The spatial distribution of superconducting properties using variable temperature scanning laser microscope (VTSLM) has been investigated. The superconducting thin film used in this study is an epitaxial YBa2Cu3O7 film photolithographically patterned to a 300 μm-wide bridge. Since the voltage response, δV(x,y) is proportional to dR/dT(x,y), the spatial distribution of superconducting transition can be obtained in VTSLM images. In the resistive transition region, there is a strong correlation between the VTSLM images and the resistance of the sample. With decreasing resistance, the area with large δV(x,y) shifts toward the ends of the bridge. This indicates that the resistive transition is not uniform and both ends of the bridge have lower transition temperature, Tc. Different currents or different output power of lasers do not affect the images. VTSLM technique is a powerful tool to image the local superconducting properties and to identify the weaker superconducting areas.

The use of magnesium diboride in superconducting magnets, transmission lines, or other large-scale applications depends on the transport-current characteristics of this material in magnetic field, and how they compare to the properties of conventional and high-temperature superconductors. Thin films of boron grown on sapphire substrates during electron-beam evaporation were exposed to Mg vapor to produce 0.5-μm thick layers of the metallic compound MgB2. Four-terminal measurements of their voltagecurrent relations, E(J), were carried out before and after exposure to Bφ =1-T and higher doses of 1-Gev U ions. These doses lowered critical temperatures Tc≈39 K less than 0.1 degree, raised the normal-state resistivity, and reduced the loss-free critical current density, Jc. Higher doses added little. The reduction of current densities was greater in the presence of applied magnetic field greater than 0.1 T.

Pulsed laser deposition of Yba2Cu3O7-δ?(YBCO) coated conductors was studied for the range of P(O2) from 120 mTorr to 1200 mTorr, higher than typically used oxygen partial pressures during deposition. The purpose of the investigation was to determine the sensitivity of YBCO film quality to varying P(O2) for scaled-up fabrication of long-length coated conductors. Deposition at high P(O2) (≥?400 mTorr) gave very high and more consistent critical temperatures (Tc ≈?92 ±?0.4 °K) than results obtained at lower oxygen partial pressures (≤?200 mTorr) as determined by magnetic susceptibility measurements. Typically, the lower partial pressures are used although the laser fluence used in this research (3.2 J/cm2) is higher than typical. Transport Jc's were consistantly high for a wide range of oxygen pressures, 5–8 ×?106 A/cm2 at 77 K, self-field for P(O2) = 200–1200 mTorr. These results indicate that pulsed laser deposition of YBCO is relatively insensitive to P(O2) at the higher pressures of oxygen considered.

High quality single crystals of Hg(Re)1223 were grown by the flux method using BaZrO3 crucible, which is stable against molten Ba-Cu-O. The maximum size of the obtained crystal was 1 × 1.1 × 0.1mm3 in dimension. X-ray diffraction analysis revealed that grown crystals are of Hg(Re)1223 single phase with c0 = 15.7 å. In the magnetic hysteresis curves for post-annealed Hg(Re)1223 single crystals under H // c, large second peak effect was found with steep increase of magnetization at approximately 2∼3kOe independent of temperature. The peak field systematically increased with a decrease of temperature, suggesting generation of field-induced pinning. Critical current density and irreversibility field of single crystals were dependent on synthesis batch, possibly due to the difference in resulting concentration of Re, while postannealing under various conditions did not affect largely for critical current properties. Irreversibility lines of the Hg(Re)1223 single crystals locate at higher fields than that of Re-free Hg1223. This suggests that electromagnetic anisotropy is reduced by Re-doping, which is consistent with the recent results on the resistive anisotropy in the normal state.

A top priority of the U.S. government is to improve the energy delivery infrastructure. According to the report issued May 2001 by the National Energy Policy Development (NEPD) Group, “For the electricity we need, we must be ambitious. Transmission grids stand in need of repair, upgrading, and expansion…if we put these connections in place, we'll go a long way to avoiding future blackouts.” Superconductivity is such an important aspect of our nation's energy future that we should “…expand the Department's research and development on transmission reliability and superconductivity.” Prototype superconducting power cables that will help upgrade our power grid when commercialized later this decade are being demonstrated today in Carrollton, Georgia and Detroit, Michigan. Much research remains, however, if the superconducting wires are to have the electrical performance and low-cost features necessary for U.S. companies to fully commercialize new transmission cables that will help eliminate the bottlenecks in urban areas. The U.S. Department of Energy (DOE) leads the U.S. national effort to develop high-temperature superconducting (HTS) wires and to demonstrate prototype electric power applications using the best wires available today. The industry-led Second Generation Wire Initiative is exploiting breakthroughs at the national laboratories that promise unprecedented current carrying capacity in HTS wires at lower cost than first-generation “BSCCO” wires. Some of the recent progress in the U.S. development of HTS “coated conductors” and in fielding prototype applications is presented

In an effort to develop alternative single buffer layer technology for YBa2Cu3O7-δ (YBCO) coated conductors, we have investigated LaMnO3 (LMO) as a potential buffer layer. High-quality LMO films were grown directly on biaxially textured Ni and Ni-W (3%) substrates using rf magnetron sputtering. YBCO films were then grown on LMO buffers using pulsed laser deposition. Detailed X-ray studies have shown that both YBCO and LMO layers were grown with a single epitaxial orientation. Rutherford backscattering spectroscopy (RBS) analyses have indicated the ratio of La to Mn ratio is 1:1. SEM micrographs indicated that 3000-Å-thick LMO films on biaxially textured Ni (100) substrates were dense, continuous and crack-free. A high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films grown on LMO-buffered Ni or Ni-W substrates. We have identified LaMnO3 as a good diffusion barrier layer for Ni and it also provides a good template for growing high current density YBCO films.

We present atomic resolution Z-contrast images, electron energy loss spectroscopy (EELS) and theoretical calculations in support of a band-bending model for the effect of grain boundaries on critical currents. In the high angle regime, dislocation cores are closely spaced and the boundary is modeled as a continuous junction, with a width determined by the dislocation density per unit boundary length. This quantitatively explains the approximately exponential reduction in critical current. In the low angle regime, where dislocations are separated by substantial good passages, explicit calculations of flux pinning are presented. Significant differences are found between a strain and band-bending mechanism. Recent data fit the band-bending model and suggest substantial improvement is possible through doping to a flat band condition.

We present a study of the {100}<100> biaxially textured Ni (001) surface and oxide seed layer nucleation by in situ reflection high-energy electron diffraction and Auger electron spectroscopy. Our observations revealed the existence of a c(2×2) superstructure on the textured Ni surface due to segregation of sulfur contained in the bulk metal. The sulfur superstructure promotes the epitaxial (002) nucleation of seed layers such as Y2O3-stabilized ZrO2 (YSZ) and CeO2 on the metal and optimizes the biaxial texture necessary for high Jc superconductors on RABiTS.

The phase diagram of La2-xSrxCuO4 is interpreted. From the virial theorem, it is argued that the cross-over from localized to itinerant electronic behavior in the range 0 < x < 0.3 is characterized by fluctuations between two equilibrium Cu-O bond lengths. Cooperative local fluctuations give rise to one-hole correlation bags of 5 to 6 copper centers on the underdoped side, to strong-correlation fluctuations in an itinerant-electron matrix on the overdoped side. Spinodal phase segregation between an antiferromagnetic, insulating parent phase and the superconductive phase occurs in the underdoped compositions, between the superconductive phase and the metallic overdoped phase on the other side of the phase diagram. Ordering of the fluctuations into a travelling bipolaronic charge-density/spin-density wave of composition x ≈?1/6 yields heavy fermions of symmetry (x2− y2) coexisting with light electrons; the high-temperature superconductive pairs are condensed out from the heavy fermions.

Biaxially aligned Indium Tin Oxide (ITO) thin films to be used as electrically conductive buffer layers were prepared by an Ion-Beam Assisted Deposition (IBAD) process on various substrates. Two Kaufman ion sources with 2.5 cm diameter were employed for the assisting and the sputtering beam, respectively. All deposited films revealed (001) oriented film growth with a strong in-plane alignment. The degree of the in-plane orientation was studied depending on the ion-beam parameters and the incident angle. Investigations (TEM and X-ray) of the texture evolution of these IBAD films during film growth were carried out. An in-plane texture of 12.6°FWHM for a 1 μm thick film has been achieved so far. The quality of the buffer has been demonstrated by the subsequent deposition of high-current carrying YBCO-films deposited by thermal coevaporation using a 3–5 nm thick Y2O3 interlayer. A jc of 0.76 MA/cm2 (77K, 0T) has been obtained for a 1 cm × 1 cm sample with ITO of 20° FWHM.

Each process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities.

We have studied the kinetics of the chemical reaction between Mg and B by differential thermal analysis. There are two exothermal peaks observed at 500 and 650 °C. We speculate that the first exothermal peak is mainly related to the chemical reaction between Mg and oxygen, forming MgO. The second exothermal peak, which coincides with the melting point of Mg, clearly indicates the chemical reaction between Mg and B. The effect of synthesis conditions and defects on the transport property of MgB2 has been investigated. A correlation between the microstrain, the lattice parameters, and the Mg concentration were observed and are discussed.

The (Bi,Pb)2Sr2Ca2Cu3O2 system [also know as (Bi,Pb)-2223] has shown promise for use in superconducting tapes and wires due to its high transition temperature and high critical current density. The tapes and wires are usually fabricated by the powder-in-tube method, after which they are subjected to thermal and mechanical treatments. Depending on the nature of the heat treatment, phase transformations occur in the powder and it is of paramount importance to understand the response of the powders to different processing conditions. In this study, we have synthesized a precursor powder of the nominal composition Bi1.8Pb0.33Sr1.87Ca2Cu3Oyby spray pyrolysis. The powder was then calcined under controlled conditions between 760 and 800°C in an atmosphere between 0 and 21% O2for 2 to 24 hours with controlled heating and cooling, such that different amounts of Pb are incorporated into the majority phase. The resultant powders were then converted to the (Bi,Pb)-2223 phase with suitable heat treatments. Using powder Xray diffraction and magnetization measurements, the volume fractions of the secondary phases in the precursors were estimated and the effect of the phases on the conversion to the (Bi,Pb)-2223 phase was studied. We show that the ratio of the intensity of the (020) and (115) reflections of the (Bi,Pb)-2212 phase can be used to tune the precursor powders for optimal conversion. While a lower fraction of the secondary phases such as CaO and CuO is desirable in the precursor powders, a higher volume fraction of Ca2PbO4 seems to help in the rapid conversion to the (Bi,Pb)-2223 phase.

AC susceptibility measurements as a function of temperature, frequency and applied ac field amplitude were performed on two rectangular bar shaped samples of nominal composition Bi1.6Pb0.4Sr2(Ca1-xMx)2Cu3Oδ, with M=Pr, Gd, and x=0.01, obtained by the usual solid state reaction route. The incorporation of the rare earth elements at low concentration stage results in an improvement of grain connectivity for the sample doped with Pr. On the other end, the ac field amplitude and frequency dependence of the susceptibility curves disclosed bulk pinning hystersis loss feature. The potential barrier height, activation energy at the grain boundary extracted from the low temperature peak revealed that flux creep is governing the pinning mechanism inside the samples. Qualitative discussion in the framework of the critical state model was highlighted

We report on the successful preparation of intrinsic Josephson junctions on high-quality BSCCO-2212/2223 superlattice thin films grown by MOCVD. The surface of as-grown films was very smooth with the roughness of the order of a half unit cell. Mesas were effectively structured on the film by the liquid-nitrogen-cooled dry etching method. A typical I-V characteristic in the c-axis direction of a BSCCO film shows the hysteresis and multiple resistive branches. The number of branches is consistent with that of junctions calculated from the height of a mesa structure. This indicates that BSCCO-2212/2223 superlattice films consist of a series array of S(CuO2 bilayer) / I(SrO, BiO layers) / S(CuO2 trilayer) junction. The formation of stacked Josephson junctions was also confirmed by the temperature dependence and the magnetic field dependence of Ic.

We report the synthesis of superconducting MgB2 thin films grown in-situ by molecular beam epitaxy (MBE). Mg-rich fluxes are deposited with B-flux by electron beam evaporation onto c- and r-plane sapphire substrates. Deposition temperature is varied between 260 ∼ 320 °C. Base pressure of the MBE chamber is at low 10-10 Torr, rising to 10-8 Torr during deposition due mostly to the presence of hydrogen and nitrogen. Asgrown MgB2 films show superconducting transition at ∼ 34 K with ΔTc < 1 K. The films on c-plane sapphire substrates exhibit c-axis oriented peaks of MgB2, and full-width at half maximum of 3 degree in their rocking curves. Azimuthal phi-scan of the MgB2(101) peak shows 12-fold symmetric peaks, which is confirmed by selected area diffraction pattern in transmission electron microscopy (TEM). Plan-view TEM shows hexagonal-shaped grain growth with grain size of about 400 Å.

The newly discovered superconductor, MgB2, has significant potential for a number of electric power applications, even though its critical temperature, TC, is “only” 39 K. In recent months, there has been rapid improvement in its critical state parameters, JC and H*, properties crucial to deployment in power devices, which now rival NbTi at 4.2 K, and equal or surpass many of the high temperature superconducting copper oxide perovskites in the 20 – 25 K range. Moreover, substantial progress has been achieved in realizing wire embodiments that appear economically scalable to commercial production. In this paper, we will review several opportunities to exploit these developments for transformer and electric cable applications, and hint at the possibility of a novel and visionary power delivery system centered on an MgB2-based dc cable cooled by gaseous or liquid hydrogen supplying both electrical and chemical energy to the end user.

YBCO films prepared from metal trifluoroacetate (TFA) precursors on oxide-buffered textured non-magnetic substrates have achieved performance levels equaling that on oxide buffered textured Ni substrates. Critical current densities of 0.7 MA/cm2 to 1.0 MA/cm2 have been achieved in 0.4 µm thick YBCO films on short-length of CeO2/YSZ/Y2O3/Ni/Ni-13wt%Cr substrates. High-quality epitaxial buffers comprising a Ni layer, Y2O3 seed, YSZ barrier and CeO2 cap layers have been deposited over meter long tapes of deformation textured Ni and Ni-13%Cr using reel-to-reel processes. High-performance TFA-based YBCO films have been deposited on 0.1 m to 0.3 m lengths of these oxide buffered substrates using reel to reel processes. Critical current densities up to 1.0 MA/cm2 have been achieved in 0.4 µm thick YBCO films on CeO2/YSZ/Y2O3/Ni substrates. Using multiple coats of the metal trifluoroacetate precursors, thicker YBCO films have been demonstrated on oxide buffered substrates. Critical currents in excess of 100A/cm-width have been achieved for 1.2 µm -1.6 µm thick YBCO films on short lengths of CeO2/YSZ/Y2O3/Ni substrates.

Bi2223 single crystals were grown by the floating zone method with an extremely slow growth rate of 0.05 mm / h. The largest size of the plate-like single crystal was approximately 3 × 2 × 0.1 mm3. The X-ray diffraction analysis and DC susceptibility measurements revealed that the grown crystals were almost single phase of Bi2223 with a very small percentage of Bi2212 intergrowth. Then carrier doping was systematically controlled in a wide range from underdoping to overdoping by post annealing under various conditions. Tc of the crystals was found to vary from 98 K (underdoped) to 108 K (overdoped) with Tc = 110 K for optimally-doped. In the optimally-doped phase the electromagnetic anisotropy factor, γ2 of Bi2223 was smaller than that of Bi2212. Abrupt resistivity drop was observed under fields below the second peak field of the magnetization hysteresis loops, suggesting a first order phase transition of the flux line lattice. Magnetic phase diagram of Bi2223 single crystals for H // c was found to be similar to that of Bi2212.

The inclined-substrate deposition (ISD) method for growth of biaxially textured MgO is of interest due to its applications in coated conductors based on high-temperature superconductor (HTS). The ISD method is especially attractive since it offers the potential to produce a high–quality biaxially textured layer in a simple and efficient process. In this work, Yba2Cu3O7-x (YBCO) coated conductors based on two-step deposited MgO buffer layers (ISD and homoepitaxial) on Hastelloy tapes were examined by high-resolution electron microscopy (HREM) to study both the structure of individual layers and, especially, the interfaces between them. Special attention was paid to the MgO buffer layer because of its importance to biaxial YBCO formation. TEM investigation shows the MgO [111] direction is not parallel to the substrate normal but tilted slightly toward the deposition direction. The second layer of MgO has a good epitaxial relationship with the first layer, while dislocations were found near the interface area of the MgO layers. Twin boundaries, which are in the (111) plane, were found between the ISD MgO columns. The multi-buffer layers gave better growth of epitaxial YBCO.