bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Si-YBaCuO Intermixed System for Patterning of Superconducting Thin Films
Authors: Ma Q. Y. , Yang E. S. , Treyz G. V. , Shu C. , Osgood R. M. , Chang Chin-An
Published: March 2011

A Si-YBaCuO intermixed system has been formed using rapid thermal annealing (RTA) of Cu/BaO/Y2O2/Si layered structures, which were deposited on MgO substrates by electron-beam evaporation. The electrical and structural properties of the Si-YBaCuO system have been analyzed by resistivity, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and Auger depth profiling measurements. It was found that Si mixed with YBaCuO during annealing, thus creating an insulating film. This effect has been used to pattern YBaCuO films. The patterning process was carried out on an underlying silicon layer, rather than the YBaCuO film itself, using conventional photolithography or laser etching. After YBaCuO film deposition and RTA, the patterned region became superconducting separated by Si-YBaCuO intermixed areas. Micron-sized line features with Tc's above 77 K have been demonstrated.
Transport Measurements on Superconducting YBa2Cu3O7-δ Thin Film Lines
Authors: Moeckly B. H. , Lathrop D. K. , Redinbo G. F. , Russek S. E. , Buhrman R. A.
Published: March 2011

Critical current densities, magnetic field response, and microwave response have been measured for laser ablated YBa2Cu3O7-δ thin film lines on MgO and SrTiO3 substrates. Films on SrTiO3 have critical current densities > 1 x 106 A/cm2 at 77K and show uniform transport properties in lines of all sizes. Films on MgO have critical current densities which range between 102 and 106 A/cm2 at 77K and show considerable variation from device to device on the same chip. Narrow lines on MgO with low critical current densities show Josephson weak link structure which includes RSJ-like IV curves, microwave induced constant voltage steps, and a high sensitivity to magnetic field. The presence of the Josephson weak links is correlated with small amounts of misaligned grains in films on MgO.
High TC Superconductor Fibers from Metallo-Organic Precursors
Authors: Chen K.C. , Mazdiyasni K.S.
Published: March 2011

Homogeneous solution for Y-Ba-Cu-0 superconductor was prepared from yttrium i-propoxide, barium i-propoxide, and copper ethylhexanoate. The solution was converted to a resin-like material and was readily dissolved in organic solvents. The resin possesses a cohesive property in a number of solvents, such as benzene and xylene. Single-phase superconducting YBa2Cu307_x fibers have been continuously spun from the viscous solution. Controlled amounts of Y2BaCu05 phase in the fibers were made possible by slight adjustments in the solution compositions. Partial substitution of copper ethylhexanoate with copper trifluoroacetate prevents barium carbonate formation In the fiber during curing and organic pyrolysis.
Effect of Magnetic Field on Critical Current Density in Bulk Superconducting Wires
Authors: Lanagan M. T. , Balachandran U. , Youngdahl C. A. , Dusek J. T. , Picciolo J. J. , Poeppel R. B.
Published: March 2011

Bulk YBa2Cu3O7‐x (YBCO) wires and tubes were fabricated by an extrusion technique. Critical current density (Jc) was measured as a function of applied magnetic field at 77 K and was found to decrease significantly in fields below 100 G. Jc was dependent on specimen geometry. In addition, when a concentric magnetic field was generated by passing a current though a copper wire, the external field from the wire could interfere constructively or destructively with the magnetic field produced by current in a YBCO tube. The change in electrical properties with magnetic field has been attributed to weak‐link behavior at the grain boundaries. Batch‐to‐batch differences in the field dependence of Jc imply the possibility of reducing the dependence by processing modifications.
Novel Processing of Hts Based Conductors
Authors: Ginley D. S. , Venturini E. L. , Kwak J. F. , Baughman R. J. , Bourceer R. J. , Mitchell M. A. , Morosin B. , Halloran J. W. , Neal M. J. , Ca- Pone D. W.
Published: March 2011

Conductor development is one of the major long term goals in high temperature superconductor research. In this paper we report on two promising processing technologies that have been utilized to produce superconducting HTS conductors. First, melt spun YBa2Cu3O7 fibers rapid thermal processed for 1‐8 sec at 950 to 1075°C have Tc's to 92 K, Jc's to 1100 A/cm2 and the orthorhombic twinned morphology typical for high quality YBa2Cu3O7 A processing matrix of time, temperature and composition for these fibers shows that slightly CuO‐rich starting compositions give the best results. Second, silver tube encapsulated wires of Bi1.7Pb0.3Sr2Ca2Cu3O10 have been made by extrusion, wire drawing and cold rolling. The resulting tapes show orientation of the crystallites, zero resistance up to 100K and improved magnetic hysteresis above 50 K. The combination of mechanical reprocessing and extended thermal anneals near 850°C appears to significantly improve these materials.
Studies on Microstructure - Property Relationship of Yba2Cu3O7-X + Ag2O Composite Wire
Authors: Samajdar S. , Gouthama  , Samanta S. K.
Published: March 2011

Silver is known to act as a compatible metal host for designing a microcomposite system with the high temperature superconducting ceramic YBCO[l,3]. The unique role played by nascent silver generated from the silver monoxide precursor during sintering as well as warm compaction of the powder mix is illustrated with the help of light optical micrography. It is seen that electrical as well as mechanical properties of the bulk composite is significantly governed by its microstructure. The microstructure, in turn, could be controlled by suitable heal treatment and proper selection of the fabrication process parameters at every step. Attempting a structure‐propcrty‐processing correlation, a microstructure controlled scheme for fabricating superconducting composite product of useful shapes is discussed. Successful fabrication of thin (0.75 mm dia.) and long (450 mm) flexible wire following this route is also reported here.
Wet Chemical Etching of High TC Superconductors by Ethylenediaminetetraacetic Acid (EDTA)
Authors: Shokoohi F. K. , Schiavone L. M. , Rogers C. T. , Inam A. , Wu X. D. , Nazar L. , Venkatesan T.
Published: March 2011

A novel chemical etchant for the high temperature superconducting material YBa2Cu3O7‐x is demonstrated. The etching solution which consists of ethylenediaminetetraacetic acid (EDTA) in water does not degrade the properties of the superconducting films and is suitable for applications with standard photolithography. We have etched 2‐200 μm wide wires which show no degradation of Tc ( within 1 K accuracy of the measurements) and show zero‐resistance temperature ≥90 K. The etchant exhibits a polishing effect by selectively removing the porous and semiconducting surface layers which are formed during high temperature annealing process. The dense bulk of the films are etched at a rate of 1400 Å/min which provides control for fine‐line patterning of thin film material. The critical current densities of the unpatterned films which are polished by reactions with EDTA remain unaffected and are measured to be about 5 x 106 A/cm2.
Structural Phase Diagram and Superconducting Behavior of the Ba1-Xkxbio3 System
Authors: Jorgensen J. D. , Pei Shiyou , Hinks D. G. , Dabrowski B. , Richards D. R. , Mitchell A. W. , Zheng Y. , Marx D. T. , Sinha S. K. , Newsam J. M. , Vaknin D. , Jacobson A. J.
Published: March 2011

We have determined the crystal structures of five phases in the Bal-xKxBiO3 system for 0≤x≤0.5 and 10K≤T≤473K. Superconductivity occurs only in a cubic perovskite phase with the maximum Tc at the transition to an orthorhombic, Ibmm, phase. The commensurate structure of this orthorhombic phase, which involves only tilting of the Bi06 octahedra, provides no explanation for its non-metallic behavior. However, an incommensurate structural modulation, observed by electron diffraction, may provide a rationalization. Thus, the maximum Tc at the phase boundary may result from competition between superconductivity and a charge density wave. Further studies of the phase diagram at high temperatures, where controlled oxygen atmospheres are required, reveal an unusual reentrant formation of a potassium-containing impurity phase which explains the need for synthesis techniques that involve initially reacting in a reducing atmosphere, followed by oxygenation at lower temperature.
Studies of Oxyfluoride Analogs of Nd1.85Ce0.15CuO4: Preliminary Results
Authors: Vanderah T.A. , Osofsky M.S.
Published: March 2011

Samarium‐based oxyfluoride analogs of the apparently “n‐type” 24 K superconductor, Nd1.85Ce0.15CuO4, were prepared. A series of compounds with general formula Sm2‐xCexCuO4‐yFy were prepared and characterized by X‐ray diffraction, bromo/iodometric titration, and measurements of electrical resistivity. Homogeneous superconducting phases have not yet been obtained; preliminary results and discussion of property trends are presented.
Superconductivity in the (Nd,Ce,Ca)2Cuo4-Z System
Authors: Sakurai Takeshi , Yamashita Toru , Ikegawa Sumio , Yamauchi H.
Published: March 2011

We have controlled the carrier (electron) density in Nd2CuO2 of the T’ structure by introducing both Ce and Ca into the Nd‐sites, and studied the superconducting transition temperature versus carrier density relationship. The phase relations in the (Nd1‐x‐yCexCay)2CuO4‐z system were studied by means of powder X‐ray dirfractron and electron‐probe micro‐analysis techniques. For the phase diagram of the (Nd1‐x‐yCexCay)2CuO4‐z system, the single phase field of the T’ phase was established. Samples of the (Nd0.9‐yCe0.1Cay)2CuO4‐z system with compositions included in the single phase field were synthesized. The carrier density in these samples was varied by controlling the Ca content. The Hall effect and DC resistivity were measured to elucidate the relation between Tc and the carrier density.
Superconducting Behavior of Tetragonal T ‘Eu2‐xCexO4±δ
Authors: Melim V. J. , Peng Weimin , Kimball C.W. , Dabrowski B. , Zheng Y. , Hinks D. G.
Published: March 2011

Eu2.xCexCuO4±δ (0 ≤ x ≤ 0.17) has been synthesized with the tetragonal T’ structure. AC susceptibility and resistance measurements show that Eu2‐xCexCuO4±δ becomes superconducting with τc∼13 K for x= 0.15 and 0.17, when prepared under reducing conditions. The 151Eu Mossbauer shift shows that the Euvalence falls into a narrow range near Eu 3+ . The temperature dependence of the Mossbauer absorption yields a Debye temperature of 319 K for the Eu ion in Eu1.85Ce0.15CuO4±δ
Oxygen Content Variation in Cation-Deficient and Chemically-Doped High-TC Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O Superconductors
Authors: Kao Y. H. , Song L. W. , Yao Y. D. , Tao Z. , Jones K. W.
Published: March 2011

Oxygen content in high‐Tc superconductors has been determined by using a charged particle activation method. Changes of oxygen content in Cu‐deficient Y‐Ba‐Cu‐O and Cu/Bi‐deficient Bi‐Sr‐Ca‐Cu‐O compounds were obtained and used as a basis for discussing the variations in other cation‐deficient materials.
X-Ray Absorption Studies of Vanadium-Containing Yba2Cu3O7
Authors: Tan Z. , Budnick J. I. , Chen W. Q. , Weinbergers B. R. , Lynds L.
Published: March 2011

Attempted V substitution leads to small but observable lattice expansions of the YBa2Cu3O7 main phase but has little effect on the superconducting transition temperature. X‐ray absorption spectra at the AT‐edges of V, Cu and Y and L3‐edge of Ba have been measured on vanadium‐containing YBa2Cu3O7 to address the question of V substitution in this material. We found that only a small amount of V can substitute into the YBa2Cu3O7 structure. The excess V forms an impurity phase in which V is tetrahedrally coordinated with oxygens.
Calcium substituted Y‐Ba‐Cu‐O superconductors with enhanced Tc
Authors: Morris D. E. , Narwankar P. , Sinha A. P. B. , Takano K. , Shum V. T.
Published: March 2011

The Tc of 124 is enhanced by Ca substitution: CaxY(1‐x)Ba2Cu4Oy prepared at 200 bar at 930°C shows Tc = 89 K for x = 0.1. The 124 phase remains stable with Ca substitution at P(O2) ≥ 50 bar. For P(O2) = 2‐16 bar, Ca substitution stabilizes a tetragonal 123 phase CaxY(1‐x)Ba2Cu4Oy, which shows a Tc (87 K for x = 0.2) comparable to that of unsubstituted orthorhombic 123. The synthesis of CaT‐123 has been achieved in oxygen overpressure as small as 1 bar.
Processing of High Current Density Yba2cu3ox Superconductors
Authors: Selvamanickam V. , Salama K.
Published: March 2011

A liquid phase processing method has been developed to fabricate oriented grained YBa2Cu30x samples with high current density. The current density in these samples, however, is sensitive to the microstructure which is controlled by processing parameters. Cooling rate through the peritectic temperature is found to be the most crucial factor in controlling the extent of grain orientation and in turn the bulk current carrying capacity. The evolution of the microstructure during the slow cooling process is studied by quench experiments at different temperatures. From microstructural analysis, the suitable temperature profile for the slow cooling process is chosen. Current density measurements across grains show a Jc in excess of 104 A/cm2. This implies that the weak link behavior of grain boundaries in polycrystalline superconductors can be suppressed to a considerable extent.
Synthesis of Cuprate Ceramic Superconductors by Oxidation of Rapidly Quenched Alloy Precursors
Authors: Luo J.S. , Michel D. , Chevalier J.‐P.
Published: March 2011

We have produced various high Tc superconductors by oxidation of rapidly quenched alloy precursors produced by planar flow casting. This method generally leads to reactive oxidized powders and improves homogeneity if there is a solubility domain in the liquid state for the alloy. The grain size distribution is often more uniform than that for specimens prepared by conventional methods from mixtures of constituent oxides and carbonates.
Highly Textured Superconducting Bi2Sr2CaCu2Oy Crystals Prepared by Unidirectional Solidification Processing
Authors: Shiohara Y. , Oyama T. , Nakagawa M. , Suga T. , Ishige K. , Izumi T. , Nagaya S. , Miyajima M. , Hirabayashi I. , Tanaka S.
Published: March 2011

Unidirectional solidification processing, including Floating Zone Melting, Vertical Bridgman, and Laser Zone Melting methods for making high Tc superconducting oxides has been investigated. The effects of processing parameters, growth rate (R) and temperature gradient (G), on texture, morphology, and structures of unidirectionally grown crystals were investigated. Two different crystallization mechanisms were recognized, one is non‐equilibrium phase transformation under high GR conditions, and the other is due to local equilibrium phase transformation under low GR conditions. Strongly aligned structures were obtained at high G/R ratios with low GR value. The interrelation between the superconducting characteristics and textured structure produced were also discussed.
Phase Chemistry and Micro‐Structure of Directionally Solidified Bi2Sr2CaCu2O8
Authors: Chow H.M. , Jiang X.P. , Cima M.J. , Haggerty J.S. , Brody H.D. , Flemings M.C.
Published: March 2011

Ceramic rods of Bi2Sr2CaCu2O8 (2212) were directionally solidified by laser‐heated float‐zone crystal growth [1]. The microstructure of the resulting material can be controlled through variation of growth rate. The 2212 phase is Sr‐deficient, having an actual composition Bi2.5Sr2CaCu2.2Oy. At slow growth rates (0.2 cm/h), plane front growth produced highly textured samples of almost phase pure 2212, and pole figures show that the solidification front proceeds along the (200) axis of the 2212 grains. Faster growth rates produced dendritic growth and polyphase microstructures. At the fastest growth rate studied (16 cm/h), no 2212 phase was observed. Observations indicate that Bi2.5Sr2CaCu2.2Oy melts peritectically into (Sr1‐x.Cax.)14Cu24Oy and a Bi‐rich liquid.
Melt Processing of Bi-Ca-Sr-Cu-O Superconductors
Authors: Cronin J.P. , Aruchamy A. , Rosenfelder S. , Kim S.-J. , Uhlmann D.R. , El-Bayoumi O.H. , Andrews R.J.
Published: March 2011

Unidirectional crystallization of melt processed 2122 and 2223 composition in the Bi-Ca-Sr-Cu-O system has been carried out. Crystallization was controlled by heating the glass or cooling the melt using a moving furnace and a stationary sample. Fairly large oriented crystalline specimens of 2122 phases were obtained by cooling from the melt in a shallow gradient furnace. Glassy samples processed under steep gradients showed better crystallinity than those processed under shallow gradients.
Evolution of the High TcPhase in Rapidly Solidified Bi-Ca-Sr-Cu Oxides
Authors: Asthana A. , Han P.D. , Xu Z. , Chang L. , Payne D.A. , Gilbert P.J.
Published: March 2011

Materials in the system Bi-Ca-Sr-Cu-O were prepared by rapid solidification. Emphasis was placed on optimizing processing conditions for enhancement of the high Tc(2223) phase. A number of starting compositions and heat-treatments were investigated. The effect of dopants (such as, Pb, Sb, Ge, Sn) on the stabilization of the high Tc phase was evaluated. Small amounts of Pb and Sb were effective in significantly increasing the 2223 yield. Improvements in superconducting properties as a function of 2223 evolution are discussed with reference to SEM, TEM, XRD and SQUID results.
Effect of Oxygen Partial Pressure on Stability of High-Tc Phase in Sintered Bi-Pb-Sr-Ca-Cu-O Superconductos
Authors: Lee H.K. , Lee K.W. , Ha D.H. , Park J.C.
Published: March 2011

The effect of oxygen partial pressure on stability of high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system has been investigated using x-ray diffraction, resistivity and a.c. susceptibility measurements. It was found that part of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system was transformed into the low-Tc phase (80 K) and insulating phases by heating in the temperature range 600 C to 880°C in O2 of one atmosphere. The original high-Tc phase was restored upon retreatment in a low oxygen partial pressure of 0.1 atmosphere. The reversible superconducting phase transformation is discussed in conjunction with the formation mechanism of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system.
Reproducible, Large-Scale Production of Thallium-Based High-Temperature Superconductors
Authors: Gay Richard L. , Stelman D. , Newcomb J. C. , Grantham L. F. , Schnittgrund G. D.
Published: March 2011

The Rocketdyne Division of Rockwell International has developed a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique.

In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination.

Bulk samples of thallium-based powder were prepared by spray calcination, collected, cold-pressed, and sintered. An optimized temperature schedule was developed to produce T12Ba2Ca2Cu3Ox. Samples were examined by X-ray diffraction and characterized by measurements of critical transition temperature, Tc. A complete transition to zero resistance at 112 K was measured.
Luminescence from Defects and Impurity Centers in Y2O3
Authors: Jahan M. S. , Cooke D. W. , Bennett B. L , Hults W. L , Maez M. A. , Ott K. C. , Smith J. L.
Published: March 2011

High-purity (99.999%) Y2O3 powder is used as a starting material for fabricating high-temperature superconductors (HTS), and is frequently found as an unreacted second phase in the final product. We have found that as-received Y2O3 contains Tb3+ paramagnetic impurity ions as determined by TSL and emission-spectra measurements. Deep luminescence traps (presumably Tb4+ ions) are formed in Y2O3 when it is exposed to frays, x rays, or fluorescent lights. These deep traps can only be removed by annealing the material to near 1600°C. Given the short coherence length of HTS it is possible that order-of-magnitude variations in the Tb impurity concentration of starting materials may affect the ultimate value of surface resistance (Rs).
Soft X‐Ray Studies of Y‐Ba‐Cu‐O Thin Films Prepared by Laser Ablation
Authors: Krol A. , Sher C.J. , Storch D.R. , Song L.W. , Kao Y.H. , Witanachi S. , Zhu Y.Z. , Patel S. , Shaw D.T. , Smith G.C.
Published: March 2011

Angular variation of x‐ray fluorescence due to oxygen atoms in high‐T Y‐Ba‐Cu‐O thin films is measured for the first time by using a new parallel plate avalanche chamber. This technique allows the possibility of nondestructive probing of the depth‐profile of oxygen atoms in the superconducting materials. Our preliminary results indicate that the near surface region of the Y‐Ba‐Cu‐O film may contain an oxygen‐depleted layer of thickness around 20 nm.
High Tc Superconducting Bi-(Pb-)Sr-Ca-Cu-O Films Deposited by Pulsed Nd:Yag Laser Ablation
Authors: Levoska J. , Hagberg J. , Pusa P. , Uusimäki A. , Leppävuori S.
Published: March 2011

High To superconducting Bi-(Pb-)Sr-Ca-Cu-O thin films were ablated on MgO(l00) substrates at room temperature using a Nd:YAG laser at 1064 or 532 nm. The target materials had compositions near Bi2-xpbxSr2Ca2+yCu3+zOy (x<0.6, y,z<l) and their zero resistivity temperatures were 101 - 105 K. The amorphous films were crystallized either by annealing near 850°C or they were first melted and then annealed. The effects of laser ablation parameters and annealing conditions were investigated. The films were studied by XRD, SEM/EDS and resistivity measurements.

The best films were annealed near 850 °C and they consisted mainly of the 2223 phase. These films had T9(midpoint) at 107 K and zero resistivity at 100 K. In the melt-treated films the amount of the 2223 phase as well as Tc was lower. The superconducting phases in the annealed films were strongly oriented with their c-axes perpendicular to the substrate surface.
Thin Film Processing for High-Tc Superconductors of Bi-System
Authors: Wasa K. , Adachi H. , Hirochi K. , Ichikawa Y. , Setsune K.
Published: March 2011

Basic thin film deposition processes for the high-Tc superconductors of Bi-systems are described. There appear several superconducting phases including the low-Tc phase Bi2Sr2Ca1 Cu2Ox and the high-Tc phase Bi2Sr2Ca2Cu3Ox. Thin films with these superconducting phases are synthesized by a selection of the substrate temperature Ts during the deposition : the high-Tc phase with Tc=100K is synthesized at Ts>800 °C; the low-Tc phase with Tc=80K, at Ts<600°C. However, these films often comprise show structure comprizing the different superconducting phases.

The close control of the superconducting phase has been achieved by the layer-by-layer deposition in the atomic layer epitaxy process.
Synthesis and Properties of Ultra-Thin YBa2Cu3O7 and YBa2Cu3O7/La2-xSrxCuO4 Multilayers
Authors: Eom C.B. , Streiffer S.K. , Sun J.Z. , Yamamoto K. , Laderman S.S. , Bravman J.C. , Geballe T.H.
Published: March 2011

Using our standard single target off-axis sputter deposition procedure[1], ultra-thin YBa2Cu3O7 superconducting films were made in-situ. We have studied the thickness dependence of superconducting properties (Tc, Jc) from 20 to 5000Å. Tc starts degrading below 125Å and falls to 50 K for the 30 Å film. Jc drops linearly with decreasing thickness below l000Å. We have grown YBa2Cu3O7/La2-xSrxCuO4 superconducting thin film multilayers in-situ by the same process. The modulation wavelength of the multilayers ranged from 45Å to 2000Å. X-ray diffraction and cross sectional TEM confirm the superlattice periodicity. The superconducting transition temperature drops in much the same way as the single layer ultra-thin films. Both the critical current density and its magnetic field dependence decrease as the modulation wavelength decreases.
In‐situ growth of yba2cu3o7‐x films by metal organic chemical vapor deposition using vertical, high‐speed rotating disk reactor.
Authors: Noh D. W. , Gallois B. , Li Y. Q. , Chern C. , Rear B. , Tompa G. S. , Norris P. , Zawadzki P.
Published: March 2011

Superconducting thin films of YBa2Cu307‐x were grown on MgO (100) and YSZ(IOO) substrates without post‐annealing by metal organic chemical vapor deposition using vertical, high‐speed (1100 rpm) rotating disk reactor. The source materials were Y(tmhd)3, Ba(tmhd)2, and Cu(tmhd)2, which were kept at 135 °C, 240 °C, and 120 °C respectively. The precursors were transported using nitrogen as the carrier gas and introduced separately into the cylindrical stainless steel reaction chamber, which was maintained at 60 torr. The oxygen partial pressure was 30 Torr. The substrates were heated resistively at 800°C. After growth, the films were cooled down at a rate of 5 °C/min under 1 atmospheric pressure of pure oxygen. The X‐ray diffraction pattern of the films showed primarily an orientation of c‐axis perpendicular to the substrates, with weak peaks of (hoo) corresponding to a‐axis orientation. Scanning Electron Microscopy of the films showed a well‐developed a‐axis and c‐axis plate‐like structure which appeared as rectangular micron‐sized features on the MgO surface. On the YSZ substrates a‐axis and c‐axis plate‐like projections were also observed, with the dense plate‐like c‐axis orientation dominant. Four probe resistance measurements showed Tc(R=0) at 91.8 K(△TC=2.2 K) and 85 K (△TC=7 K) on YSZ and MgO substrates respectively.
Rapid Chemical Vapor Deposition of Yba2cu3ox Coatings
Authors: Lackey W.J. , Carter W.B. , Hill D.N. , Barefield E.K. , Hanigofsky J.A. , Shapiro M.J. , Moss III T.S. , Green A.J. , O'Brien D.F. , Jake R.A. , Efferson K.R.
Published: March 2011

A rapid, controllable process for CVD of superconducting Yba2Cu30x has been developed. The new process relies on slowly feeding and pneumatically transporting powdered solid reagents directly into the CVD furnace; vaporizers are not used. Deposition rates two orders of magnitude greater than those achievable by reagent sublimation have been obtained using a powder feed mixture of Y, Ba, and Cu tmhd complexes (tmhd is tetramethylheptanedionate). Potentially, the process is applicable to thermally unstable, less volatile, lower cost reagents such as the acetylacetonates.
Lou Temperature Growth of Superconducting Ybaacu,07‐X Thin Films by Metalorganic Chemical Vapor Deposition
Authors: Kanehori Keiichi , Sugii Nobuyuki , Miyauchi Katsuki
Published: March 2011

Thin YBa2Cu307‐xfilms were grown by thermal and plasma enhanced MOCVD, and the effects of growth teiperature on the film properties were studied. The crystal Iinity of the fills deteriorated with growth teiperature, so superconductity decreased with growth teiperature. Thin fills grown by therial MOCVD at 600°C, 650°C, 700°C and 750°C had zero‐resistivity at 10K, 71K, 83K and 84K, respectively. The growth teiperature for superconducting fids is decreased by plasia enhancement. Thin films grown by plasma enhanced MOCVD at 515°C and 580 °C had zero‐resistivity at 60K and 85K. The critical current density of fills grown by plasia enhanced MOCVD at 580°C was 105A/cm2 at 77K.
Low Temperature Preparation of y‐bA‐cU‐0 Films by Omcvd
Authors: Tsuruoka Taiji , Kawasaki Ryodo , Abe Hitoshi , Shibata Susumu
Published: March 2011

By using N2O for oxygen source, Y‐Ba‐Cu‐O films prepared at 650” C on the SrTiO3 substrates showed zero resistance at 79K. The deposition rate of Y‐Ba‐Cu‐0 films on MgO(l00) substrates by using N2O gas was nearly half of that using 02 gas. X‐ray diffraction patterns of Y‐Ba‐Cu‐0 films grown on SrTiO3(100) and MgO(l00) substrates indicate c‐axis orientation.
Athermochemical Investigation of the La-Sr-Cu-O System
Authors: Bularzik Joseph , Navrotsky Alexandra , Scott Bruce , Bringley Joe , Trail Steve
Published: March 2011

The perovskite related La2‐xMxCuO4‐y oxides substituted with alkaline earth metals were one of the first classes of high temperature superconductors discovered. Determining the thermodynamic properties is important to understand the stability and superconducting mechanism of these structures. High temperature solution calorimetry, using a molten lead borate solvent, has been performed on La2CuO4 and the related Sr substituted oxides. Calorimetric measurements on CuO, La2O3 and SrCO3 yield heats of formation. A change in the trend of the heats of formation appears at Sr content 0.1, the reported orthorhombic to tetragonal transition, the onset of superconductivity and loss of oxygen.
Tem Study of Cvd‐Grown Bi‐Sr‐Ca‐Cu‐0 Thin Films on (001) Mgo Substrates
Authors: Ueda O. , Kimura T. , Yamawaki H. , Ihara M. , Ozeki M.
Published: March 2011

CVD‐grown Bi‐Sr‐Ca‐Cu‐0 thin films on (OOl)MgO with T at 110 K have been investigated by transmission electron microscopy. The films are found to consist of large domains oriented along the c‐axis, with diameters of 15‐100 um. These domains exhibit incommensurate superstructures along the fa‐axis. In addition, we have observed similar superstructure spots in two equivalent directions normal to each other. It has also been found that the interface between the thin film and the substrate is very abrupt. Five different perovskite‐related layers along the c‐axis with different thickness are present. In the thin film, 80K phases are dominant and 110 K phases are less likely. Three other phases are very rarely observed. Furthermore, boundaries where the layered structure is different on both sides are often found.
A New Hybrid Pvd/Omcvd Route to High‐Tc Superconducting Thin Films of Tl‐Ba‐Ca‐Cu‐O
Authors: Richeson D. S. , Tonge L. M. , Wang X. K. , Marcy H. O. , Marks T. J. , Ketterson J. B. , Chang R. P. H. , Kannewurf C. R.
Published: March 2011

Superconducting thin films of Tl‐Ba‐Ca‐Cu‐0 have been prepared by a unique hybrid technique that combines electron beam evaporation with organometallic chemical vapor deposition (OMCVD). Multilayer thin films of Ba‐Ca‐Cu‐O are prepared by sequential electron beam evaporation of BaF2, CaF2, and Cu sources onto single crystal MgO (100) or yttria‐stabilized zirconia (YSZ) substrates followed by annealing in a water vapor‐saturated oxygen atmosphere. Thallium is then incorporated into these films in either of two ways: (1) via OMCVD using thallium(cyclopentadienide) as the source, or (2) rapid annealing of the Ba‐Ca‐Cu‐O film in the presence of bulk thallium superconductor. The resultant films primarily consist of single phase TlBa2Ca2Cu3Ox with the Cu‐O planes preferentially oriented parallel to the substrate surface. Resistivity measurements indicate superconducting onset temperatures above 120 K with zero resistance by 104 K. By eliminating the water vapor anneal, residual fluoride, originating from the sources, may be left in the film. This leads to formation of predominantly c‐axis oriented crystallites of the TlBa2CaCu2Ox phase.
Routes to High‐Tc Superconducting Tl‐Ba‐Ca‐Cu‐O Films Using Organometallic Chemical Vapor Deposition
Authors: Richesonw Darrin S. , Tonge Lauren M. , Zhao Jing , Zhang Jiming , Marcy Henry O. , Marks Tobin J. , Wessels Bruce W. , Kannewurfcc'd Carl R.
Published: March 2011

Films of the Tl‐Ba‐Ca‐Cu‐O high‐Tc superconductor can be prepared by several organometallic chemical vapor deposition routes. Two of these involve Ba‐Ca‐Cu‐0 films that are first prepared using the volatile metal‐organic precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2‐ Deposition is carried out at a pressure of 5 Torr with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated into these films either by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source, or by vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O as the source. Thallium deposition is carried out at atmospheric pressure with an argon carrier and water‐saturated oxygen reactant gas, followed by rapid thermal annealing. Both procedures yield films that consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the Cu‐O planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼125 K with zero resistance by 100 K.
Effect of Glow Discharge Current on Composition of Y‐Ba‐Cu‐0 Films by High Pressure Dc Sputtering Process
Authors: Lin R.J. , Chen Y.C. , Wu P.T.
Published: March 2011

The Y‐Ba‐Cu‐0 (YBCO) films were grown on (100)Mg0 substrate by the high pressure DC diode sputtering process. The targets were YBCO compounds made by solid‐state reaction. The sputtering gas was Ar‐50%02, and total pressure was 1.5 torr. As‐deposited superconducting YBCO films can be prepared at low substrate temperature at high discharge current. For Y1Ba2Cu30x target, the atomic ratio Ba/Y in the films almost remains constant (Ba/Y = 1.7) and Cu content monotonically increases with increasing discharge current. The Cu content in the film approaches to that of the target at low discharge current. Concentrations of 0 and 02+ in plasma markedly increase during increase of discharge current. High Cu content at large discharge current may be caused by action of electrical field on Ba+ and Y+.
The Transport Properties and Defect Chemistry of La2-XSrXCuO4-δ
Authors: Tsai Ming-Jinn , Opila Elizabeth J. , Tuller Harry L.
Published: March 2011

La2‐xSrxCuO4‐δ has been studied to determine the role of dopants and oxygen stoichiometry on the transport properties and defect chemistry of this system. The conductivity was found to reach a maximum for 0.2 < x < 0.3 which reflects a change from electronic to ionic compensation of the Sr dopant at large values of x. A metal to semiconductor transition is observed for x > 0.6 for temperatures below ∼ 600°C. However, the source of this behavior is not clear, given that an increasing amount of second phase was observed for x > 0.4. The conductivity and thermoelectric power (TEP) of La2CuO4 show a Po2⅙ dependence and a temperature independence, implying that the hole mobility is not thermally activated and the enthalpy of oxidation is nearly zero. This last conclusion is confirmed by TGA data.
As‐Grown Superconductivity of Bi‐System Thin Films Prepared by Magnetron Sputtering with Three Pb Doped Targets: (Bi 1.6 Pb0.4) 1 + a (SrCa)2 Cu3 O x, (Bi 1.6 Pb0.4) 1 (SrCa)2+c Cu3 Ox and (Bi 1.6 Pb0.4) 1 (SrCa)2Cu3+cOx (a = 0.5, b= 1,c= 1.5)
Authors: Kuroda Ken'ichi , Tanioku Masami , Kojima Kazuyoshi , Hamanaka Koichi
Published: March 2011

Superconducting Bi system thin films have been formed on MgO(100) substrates by RF magnetron sputtering from three Pb‐doped targets: Bi2.4 Pb0.6 Sr2 Ca2 CU3 O x ,Bi 1.6 Pb0.4 Sr3 Ca3 CU3 O x and Bi 1.6 Pb 0.4 Sr2 Ca2 CU4.5 O x. The as‐grown films formed at substrate temperatures above 600 °C showed superconductivity, though, they did not contain Pb.
The film, formed at 660°C and kept at the same substrate temperature and gas pressure as the sputtering conditions for 5 h after deposition, showed a resistivity drop at 115 K and zero resistivity at 83 K. The Jc value of the film was 4x105 A/cm2 at 77 K and 3x107 A/cm 2 at 20 K.
Metal‐Organic Decomposition and Microstructure Development in Ba2ycu3o7‐X Films from Metal Trifluoroacetate Precursors
Authors: Mcintyre Paul C. , Chiu Raymond C. , Cima Michael J. , Rhine Wendell E.
Published: March 2011

Decomposition of metal‐organic precursors to Ba2Ycu3O7‐X films is difficult because of the high reaction temperature required to decompose the BaCO3 intermediate. The recently proposed use of metal trifluoroacetate (TFA) solutions offers an alternative path to barium‐containing superconducting films. The TFA salts decompose to the metal fluorides forming BaF2, eliminating BaCO3 from the system. Ultimate conversion to BYC, however, is shown not only to depend on hydrolysis of the BaF2 at high temperatures, but also hydrolysis of copper trifluoracetate at low temperatures to prevent the volatilization of Cu(TFA)2. These processes result in unique microstructural behavior which can be characterized by electon microscopy and Auger spectroscopy. Effects due to substrate interactions have been eliminated by use of a chemically inert substrate material, BaZrO3.
Electrophoretic Deposition of High-Temperature Superconductor Thick Films
Authors: Mooney J. B. , Sher A. , Riggs M.L. , Sabo K.A. , Rosengreen A. , Kingsley B. , Terry J.C.
Published: March 2011

Thick films of high-temperature superconductors have been deposited electrophoretically using techniques developed for office copier toning. The resultant films are dense because of the high charge density per particle and the high fields during deposition. Orientation by electrostatic and magnetic fields has been demonstrated.
High Resolution Transmission Electron Microscopy Study of Defect Structures in Mixed-Phase YBaCuO
Authors: Fendorf M. , Kvam E. , Gronsky R.
Published: March 2011

Mixed-phase superconducting YBaCuO is characterized by means of high-resolution transmission electron microscopy. This technique reveals that such material contains numerous crystallographic defects of various types. Several of these are described in detail, and their origins discussed.
Domain Structures and Pinning in Oxide Superconductors
Authors: Roytburd Alexander L.
Published: March 2011

The domain structure of oxide superconductors arises as a result of twinning associated with the tetragonal-orthorhombic transition inside a restricted volume (a grain in a polycrystal, an epitaxial layer, or a part of an initial single crystal). A thermodynamic theory of the size and arrangement of the domains has been developed. There are two types of interfaces in equilibrium domain structures: coherent twin boundaries and boundaries between polytwin layers with microstresses. Elastic vortex-interface interactions have been estimated.
Oriented Microstructure of Ybco Thick Films
Authors: Wellhofer F. , Shields T.C. , Abell J.S. , Taylor K.N.R.
Published: March 2011

The surface morphology and internal structure of a superconducting screen printed thick film of YBCO has been examined by means of optical and scanning electron microscopy. The highly textured track was sintered at a temperature above the peritectic temperature of the 123 phase, and the resulting characteristic spherulitic morphology has been found to be associated with underlying elongated strands of CuO. The composition of the inter‐diffusion layer formed at the film/substrate boundary is consistent with a Ba(Zr,Cu)O3 solid solution with small concentrations of yttrium.
Effect of High Temperature Deformation on Grain Boundary Defects in Yba2Cu3O7-X
Authors: Garcia R. , Misiolek W.Z. , Wright R.N. , Rajan K.
Published: March 2011

The results of transmission electron microscopy studies on YBa2Cu3O7‐x subjected to high temperature extrusion are presented. Particular emphasis is put on high temperature accommodation processes of lattice dislocations into sub‐grain boundaries. It is suggested from the electron microscopy observations that stress induced climb mechanisms for dislocations are operative. Also presented is evidence of localized lattice distortions near twin boundaries due to isothermal high temperature deformation. Preliminary results on the structure of grain boundary facets and steps is described. The implications of these results for texture development in bulk ceramic superconductors is also discussed.
Vortex Structure: Lattice, Glass, or Liquid?
Authors: Soulen Robert J. , Wolf Stuart A.
Published: March 2011

Recent measurements of the dissipation in cuprate superconductors in a magnetic field have been interpreted as providing evidence for the presence of new phases in type II superconductors: flux liquids or flux glasses. We suggest that a more conventional interpretation in terms of the electrodynamics of vortices can adequately account for all the observations. Based on this model, we propose a magnetic phase diagram.
High Critical Current Density in Ultrathin Ybco Films
Authors: Xi X.X. , Schauer W. , Windte V. , Meyer O. , Linker G. , Li Q. , Geerk J.
Published: March 2011

Measurements of the critical current density Jc for ultrathin YBa2Cu307‐X (YBCO) films are presented.A high Jc value at 77K in zero field of 2xl06A/cm2 was obtained in a 30nm thick film and even a 5nm thick film could carry a supercurrent of 3.5x105 A/cm2 at 4.2K in zero field. A very weak field‐dependence of Jc was observed when the field was in the (a,b) plane showing greatly depressed dissipation.
Electrical Transport Dissipation Effects in Epitaxial Y1ba2cu3o7.X Thin Films
Authors: Christen D. K. , Klabunde C. E. , Feenstra R. , Lowndes D. H. , Norton D. , Kerchner H. R. , Thompson J. R. , Sekula S. T. , Budai J. D. , Boatner L. A. , Narayan J. , Singh R.
Published: March 2011

The electrical transport properties of a series of Y1Ba2Cu307.x thin films deposited onto single crystal substrates by thermal coevaporation and laser ablation were investigated. For fully epitaxial, c‐oriented films on (001) substrate surfaces, the critical current density Jc showed large high‐field enhancements for the film aligned with H parallel to the copper‐oxygen planes. With H||c, a precipitous decay of Jc with increasing field is described by thermally activated flux motion. Films on (110) SrTiO3 substrates were comprised of finely‐divided arrays of grains having [110], and <103>‐type orientations, and exhibited granular behavior. For these “triaxial” films, the transport dissipation was also thermally activated but with much smaller energy barriers.
Thin Film Deposition and Transport in 2223 Bi‐Sr‐Ca‐Cu‐O
Authors: Kucera J.T. , Steel D.G. , Face D.W. , Graybeal J.M. , Orlando T.P. , Rudman D.A.
Published: March 2011

We have reproducibly prepared thin films of Bi‐Sr‐Ca‐Cu‐O with Tc ≥ 105K. Depositions were done at ambient temperature with a subsequent post‐deposition anneal, and did not include lead substitution. X‐ray diffraction data indicates a majority fraction of the 2223 phase. These films possess very large grains of the order of 20‐30 u.m in size. Post‐deposition annealing conditions are a sensitive function of composition. Detailed transport measurements as a function of temperature and magnetic field have been obtained.
Easily Activated Flux Creep and Anisotropic Fluctuation in Ndcecuo Thin Films
Authors: Hatta S. , Hayashi S. , Adachi H. , Wasa K.
Published: March 2011

The diamagnetic properties of NdCeCuO films with electron carriers were studied. The,critical current density ( Jc ) was calculated to be 0.73 x 106 A/cm2 . These films indicated the very strong magnetic relaxation with small activation energy, the significant resistive broadening in the critical region and the largely fluctuated diamagnetization. These results suggested the very weak pinning forces to cause the easily activated flux motion in these specimens.
Correlations Between the Cu‐O Bonding States and the Superconductivity ‐ an Xps Investigation
Authors: Han S.C. , Liu D.Z. , Xie X.M. , Wu Z.L. , Huth G.C.
Published: March 2011

Auger electron spectroscopy (AES) and core‐level x‐ray photoelectron spectroscopy (XPS) have been used to study the compositional and electronic‐state variations from the contaminated surface layer to the inner region of YBa2Cu3Ox and Bi2(Sr,Ca)n+1Cun02n+4 compounds. The results showed that the carbon‐rich contamination layer in BSCCO is thin and easier to be removed by Ar+ sputtering, indicating a much more stable surface than that of YBCO. This layer is oxygen deficient and contains higher Cu2+ satellites ( 2p3d9 final states) than in the bulk materials. Line‐shape analysis suggests three‐Gaussian features for both Cu 2p3/2 and O Is lines. The 529 eV signal is observed in both YBCO and BSCCO O Is spectra.
Large Enhancement of JC in YBacuo Single Crystals Induced by Proton Irradiation
Authors: Civale L. , Marwick A.D. , Mcelfresh M.W. , Malozemoff A.P. , Holtzberg F.
Published: March 2011

We have used magnetization measurements to study the effect of proton irradiation on the critical current density of a YBaCuO single crystal. We have obtained a maximum value of 1.5x105 A/cm2 at 77 K and 1 T at a fluence of 2 x 1016 cm-2, representing a 50-fold increase with respect to the unirradiated sample.
Flux Pinning and Weak Link Structure in Ca2Cu1O3 Doped LnBa2Cu3O7-y (Ln=La and Y)
Authors: Mizuno F. , Masuda H. , Hirabayashi I. , Tanaka S.
Published: March 2011

Flux pinning and weak link structure were studied on the effect of Ca doping in LnBa2Cu3O7-y system (Ln=La and Y). The magnitude and the magnetic field dependence of the critical current density were improved by Ca doping. A small amount of impurity phase of such as Ca2Cu1O3 may work as a desirable flux pinning center. Moreover, it was found that the current-temperature characteristics for Ca-doped samples showed the evidence of two kinds of superconducting phases which have different transition temperature Tc and Tc'. The experimental result agrees well with the Ambegaokar-Baratoff theory for asymmetric Josephson junctions (S-I-S') in the temperature range of T < Tc' and with the proximity junction theory (S-N-S) in the range of Tc'<T<Tc.
Electron Tunneling into Single Crystals of YBa2Cu3O7-δ
Authors: Valles J. M. , Gurvitch M. , Cucolo M. , Dynes R. C. , Garno J. P. , Schneemeyer L. F. , Wasczcak J. V.
Published: March 2011

We have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu3O7-δ and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3O7-δ, Tc, the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below Tc, additional structure associated with the superconductivity appears in G(V). At T>>Tc there is a reproducible finite zero bias conductance.
Proximity-Effect and Tunneling in YBa2Cu3O7/Metal Layered Structures
Authors: Greene L. H. , Feldmann W. L. , Barrier J. B. , Farrow L. A. , Miceli P. F. , Ramesh R. , Wilkens B. J. , Bagley B. G. , Giroud M. , Rowell J.M.
Published: March 2011

Superconducting thin films of YBa2Cu3O7 are prepared in-situ by on-axis, sputter deposition from a single, composite target. Our planar magnetron target composition of Y:Ba:Cu = 1.08:1.76:4.5 sputtered onto MgO at T~750°C in a 600mTorr Ar-O2 atmosphere yields reproducible superconducting films having Tc(R = 0)>80K and stoichiometry 1:2:3, that are shiny and of near epitaxial, crystalline quality. In order to ensure clean interfaces, YBa2Cu3O7/normal metal bilayers (to form SNS' Josephson junctions) and YBa2Cu3O7/normal metal/insulating barrier trilayers (to form SNIS' proximity tunnel junctions) are grown completely in-situ. (The S' = Pb counter electrode is evaporated ex-situ.) A supercurrent and Shapiro steps are observed in microwave irradiated SNS' (N = Ag) small area (5x10-5cm2) junctions. In SNIS' tunnel junctions, high-quality Pb tunneling is observed.
Selective Mn Doping of Thin Film Zns:Mn Electroluminescent Devices by Laser Photochemical Vapor Deposition
Authors: Kitai A. , Wolga G.J.
Published: March 2011

U.V. laser radiation from a krypton ion laser was used to dissociate manganese carbonyl [Mn2 (CO)10*] at the surface of a ZnS thin film. The resulting Mn deposit was thermally diffused into the film to form a ZnS:Mn thin film electroluminescent (TFEL) device with spatially selective Mn doping. Process parameters and techniques are described as well as electroluminescence measurements on display elements. Finally we suggest applications of this process to future TFEL displays.
Laser Spectroscopic Investigation of Gas-Phase Processes Relevant to Semiconductor Device Fabrication
Authors: Karlicek R. F. , Donnelly V. M. , Johnston W. D.
Published: March 2011

Chemical vapor deposition (CVD) and plasma etching are important gas-phase techniques used in fabricating semiconductor devices. These processes frequently involve poorly understood multicomponent gas-phase reactions which control reproducibility and product quality. Laser spectroscopic techniques have recently been developed to investigate CVD and plasma etching. These methods offer several advantages for probing complex systems. A comparison of various probing techniques will be presented, and recent results of laser spectroscopic investigations of plasma etching and CVD of silicon and III-V compounds will be reviewed.