1,721,304 research outputs found
Epitaxial Growth of SrTiO3 Films on Cube-Textured Cu-Clad Substrates by PLD at Low Temperature Under Reducing Atmosphere
No full textThe growth of epitaxial {001}<100> SrTiO3 (STO) on low-cost cube-textured Cu-based clad substrate at low temperature was carried out by means of pulsed laser deposition (PLD). STO film was deposited in one step under a reducing atmosphere (5% H2 and 95% Ar mixture) to prevent the oxidation of the metal surface. The optimization of PLD parameters leads to a sharpest biaxial texture at a temperature as low as 500 °C and a thickness of 500 nm with a (100) STO layer. The upper limit of highly textured STO thickness was also investigated. The maximum thickness which retains the best quality {001}<100> texture is 800 nm, since the texture is preserved not only through the layer but also on the surface. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements showed that STO films are continuous, dense, and smooth with very low roughness (between 5 and 7 nm). This paper describes the development of STO layer by means of PLD in absence of oxygen throughout the process, suggesting an alternative and effective method for growing highly {001}<100> textured STO layer on low-cost metal substrates. © 2017, The Author(s)
Anisotropy and directional pinning in YBa2Cu3O 7-x with BaZrO3 nanorods
No full textMeasurements of anisotropic transport properties (dc and high-frequency regime) of driven vortex matter in YBa2Cu3O 7-x with elongated strong-pinning sites (c-axis aligned, self-assembled BaZrO3 nanorods) are used to demonstrate that the effective-mass angular scaling takes place only in intrinsic physical quantities (flux-flow resistivity), and not in pinning-related Labusch parameter and critical currents. Comparison of the dynamics at different time scales shows evidence for a transition of the vortex matter toward a Mott phase, driven by the presence of nanorods. The strong pinning in dc arises partially from a dynamic effect. © 2013 Author(s)
A new approach to the synthesis of parameter dependent Lyapunov functions for the estimation of the stability margin in the presence of slowly-varying parameters.
No full textIn this paper we consider a MIMO asymptotically stable linear plant. For
such a system the classical concepts of {\em quadratic stability margin}
and {\em multivariable gain margin} can be defined. These margins have
the following interpretation: consider the closed loop system composed
of the plant and some real parameters, one inserted in each channel
of the loop; then any time-varying (time-invariant) parameters whose
amplitudes are smaller than the quadratic stability (multivariable gain)
margin result in a stable closed loop system. For time-varying
parameters whose magnitudes are between these two stability measures,
stability may depend on the {\em rate of variation} of the parameters.
Therefore it makes sense to consider the stability margin given by the
maximal allowable rate of variation of the parameters which guarantees
stability of the closed loop system. As shown in previous papers, an
estimate of this margin can be obtained with the aid of parameter
dependent Lyapunov functions. In this paper we propose a new approach to
the search of parameter dependent Lyapunov functions which leads to a
{\em much less conservative} algorithm to estimate such margin at the
price of a greater computational burden; this limits the application of
the methodology to systems containing up to three parameters.
In this context, an example will show that the proposed
methodology introduces a strong improvement with respect to
existing techniques
Hybrid superconducting neutron detectors
No full textA neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, 10B + n → α + 7Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current Ic, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed. © 2015 AIP Publishing LLC
A new approach to the synthesis of parameter dependent Lyapunov functions for robust stability analysis: With applications
No full textInvestigation of Soldered REBCO Tape-Copper Joints for Superconducting Applications
No full textIn the growing field of higherature superconductor (HTS) applications, soldered tape-copper joints are of significant importance. This is because the resistance of the joint often plays a decisive role in the design of a superconducting device, such as current leads or current terminations of cables. A common requirement to the joint is as-low-as-possible resistance and reliable reproducibility, which is crucial for achieving a homogeneous current distribution being independent within each HTS tape placed in a superconducting device. From previous studies, it is known that resistance of HTS tape-copper joint can vary for different tapes and solders. This resistance can be considered as a sum of several contributions: REBCO-layer-copper-laminating-layer interface resistance in HTS tape, copper-laminating-layer-solder and solder-copper interface resistances, and solder and copper resistances. Here, we present current status of investigations on tape-copper joints and trials to estimate different contributions in their resistance value. © 2002-2011 IEEE
Pushing the limits of applicability of REBCO coated conductor films through fine chemical tuning and nanoengineering of inclusions
No full textAn outstanding current carrying performance (namely critical current density, Jc) over a broad temperature range of 10-77 K for magnetic fields up to 12 T is reported for films of YBa2Cu3O7-x with Ba2Y(Nb,Ta)O6 inclusion pinning centres (YBCO-BYNTO) and thicknesses in the range of 220-500 nm. Jc values of 10 MA cm-2 were measured at 30 K-5 T and 10 K-9 T with a corresponding maximum of the pinning force density at 10 K close to 1 TN m-3. The system is very flexible regarding properties and microstructure tuning, and the growth window for achieving a particular microstructure is wide, which is very important for industrial processing. Hence, the dependence of Jc on the magnetic field angle was readily controlled by fine tuning the pinning microstructure. Transmission electron microscopy (TEM) analysis highlighted that higher growth rates induce more splayed and denser BYNTO nanocolumns with a matching field as high as 5.2 T. Correspondingly, a strong peak at the Bc-axis is noticed when the density of vortices is lower than the nanocolumn density. YBCO-BYNTO is a very robust and reproducible composite system for high-current coated conductors over an extended range of magnetic fields and temperatures. © 2018 The Royal Society of Chemistry
The Vortex Path Model Analysis of the Field Angle Dependence of the Critical Current Density in Nanocomposite YBa2Cu3O7-x – BaZrO3 Films Obtained by Low Fluorine Chemical Solution Deposition
No full textIn the present paper, we analyze the role of in situ grown BaZrO3 (BZO) inclusions in YBa2Cu3O7-x (YBCO) thin films prepared by chemical solution deposition using a low fluorine coating solution, on the field angle dependence of the critical current density, Jc(), data using the vortex path model. In order to form a coherent picture on the BZO doping influence on the pinning properties of the YBCO matrix, detailed structural analyses performed by X-ray diffraction techniques and microstructural evaluation by transmission electron microscopy are also presented. The evaluation of different contributions to the overall, Jc, permitted us to prove the effectiveness of the BZO inclusions acting as isotropic pinning centers, reflected in a uniform component of high relative value with respect to other components. For the studied 10 mol % BZO doping concentration, a threefold increase in the critical current density, Jc, of the YBCO host is measured, in self-field at 77 K, corresponding to a value of Jc=2.9MA/cm2, whereas a factor 10 is measured at 1 T (Jc=0.35 MA/cm2)
Microwave Measurements of Pinning Properties in Chemically Deposited YBCO/BZO Films
No full textWe present a comparative study of vortex pinning in chemically deposited YBaO nanocomposite films, with the aim of correlating the preparation method to the superconducting properties. Two sets of samples have been prepared by different low fluorine routes (one set followed the in situ approach), with different starting YBCO coating solution and with a different amount of BaZrO. The short-range vortex pinning properties have been assessed using a contactless microwave (48 GHz) technique, which yielded the vortex pinning constant (Labusch parameter) and the vortex viscosity as a function of the applied field up to 0.8 T, and for temperatures between 60 K and. The results were compared to more usual (long-range vortex motion) measurements. Despite the supposed similarity in pinning as determined from, we found significant differences between the pinning properties of the two sets of samples. It appears that the in situ approach results in stronger pinning at microwaves in the whole temperature range explored, and that this behavior is due to the smaller dimensions of BaZrO nanoparticles. This information can be very useful in the search of optimized chemical route to strong pinning superconducting nanocomposite materials. © 2002-2011 IEEE
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