The frequency/wave-vector dispersion relation for symmetry directions in niobium was measured at 296 deg K by means of inelastic neutron scattering. Analysis the data on basis Born-von Karman theory indicates that effective interatomic forces are very long range. force model also used to calculate frequency distribution function. (C.E.S.)

Experimental evidence of c-axis correlated vortex pinning in superconducting Y Ba2Cu3O7−δ (YBCO) thin films deposited on annealed CeO2-buffered sapphire was obtained. YBCO were grown by pulsed laser deposition () substrates. Prior to the film deposition, a self-assembly process initiated where high-temperature (1025 °C) O2 annealing induced surface reconstruction CeO2 The result an atomically flat layer, self-assembled formation nanodots top wetting and high critical current density such...

The magnetic field angle dependence of the critical current density Jc(H,θ) was measured in epitaxial YBa2Cu3O7−δ (YBCO) thin films with strong flux pinning (Jc>25 GA m−2 at 77 K). YBCO were classified into two categories: (1) that showed Jc(θ) peaks around shape a stratovolcano (i.e., like Mount Fuji) and (2) high, broad centered addition to less prominent peaks. Transmission electron microscope observations revealed category 1 contained high very small precipitates, most which than 7 nm, 2...

We evaluated for the first time thickness dependence of critical current density (Jc) micrometre thick YBCO films on CeO2-buffered sapphire. were successfully grown in microcrack-free form up to a by large-area pulsed laser deposition. Jc was found decrease exponentially with thickness. Results suggest that reduction film can be attributed an evolving microstructure as function thickness, well corresponding change defect structures responsible flux pinning. It observed porosity and roughness...

Flux pinning centres having correlation along the c-axis in epitaxial YBCO films were investigated by measuring magnetic-field angle ψ dependence of critical current density JC and observing microstructure. First, oriented prepared on four different substrates at three target-to-substrate distances D using a pulsed-laser-deposition method. Films deposited LaAlO3 (100) CeO2/Al2O3 with large (112 or 142 mm) showed narrow peaks versus curves when magnetic field was applied parallel to (B//c)....

Flux pinning properties of centres having correlation along the c-axis in epitaxial YBCO films were investigated by measuring magnetic-field angle ψ-dependence critical current density JC and E–J-characteristics. prepared using pulsed-laser-deposition method on four different substrates at three target-to-substrate distances D. The showed large peaks when magnetic field B was applied parallel to (), we observed two types JC-peak: that is, a broad peak for deposited small D (50–60 mm), narrow...

Nondestructive, ac inductive methods are widely used to measure critical current densities J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of large-area superconducting films. However, conventional not accurate because they have considered the electric-field E criterion measurement. In these methods, magnetic fields generated with currents I xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> cos wt in a small coil mounted just above...

Experimental evidence of a cooperative self-assembly process was obtained where high-temperature O2 annealing (1000 °C) induced mass transport CeO2 deposited on R-cut sapphire substrates to form surface reconstruction the substrate. When film exceeded critical thickness (∼10 nm), an atomically flat with high density nanodots preferred by (revealed scanning atomic force microscopy) and layers had lattice perfection x-ray diffraction). YBa2Cu3O7−δ films grown such CeO2-buffered transition...

High-temperature annealing performed at ~1000 °C or higher in an oxidizing atmosphere is a simple technique to significantly modify the as-grown nanostructures of CeO2 films, which are typically granular with high surface roughness. We evaluated effect high-temperature on various films deposited by three deposition methods, namely standard pulsed laser (PLD), large-area deposition, and electron-beam evaporation. promotes epitaxy crystallinity, as well stabilization flat (001) surfaces CeO2....

YBa 2 Cu 3 O 7 − δ (YBCO) films were fabricated by pulsed laser deposition on deliberately miscut Al2O3(11¯02) buffered with CeO2. Scanning electron microscopy observations demonstrated that 1-μm-thick YBCO microcrack free. Characterization of the revealed porous morphology and high crystalline quality CuO planes tilted vertically terminated frequently. These features are considered to be a contributing factor strain-relieving mechanism responsible for increase in film thickness without...

The surface morphology of YBCO films deposited by a large-area PLD system is characterized pores varying depths and sizes. presence these has been correlated to the yttrium-rich composition in films. In-depth studies on interplay parameters including oxygen background pressure, target–substrate distance, film composition, target stoichiometry porosity LAO (100) substrates have conducted. Off-stoichiometry attributed scattering ablated species with ambient. relative excess yttrium causes...

In an ac inductive method to measure critical current densities J/sub c/ of superconducting films by detecting third-harmonic voltages V/sub 3/ cos 3/spl omega/t, magnetic fields are generated with currents I/sub 0/ /spl omega/t in a small coil mounted just above the film. is calculated from threshold th/, at which full penetration field achieved and starts emerge. For convenience, th/ has been usually determined constant-voltage criterion, e.g., 3///spl radic/2 = 50 mu/V. However,...

Relatively thick YBCO thin films (thickness d>0.5 /spl mu/m) ideal for fault current limiter as well microwave applications have been successfully prepared by large-area pulsed laser deposition (PLD) on CeO/sub 2/-buffered sapphire substrates. The attainment of an unusually high film thickness (up to 2.0 without microcracking is attributed in part the presence pores correlated with yttrium-rich composition films. effect using targets varied Y:Ba:Cu ratios porosity and surface morphology was...

Critical current density (Jc) was measured inductively at 77.3 K over large-area YBa2Cu3O7−δ (YBCO) films deposited by pulsed laser deposition (PLD) and its behaviour with increasing YBCO film thickness (d) investigated. Jc found to decrease exponentially the thickness. In Jc–d curve two regions can be distinguished: a 'thin-film' region characteristically high exhibiting a rapid thickness, 'thick-film' region lower slower decay The magnetic-field angular dependence of for several ranging...

High-quality CeO2 buffer layers are requisite for the successful growth of YBCO thin films with excellent properties on sapphire substrates. In this study, we evaluated effect surface modification prepared by large-area pulsed laser deposition (PLD), in particular critical current density Jc and defect microstructure. High-temperature annealing (1050 °C) has been found to significantly smoothen very rough granular surfaces as-grown (surface roughness rms~5–10 nm) atomic flatness...

Critical current densities Jc were measured in as-deposited, c-axis-oriented Bi2Sr2Ca2Cu3Ox thin films with Tc values as high 97 K, which prepared by metalorganic chemical-vapor deposition. These showed (≳109 A/m2) at 77.3 K magnetic fields (≥1 T, H∥a-b plane). The best are 3.3×109 A/m2 1 T and 9.1×108 8 the highest for Bi-oxide among those reported so far. There no signs of weak links Jc(H) behavior, surface morphology examined scanning electron microscopy apparent grain boundaries....

The local critical current density Jc of Bi-2223 thick films (thickness mm) was nondestructively measured using an ac inductive technique previously developed for measuring large bulk superconductors (Mawatari et al 2003 Appl. Phys. Lett. 83 3972). In this method magnetic field is generated by drive (I0cosωt) in a small flat coil placed just above the superconducting specimen. When fluxes penetrate superconductor, third-harmonic voltage (V3cos3ωt) coil, and V3 can then be calculated as =...

Relatively thick REBa2Cu3O7?? (RE = rare?earth) films (thickness ~400?600?nm) with significantly improved surface morphology and critical current properties using a multilayered structure which alternates main layers of YBa2Cu3O7?? (YBCO) intermediate DyBa2Cu3O7?? (DyBCO) on CeO2-buffered sapphire substrates were investigated. The DyBCO layer, has close lattice matching YBCO, functions as good starting template for the growth high-quality YBCO layers. Critical density (Jc) drastically...

We investigated the effect of oxygen annealing on magnetic-field angular-dependent critical current density (Jc (θ)) in YBa2Cu3O7−x films deposited by large-area pulsed laser deposition. In an as-grown film, Jc (θ) exhibits a large maximum centered at , and small one . After 425 °C, peak grew surpassed peak. analyzed curves using anisotropic scaling theory, result shows that mostly due to random pinning increased with annealing. It is shown center defects more sensitive content film.