bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetically-Related Properties of Bismuth-Based High Tc Superconductors
Authors: Vezzoli G.C. , Chen M.F. , Craver F. , Burke T. , Moon B.M. , Safari A. , Lalevic B. , Stanley W.
Published: March 2011

The effect of magnetic fields to 15T on the electrical resistance (R) of Bi-Sr-Ca-Cu-O superconductors has been measured at precise temperatures during the transition to the superconducting state. The results show that the temperature at which the externally-applied magnetic field causes a divergence of resistance (R) as a function of inverse temperature is approximately at the same temperature where the positive Hall coefficient begins its steep descent to zero. At slightly higher temperature the Hall coefficient shows a singularity peak akin to a delta function. Internal electric field calculations show that the structure of the superconducting oxides, having more than a single building block polyhedron, gives rise to strong electrostatic fields in the unit cell which in turn causes charge separation or polarization. The charge separation is in accord with the importance of high oxidation states of the multivalence cations and suggests the use of high oxygen overpressure during processing. The magnitude of Tc scales closely with the number of bound holes (associated with the charge transfer excitations) per unit cell. Extensive computer calculations using this model indicate attractive pairing of electrons at inter-electron separations of about 10–15A.
Structural and Physical Properties in the Bi‐Sr‐Cu‐O System
Authors: Sunshine S. A. , Schneemeyer L. F. , Fleming R. M. , Fiory A. T. , Martin S. , Glarum S. H.
Published: March 2011

The structure/property relationships in the Bi‐Sr‐Cu‐O system near Bi2Sr2CuOx have been investigated. The properties and phase limits of the solid solution Bi2+xSr2_yCuO6±δ have been determined and a structural model for Bi2Sr2CuO6 is proposed.
Superconductivity of Bi1.6Pb0.4Sr2Ca2(Cu1-xAgx30y and Bi1.6Pb0.4Sr2Ca2Cu30y + wt% Ag
Authors: Vei Chongde , Lin Chin , Peng Qingrong , Liu Zunxiao , Lan JIAN , Sun YUNXI , Li Guozhong , Vu Ke , Xue Lixin , Gan Zizhao
Published: March 2011

Both interstitially Ag-doped Bi1.6Pb0.4Sr2Ca2Cu30y + x(wt%) Ag with x = 0.5, 1.0, 5.0, 10.0, 15.0, and substitutionally doped Bi1.6Pb0.4Sr2Ca2(Cu1-xAgx)0y with x = 0.025, 0.05, 0.10, 0.20, 0.40 systems were studied. Magnetic susceptibility Measurements indicate that both the interstitial and substitutional Ag-doping yield auch higher diaiagnetic signal for ZFC in a field of 60 0e at 5 K. At 80 K, -4πH/H was also enhanced by Ag-doping for H<200 Oe. Substitutionally Ag-doping also enhances the Magnetic critical current for x ≤ 0.2. Possible explanation was discussed.
Partial Superconductivity in YBa2Cu3O7 at 90 K < T < 300 K
Authors: Munger R. , Smith H.J.T.
Published: March 2011

Partial superconductivity has been observed in bulk polycrystalline samples of YBa2Cu3O7 at temperatures as high as room temperature. The technique used was to measure the current-voltage characteristics of bulk samples in the presence of microwaves and magnetic fields. The measurements have been repeated on three samples that had been prepared separately.
Investigation of Possible Superconductivity in Titanium Borides
Authors: Ahern Brian S. , Bachowski Stephen , Horrigan Jane
Published: March 2011

Interest in the titanium boride system stems from a patent disclosure by Vahldiek in 1982. In that disclosure TiBx(x=1.6) crystals were subjected to pressures of 300,000 psi and found to have vanishingly low resistivities at room temperature. In this study we processed TiBx crystals by a variety of techniques and pressurized the samples up to 350,000 psi. No high temperature superconductivity was observed.
The Electrochemical Response of YBa2Cu3O7-x in Aqueous Solutions
Authors: Chin T.S. , Shih H.C. , Lin C.A. , Huang T.W. , Tsai W.T. , Hung M.P.
Published: March 2011

Electrochemical behavior of a YBa2Cu3O7 (YBCO for short) superconductor was studied by potentiodynamic scanning in different aqueous solutions with 0.1 M concentration. The electrochemical stability of the YBC0 compound was found to be superior in sulfurous acid, NaC1, or KC1 solutions. The dissolution potential in the above solutions ranges from 36 – 92 mV, polarization wasn't possible. However, E raised up to 360 – 960 mV in acids corr solutions with oxidizing potential including suluric, phosphoric and nitric acids indicating a passive behavior. Polarization was observed in sulfuric, sulfurous, and phosphoric acids depicting their potential to be used as etching solutions in lithography of this oxide superconductor. Its electrochemical behavior in HC1 solution is peculiar and informative. It shows three transitions in the polarization curve, corresponding to 272, 756, and 1013 mV, respectively. This is probably related to the transition in the valence states of copper ions during dissolution which is suppressed in the oxidizing acids. In comparison with metallic copper, the YBCO is more stable in the above solutions. The Galvanic current decreases at the order of A1 > Cu > Ag, when the YBC0 is coupled with each of them in 1 M phosphoric acid solution.
High-Tc Superconductor Multilevel Structures formed with Ta205 Spacer Layers
Authors: Bhattacharya Rabi S. , Kosel P.B. , Peterson T.
Published: March 2011

An important class of electronic devices could be realized with current state-of-the-art high-Tc superconductor (HTSC) thin films if a method were found for the formation of multilevel structures separated by thin dielectric layers. It has been found that such structures can be formed with tantalum oxide as the spacer layer because of its high melting point (1870°C) and good chemical stability at the high temperatures commonly used to anneal thin films of YBaCuO superconductor. Good results have been achieved with thin films prepared by electron beam (EB) sequential deposition from Y, BaF2 and Cu targets onto oriented (100) strontium titanate substrates and oxygen furnace annealing at 850°C to promote the epitaxial alignment and growth of the superconducting crystalline phase. Two-layer structures have been formed by interposing a tantalum oxide barrier deposited by EB evaporation between two successive layers of HTSC films. The transition temperatures of both layers were checked by resistance measurements and found to display superconductivity after annealing. However, the top (second) layer was found to always show a reduced abruptness of the transition characteristic thereby indicating, perhaps, a lesser degree of epitaxial alignment since it makes no direct contact with the substrate surface.
Oxide Films for the Protection of Cuprate Superconductors
Authors: Baney Ronald H. , Bergstrom Debora F. , Carpenter Leslie E. , Petersen Donald R. , Elwell Dennis F. , Shapiro Andrew A. , Fleishner Paul S.
Published: March 2011

The cuprate superconductors rapidly degrade in moisture and in the presence of organic compounds. A protection method has been developed with a coating process using sol/gel routes to the low temperature formation of oxide films. In contrast to traditional protective films, amorphous silica films formed from a solution precursors gave excellent protection and caused little degradation of the superconductors.

The protective abilities of the films were assessed by monitoring the degradation of Y1Ba2Cu307-d in the presence of 85% relative humidity at 85 C. Volume magnetic susceptibility, four-point probe resistivity, current density measurements and x-ray diffraction were performed. Without protection, degradation was almost complete within 30 minutes of exposure. With protection, superconducting properties were maintained even after 48 hours of exposure.
Investigation of Potential Diffusion Barriers Between YBa2Cu3O7-x and Silicon
Authors: Lubig A. , Buchal Ch. , Zander W. , Stritzker B.
Published: March 2011

Thin films of ZrO2, BaF2, and noble metals on TiN have been examined by RBS as potential diffusion barriers between Si(100) substrates and high-temperature superconductors. As best result so far, a buffer layer of 260 nm ZrO2 enabled the growth of a 230 nm film of YBa2Cu3O7-x, which had been deposited by laser ablation. The relatively low zero resistance temperature of about 60 K may result from some interdiffusion between YBaCuO components and the ZrO2 layer or from holes in the film. A 520 nm BaF2 layer was able to prevent Si outdiffusion towards the surface, when exposed to an oxidizing ambient at typical YBa2Cu3O7-x deposition temperatures between 750 and 800°C. A strong reaction between YBaCuO components and BaF2, however, resulted in non-superconducting films. At high temperatures in oxidizing ambient the noble metal/TiN/Si samples suffered severely from oxidation and surface roughening.
On the Stability of YBa2Cu3O7-y with Refractory Ceramics
Authors: Del Angel P. , Dominguez J. M. , Falcony C. , Guzman O. , Montoya A. , Vicente L.
Published: March 2011

A series of ceramic oxides were prepared by adding alumina to the superconductor YBaCuO. The solids were characterized by X-ray diffraction, transmission (TEM) and scanning electron microscopy (SEM) with EDS and electrical measurements. Partial drops in electrical resistance (R ≠ 0) indicate the presence of superconducting phases trapped in ceramic masses. Additionally, the systematic diminution of Tc could indicate a partial substitution of Cu by Al.
Cation Interdiffusion at YBCO/MgO Interfaces
Authors: Lanham M. , Mayer J. , Golden S.J. , Lange F.F. , Rühle M.
Published: March 2011

Resistivity measurements of YBCO thin films on MgO substrates show that the transition to the superconducting state depends on film thickness. TEM investigations of the films revealed interdiffusion of Cu and Mg. The concentrations of the cations at the interface were quantitatively measured. These data show that their diffusion rates are much different (MgODCu/YBCODMg=30); this indicates that the diffusion mechanism is complicated by the layered structure of the perovskite-like films. No impurity segregation was detected at the interface. Diffraction study of several YBCO grains confirms that the film c-axis is oriented perpendicular to the substrate, but that the a/b plane has no fixed orientation, indicating that no epitaxial relationship exists.
Evaluating the Chemical Compatibility of Potential Substrate Materials for Bi-Sr-Ca-Cu-O Films
Authors: Williams K.E. , Matthiesen M.M. , Rudman D.A.
Published: March 2011

Potential substrate and buffer layer materials for Bi2Sr2CaCu2Ox (BSCCO) were surveyed using bulk ceramic processing techniques. Of the materials tested, only Ag was inert with respect to BSCCO. MgO slightly degrades the superconducting onset temperature and volume fraction. LaGa03 may be a feasible ceramic substrate for BSCCO, although some reaction appears to occur.
Formation of Sputtered Y-Ba-Cu-O Superconducting Thin Film on Metal Substrate
Authors: Hayakawa H. , IIJIMA Y. , Sadakata N. , Kohno O.
Published: March 2011

Y1Ba2Cu3O7-x superconducting composites have been prepared on metallic substrate by rf magnetron sputtering method. Buffer layer of thin SrTiO3 layer between superconducting film and the substrate was found to be effective to realize superconductivity. Preferable grain alignment of c-axis was also obtained. The critical current density at 77K was 2.2x103 A/cm2 with Tc at 83K, and it was found that the thicker films had the higher Jc values.
Fabrication of YBa2Cu3O7-x Filaments by Extrusion of a Cu3O3Ba2Y(meoEt)7 (meoEt = 2-Methoxyethoxide) Precursor
Authors: Rupich M. W. , Cogan S. F. , Lagos B. , Hachey J. P.
Published: March 2011

YBa2Cu3O7-x filaments, with a zero resistance Tc of 89.5 K and a Jc of 225 A/cm2 in zero field at 77 K, were prepared from precursor filaments fabricated by extrusion of a polymeric Cu-Ba-Y precursor. The precursor was prepared by reaction of linear a (CuO)n polymer with Y and Ba alkoxides in non-aqueous solvents. Characterization of the precursor and superconducting filaments, along with the optimum extrusion and pyrolysis conditions, are described.
Processing and Performance of Metal Fiber Reinforced High Temperature Superconductor
Authors: Salib S. , Vipulanandan C. , Stone T.
Published: March 2011

Aggregation of YBa2Cu3O7‐x powder by compaction molding and sintering results in porous ceramic with poor mechanical properties and hence improving the ceramic properties using continuous stainless steel fibers have been studied. Fiber reinforced beam specimens (2% of fibers by weight) were prepared by modifying the standard processing method. Fibers were pretreated with silver to reduce the contamination of the superconducting matrix. The mechanical and electrical properties of the superconducting ceramic‐fiber composite was evaluated at 77K. Continuous stainless steel fibers improved the performance of the superconducting ceramic.
X-Ray Characterization of the Crystallization Process of High-TC Superconducting Oxides in the Sr-Bi-Pb-Ca-Cu-O System
Authors: Wong-Ng Winnie , Chiang Chwan K. , Freiman Stephen W. , Cook Lawrence P. , Hwang Nong M. , Hill Michael D.
Published: March 2011

Phase assemblages in two Sr-Bi-Pb-Ca-Cu-O glasses and their crystallization into glass-ceramics through a sequence of heat treatments are described. Samples were heat treated at various temperatures based on differential thermal analysis (DTA) analysis of the as-quenched glasses. X-ray powder diffraction was used to identify the compounds in each sample; and the different phases formed in these two samples were compared. Results of microstructural characterization of selected samples using scanning electron microscopy are discussed.
Thermal Annealing Study of High-TC Ybacuo and Bisrcacuo Superconducting Wires
Authors: Yao Y. D. , Chen J. W. , Chen Y. Y. , Pern W. S. , Yong H. A. , Lin I. N. , Yao P. C. , Yang S. J. , Hsu S. E.
Published: March 2011

High‐T YBaCuO and BiSrCaCuO Superconducting wires have been fabricated by powder metallurgy technique. Copper and silver tubes were used as the external jackets. Thermal annealing treatments for all the wire‐type samples were performed between 773 K and 1223 K. Both electrical and magnetization studies show that the superconducting properties can be improved after properly thermal annealing these samples with silver jacket. Our experimental results show that proper thermal annealing treatment can enhance the intragrain critical current density more than 100 times; however, the intergrain critical current density improves only a few times.
The Interface Between High Tc Superconductors and Silver Contacts
Authors: Mcconnell Malcolm D. , Morris William G.
Published: March 2011

Silver diffuses into the lattice of YBa2Cu307 during the annealing of silver contacts at 500°C. Depth profiles using Auger electron spectroscopy, with a focused electron beam, show an extensive diffusion zone, as well as segregation of barium and oxygen to the surface of the contact. There appears to be a slight loss of silver from the surface region, which could be explained by enhanced concentration at grain boundaries. High resolution SEM analysis of a fracture surface did not reveal the presence of silver on the grain boundaries. Diffusion rates were correlated with grain orientation by using magnetically aligned samples, and were found to be greater for the direction parallel to the C axis.
Role of Silver in Yba2Cu3AgXO7-δ Composite Superconductors
Authors: Ganapathi L. , Kumar Ashok , Narayan J.
Published: March 2011

Superconducting properties and microstructures of the YBa2Cu3AgxO7‐δ composites have been studied as a function of silver content, 0 ≤ x ≤ 6, using a variety of techniques.The superconducting transition temperature,Tc, of these composites was found to be the same, ∼ 90 K, for the above range of compositions. The composites with x > 3 are found to have resistivity behavior identical to silver metal above the superconducting transition temperature. The peritectic transformation temperature of the 123 material in the composite is lowered. Alloy formation between Ag and Cu is proposed to take place triggering the peritectic transformation at lower temperatures. The silver is observed in the form of precipitates at very low concentrations of silver, indicating that silver does not substitute for copper in YBa2Cu3AgxO7. Lattice parameters of the composites were found to be invariant throughout the above composition range. The addition of Ag2O in the starting composition seems to stabilize the stoichiometric YBa2Cu3AgxO7 by way of decomposition to Ag and O, also, the better diffusion of oxygen through silver in comparison with that through the superconductor helps the regeneration of superconductivity in the composite superconductor. As a result, the incorporation of oxygen and recovery of superconducting properties is enhanced in the silver composites.For values of x > 3 small quantities of 211 phase were detected along the grain boundaries, which makes the residual composition poor in copper resulting in the formation of non‐superconducting 211 phase.
The Effect of the Distribution of Ag in High TC Bi- Compound Superconductors
Authors: Nash Alexis S. , Goretta K. C. , Nash Philip , Poeppel R. B. , Shi Donglu
Published: March 2011

A series of 4336 Bi‐Sr‐Ca‐Cu oxide samples doped with 1 to 5% metallic Ag was prepared by solid state reaction. The distribution of Ag, the microstructure and the crystal structure of the samples were studied using energy dispersive spectrometry, EDS, scanning electron microscopy, SEM, and x‐ray diffractometry, XRD. Addition of Ag leads to a marked increase in preferred orientation with (001) planes perpendicular to the pressing direction in sintered pellets. The resistivity‐temperature data show an enhanced Tc in Ag‐doped samples under certain conditions. Energy dispersive spectrometry indicates that the dopant mostly segregates to the grain boundaries.
Growth of nd2‐xcexcuo4‐y Singlk Crystals by a Flux Method
Authors: PiñOl S. , Miravitlles C. , Fontcuberta J. , Paul D. Mck.
Published: March 2011

We have investigated single‐crystals growth of Nd2‐xCexCu04‐y By using a flux method. The phase diagram Nd203 ‐CuO has been determined For a number of compositions. In addition, the corresponding diagram for some Nd2O3CeO2‐CuO composition is also reported. Plate single crystals having dimensions up to 5 x 5 x 0.2 m have been prepared by the melt mixtures from 1250℃ to 800℃ at a rate of 5℃/h.

The yield of CeO2 concentration in the starting compositions and the corresponding x values in the crystals has been investigated in order to improve superconducting properties of the crystals. Superconducting single crystals have been found from flux compositions 70% CuO, (30‐z)% NdO1.5and z% of CeO2 with 2.50 < z < 4 5.
Synthesis, Transport And Microstructural Properties of Nd1.85Ce0.15CuO4‐δ
Authors: Lee Jong‐Gyu , Ramanujachary K.V. , Greenblattî M.
Published: March 2011

The n‐type superconductor, Nd1.85Ce0.15CuO4‐δ has been prepared by solid state reaction and solution precursor techniques under various conditions and characterized by means of X‐ray diffraction, magnetic susceptibility, electrical resistivity and SEM measurements. Samples prepared by solution method displayed higher normal state resistance but better superconducting volume fractions than those prepared by conventional ceramic techniques. In addition, the solution precursor technique reduces the sintering temperature from 1150°C (used for solid‐state route) to 1000°C in achieving the superconducting phase. The solution‐route yields particles with relatively uniform size distribution, but poor connectivity between the grains. In contrast, the solid state preparations yield well connected grains but with a larger distribution of sizes. The observed differences in the superconducting properties of samples prepared by different techniques have been attributed to the differences in their microstructure.
Activation Energy of Decomposition of Y2bacuo5 Compound in Wet Co2 at Elevated Temperatures
Authors: Simmins John J. , Hanagan Michael J. , Fischman Gary S. , Snyder Robert L.
Published: March 2011

Decomposition of the Y2BaCuO5 in C02 was studied using simultaneous thermal analysis (STA) and X-ray diffraction (XRD). The time derivative to the thermo-gravimetric analysis data (DTG) was used to calculate the activation energy. The activation energy of decomposition by CO2 into barium carbonate, copper oxide and yttrium oxide was found to be <
High Tc Oxide Solid State Reaction Kinetics Via Complex Impedance Spectroscopy
Authors: Cooper E. A. , Mason T. O. , Balachandran U. , Kullberg M. L.
Published: March 2011

Impedance spectra (5Hz ‐ 13MHz) were collected during the solid state reaction of Yba2Cu2O6+y from large monosized CuO particles imbedded in a finely divided Y2 O3 /BaCO3 matrix. No particle size effect was observed, but a large temperature effect was observed corresponding to an activation energy of approximately 1.8eV (175kJ/mol) over the range 700‐900°C.
Synthesis of Unidirectionally Solidified Y‐Ba‐Cu‐0 Bulk Superconductors with High Critical Current Densities
Authors: Yanagisawa E. , Kondoh S. , Shimoyama J. , Kase J. , Matsubara T. , Morimoto T.
Published: March 2011

(Y,Ho)‐Ba‐Cu‐0 superconductors with the high critical current densities (Jc) in an applied magnetic field have been synthesized by a unidirectional melt solidification method. Melt solidified bulk materials are composed of large plate‐shape (Y,Ho)Ba2Cu3Oy crystals which contain small (∼5 um) particles of (Y.Ho)2BaCuO5. The Jc value of the melt solidified (Y,Ho)‐Ba‐Cu‐0 sample is ∼10000 A/cm2 at 77K, H = IT and this value is much higher than the value of 4200 A/cm2 of the melt solidified Y‐Ba‐Cu‐O sample.
New Method for Synthesizing Bi-Sr-Ca-Cu-O Superconductor
Authors: Tanaka Masahiro , Habu Kazutaka
Published: March 2011

Ceramics of the phase Bi2Sr2Ca2Cu3O10 (2223) without Pb are synthesized by a modified conventional ceramic process. The influence of the absence of Pb is observed in the lattice constant.
Preparation of 110k Superconductor in Bi-Sr-Ca-Cu-O System
Authors: Zuyao Chen , Rong Lin , Xianhui Chen , Yitai Qian
Published: March 2011

To explore high Tc in Bi-Sr-Ca-Cu-O system, many different nominal compositions have been prepared by using the traditional solid state reactions and using the method of crystallizion from glass samples. The better results are as follows: single high-Tc phase and essentially single high-Tc phase have been obtained from Bi1.8Pb0.35Sr2Ca2Cu3O and Bi2Sr2Ca6Cu7O respectively, by solid reaction. Basically single hign-T phase material with nominal composition Bi2Sr2Ca3Cu4Oy has been produced by the method of crystallizion from glass samples. The relationship between the starting composition heat treatment, preparation methods and high Tce is briefly discussed.
Relation Between the Characteristics of Powder and Microstructure; Properties of Ceramics for YBa2Cu2Ox Superconductors
Authors: Zhao Meiyu , Li Chengen , Jin Xingyun , Huang Yeming , Zhou Enji , Ni Huanyao , Qu Yaoming , Song Xiangyun , Wu Wenjun
Published: March 2011

Four kinds of YBa2Cu2Ox (YBCO) superconducting powders with different particle sizes, shapes and different amounts of twins have been prepared in this work. The density, grain sizes, XRD of phase composition, configuration of twins of the ceramics have been investigated. The relation between the characteristics of YBCO powders and the microstructure, current density of the bulk materials are also discussed. In contrast to the YBCO powder prepared by solid state method, the YBCO powders through the improved coprecipitat ion approach have less impurities, smaller particle size and much more amounts of twins, as well as the sintered pellets show a higher density, an orthorhombic single phase, and moreover, the pellets have finer grain boundaries and well developed twins. As a result these samples exhibit current densities (about 1500 A/cm2) higher than those prepared by solid state method. Using BaOx instead of BaCO3 as the starting material, a more dense bulk YBCO ceramics with orthorhombic single phase and Jc (about 1,000 A/cm2) can have also been fabricated by solid state mat hod.
Pulsed Laser Deposition of High Tc Superconducting Thin Films: Deposition Physics and in-Situ Processing
Authors: Singh Rajiv K. , Narayan J.
Published: March 2011

The pulsed laser evaporation (PLE) technique for deposition of thin films is characterized by a number of unique properties. Based on the experimental characteristics, a theoretical model is developed which considers the formation and anisotropic three dimensional expansion of the laser generated plasma. This model explains most of the experimental features observed in PLE. We have also employed the PLE technique for in-situ fabrication of YBa2Cu3O7 superconducting thin films on different substrates in the temperature range of 500–650°C. At temperatures below 600–C, a biased interposing ring between the substrate and the target was found to significantly improve the superconducting properties. The minimum ion channeling yields were between 3-3.5 % for films deposited on (100) SrTiO3 and (100) LaA1O3 substrates. The films exhibit very high critical current densities (Jc) with maximum values exceeding 6.5 x 106 amps/cm2 for silver doped YBa2Cu3O7 films on (100) LaA1O3 substrates, and the Jc also varies anisotropically with the magnetic field.
In Situ Growth of High Quality Epitaxial Yba2cu3O7‐X Thin Films at Moderate Temperatures by Pulsed Laser Ablation
Authors: Lowndes Douglas H. , Norton David P. , Mccamy J. W. , Feenstra R. , Budai J. D. , Christen D. K. , Poker D. B.
Published: March 2011

Pulsed KrF (248 nm) laser ablation has been used for in situ growth of smooth, high‐quality YBa2Cu3O7‐x epitaxial films of variable thickness on SrTiO3, KTaO3, LaGaO3, LaA1O3, cubic ZrO2, and MgO substrates, at temperatures of ∼60O‐730°C, without higher temperature post‐annealing. A rotating target pellet, fine focusing by a single cylindrical lens, laser‐beam scanning over the target, and laser energy densities ∼2.5‐3 J/cm2 can be combined to yield films of completely uniform composition and with ∼25% thickness variation over areas ∼8 cm2. The best films have Tc > 92 K and JC(H = 0, T = 77 K) > 2 MA/cm2. Film‐growth procedures are described, together with results of superconducting and normal‐state transport measurements.
The Influence of Target-Substrate Bias on Pulsed Laser Deposited Yba2Cu307-6
Authors: Chrisey D.B. , Horwitz J.S. , Grabowski K.S. , Reeves M.E. , Osofsky M.S. , Gossett C.R.
Published: March 2011

We have deposited YBa2Cu307.$ thin films onto <100> SrTi03 substrates at 700°C as a function of target‐substrate bias (0 to 300 V) in order to make use of the positive ions in the laser produced plume to assist in the deposition. The films were extensively characterized to determine differences in film properties (composition, structure, and transport). The results suggest that film properties were optimized at or near a target‐substrate bias of 100 V, although, the differences in film properties were within the margin of reproducibility.
Pulsed Laser Deposition of High TC Superconducting Thin Films
Authors: Russek S.E. , Moeckly B.H. , Buhrman R.A. , McWhirter J.T. , Sievers A.J. , Norton M.G. , Tietz L.A. , Carter B.
Published: March 2011

In this paper we present results of studies of the effect of process variations and substrate surface conditions on the microstructure and electrical properties of laser deposited YBa2Cu3O7‐δ thin films. The principle conclusions are as follows. The film properties of YBa2Cu3O7‐δ are relatively constant over a large range of substrate temperatures (620C‐720C) and oxygen pressures (150‐800 mT). There are small compositional variations with substrate temperature similar to, but much smaller than, those seen in reactively sputtered films. The best films were grown at 670C in 400mT of oxygen and have a zero resistance Tc of 89K and Jc > 1x106A/cm2 at 77K. There are, however, variations in the Tc, Jc, and orientation of films grown on MgO under similar deposition conditions. These variations reflect differences in the nucleation and growth process of YBa2Cu3O7‐δ on MgO which can arise from subtle changes in substrate surface properties. In particular, while the films are predominantly oriented with c axis perpendicular and a,b axes in the plane of the substrate along the MgO[100] direction, there are variable amounts of grains whose in‐plane orientations are at large angles to the MgO [100] direction, leading to large angle grain boundaries in some films. These large angle grain boundaries are correlated with the presence of Josephson weak links in some small constrictions for films on MgO.
In-Situ Processing of Epitaxial and Textured High Tc Superconducting Hoba2Cu3O7.X Thin Films By Pulsed Laser Evaporation Technique
Authors: Lee C. B. , Prasad R. , Singh A. K. , Sharan S. , Singh R. K. , Tiwari P. , Narayan J. , Holland O. W. , Boatner L. A.
Published: March 2011

Excellent quality epitaxial and textured superconducting HoBa2Cu307.x (Ho 123) thin films have been fabricated on lattice matched (100) KTaO3 and (100) LaAlO3, and lattice mismatched (100) MgO substrates by the pulsed laser evaporation (PLE) technique. A bulk Hol23 target was evaporated using nanosecond excimer laser pulses with the evaporating material depositing on a substrate maintained in the temperature range of 550‐650°C. The temperature for zero resistance for HoBa2Cu3O7_x films deposited on various substrates at 650°C varied between 85 to 89K. The epitaxial films deposited on (100) LaA103 substrates exhibited critical current densities greater than 3.5 x 106 Amps/cm2 at 77 K. The superconducting properties of the Ho 123 films were found to be similar to Y123 films.
Study of In‐Situ Laser‐Deposition of Superconducting Thin Films by In‐Situ Resistance Measurement
Authors: Ying Q.Y. , Kim H.S. , Shaw D.T. , Kwok H.S.
Published: March 2011

The electric resistance was measured in real time during laser evaporation deposition of superconducting thin films. It was found that different substrates led to different behaviors in the temporal change of the resistance. The results are consistent with the processes of nucleation, interface reaction and bulk‐like growth. Structural transformation was also observed due to oxygen backfilling at the final stage of the deposition.
Arf Laser Ablation of Yba2Cu3O7‐X as Studied by Emission Spectroscopy, Sem and Edax
Authors: Hoffman Alon , Manory Rafael R.
Published: March 2011

The fluorescence emission spectra from the plasma plume induced by ArF excimer laser irradiation of YBa2Cu3O7‐x was studied and compared to the spectra of Y, YO, Cu, CuO, and YCuO under similar conditions. The only compound detected in the Y‐Ba‐Cu‐O ablated material spectra was YO. Spatially resolved measurements from the plasma plume emanating from the irradiated superconducting material were performed also as a function of distance from the surface.

The effect of laser ablation on the morphology and composition of the irradiated YBa2Cu3O7‐x material was studied by SEM and EDAX. It was found that the 1‐2‐3 composition ratio of the near surface region was maintained after ablation. Changes in the morphology were observed in the track region and three distinctive regions could be identified as a function of distance from the beam center.
Textured Superconducting Thin Films of Bismuth Cuprate by Laser Ablation Method
Authors: Kumar Ashok , Ganapathi L. , Narayan J.
Published: March 2011

We have prepared highly textured superconducting thin films from Bi1.5pb0.5Ca3Sr2Cu4Ox (2324) on (100) YS-ZrO2 (Yttria stabilized zirconia) and Bi1.5Pb0.5Ca2Sr2Cu3°x (2223) on LaAlC-3 (100) and MgO (100) substrates at 650°C by pulsed laser ablation method.These films showed 2212 type of phase of the (BiPb)2(Ca,Sr)n+1CunO2n+4+5 family with onset transition temperature ( Tc ) ~ 110 K, confirming our earlier observations of 110 K superconductivity in a n = 2 bulk material. Thin films deposited from 2324 bulk target on YS-Z1O2 showed zero resistance temperature (Tco ) of 68 K but post annealing for one hour at 400°C in oxygen improved Tco from 68 K to 82 K. Thin films from 2223 target on LaAlO3 ( 100 ) and MgO ( 100 ) exhibited a Tco of 65 K and 74 K respectively while onset remained the same at 110 K. Further annealing at 400°C for one hour in oxygen did not show any improvement in Tco. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rutherford backscattering (RBS) channeling studies were performed on these films for correlation between crystal structure, microstructure and superconducting properties. X-ray diffraction patterns indicated 2212 type phase with a= 5.39 Å and c=30.76 Å; preferential orientation of c-axis perpendicular to the substrate was observed. The lattice parameter and x-ray diffraction patterns were found to be invariant with annealing treatments.
Tailored High-Tc Superconducting Thin Films Prepared by Layer-By-Layer Deposition with Excimer Laser
Authors: Kawai Tomoji , Kanai Masaki , Tabata Hitoshi , Kawai Shichio
Published: March 2011

By using 1ayer-by-1ayer successive deposition method with excimer laser ablation, the distance between CuO2 planes in the Bi2Sr2Ca1Cu2Oy superconductor has been controlled and super lattices with concentration modulation of Y and Ca have been formed. From the properties of these ‘Tailored films’, it is suggested that there is an interaction between CuO2 layers across Ca layer to affect the Tc value, but there is a very weak interaction across Bi2O2 blocking layers.
Fabrication of Yy‐Pr1‐y ‐Ba‐Cu‐O Thin Films and Superlattices of ‐Ba‐Cu‐O/Yy‐Pr1‐y ‐Ba‐Cu‐O
Authors: Wu X. D. , Hegde M. S. , Xi X. X. , Li Q. , Inam A. , Schwarz S. A. , Martinez J. A. , Wilkens B. J. , Barner J. B. , Chang C. C. , Nazar L. , Rogers C. T. , Venkatesan T.
Published: March 2011

We have prepared epitaxial thin films of Yy‐Pr1‐y‐Ba‐Cu‐O (y= 1 to 0) and superlattices of Y‐Ba‐Cu‐O/Yy‐Pr1‐y ‐Ba‐Cu‐O using pulsed laser deposition technique. The zero resistance transition temperatures of Yy‐Pr1‐y‐Ba‐Cu‐O bulk samples are reproduced in the films. The composition oscillations in the superlattices are observed by SIMS. The films and superlattices are found to have c‐axis orientations and good crystallinity.
Superconducting and Semiconducting Thin films of La123 and123 and their Superlattices
Authors: Ganapathi L. , Kumar Ashok , Narayan J. , Holland O. W.
Published: March 2011

Thin films of La123 and their superlattice with Y123 are deposited on various substrates for the first time. Thin films of La123 can be made semiconducting or superconducting within a small range of oxygen stoichiometry. A multiple target holder has been used for insitu processing of superlattice thin films. The ability of the La123 compound to exhibit either semiconductivity or superconductivity has been utilized to construct semiconductor / superconductor superlattice structures with Y123- X-ray diffraction studies have shown clearly the presence of two distinct type of layers in the superlattice films with a individual layer thickness of ∼ 120 and 300 Å, although this did not happen for ∼ 24 Å thickness of the individual layers. Rutherford backscattering experiments showed good quality of the films with channeling yields < 10%. Resistivity measurements showed a Tc (onset) = 90 K and Tc(zero) = 85 K for the La123 as well as superlattice thin films.
Ion Beam Thinning of YBa2cu3o7 Films: Approach to a Limiting Thickness for Superconductivity of One Lattice Constant
Authors: Hebard A.F. , Eick R. H. , Siegrist T. , Coleman E.
Published: March 2011

Grazing angle ion-beam milling of c-axis oriented YBa2Cu3O7 films is shown to give smooth films which have metallic-like resistance transitions and superconduct at thicknesses approaching a lattice constant. The zero resistance transition temperature decreases uniformly with increased milling with most of the change occurring for thicknesses less than 100Å. The crossover to non-superconducting behavior occurs at “electrical” thicknesses near 10 Å with a sheet resistance above the onset of the superconducting transition having a value near h/4e2 = 6450Ω, a combination of fundamental constants predicted by theory and observed previously in low-Tc superconductors. Continued milling beyond this limit results in semiconducting behavior without a superconducting transition.
As‐Deposited Superconducting Y‐Ba‐Cu‐0 Films on GaAs Substrate by High Pressure Dc Sputtering Process
Authors: Lin R.J. , Lin Y.L. , Pan F.M. , Wu P.T.
Published: March 2011

Superconducting Y‐Ba‐Cu‐0 thin films on (100)GaAs substrate have been successfully prepared by the high pressure DC sputtering process without further post‐annealing treatment. The target was compound Y1Ba2Cu3Ox made by solid‐state reaction. The sputtering gas was Ar‐50%02, and total pressure was 1.5 torr. The substrate temperature was lower than 450°C. The best superconductivity of the film is Tc(onset) = 95K and Tc(R=0) = 40K. There are no mi‐crocracks on the film surface. The interdiffusion between the film and GaAs is limited.
Superconducting Yba2Cu3O7-δ Thin Films on Srtio3 and Si Grown In-Situ by Ion Beam Sputtering
Authors: Kellett B.J. , James J.H. , Gauzzi A. , Affronte M. , Pavuna D.
Published: March 2011

Superconducting YBa2Cu3O7‐δ (YBCO) films 100‐300nm thick have been grown in‐situ on (100) SrTiO3 at 650°C by ion beam sputtering. Targets of Cu, CuO, Y, Y2O3, BaF2, BaCO3 and YBa2Cu3O7‐δ have been studied. Uniform composition throughout the film thickness has been achieved by co‐sputtering. Films are metallic (p300=300μΩcm) and textured, with Tc onsets at 92K and Tco=82K. Jc(77K) exceeds 105 Acm‐2. Films grown in‐situ on Si with ZrOx/Y2O3 and In2O3(10 at.%SnO2) buffer layers show Tc onsets at about 90K and Tco at about 50K, annealing improves Tco to 60K with resistivities p30o=2000μΩcm and 4000μΩcm respectively.
The Effect of Annealing Conditions on Magnetron Sputtered Superconducting Tl-Based Thin Films
Authors: Liou S.H.
Published: March 2011

The annealing steps have been shown to be a crucial determinant of the quality of Tl‐based superconducting films. In this study, we discuss the formation of the superconducting Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 phases with varied post‐annealing temperature and fixed annealing time. A x‐ray, electron micro‐probe, and scanning electron microscopy were carried out to evaluate the structure of superconducting phases formed for each annealing condition. For films deposited on SrTiO3 substrates and heat‐treated at 870°C for 15 min, the lower Tc phase Tl2Ba2CaCu2O8 becomes a major phase. The films consist of nearly pure Tl2Ba2Ca2Cu3O10 phase with Tc (R=0) in the range of 100K to 118K and c‐axis perpendicular to the film plane were obtained after annealing 880‐890°C for 15 min. These films were epitaxy growth on SrTi03 substrates.
In-Situ Preparations and Properties of High Tc Ybco Poly-Crystalline Thin Films
Authors: Harada N. , Sato K. , Yamamoto K.
Published: March 2011

Highly oriented YBCO films were produced on MgO(100) single crystal substrates. The direction of c axis was perpendicular to the film plane, whereas those of a and b axes were at random directions. The critical current density of the films was significantly high ca. 7x105 A/cm2. The critical transition temperature (Tc) of the YBCO film formed on a metal substrate, predeposited with YSZ as a buffer layer, was similar to those of the YBCO on MgO substrate. The possibility for the formation of superconductor films on metal substrates is suggested from these results.
In‐Situ Growth of Superconducting Bi‐Sr‐Ca‐Cu‐O Thin Films by Activated Reactive Co‐evaporation
Authors: Yoshikawa K. , Satoh T. , Sasaki N. , Nakano M.
Published: March 2011

The effect of in‐situ cooling conditions on surface roughness and superconducting properties have been studied. Bi‐Sr‐Ca‐Cu‐0 thin films were grown in‐situ on (100) MgO substrates at 700°C by activated reactive co‐evaporation. The films cool‐down in 760 Torr oxygen showed a transition temperature (Tc(onset)) of 100 K and zero resistance temperature (Tc (zero)) of 65 K. Smooth surface was obtained for the sample cooled‐down in oxygen plasma.
Molecular Beam Epitaxy of Rubidium Barium Bismuth Oxide: Structural Phenomena in Perovskite Heteroepitaxy
Authors: Hellman E. S. , Hartford E. H. , Werder D. J. , Fleming R. M.
Published: March 2011

The simple cubic perovskite crystal structure of superconducting (Rb,Ba)BiO3 makes it an ideal system for the study of perovskite heteroepitaxy. We report novel growth phenomena which have been observed in (Rb,Ba)BiO3 films grown by molecular beam epitaxy (MBE). For growth on MgO, the orientation of the film is observed to depend on the substrate temperature during growth, changing from (1 1 0) to (1 0 0) with increasing temperature. For films on SrTiO3, the large (10%) lattice mismatch appears to cause small grain rotations, resulting in a film with many low angle grain boundaries. In at least one growth regime, (2 2 1) oriented grains nucleate and grow on Ʃ3 coincidence boundaries on a faceted (1 0 0) oriented film.
Highly Oriented Superconducting Bi ‐ Sr ‐ Ca ‐ Cu ‐ Oxide Thin Films by the Solution Sol ‐ Gel Process
Authors: Ravindranathan P. , Komarneni S. , Bhalla A. S. , Roy R.
Published: March 2011

Highly oriented Bi2Sr2CaCu2O8+x films were prepared on MgO and SrTiO3 substrates by the solution sol ‐ gel (SSG) method. The tetra phasic sol containing bismuth, strontium, calcium and copper oxides was coated on the substrate by spin casting and calcined at 870*C for 10 minutes. X‐ ray diffraction patterns of the films showed the formation of the superconducting phase with preferential orientation along the C‐ axis. The microwave absorbtion data as a funtion of temperature revealed the onset temperature to be 90*K for the film coated on MgO substrate.
Preliminary Investigation of Processing and Phase Diagram Construction in the Y‐Sr‐Cu‐O System
Authors: Rolin T. D. , Cheng F. S. , Ashburn J. R. , Cheng H. Y. , Anderson E. E.
Published: March 2011

We have investigated the Y‐Sr‐Cu‐O system which has been reported to form a K2NiF4‐type superconducting phase (TC∼40K) and a “123”‐type phase (Tc‐80K). Difficulties in preparing single phase materials by standard solid state reaction of carbonates and oxides have compelled us to explore other methods. A two‐stage solid state processing technique in addition to a coprecipitation method will be discussed along with the relative advantages and disadvantages of each. Using data obtained from XRD and EDS, we have mapped some of the YO1.5‐SrO‐CuO ternary phase diagram in anticipation of continued efforts at single crystal growth.
Microstructure and Properties of Mixed Yba2Cu3O7-X and Y2Ba4Cu8O16 Thin Films
Authors: Marshall A.F. , Kapitulnik A. , Char K. , Barton R.W.
Published: March 2011

Post-annealed thin films comprised of mixed YBa2Cu3O7-x (123) and Y2Ba4Cu8O16 (248) phases with both faulted and unfaulted microstructures have been characterized by planar and cross-section transmission electron microscopy. The influence of 248-type faults on the 123 structure, possible mechanisms for the higher Tc's of faulted films, and observations of a fourfold ordered structure are discussed.
Structural and Magnetic Properties of Untwinned Yba2Cu3O6+x Single Crystals
Authors: Kaiser Debra L. , Gayle Frank W. , Swartzendruber Lydon J. , Wong-Ng Winnie , Watkins Steven F. , Fronczek Frank R.
Published: March 2011

We have conducted structural and magnetic investigations on thermomechanically-detwinned YBa2Cu3O6+x single crystals. Single crystal x-ray diffraction studies on a fully untwinned crystal with a superconducting onset temperature of 54 K have revealed that oxygen atoms in the basal plane are offset from the crystallographic mirror plane in the a direction, leading to “zig-zag” Cu-O chains. Magnetic measurements on untwinned and twinned crystals at 77 K indicate low levels of flux pinning in both crystals, with a slightly larger amount of pinning in the twinned crystal.
Orthorhombic Splitting and Chemical Etching of Ba2Ycu3O7-δ Crystal Surfaces
Authors: Werder D. J. , Chen C. H. , Gurvitch M. , Miller B. , Schneemeyer L. F. , Waszczak J. V.
Published: March 2011

We find by transmission electron diffraction (TED) that the orthorhombic splitting of the upper surface layers (< 1 μm) of single crystal Ba2YCu3O7-δ(YBCO) is reduced, differing by 10 to 30 percent from the bulk value. We also find by transmission electron microscopy (TEM) that in general the surfaces are of inferior quality, and thus, not representative of the bulk. These results have important consequences for those experiments that probe only the upper surface layers. By etching with either Br/ethanol or HClO4/NaClO4 the poor quality surfaces can be removed.
Grain Boundary Modelling and Correlation with Critical Current Densities in High‐Tc Superconductors
Authors: Jagannadham K. , Narayan J.
Published: March 2011

Geometrical modelling of grain boundaries in 123‐YBaCuO and 2223‐TlBaCaCuO systems is carried out for several misorientat‐ions. The a‐b and the a‐c type coincidence boundaries are analyzed to determine the fraction of Cu‐O planes that are continuous and the excess charge present at the boundary voids. The interg‐rain critical current density is determined as a function of the misorientation and the width of the boundary. The tunneling of superconductor pairs through the regions of distortions, giving rise to depression of the order parameter at the boundaries,is used to determine the critical current density in the weak coupling limit.
In-Situ Transmission Electron Microscopy and Computer Simulation Study of the Kinetics of Oxygen Loss in Yba2Cu3OZ
Authors: Burmester C. P. , Wille L. T. , Gronsky R. , Ahn B. T. , Lee V. Y. , Beyers R. , Gür T. M. , Huggins R. A.
Published: March 2011

High resolution transmission electron microscopy during in‐situ quenching of YBa2Cu3Oz is used to study the kinetics of microdomain formation during oxygen loss in this system. Image simulations based on atomic models of oxygen‐vacancy order in the basal plane of this material generated by Monte Carlo calculations are used to interpret high resolution micrographs of the structures obtained by quenching. The observed domain structures agree well with those obtained from the simualtions.
Superconducting Phases and Modulated Structures in (Bi, Pb)-Sr-Ca-Cu-O Wires
Authors: Feng Y. , Smallman R. E. , Jones I. P. , Wellhofer F. , Alford N. Mcn. , Button T. W.
Published: March 2011

(Bi, Pb)-Sr-Ca-Cu-O ‘2223’ wires with varying Bi/Pb ratios and sinter times have been investigated by parallel physical measurements and analytical electron microscopy. The numbers of phases present, their relative amounts, compositions and structures are reported and correlated with the superconducting properties. In particular, the recently reported long period (010) modulation (2b*/q*=7.7) is found to be connected with the “2223” high Tc phase.
Considerations Limiting Zero-Resistance Currents in High-Temperature Superconductors
Authors: Tinkham M.
Published: March 2011

The fundamental processes governing the appearance of dissipation due to flux motion in superconductors are reviewed. The dominant thermally‐activated resistive processes are discussed, and evidence for a sharp melting transition of the flux lattice is assessed.
Crystal Chemical and Functional Representation of High‐Tc Superconductors and Related Phases
Authors: Sigalovsky J. , Giessen B.C.
Published: March 2011

Using crystallographic data on HTSC's and a recently developed description of many HTSC's as intercalation compounds, we review briefly the structural evidence and develop some structural correlations involving the dimensions, coordination and connectivities of functional units.