacity, fast response time bolometric IR detectors and paves the way for the use of HTSC on diamond for interconnect layers in multichip modules.
Vortex Dynamics and Dissipation in High Temperature Superconductors — from DC to Microwave Frequencies
Authors: Yeh N.-C. , Jiang W. , Reed D. S. , Kriplani U. , Holtzberg F. , Gupta A. , Kussmaul A. 
Published: March 2011

ABSTRACTA second-order vortex-solid melting transition in twinned Y-Ba-Cu-O single crystals is manifested by two independent types of electrical transport measurements: the electric field (E) versus current density (J) isotherms, and the ac resistivity (ρ) vs current frequency (ω) isotherms. Universal static and dynamic exponents (ν ≈ 2/3 and Ζ ≈ 3, respectively) are found for magnetic fields ranging from 1 to 90 kOe, frequencies ranging from 0 to 2 MHz, magnetic directions parallel and perpendicular to the crystal c-axis, as well as samples with and without proton irradiations. At microwave frequencies, we find that the vortex dissipation in Nd-Ce-Cu-O epitaxial films is consistent with the viscous motion of individual vortices, due to the break down of the critical scaling theory in the high frequency limit.
The Effect of Er2BaCuo5 Additions on the Microstructure and Magnetic Properties of Zone Melt Textured YBa2Cu3O6+x Wires
Authors: Balkin D. , Varanasi C. , McGinn P. 
Published: March 2011

ABSTRACTYBa2Cu3O6+x (Y-123) wires with Er2BaCuO5 (Er-211) and Y2BaCuO5 (Y-211) additions were vertically zone melted using a single element resistive furnace. The microstructure and magnetic Jc of wire segments taken from different sections of well textured wires were analyzed and compared. In both Er-211 and Y-211 doped wires the 123 plate width and the magnetic Jc decreased with increasing 211 additions. Microstructural analysis on the Er-211 doped wires confirms that Er-211 dissolves in the melt and results in the formation of a YzEr(1-z)Ba2Cu3O6+x superconducting phase upon solidification which shows improved magnetic properties over Y-211 doped wires.
A Study of Parameters that Influence Growth and Stability of the (Bi1−xPbx)2Sr2Ca2Cu3Oy Phase
Authors: Luo J. S. , Merchant N. , Maroni V. A. , Gruen D. M. , Tani B. S. , Carter W. L. , Riley G. N. , Sandhage K.H. 
Published: March 2011

ABSTRACTThe growth and stability of the (Bi1-xPbx)2Sr2Ca2Cu3Oy (Bi-2223) phase contained in silver-sheathed wires has been investigated by a combination of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and transmission electron microscopy. Silver tubes loaded with Bi-2223 precursor powders were processed into filaments using established metallurgical techniques. The filaments were then heat-treated at selected temperatures (800 to 845°C) for a range of times (10 to 6000 min) in a 7.5% oxygen atmosphere. From these studies it has been possible to investigate the time-temperature-oxygen pressure domains wherein Bi2Sr2CaCu2O8 (Bi-2212) + second phases transform to Bi-2223. Fractional conversion (Bi-2212 --> Bi-2223) versus time data show good conformance to the kinetic model for a diffusion-controlled reaction at the interface between thin sheets and a fine powder or a fluid. Quenching experiments also reveal that the Bi-2223 phase is stable in a limited temperature interval between 810 and 830°C.
Metal Organic Deposition of Ybco from Neo-Decanoates
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Rellecati P. , Mauro L. , Volpe P. , Andreone D. 
Published: March 2011

ABSTRACTBulk YBCO samples have been prepared for the first time by using Metal-Organic Deposition (MOD) technique.Solutions of Y, Ba and Cu neodecanoates have been used in order to obtain directly YBCO powders (not exactly, but approximately stoichiometric) after a back-up and a pyrolysis step at 500°C. The powders have been successively pressed and subjected to two annealing steps in order to built up the YBCO structure, to increase grain dimensions and to adjust oxygen stoichiometry. The samples, which are disk-shaped, 1 mm thick and 1 cm wide, display a sharp superconducting transition at 93 K and possess a relatively large critical current.Diffraction patterns indicate a strong degree of orientation of (a,b) planes along the surface. The superconducting gap has been measured by SIS' tunneling with Nb and by investigation on SS' Andreev reflection.
Proton Irradiation Enhancement of Implanted Layers on Ceramic YBCO Bulk
Authors: Andreone D. , Cherubini R. , Colombo S. , Gerbaldo R. , Mezzetti E. , Minetti B. , Periale F. 
Published: March 2011

ABSTRACTIn this work the possibility of enhancing the critical current density in proton implanted surface layers on YBCO bulk is discussed. A complete transport characterization shows that, for what concerns two samples from different irradiation runs, the critical current density has been enhanced. Increases of other meaningful parameters, such as average pinning energy and vortex-antivortex coupling strength, have also been found, although the relative effect of the implanted layer on the whole specimen cannot be evaluated in a fully quantitative way.
High Tc YBa2Cu3O7−x Thin Films on GaAs-Based Substrate Using MgO Buffer Layers with Sb Passivation Technique 1
Authors: Tseng M. Z. , Jiang W. N. , Hu E. L. , Mishra U. K. 
Published: March 2011

ABSTRACTHigh quality YBCO films have been grown on GaAs-based substrates via depositing MgO epitaxial buffer layers prior to YBCO growth. The critical temperature of the best YBCO film, Tc(0) was 87K and Jc>6.7×104 A/cm2 at 77K. The MgO buffer layers are usually [100] oriented along the normal of GaAs (100) substrates with full-width-half-maximum (FWHM) of rocking curve varying from 1–3 degree. We found that the uniformity and quality of MgO buffer layers are very sensitive to the pre-deposition preparation of GaAs-based substrates. Nonuniform MgO buffer layers are often obtained on those substrates prepared by wet chemical processing. Reproducible, controlled formation of the MgO buffer layer was achieved using an antimony passivation scheme, after molecular beam epitaxial (MBE) growth of the desired structure of the substrate.
On the Determination of Intrinsic Properties of Ceramic High-Tc Superconductors by Ac Susceptibility Measurements
Authors: Ludwig F. 
Published: March 2011

ABSTRACTVarious models have been proposed to interpret ac susceptibility curves measured on sintered high-To superconductors (HTSC) and to deduce parameters like critical current densities and critical fields. To get more clearness, systematic studies of position and height of the intergranular maximum in χ'' have been performed on several ceramic HTSC samples in dependence of both ac field amplitude and sample size. In the present paper, the data are used to discuss the various models proposed in the literature. It is shown that modifications of the critical state model using incorrect jc(Hi) functions as well as other interpretations of the χ'' peak yield not actually intrinsic but sample size and geometry dependent parameters. The dependence of both position and height of the intergranular maximum in χ '' on ac field amplitude and sample size can be explained in the framework of a modified critical state model using a power law for the jc(Hi) dependence.
Synthesis, Microstructure, Critical Current Density, Magnetization and Relaxation of Hot-Pressed YBa2Cu3O6+δ Through Partial Melting Post-Oxygenation
Authors: Kunga P. J. , Maleya M. P. , Mchenry M. E. 
Published: March 2011

ABSTRACTHot-pressed YBa2Cu3O6+δ superconductor with plate-like grains annealed at the partial melting temperature ( ∼ 1,000 C) followed by slow cooling in oxygen atmosphere has resulted in enhanced magnetization hysteresis loops which show weak dependence on magnetic field. The X-ray diffraction pattern exhibits the significant features associated with the reflection (003) and (006), and a higher compaction density in hot-pressed samples compared with cold-pressed samples was observed from the SEM micrographs. Morphology study and microstructural analysis by SEM and TEM, respectively, indicate that grains were well aligned during hot-pressing mostly with their c-axes parallel to the pressing axis, and many intersecting twins were actually formed during post-oxygenation. Local oxygen-deficient regions likely existing in these hot-pressed and oxygenated samples are believed to act as effective flux pinning centers at high temperatures (∼ 50 K and above). The measurement of magnetic relaxation was employed to interpret the observed pinning behavior. The critical magnetization current density (Jc) calculated using the Bean model and the average grain dimension is in the order of 104 Amp/cm2 at 75 K up to 1 T. Because of a shorter period of oxygenation and a weak field dependence of Jc values, the process of hot-pressing combined with partial melting post-oxygenation is technologically practical in forming various shapes as desired from oxide superconductors.
Oxygen Deficiencies at Defects in YBa2CU3O7-δ as Determined by High Resolution Parallel Electron Energy Loss
Authors: Kramer M. J. , McCallum R. W. 
Published: March 2011

ABSTRACTThere has been considerable discussion on the exact nature of the pinning defects in the high temperature ceramic superconductors, and the YBa2Cu3O7-δ (Y123) structure in particular. High resolution parallel electron energy loss spectrometry (PEELS) allows for fine spatial resolution (< 17 nm) and fast acquisition times to probe the oxygen content of defects (i.e., dislocations, stacking faults, twin boundaries and grain boundaries), all which have been proposed as potential pinning sites or weak-links. Oxygen deficiencies up to 13% were measured at twin boundaries, and 20% at grain boundaries while stacking faults showed an increase in oxygen and copper content. Regions of low oxygen (0.5 < δ < 1) were usually confined to an area within approximately 50 nm of the defect, which is within the spatial resolution of the measurements. Examination of the fine structure of the oxygen K-edge suggests that the oxygen holes are absent at the twin and grain boundaries.
Superconducting behavior of YBa2Cu3O6–8/Bi2Sr2CanCun-1Ox multilayers
Authors: Narumi E. , Lee J. , Li C. , Patel S. , Shaw D. T. 
Published: March 2011

ABSTRACTComposite YBCO/BSCCO films on MgO(lOO) substrates were fabricated by using laser deposition. The structures and transport properties of these composite films were studied. The model of 3D percolating network in YBCO thin films will be discussed.
In-Situ Surface Observation of C-Axis Oriented YBa2Cu3O7−x Thin Films by Leed, XPS and ISS
Authors: Tanaka S. , Nakamura T. , Tokuda H. , Iiyama M. 
Published: March 2011

1. AbstractIn an ultra-high vacuum equipment, YBa2CU3O7−x (YBCO) thin films were deposited by the ozone-assisted co-evaporation method and their surfaces were investigated by LEED, XPS and ISS without breaking the vacuum. A LEED pattern was observed for the first time at an as-deposited surface. A clean, crystalline and superconducting surface was preserved to the top of the film. Only Cu atoms were detected at the first monolayer by ISS, suggesting that clean surfaces are stabilized by Cu-O layers.
Microstructure of In-Situ Grown YBa2Cu4O8 Thin Films Deposited by MOCVD
Authors: Uehara K. , Sakai H. , Hayashi H. , Shiohara Y. , Tanaka S. 
Published: March 2011

ABSTRACTHigh-resolution transmission electron microscopy (HREM) has been used to study the microstructures of Y-Ba-Cu-0 superconducting thin films in which the YBa2Cu4O8 phase was the main phase. From cross-sectional observations, the c-normal 123 phase predominated in the film near the substrate surface, while the c-normal 124 phase occupied the region near the film surface. Another remarkable microstructure was that a-normal 123 variants overcame the c-normal 123 region, but the c-normal 124 phase surpassed the a-normal 123 phase in the upper part of the film.
Growth of Cerium Oxide Buffer Layers and Superconducting thin films on Silicon
Authors: Amirhaghi S , Beech F , Craciun V , Sajjadi A , Vickers M , Tarling S , Barnes P , Andboydi W 
Published: March 2011

ABSTRACTFilms of CeO2 have been grown on Si and glass substrates using the laser ablation deposition technique. X-ray diffraction measurements for the films deposited on glass indicated that they are the same as films grown on Si covered with the native oxide. This evidence supports a picture in which chemical rather than crystal-lographic effects constrain the film growth. The crystal quality for films grown on Si was shown to improve with increasing film thickness away from the amorphous layer. Low cooling rates as well as reduced film thickness were effective in avoiding the formation of micro-cracks. The surface morphology was shown to be dependent on the laser wave-length as well as the oxygen partial pressure. Thin films of YBa2Cu3O7δ could easily be grown on CeO2/Si showing c-axis orientation, whereas the growth of BiSrCaCuO (2212) on CeO2/Si resulted in the two films mixing with each other.
Tl-Based Films: A Comparison of Processing Procedures
Authors: Morosin B. , Venturini E. L. , Tigges C. P. , Ginley D. S. , Volk S. R. 
Published: March 2011

ABSTRACTThe structural, electrical and magnetic properties are compared for three superconducting Tl-Ca-Ba-Cu-O thin films prepared by different deposition and sintering protocols. One film containing a mixture of Tl2Ca2Ba2Cu3Ox and Tl2Ca2Ba2Cu3Oy structural phases has the best superconducting properties. Deposition of a Tl-free Ca-Ba-Cu-O precursor film followed by sintering in Tl-O vapor may be the preferred protocol to obtain a single structural phase.
Reflection High Energy Electron Diffraction Studies of the Growth of DyBa2Cu3O7−x Films and Structures Grown on SrTiO3 Substrates
Authors: Achutharaman V. S. , Chandrasekhar N. , Goldman A. M. 
Published: March 2011

ABSTRACTIntensity oscillations of the specular reflection high energy electron diffraction (RHEED) beam contain useful information on the mode of growth and the evolving structure of thin films. We present RHEED studies of the growth of DyBa2Cu3O7−x films and DyBa2Cu3O7−x/DY2O3/DyBa2Cu3O7−x structures on SrTiO3; substrates deposited by ozone-assisted molecular beam epitaxy. The effect of substrate temperature, ozone flux and surface step densities on the epitaxial relationship and evolving microstructure will be discussed. The strong damping of the oscillations and identical time periods under different nuoleation and growth conditions suggest that the intensity oscillations are a consequence of to diffuse scattering from step edges rather than a layer-by-layer growth mode. It was also found that Dy2O3 can be used to fabricatee tri-layer type structures but not superlattice structures.
Ultrafast Electrical Superconducting to Normal States Switching in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O Microstrips
Authors: Balevičius S. , Bičūnas A. , Butkute R. , Jasutis V. , Lisauskas V. , Vailionis A. , Flodström A. , Vengalis B. 
Published: March 2011

ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was found that two reversible processes: fast electronic (τ∼10∼−12 s) and slow thermal (τ∼10∼−8s) one take place during switching. At high current densities (∼107 A/cm2) irreversible changes in strip material induced by thermal runaway occurred. The use of a superconducting element as fast fault-current limiter or pulse sharpening device is pointed out.
Multifilamentary Bismuth(2223) Multilayer-Wound Conductors for Power Transmission Lines
Authors: Mukai H. , Shibuta N. , Sato K. , Hara T. , Ishii H. , Yamamoto T. 
Published: March 2011

ABSTRACTThe fundamental problems of applying high-Tc superconductors to power transmission lines were studied, and prototypes of multilayer-wound conductors were fabricated and evaluated.Multifilamentary silver sheathed wires have good anti-strain. properties. A 61-filament bismuth(2223) wire proved to maintain 90% of initial transport current property after 150 cycles of bending (bent-straightened-bent reversely-straightened) with 0.18% strain. A 61-filament wire of 114m unit-length was produced and proved to have a Jc of 9,700 A/cm2 with an Ic of 9.34A for the whole length at 77.3K.Using these multifilamentary wires, prototypes of multilayer-wound conductors were produced by the react-and-wind technique. A 1.4m long three layer-wound conductor could carry 590A (Jc=7.020A/cm2) in liquid nitrogen.These results indicate that the basic problems of high-Tc superconductor application to power transmission lines will be overcome using this technology.
Solidification Mechanism of YBa2Cu3Ox Superconductors
Authors: Nakamura Yuichi , Izumi Teruo , Shiohara Yuh , Tanaka Shoji 
Published: March 2011

ABSTRACTDirectional solidification of the zone melting method was performed in order to clarify the growth mechanism on YBa2Cu3Ox (123) superconductors from the partial molten state. The effect of a platinum addition for crystal growth was also investigated. Results indicate that a higher G/R ratio was preferable for the continuous growth of 123 crystals, and lead to the idea that the necessary solute for the peritectic reaction is provided from dispersed Y2BaCuO5 (211) particles in liquid to 123 interface through the liquid. Based on this idea, we developed a solidification model which is in good agreement with the experimental results. In the case of a platinum addition, the coarsening rate of 211 particles decreased, and the cell spacing of 123 crystals also decreased. It is tentatively suggested that the platinum addition decreases the products of the diffusivity in liquid and the Gibbs-Thomson coefficients, which include the surface energy between 211 or 123 phase and liquid,(DLΓ211 and DLΓ123).
On Extrinsic Effects in the Surface Impedance of Cuprate Superconductors
Authors: Halbritter J. 
Published: March 2011

ABSTRACTPresently, the rf surface impedance Z of cuprate superconductors is still shrinking with material improvements, which is shown clearly by Z = Z1+Zres still dominated by extrinsic properties summarized in Zres. We present evidence that Zres is due to the large leakage current jbi and the small critical current jcj of weak links. The latter destroys the intrinsic shielding from a λ1 -thin seam λJ deep into the bulk. This causes rf residual losses Rres ≈ (ΩμO)2λJ3 σb1/2. Rres stays finite at T≃O by σb1(T→O)≈σb1(αjb1) being amplified by (λj/λ1>103 as a weighting factor. An appropriate measure of weak links is the grain boundary resistance Rbn(∝ρ(O)) enhancing λj ∝ Rbn and Rres ∝ Rbn2. Thus, Zres is minimal for minimal extrapolated normal conducting resistivity ρ(T→O).To identify the weak links as new entity the H-field dependence is most helpful, because at very low fields Hc1J∝ 1/λJ Josephson fluxons penetrate into the weak links. These Josephson fluxons show negligible flux flow or flux creep, and enhance Zres by λJ(H, T) ∝ l/√Jjc (H, T). The measured JcJ (H, T) - and Jbl - values explain Zres quantitatively as well as in temperature ∝ ( a+ Tn) (n ≈ 1, T<Tc/2) and in field ∝ (b + Hn) (n≈1, H>Hc1J) dependence being thus a unique method to obtain the different Hc1-values. The strength of the field dependence d Zres/dH ∝ Zres (Hc1J*)/Hc2J(T) is not only a measure of Zres and HC2j(T) but is crucial for nonlinear effects and (fluxon) noise also, which limits the performance of rf devices.
Processing Effects on the Contact Resistance of Ion Beam Sputtered Silver on Highly Oriented C-Axis and A-Axis YBCO Films
Authors: Narbutovskih M. , Rosner J. , Merchant P. , Jacowitz R. D. 
Published: March 2011

ABSTRACTThis paper reports on the processes used to achieve low resistance silver contacts to YBCO thin films that have either c-axis or a-axis orientation. Characterization by x-ray diffraction and TEM verified that these films are highly oriented with either the a or the c axis oriented perpendicular to the substrate surface. TEM examination of some of the Ag/YBCO interfaces reveals the presence of an amorphous layer. We will describe the effects of ion beam etching and RTA alloying on the contact resistivity for both orientations.