bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface Effects of Laser Ablated and Sputtered High Tc Superconducting Thin Films
Authors: Dam B. , Baller T. S. , Van Veen G. N. A. , Van Hal H. A. M. , De Vries J. W. C. , Stollman G. M.
Published: March 2011

High Tc superconducting thin films were prepared by DC triode sputtering and laser ablation. With both deposition methods we were able to fabricate thin films on SrTiO3 which show an onset at Tcf=92 K. The superconductive transition is complete at Tcf=86 K. On other substrates like Al2O3, MgO and ZrO2 relatively poor results were obtained.
Formation of thin film YBaCuO Superconductors from Cu/BaO/Y2O3 Layer Structures
Authors: Chang Chin-An , Tsuei C. C. , Chi C. C. , Scheuermann M. R. , Yee D. S. , Berosh J. P.
Published: March 2011

Thin film superconductors of the YBaCuO family have been fabricated using layer structures of Cu/BaO/Y2O3 deposited by electron-beam evaporation. Using layer thicknesses off the stoichiometric YBa2Cu3O7, we have formed superconducting films with zero resistance above 77°K using MgO and SrTiO3 substrates. The films were found to be composed of both the superconducting YBa2Cu3O7 phase, and the non-superconducting green Y2BaCuO7 phase. Dependence of transition temperatures on the annealing temperatures and the substrates has also been studied.
Preparation of Y-Ba-Cu-O Superconducting Films by Modified Dc Sputtering Process
Authors: Lin R. J. , Chen Y. C. , Kung J. H. , Wu P. T.
Published: March 2011

High Tc Y-Ba-Cu-O superconducting thin films have been successfully deposited by DC sputtering techniques with excellent adhesion properties. Onset temperature of 95K had been achieved without any heat treatment nor annealing. Typical deposition rate is 1–2A/sec. It is possible to fabricate the superconducting thin films on a variety of substrates with this techniques, i.e., SiO2, Si and MgO. Analysis indicated that the films were predominantly the orthorhombic perovskite structure with traces of copper oxide.
Preparation of thin Film YBa2CU3O6+X Ceramic Superconductors by the Sol-Gel Process
Authors: Kramer S. , Wu K. , Kordás G.
Published: March 2011

High Tc superconducting powders and thin films on silicon have been fabricated by the sol-gel process. Both powder and film preparation involved the synthesis of metal alkoxides, followed by the complexation of yttrium, barium, and copper alkoxides in a common solvent. Bulk gels were then vacuum dried and fired at 700 and 950 °C in flowing oxygen. Thin films on (100) silicon were fired at 700 °C in flowing oxygen. Susceptibility vs temperature measurements showed that the thin films on silicon had a Tc of 40 K while the bulk gels fired under the same conditions had a Tc of 75 K. The sample fired at 950 °C was superconducting at 90 K.
Materials Aspects of Oxide Superconductors - Effect of Ambient Water on Superconductivity-
Authors: Kitazawa K. , Kishio K. , Hasegawa T. , Ohtomo A. , Yaegashi S. , Kanbe S. , Park K. , Kuwahara K. , Fueki K.
Published: March 2011

It has been found that the chemical instability of Ba2LnCu3O7 causes some problems in the measurements of critical temperature and creates a highly resistive grain boundary contact which is the major cause of the low critical current density at the present moment. Firstly, measurements of the superconductive critical temperature could be seriously misled if based solely on resistive transition because apparent resistivity anomaly is observed due to electrochemical EMF which appears when the electrode contact is attacked by water. Secondly, the barrier nature of the grain boundary against charge carriers is significantly enhanced by the chemical attack of the boundary region with water and water/carbon dioxide in the annealing atmosphere. This leads to a further weakening of the Josephson weak link between polycrystalline grains in the high Tc oxide superconductors.
Thin Films of Y-Ba-Cu-O by Rf Sputtering
Authors: Ballentine Paul H. , Kadin A. M. , Árgana J. , Rath R. C.
Published: March 2011

Thin films of Y-Ba-Cu-O have been prepared by rf diode sputtering from a single mixed-oxide powder target. The films were deposited on sapphire and cubic zirconia substrates, with the substrates either cooled, heated, or left to establish thermal equlibrium. The Cu content in the films decreased with increasing substrate temperature. Films having composition close to the desired 1–2–3 stoichiometry were fabricated either by enriching the target with CuO or by cooling the substrate. Using the latter approach, a single target was used for over 20 depositions yielding films that were uniform in composition (although slightly Cu-rich), and consistent from run to run. These films had as-deposited room temperature sheet resistances on the order of 100 kΩ. Subsequent annealing at temperatures up to 850 C resulted in films that were superconducting with an onset around 90 K and zero resistance at 50 K. The critical current was found to exceed 2000 A/cm2 at 4.2 K.
Magnetic Investigations of Superconductive, Polycrystalline (RE)1Ba2Cu3O7−x Compounds (RE = Y, Gd, Ho, Dy)
Authors: Thompson J. R. , Boatner L. A. , Brynestad J. , Christen D. K. , Kim Y. C. , Sales B. C. , Sekula S. T.
Published: March 2011

Magnetic properties have been investigated for several rare-earth based, polycrystalline samples of high Tc superconductive “123” compounds with magnetic onset temperatures between 90 and 95 K. Analysis of the susceptibility × of samples based on Gd, Ho, and Dy indicates that the superconductive and magnetic properties are independent of one another to a substantial degree. Studies of the critical current density Jc are reported.
Effect of Temperature Cycles on the Critical Current Density of YBa2Cu3O7-δ
Authors: Tiefel T. H. , Jin S. , Sherwood R. C. , Fastnacht R. A. , Nakahara S. , Fisanick G. , Boone T.
Published: March 2011

The transport Jc of the polycrystalline YBa2Cu3O7-δ superconductor seems to be dominated by weak links between high Jc regions as evidenced by low Jc values and their strong field dependence. The possible effects of thermal expansion-contraction and the tetragonal-orthorhombic transformation on the weak links and the Jc values were investigated by repeated thermal cycling of sintered pellets between -196°C and various high temperatures (600–850°C) using a furnace heating and cooling in an oxygen atmosphere. While more than a five-fold decrease in Jc from -400 to -70 A/cm2 (at 77K in zero field) is observed after 5 temperature cycles between -196'C and 850°C, only a slight decrease (to -370 Atm2) is noticed after 5 cycles between -196*C to 600°C, the temperature span of which is not all that much smaller than the former cycles. Transmission electron microscopy analysis clearly indicates that the drastic deterioration in Jc by repeated phase transformation is caused by increased amount of microcracks on (001) basal planes near the grain boundaries. The results will be discussed in terms of the large thermal expansion anisotropy of this layer-structured compound.
Reentrant Softening in Copper-Oxide Superconductors
Authors: Violet C. E. , Datta T. , Ledbetter H. M. , Almasan C. , Estrada J.
Published: March 2011

On the basis of our reentrant-softening model, sound-velocity results in La1.85Sr0.15CuO4 and YBa2Cu3O7−x are shown to be neither dissimilar nor inconsistent with thermodynamic requirements. In both materials, as temperature decreases, the lattice softens just above Tc. Below Tc, this softening is offset by increased stiffness associated with the developing superconducting phase. This model agrees with results from other physical-property measurements, and it predicts that elastic stiffness is higher in the normal state than in the superconducting state.
Changes in Microwave Absorbtion of New High Tc Superconductors with Small Magnetic Fields
Authors: Khachaturyan K. , Weber E. R. , Tejedor P. , Stacy A. , Portis A.
Published: March 2011

A low field microwave absorbtion peak was observed with an EPR spectrometer in the new superconducting oxides‥ The peak disappeared above the superconducting transition temperature after exponential decrease with temperature in the transition region. The peak was sensitive to the magnetic fields the sample has been exposed before in the superconducting phase. Magnetic field dependent stochastic oscillations of the EPR baseline are ascribed to flux trapping in Josephson junctions.
Penetration Depth Measurements of YBa2Cu3O7-δ at 4 MHz
Authors: Wiesmann H. , Corderman R. R. , Moodenbaugh A. R. , Ruckman M. W. , Strongin Myron
Published: March 2011

Measurements were made of the penetration depth of bulk and powder samples of YBa2Cu3O7-δ. The samples were placed in an inductor which was part of the resonant circuit of a 4 MHz tunnel diode oscillator. The oscillator was stable to at least 1 part in 106 at 77 K. Changes in the sample susceptibility were easily detected by changes in the oscillator frequency. Analysis of the smallest powders fabricated gave a value of the measured penetration depth λmea = 0.23 μm. The measurement methodology is quantitative and the value of Xmea is believed to be an upper bound of the true penetration depth.
Radiation Damage in YBa2Cu3O7 by Fast Neutrons
Authors: Willis J. O. , Cost J. R. , Brown R. D. , Thompson J. D. , Peterson D. E.
Published: March 2011

The superconducting transition temperature of sintered YBa2Cu3O7 decreases at a rate of 2.7 K/1018 n/cm2 (E > 0.1 MeV) for fast neutron irradiation. The critical current density Jc increases a factor of three at zero field and more than three at nonzero fields for fluences up to 2×1018 n/cm2. At both 7 and 75 K, Jc is decreasing with fluence near 3×1018 n/cm2.
Electronic Structure of Fluorine-Substituted YBa2Cu3O7 Superconductor
Authors: Ching W. Y. , Xu Yongnian , Wong K. W.
Published: March 2011

The electronic structures of fluorine-substituted YBa2Cu3O7. crystals are studied by means of first-principles calculations. The most likely site of substitution is 0(1) and the most unlikely site is 0(4).
Critical Current Density Enhancement and Moisture Destruction Studies of the Compound Superconductor Y-Ba-Cu-Ag-O
Authors: Yao Y. D. , Krol A. , Krol Y. H. , Walters C. , Spagna S. , Althoff J. , Woronick S. , Jang L. Y. , Xu F.
Published: March 2011

We have fabricated a series of samples of YBa2(Cu1−x Agx)3Oy compounds where 0 ≤ × ≤ 1, with the intention to study the changes in critical current density and the effect of moisture treatment on normal state resistance R in these high transition-temperature superconductors. The samples exhibited a decrease of the transition-temperature Tc vs the Ag concentration x. Tc is about 93 K for YBa2Cu3Oy and 20 KCfor YBa2Ag3Oy, but it is almost unaffected by the presence or Ag for × < 0.2. An enhancement of the critical current density Jc by nearly an order of magnitude for the samples with 0 < × ≤ 0.1 has been observed. Both Jc and R are found to be sensitive to the ambient moisture conditions.
Oxygen Vacancy Ordering in BaYCu3O7−x, 0 ≤ x ≤1, by Electron Diffraction Studies
Authors: Alario-Franco M. A. , Capponi J. J. , Chaillout C. , Chenavas J. , Mareziom M.
Published: March 2011

Electron diffraction photographs of Ba2YCu3O7−x with x ∼ 0.15, ∼ 0.50, and ∼ 0.85, show diffuse scattering which can be attributed to the partial ordering of the oxygen vacancies. For x ∼ 0.15 and ∼0.85 it consits of continous rods which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the unit cell 2√2ac × 2√2ac × 3ac. This cell is orthorhombic or tetragonal for x ∼ 0.15 and ∼ 0.85, respectively. For the former composition every fourth O4 atom is removed from every other CulO4 chain. For the later the ordering is the same, however, the occupied oxygen positions become vacancies, and vice versa. Both orderings are uncorrelated along the c axis. For x ∼ 0.5 the diffuse scattering consits of either continuous rods or continous ribbons which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the orthorhombic unit cell 2ac × ac × 3ac. The ribbon widths are sample dependent. For this type of compounds all O4 atoms of every other CulO4 chain running along the b axis, are removed. As in the previous cases the ordering is uncorrelated along the c* axis. The ribbon elongation along the a* axis is indicative of additional disorder along this axis. This disorder seems to be related to the oxygen stoichiometry.
Raman Scattering Studies on Superconducting YBa2Cu3O7−x, Semiconducting YBa2Cu3O6+x, and Possible Impurity Phases
Authors: Mascarenhas A. , Katayama-Yoshlda H. , Geller S. , Pánkové J. I. , Debt S. K.
Published: March 2011

A Raman spectroscopie investigation of specimens of superconducting YBa2Cu3O7−x and semiconducting YBa2Cu3O6+x indicates that in the range 100 to 700 cm-1, the characteristic lines of the superconductor at 13 K, are at 150, 338, 441, 507, 590, and 644 cm-1. Comparison of the Ranan spectra of the superconductor and the semiconductor indicates a mode stiffening of the pair at 338 and 441 cm-1, hut a mode softening of the pair at 507 and 590 cm-1. A factor group analysis leads to a tentative assignment of the Raman and infrared allowed modes. At temperatures 12K < T < 180K the Raman spectra of the superconductor indicate that the phonon mode at 338 cm-1 has an anomalous temperature dependence below the superconducting critical temperature (Tc).
Flux Trapped State Versus Glassy State in Superconducting BaErCuO and BaYCuTiO
Authors: Nam Sang Boo
Published: March 2011

The temperature dependent magnetization, M(T), of superconducting BaErCuO and BaYCuTiO was measured via the BTi SQUID susceptometer. In the zero field cooling case, M(T) of BaErCuO was found to be similar to that of Pb. But, M(T) of BaYCuTiO was found to decrease rapidly with T and be almost linear in T. However, in the field cooling case the fluxoids were found to be trapped at all T below Tc, and its amount was found to depend on Ts at which the sample starts to be cooled, as observed in Pb. The ergodic limiting points were not observed within the chosen parameters. The irreversibility of magnetization observed in both BaErCuO and BaYCuTiO is attributed to the fluxoids, trapped during the field cooling process.
Effect of Oxygen Annealing on the Magnon-Pair Raman Scattering in La2CuO4-y
Authors: Ohana I. , Liu Y. C. , Dresselhaus M. S. , Dresselhaus G. , Strauss A. J. , Zeiger H. J. , Picone P. J. , Jenssen H. P. , Gabbe D. R.
Published: March 2011

Polarized Raman scattering spectra at 300K and 20K are reported for a single crystal of La2CuO4-y before and after annealing in oxygen at 1000°C for 24 hours. Oxygenation strongly quenches the temperature sensitive line at ∼1430 cm-1 (for T ∼ 300K) in the “as grown” crystal, previously identified with magnon-pair excitation associated with two-dimensional antiferromagnetic ordering. In addition, the phonon spectrum is greatly modified by the addition of oxygen, indicating a more uniform local crystalline environment after oxygenation. Raman scattering is thus a sensitive probe of the effect of oxygenation on the near surface magnetic and phonon properties of La2CuO4-y.
Derivative Analysis of the High Temperature Superconducting Transition
Authors: Almasan Carmen , Estrada J. , Poole C. P. , Datta T. , Farach H. A. , Gubser D. U. , Wolf S. A. , Toth L. E.
Published: March 2011

The shape of the normalized temperature derivative of the dc susceptibility provides useful information about superconducting materials. We propose that the position of the derivative peak be defined as the transition temperature Tc and the width of this peak define its sharpness.
Calorimetric Studies of High Temperature Oxide Superconductors
Authors: Saito Yasutoshi , Nakamura Tetsurõ , Atake Tooru
Published: March 2011

The heat capacities of single phase samples of Ba2DyCu3O7 and Ba2ErCu3O7 which were prepared by the method of powder-calcination have been measured over the temperature range 13–300 K by using a laboratory-made adiabatic calorimeter. A typical second-order type of anomaly was observed due to the superconducting phase transition at 92.5 K in Ba2DyCu3O7 and at 91.2 K in Ba2ErCu3O7. From the heat capacity jump at the transition temperature, the electronic heat capacity coefficient was estimated as 30 mJ·K-2.mol1 for Ba2ErCu3O7 and 32 mJ·K-2. mol-1 for Ba2ErCu3O7. Large differences were found in the low temperature heat capacities between the two samples, which were analyzed on the basis of Schottky-type of anomalies owing to the magnetic ions of Dy and Er.
Carrier Concentration amd High Tc Superconductivity
Authors: Karpe N. , Szymczak I. , Chen D.-X. , Sanchez A. , Nogues J. , Rao K. V.
Published: March 2011

A systematic study of the influence of oxygen depletion on the carrier concentration and the occurence of superconductivity in a single-phase 1–2–3 Y-Ba-Cu-Oxide material is presented. This is accomplished by successive measurements of the Hall and electrical resistivities, ac-susceptibility, and x-ray diffraction on the same sample, in which the oxygen deficiency is controlled and determined from thermogravimetry. With increasing oxygen depletion, we monitor how the 93K orthorhombic superconductor, with an estimated carrier concentration of 0.6·1022 carriers/cm3 at 100K, is transformed into a tetragonal semiconductor with a very low carrier concentration.
The Preparation of Bulk and Thick Films of YBa2Cu3O7-y Using a Solution Technique
Authors: Barboux P. , Tarascon J. M. , Bagley B. G. , Greene L. H. , Hull G. W. , Meagher B. W. , Eom C. B.
Published: March 2011

We have synthesized the high Tc superconducting oxide YBa2Cu3O7-y using a solution technique and compare the resultant properties to materials synthesized by solid state reactions. Because the cations are mixed at the microscopic level, we observe that this solution technique allows lower reaction temperatures and shorter reaction times to obtain the superconducting material. They yield materials with particle sizes of about 1 μm and having a narrow size dispersion (as compared to the typically 50 μm particle sizes obtained by solid state reactions). The smaller, uniform particle sizes yield denser compacts upon sintering. Densities of 90% have been achieved and metallic-like behavior improves and is correlated with increasing density. The solution derived materials superconduct at 91 K and have narrow transition temperatures (0.6K width) which we attribute to sample compositional and structural homogeneity. Because we are able to produce stable, viscous gels, we have investigated the preparation of large area thick films on various substrates of technological interest (e.g. alumina, zirconia.strontium titanate).
Oxygen Stoichiometry in LA-BA-CU-O Perovskites
Authors: Sunshine S. A. , Schneemeyer L. F. , Murphy D. W. , Wasczcak J. V.
Published: March 2011

The oxygen ordering and exchange properties of Ba2−xLa1+xCu3O7±δ and BaLa4Cu5O13±δ are detailed. The crucial role of oxygen ordering for superconductivity is described.
Ionic Models for YBa2 Cu3 O7
Authors: Wright N. F. , Painter G. S. , Busing W. R. , Butler W. H.
Published: March 2011

Simple ionic models are applied to YBa2 Cu3 O7. It is found that additional forces are needed to constrain the barium and the planar coordinated copper atoms to be stable in their observed positions. These additional forces are compared to forces calculated from first principles. It is observed that the restoring forces are small for motion of the “in chain” oxygen atoms perpendicular to the chains.
Superconductivity in Pseudo-Quaternary System
Authors: Yao P. C. , Chiang C. I. , Hsieh C. W. , Chen J. W. , Lin I. N. , Yang S. J. , Hsu S. E.
Published: March 2011

The superconductivity of pseudo-quternary system Y1−xMx Ba2 Cu3 O7-δ, YBa2 Cu3−xM x O7-δ, where M stands Co,Cr,&Zn and with x=0,0.001,0.005,0.01 & 0.02, has been investigated.

The XRD analysis shows that the perovskite structure is preserved and a stabilization effect on orthorhombic structure by 3d elements addition was proposed. On the contrary, the microstructure has been modified prominently and it is determined by the sintering mechanism involved and/or diffusion process in each doped sample. Second phase precipitate can be found at grain surface. The superconductivity, however, has not been greatly affected.
On the Defect Structure of Grain Boundaries in Ba2YCu3O7−x
Authors: Nakahara S. , Fisanick G. J. , Yan M. F. , Van Dover R. B. , Boone T. , Moore R.
Published: March 2011

Correlations between observed defect structures and the orientation of planes involved in grain boundary (GB) formation in single phase, near ideal density orthorhombic Ba2YCu3O7−x are presented. Coherent boundaries involving only a low energy network of dislocations at the interface are associated with boundaries not involving the (001) basal plane, while basal-plane-faced GBs are highly defective. These results are interpreted using a model for local stress based on the known anisotropie thermal contraction of the material during cooling from sintering temperatures. Scanning Auger microscopy of in situ fractured surfaces demonstrates that there is preferential segregation of carbon at the GBs as well.
Epr Spectroscopy on Zn-Substituted YBa2Cu3O7
Authors: Ponte Goncalves A. M. , Jee Chan-Soo , Nichols D. , Crow J. E. , Myer G. H. , Salomon R. E. , Schlottmann P.
Published: March 2011

The temperature and concentration dependence of the electron paramagnetic resonance spectra of YBa2(Cu1−xZnx)3O7 has been measured for 0≤x≤0.16. Zn substituted on the Cu-site cause a rapid nearly linear depression of the superconducting transition temperature Tc with Tc going to zero in the vicinity of x=0.10. Only weak EPR spectra due to ≤1% of the Cu-ions are seen in the superconducting phase of YBa2Cu3O7. These spectra are most likely attributed to Cu-ions in the vicinity of grain boundaries and do not represent a bulk response. However, a strong asymmetric resonance is observed in the Zn-substituted samples with x>0.1. The EPR results obtained for YBa2(Cu1−xZnx)3O7 are discussed in terms of a possible localization of d-electrons.
Effect of Oxidizing Atmosphere on Superconductivity in RBa2Cu3−xMxOz
Authors: Robinsonem David A. , Maginnis Abbot , Morrobel-Sosa A. , Alexander Chester , Asavaroengchai C. , Metzger Robert M. , Stanley Donald A.
Published: March 2011

The dependence of the superconducting properties of RBa2Cu3−xMxOz (R = Y, Gd, M = Cr, Mn, Fe, Co, Ni, and x = 0.0, 0.025, 0.05, 0.1, 1.0, 3.0) on the oxidizing environment used during the processing (sintering/annealing) of these materials has been investigated. Samples of nominal composition, YBa2Cu3Oz, were prepared from the same starting materials and subjected to two different controlled heat treatments, under both controlled oxygen and ozone atmospheres. Measurements of ac electrical resistance versus temperature indicate that the critical temperatures are increased, and the widths of the superconducting transitions are narrowed for identically heat-treated samples when processed under ozone atmosphere rather than under an oxygen environment. Thermogravimetric analysis data indicate this trend to be correlated with increased oxygen content and thermal stability. This effect is also observable for materials with metal substitution for Cu, although the measured Tc's are generally lower for increased values of x. X-ray powder diffraction analysis showed the materials to be mostly single phase.
Electron Diffraction and TEM Studies of Y1Ba2Cu3O7−x
Authors: Pérez R. , Pérez-Ramírez J. G. , Avalos M. , Reyes J. , Martinez L. , Orozco E. , Carrillo E. , Mendoza A. , Albarran J. , Fuentes Maya J. , Boldú J. L. , José-Yacamán M.
Published: March 2011

Optical microscopy and transmission electron microscopy show that most of the crystalline grains in Y1Ba2Cu3O7−x superconducting specimens have large number of twins. These bands of different image contrast have similar microdiffraction patterns. However the diffraction conditions are different and correspond to different tilts of the crystalline grains along one of the zone axis. HREM images of these twin boundaries indicate that the boundary area has appreciable dimensions and both matrix and twin crystals show the existence of a superstructure with double of the common periodicity obtained under [001] diffraction conditions.
Local Environment Around Barium Atoms in the Superconductor Y-Ba-Cu-O
Authors: Krol A. , Xu F. , Jang L. Y. , Sher C. J. , Spagna S. , Althoff J. , Kao Y. H.
Published: March 2011

The local structure around Ba atoms in the compound superconductor Y-Ba-Cu-O has been studied by measuring the extended x-ray absorption fine structure (EXAFS) near the Ba K edge. This technique is used to investigate the changes in the short range order structure when the system is doped with impurities.
Possibility of High-Tc Copper Fluoride Oxide Superconductors
Authors: Wu P. T. , Liu R. S. , Sung H. M. , Rung J. H.
Published: March 2011

Superconductivity of YBa2Cu3FxOy system prepared by using a mixed solid state and gel method. A consistent and non-zero resistance drop near 280K was achieved in the nominal YBa2Cu3FxOy system for x=l and 2, with complete loss of resistance at 90K. The metal-semiconductor transition occurs at x value between 2 and 3. Temporal room temperature superconductivity with zero resistance was observed in a YBa2Cu3F2Oy sample at 308K. The phenomenon lasted for three minutes and was not reproducible.
Processing Relationships in YBa2Cu3O7−x Superconductors
Authors: Heber W. J. , Pederson L. R. , Maupin G. D. , Leblanc E. J.
Published: March 2011

Samples of YBa2Cu3O7−x were prepared by solid state reaction of Y2O3, BaO2, and CuO powders mixed in stoichiometric proportions. Powders reacted at 900°C-925°C in air were pressed at 35 MPa into rectangular bars and sintered at 950°C in air for six hours. Slow cooling at 50°C/hour promoted complete transformation to the orthorhombic structure. The effects of subsequent oxidation processing on superconducting properties were also investigated. Oxidation anneals at one atmosphere pressure in flowing O2over the temperature range from 300 to 550°C were performed. Results indicate that oxidation at 450°C optimized the superconducting transition temperature at 91K with a 2-degree transition width. Subsequent high-pressure oxidation (2000 psi O2) at 200°C for one week significantly degraded the superconducting characteristics. Results based on i udometric titration, thermogravimetric analysis, and x-ray photoelectron spectroscopy suggest that the copper valency is about 2.3 and oxygen stoi chiometry is 6.94 (x = 0.06) in samples processed to optimize superconducting properties.
Laser Processing and Characterization of High-Tc Superconductors
Authors: Weber W. H. , Logothetis E. M. , Soiitis R. E. , Graham G. W. , Chen J. T. , Wenger L. E.
Published: March 2011

Raman spectra of several samples of YBa2Cu3O7 presented, correlated with resistivity and structural data, and compared with previous results. Laser heating to ∼1100°C in air is shown to produce a surface layer of Y2O3 and Y2BaCuO5. Similar heating of La2−x(Sr,Ba)xCuO4 produces a layer of La2O3. All of these compounds are readily identified by their Raman spectra.
Improved Magnetization for YBa2Cu3O7-δ Annealed in Oxygen Above 1000°C
Authors: Venturini E. L. , Ginley D. S. , Baughman R. J. , Morosin B. , Kwak J. F.
Published: March 2011

Air sintering and subsequent oxygen annealing at high temperatures are integral to the production of ceramic superconducting YBa2Cu3O7-δ. We present results directed toward optimizing the temperature for these two process steps, using static magnetization to determine the intragranular properties. Surprisingly, pure oxygen stabilizes the material against decomposition at temperatures near the melting point, allowing the production of significantly higher quality single phase material.
Effects and Behavior of Implanted Fluorine in High Temperature Superconductors
Authors: Tesmer J. R. , Maggiore C. J. , Nastasi M. , Cheong S-W. , Dick C-M.
Published: March 2011

The effects of implanted fluorine on the resistivity of high temperature superconductors and its diffusion within the superconductors have been studied in an attempt to duplicate a recent report of enhanced critical temperatures. Implanted fluorine was found to have no effect on the critical temperature and, upon heating, the fluorine diffuses out of the near surface.
Gkowth of YBa2Cu3O7-δ Single Crystals and Films by a Flux and a Sputtering Methods
Authors: Takagi K. , Hirao M. , Hiratani M. , Kakibayashi H. , Aida T. , Takayama S.
Published: March 2011

YBa2Cu3O7-δ single crystals and epitaxial films are grown and characterized. In flux growth for bulk crystals, effects of growth conditions on yield and electric resistivity of crystals are examined. The yield of flaky crystals depends on the formation of cavities. The transition temperature is 86 K after annealing in an oxygen atmosphere. Films are prepared on SrTiO3 by sputtering and epitaxial growth is confirmed by high resolution electron microscopy. Periodic lattice defects are observed near the interface between the substrate and the film. It seems that these defects result from the diffusion of impurities from the substrate.
Preparation of Superconducting thin Films of High Tc Cuprates by a Novel Spin-on/Pyrolysis Technique
Authors: Rice C. E. , Van Dover R. B. , Fisanick G. J.
Published: March 2011

Superconducting thin films of high Tc cuprates have been prepared using wet chemical precursors, which are spun on a substrate, pyrolyzed and heat-treated. This new method is simple and inexpensive, and is easily amenable to scale-up to cover large areas. No vacuum equipment is required. The technique allows easy manipulation of film stoichiometry and gives films having excellent compositional uniformity. A 1600 A film of Ba2YCu3O7 prepared by this method had a room temperature resistivity of 500/xfzcm, Tc/(onset) of 90K, and R=0 at 58K. The preparation and electrical and microstructural characterization of thin films of Ba2YCu3O7 and other high TC cuprates will be discussed.
Magnetism, Specific Heat, and Surface Topography of Oxide Superconductors
Authors: Jenny H. , Bretscher H. , Frey T. , Anselmetti D. , Heinzelmann H. , Wiesendanger R. , Leemann G. , Walz B. , Säckinger D. , Güntherodt H.-J.
Published: March 2011

Samples of the composition MBa2Cu3O7−x with M = Y, Eu, Er, and Gd have been prepared by the standard solid state reaction method. The magnetic susceptibility has been investigated above room temperature up to 187O K in vacuum. Specific heat measurements have been performed with a differential scanning calorimeter (DSC) working at low temperatures in a differential mode using superconducting and non-superconducting samples. The surface topography of the high-Tc superconductors has been investigated at room temperature by scanning tunneling microscopy (STM).
Grain Boundaries in YBa2Cu3O7−x
Authors: Tietz L. A. , Carter C. B. , Lathrop D. K. , Russek S. E. , Buhrman R. A.
Published: March 2011

Grain boundaries in YBa2Cu3O7−x. thin films deposited on yttria-stabilized cubic zirconia have been characterized using selected-area diffraction. In addition to twin boundaries, several types of low-angle and high-angle grain boundaries are frequently found in these films. The high-angle boundaries include 23.5°, 29°, and 45° rotations about [001] and 90° rotations about [100] or [010]. These boundaries are compared to special high-angle grain boundaries in cubic materials.
High-Tc Superconducting Films of Y-Ba-Cu Oxide Prepared by a CO2 Laser Beam Evaporation
Authors: Tachikawa K. , Atanabe I. , Kosuge S. , Ono M.
Published: March 2011

The high-Tc YBCO superconducting films have been prepared using a cw CO2 laser evaporation from a single bulk target. The adjustment of the target composition, especially the yttrium concentration, was found to be a key factor to achieve a desired film composition. After post-annealing at 930°C, the films deposited on YSZ substrate exhibited a zero resistance temperature of 85K. The deposition rate of the films was about lOOA/sec.
A Versatile new Metallo-Organic Spin-on Process for Preparing Superconducting Thin films
Authors: Gross M. E. , Hong M. , Liou S. , Gallagher P. K.
Published: March 2011

A new metallo-organic spin-on technique is described for producing thin films of the high temperature perovskite superconductors, LnBa2Cu3O7−x, where Ln represents a rare earth element. Pyrolysis of the spin-coated films leads to black films up to several microns thick whose degree of orientation is a function of the processing temperature and duration. Representative films of YBa2Cu3O7−x on MgO begin to exhibit orientation with the c-axis perpendicular to the film at heat treatments above 900 'C. The superconducting behavior of a highly oriented film produced at 990 ° C is characterized by Tc (onset) = 89 K, Tc (R=0) = 77 K and Jc = 104 amp cm-2 at 65 K.
External and Internal Diffusion of Oxygen in Superconducting YBa2Cu3O7−x Composite Conductors
Authors: Gaowacki B. A. , Evetts J. E.
Published: March 2011

We report a systematic investigation of the critical current at 77K for a number of different composite conductors based on the high critical temperature superconductor YBa2 Cu3 O7. Results are reported for an ‘external’ diffusion composite where the oxygen diffuses through an outer cladding of silver, and for an ‘internal’ diffusion design where the composite is clad externally with an oxygen impermeable layer and oxygen diffuses internally from a channel within the conductor. Measurements are reported of the dependence of the critical current on i) the preparation route for the superconducting powder, ii) the preform particle size, iii) the presence of air or vacuum during compaction, iv) the time of the sintering anneal and v) the applied load on the conductor during a critical current test.
Crystal Structures and Superconductivity in the La1.5−xBa1.5+Cu7+ySystem
Authors: Greedan JE. , O'Reilly A. H. , Stager C. V. , Razavi F. , Abriel W.
Published: March 2011

Members of the solid solution system La1.5−xBa1.5+Cu7+ywith x = 0, 0.125, 0.25. 0.375 and 0.5 have been prepared both in air and under one atmosphere of flowing oxygen. In general, except for x =0, the oxygen annealed compounds are superconducting while the air-annealed samples are semiconductors. Tc's measured by Meissner effect and resistivity data range to 70K. The crystal symmetry in all cases is apparently tetragonal as verified for x = 0.375 by variable temperature Guinier x-ray experiments at temperatures down to 8K. Crystal structures have been refined from neutron powder diffraction data. A correlation is noted between Cu-0 distances which connect adjacent Cu planes - the average copper valence and the occurrence of superconductivity.
Evidence for d-Electron Localization in YBa2(Cu1−xZnx)3O7 for 0<x<0.16
Authors: Jee C. , Nichols D. , Ciasullo J. , Crow J. E. , Mihalisin T. , Myer G. N. , Kuric M. V. , Bloom S. H. , Guertin R. P.
Published: March 2011

Zn substitution for Cu in YBa2Cu3O7 rapidly reduces the superconducting transition temperature, Tc. Superconductivity is quenched between x=0.08 (T =30 K) and x=0.10. The normal state paramagnetism grows with Zn substu-tition, presumably due to increased localization on the Cu sublattice. Susceptibility studies of oxygen depleted (nonsuperconducting) Zn-substituted samples support this. Strong non-linear isothermal magnetization suggesting an internal magnetic field is found at T=4.2 K in samples with Zn concentration near to the critical value for suppression of superconductivity. The results are discussed in terms of increased localization of d-electrons on the Cu sites with increasing Zn concentration, which is consistent with recent EPR data.
The Effects of Oxygen Stoichiometry and Oxygen Ordering on Superconductivity in Y1Ba2Cu3O9−x
Authors: Beyers R. , Engler E. M. , Grant P. M. , Parkin S. S. P. , Lim G. , Ramirez M. L. , Roche K. P. , Vazquez J. E. , Lee V. Y. , Jacowitz R. D. , Ahn B. T. , Gür T. M. , Huggins R. A.
Published: March 2011

This paper reports on the structures and properties of Y1Ba2Cu3O9−x samples prepared in precisely controlled oxygen environments using a solid-state ionic technique. By titrating out oxygen at low temperatures, orthorhombic Y1Ba2Cu3O9−x samples were prepared with oxygen contents below 6.50. Resistivity and magnetometry studies indicated that these reduced, orthorhombic samples were marginally superconducting, with their superconductivity probably arising from local regions of higher oxygen content.
Critical Current Density of the YBa2Cu3O7-δ Superconductor as Affected by Microstructuralxontrol
Authors: Jin S. , Sherwood R. C , Tiefel T. H. , van Dover R. B. , Kammlott G. W. , Davis M. E. , Fastnacht R. A. , Nakahara S. , Yan M. F. , Johnson D. W.
Published: March 2011

The recent discovery of the YBa2Cu3O7-δ type high Tc superconductors stimulated worldwide R&D interest in this field. However, the relatively low critical current density (Jc) in the polycrystalline, bulk superconductors (as well as its significant deterioration in weak magnetic fields) has been a major roadblock to the rapid technical advancement toward applications. In this paper, we investigated the effect of processing and microstructural control on Jc of the superconductor. Improved Jc values of -3100 A/cm2 at 77K with somewhat reduced field dependence have been obtained through appropriate microstructural modifications.
Evaluation of Critical Current Density in Ba2Y1Cu3O7-y, Compound
Authors: Kumakura Hiroaki , Uehara Mitsuru , Takahashi Kazuhiko , Togano Kazumasa
Published: March 2011

Magnetization measurement was carried out for Ba2Y1Cu3O7-y bulk and powder samples at 77K and 4.2K in order to evaluate intrinsic Jc. Excellent Jc values above 10 A/cm were obtained for powder samples at 77K and lOkOe. These Jc values were somewhat increased by substiution of Er for Y. High temperature sintering at 1030°C brings about drastic increase in magnetization which can be explained by the grain coarsening.
L3 White line Splitting of Copper in the Electron Energy loss Spectrum of YBa2Cu3O7−x
Authors: Ahn Charming C. , Lee David S. , Samwer Konrad
Published: March 2011

We have used electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM) to probe the L23 excitation of the 930 eV copper 2p to 3d transition in YBa2Cu3O7−x. Unlike UPS and XPS which are surface sensitive, EELS permits analysis of bulk properties from submicron regions of a single crystal. In addition, EELS probes the lowest unoccupied states and is particularly suited to the analysis of Cu valance states in YBa2Cu3O7−x We observe a splitting of the L33 peak of ∼2.7 eV, which we attribute to contributions from both Cu 2+ and Cu 3+. The intensity contribution Cu 3+ is maximized when a two beam condition is used to enhance channeling of the electrons between the {033} planes of the crystal near a [100] orientation. Upon prolonged exposure of the compound to the incident electron beam, the splitting disappears and the only contribution to the L3 white line is from divalent copper.
Magnetic Transitions in High-Tc Superconductors
Authors: Barrio R. A. , Wang C. , Tagüeña-Martinez J. , Rios-Jara D. , Akachi T. , Escudero R.
Published: March 2011

Based on very recent experimental evidence about magnetic transitions in high-Tc superconductors the role of superconductivity and magnetism is analyzed. A model of interacting electrons in a one-dimensional system is constructed, taking into account that antiferromagnetic interactions in the underlying lattice are present. The origin of this antiferromagnetism could be due to local Y d-electrons or rare earth f-electrons, related to the structure. Self-consistent calculations in this model show the possibility of a new state, with a gap, in which there are electron pairs. The characteristics of this new state are discussed in relation to superconductivity. The results of this model suggest that an extension of it could be applied to the new superconducting ceramics.
Raman and Infrared Studies of Sr2TiO4 - an Isomorph of (La,Sr)2CuO4
Authors: Burns Gerald , Dacol F. H. , Kliche G. , König W. , Shafer M. W.
Published: March 2011

In order to better understand the phonon spectra obtained from ceramic (La,Sr)2CuO4 superconductors, we have studied the infrared and Raman spectra of the isomorphic material Sr2TiO4 (as well as related materials). As a consequence, various aspects of the spectra of both materials are better understood, and this is discussed.
Lattice Dynamics and Ionicity in the High-Temperature Superconductors
Authors: Cohen R. E. , Pickett W. E. , Boyer L. L. , Krakauer Henry
Published: March 2011

Using a non-empirical ionic model, we find harmonically unstable, double well potential surfaces for both La2CuO4 and YBa2Cu3O7 which may be related to the high temperature superconductivity. We have applied the Potential Induced Breathing (PIB) Model to La2CuO4 and YBa2Cu3O7 and find that the ionic description gives semiquantitative agreement with structural and vibrational observations. Furthermore, comparison with self-consistent linearized augmented plane wave [1] (LAPW) calculations shows that ionic contributions to the bonding and lattice dynamics of oxide superconductors are large. For La2CuO4 we find that an ionic description predicts the observed tetragonal to orthorhombic distortion, predicts a lower symmetry ground state, and predicts a stable oxygen breathing mode. We find harmonically unstable phonon branches that we relate to phase transitions. Unstable (anharmonic) modes will couple via ionic forces to the charge density in the metallic planes. This ionic coupling has not been included in previous lattice dynamics calculations. For YBa2Cu3O7 we find similar unstable phonon branches that involve oxygen motions perpendicular to the Cu-O bonds. We find the crystalline charge density is best approximated by overlapping ions if Cu and O ions of charge +1.6 and -1.8, respectively, are used.
Magnetic Measurements on YBa(2)Cu(3)O(x) Ceramic High Temperature Superconductors
Authors: Cornelis J. , Van Den Bosch A. , Vansummeren J. , Ooms H. , Gilissen R. , Cooymans J. , Maene N. , Biermans F.
Published: March 2011

Static magnetic susceptibilities have been measured, following the Faraday method, on a disc of home-made YBa(2)Cu(3)O(x). The superconducting ceramic disc was oriented perpendicular to the applied magnetic induction field < 10 mT. On cooling the sample in a constant field from above to below the critical temperature a Meissner-Ochsenfeld effect is observed. The interpretation of the data yields partial flux expulsion. That the flux is not completely expelled from the sample is understood on the basis of the flatness of the disc. Part of the flux which had not been expelled by the Meissner-Ochsenfeld effect remains trapped in the cooled superconducting material.
Far Infrared Spectroscopy of RBa2Cu3Ox with Variations in R and x
Authors: Crawford M. K. , Farneth W. E. , Bordia R. , Mc Carron E. M.
Published: March 2011

We report far infrared reflectance measurements of RBa2Cu3Ox, where R-Y, Er and Nd and 6<×<7 for YBa2Cu3Ox. Based on these measurements we assign the observed phonon features. In particular, one vibration is clearly identified as an R vibration, while the lowest energy mode (near 151 cm-1) is associated with the linear Cu-O chains.
Ultra-Low-Field Squid Magnetic Measurements on High Temperature Ceramic YBaCuO Superconductors
Authors: Cronemeyer D. C. , Malozemoff A. P. , Mcguire T. R.
Published: March 2011

We report ultra-low-field (5 mOe - 1 Oe) magnetic measurements on a ceramic sample of YBaCuO. A positive remanent moment is observed which accurately equals the difference of the field-cooled and zero-field-cooled moments throughout the temperature range. At higher fields this relationship breaks down. A reversible region is observed near the superconducting transition temperature which is independent of field. These results are discussed in the context of recent models.
Frequency Dependence of the Absorption Component of the Magnetic Susceptibility in Superconducting Y1Ba2Cu3O7
Authors: Ducharme S. , Durny R. , Hautala J. , Symko O. G. , Taylor P. C. , Kulkarni Sudhir
Published: March 2011

We report measurements of an apparent magnetic-field-dependent absorption (imaginary part of the a.c. magnetic susceptibility) in superconducting Y1Ba2Cu3O7 ceramics and crystals. The absorption, which is observed over a wide range of frequencies but only when the material is below the superconducting transition temperature, is characterized by a narrow (∼ 30 Gauss FWHM at 6 MHz) peak and a wide (> 10 kG) feature, both of which are maximum at zero magnetic field. The absorption strength varies approximately as one over the square root of the frequency. The unusual magnetic-field-dependent peaks in the magnetic susceptibility are inherent in single grains and therefore do not originate from intergrain Josephson currents or multigrain (i.e., percolative) loops. The susceptibility peaks must be due to bulk behavior, interactons at grain surfaces, intragrain current loops, or intra-grain Josephson Junctions.
Photoinduced Absorption in the La2−xSrxCuO4–5 System: 2 eV Bandgap and Long-Lived Defect States
Authors: Epstein A. J. , Roe M. G. , Ginder J. M. , Zuo F. , McCall R. P. , Song Y. , Chen X.-D. , Golben J. P. , Gaines J. R. , Wigen P. E. , Ehrenfreund E.
Published: March 2011

The discovery of high temperature superconductivity in the La-Ba-Cu-O system [1] has stimulated extensive study of these and related materials. A number of band structure calculations [2,3] have been performed for these materials to explain their electronic structure, and models invoking electron-phonon, electron-electron, or excitonic mechanisms have been proposed for the unusually high Tc [4–9]. Several optical studies were performed[10–12] on sintered pellets or single crystals in an attempt to reveal the electronic structure. It is important to understand the electronic structure of the parent La2CuO4 compound and the defect states that are introduced into the system upon addition or removal of electrons- accomplished by doping or photoexcitation-as they are critical in understanding the mechanism for superconductivity.
Effect of Oxygen Pressure on the Phase Transformation in the Y-Ba-Cu-O and Related Superconducting Oxides
Authors: Kubo Y. , Nakabayashi Y. , Tabuchi J. , Yoshitake T. , Manako T. , Ochi A. , Utsumi K. , Igarashi H. , Yonezawa M.
Published: March 2011

The orthorhombic-tetragonal YBa2Cu3O7-δ phase boundary in the δ-T diagram was determined by the detailed isobar TG measurement under the oxygen partial pressures of 1 to 0.01 atm. The phase boundary was found not to be located at 5 = const, but to have a slope of dδ/dT∼−4.7 × 10-4K-1. Using the same method, the transformation temperatures of a series of lanthanide substituted systems were measured at 1 atm. O2. The transformation temperature increased with increasing the atomic number of the lanthanide element. All these experimental results are well explained in terms of the order-disorder transformation caused by the repulsion energy between the nearest neighbor oxygen atoms on the Cu plane sandwiched by Ba planes.
Synthesis and Superconducting Properties of Metastable Y(Ba2−xYx)Cu3O7+δ
Authors: Iqbal Z. , Reidinger F. , Bose A. , Cipollini N. , Eckhardt H. , Ramakrishna B. L. , Ong E. W.
Published: March 2011

The oxygen-deficient orthorhombic oxide YBa2Cu3O7-δ has been the center of intense recent interest because of its high Tc superconducting proper-ties[l-3]. Recently, the structurally related La3Ba3Cu3O15-δ, has received increasing attention[4–9]. The pure Y analog[10,11] cannot be synthesized by usual solid state reaction routes probably because of its metastability near 880°C. Here we report on the successful synthesis of pure tetragonal Y3,Ba3CU6O15-δ (referred to as Y 3–3–6), via the firing of an atomically mixed citrate precursor at a relatively low temperature. X-ray diffraction data characterize Y 3–3–6 to be isostructural with the corresponding La compound[4]. The unit cell composition can then be written as: Y(Ba2−x Yx) CU3O7+δ with the parent compound at x = 0.50. Specimens of Y 3–3–6 at × = 0.50 and 0.375 annealed at 650°C under 1 atmosphere of O2 are non-superconducting. Higher pressure O2 annealing and fluorine-doping leads to a 1–5% superconducting volume fraction with onset at 85K. Annealing near 880°C creates a 10% superconducting fraction which shows near-zero resistivity at 62K and a reproducible, small resistive transition near 260K.