Sergey Samoilenkov

Development and production of second generation high T c superconducting tapes at SuperOx and first tests of model cables

The SuperOx and SuperOx Japan LLC companies were founded with the goal of developing a cost-effective technology for second generation HTS (2G HTS) tapes by utilizing a combination of the most advanced chemical and physical deposition techniques, together with implementing original tape architectures. In this paper we present a brief overview of our production and experimental facilities and recent results of 2G HTS tape fabrication, and describe the first tests of the tapes in model cables for AC and DC power application.

Customised 2G HTS wire for applications

Reproducibility of superconducting properties and suitability for specific applications by means of customised finish are two important attributes required from commercial 2G HTS wire. This paper reviews the consistent performance of SuperOx production 2G HTS wire and describes two novel customisation options: surround polyimide varnish insulation and composite bulk materials assembled with 2G HTS wires soldered together.

MOCVD of YBCO and Buffer Layers on Textured Ni Alloyed Tapes

A RTR MOCVD was used for the deposition of YBCO and various oxides. A new MOCVD technique enable us to coat the metal tape directly without formation of NiO. At a low oxygen partial pressure the buffer layers were grown on the metal tape with good in plane and out of plane texture. The texture of the MgO buffer layers depend on the surface of the alloyed Ni-tape. YBCO layers exhibit excellent out of plane texture with FWHM(005) = 1.4 - 3.5deg and good in plane texture of FWHM(103) = 5-7deg. On MgO buffered Ni5at%W the inductive measured jc was 0.3-0.7 MA/cm2 at 77 K.

In situ growth of superconducting (Pb,Cu)2(Ba,Pb)2YCu2Oy epitaxial thin films by MOCVD

Abstract Superconducting ( T c =38 K) thin films of (Pb,Cu) 2 (Ba,Pb) 2 YCu 2 O y have been grown by MetalOrganic Chemical Vapor Deposition (MOCVD) on single crystal (001)LaAlO 3 substrates in a single deposition run. The critical parameters for stabilizing lead-containing compounds in thin films are considered. It was found that a high vapor pressure of lead-containing species in the gas phase during the film growth determines the stability of formed compounds. The results of high-resolution transmission electron microscopy (HREM) and X-ray diffraction analysis (XRD) analyses of (Pb,Cu) 2 (Ba,Pb) 2 YCu 2 O y thin films are presented.

MOCVD Buffer and Superconducting Layers on Non-Magnetic Biaxially Textured Tape for Coated Conductor Fabrication

In this article, we present recent developments in the metal-organic chemical vapor deposition (MOCVD) route to coated conductor fabrication made at SuperOx. Two new buffer layer architectures on nonmagnetic Ni-Cr-W biaxially textured substrates are described. With the use of these architectures we have achieved critical currents in the range of 100-140 A/cm-width for the fully MOCVD produced coated conductors on Ni-Cr-W in the reel-to-reel mode. We have also demonstrated over 10-m-long MOCVD-high temperature superconductor tapes on the ion beam assisted deposition templates with Ic exceeding 300 A/cm-width.

Epitaxial phase stabilization in thin films of complex oxides

Abstract A survey of experimental results is given presenting the successful growth of oxide epitaxial thin films in thermodynamic conditions ( T , pressure, p (O 2 ), composition), which are far from those necessary for the stable existence of these phases in polycrystalline state. The unstable-in-bulk BaCu 3 O 4 , NdMn 7 O 12 , rare earth nickelates RNiO 3 and unusual phase relations in R–Ba–Cu–O systems are the examples. The stabilizing effect was observed in thin films only if the epitaxial growth was induced. The effect is thought to be of thermodynamic origin, rather than of kinetic one, and it is supposed to be the result of the low surface energy of coherent interfaces formed at the epitaxy.

Pinning Properties of PLD-Obtained GdBa2Cu3O7-x Coated Conductors Doped With BaSnO3

This work is devoted to high-rate pulsed laser deposition of BaSnO₃-doped superconducting films on long buffered metal tape substrates with the use of pilot-scale equipment and common deposition conditions typical for commercial 2G high-temperature superconducting wire production at SuperOx Japan. BaSnO₃ inclusions were found to grow as nanocolumns elongated along the vertical direction and having biaxial texture. With BaSnO₃ doping, the angular dependence of critical current measured at 77 K became much more isotropic. At 77 K, the lift-factor (<italic>I_c/I_c^s^f)</italic> values in BaSnO₃ -doped samples increased almost twice in 0.5–3 T magnetic field in perpendicular orientation; at the same time, the absolute critical current increased only by 10%. At 4.2 K, in 0.5–3 T perpendicular field, the absolute critical current in doped samples increased 1.8 times.

Possible Reasons of Lorentz Force Direction Influence on Anisotropy of 2G HTS Tapes Critical Currents

Progressive advance in technology of second-generation (2G) high-temperature superconducting (HTS) superconductors leads to the continuous rise of their critical-current density. Critical current of 200 A at 4-mm tapes and ~600 A at 12-mm tapes is already state of the art. One problem is that critical currents of HTS tapes have sounding anisotropy. Moreover, it was found that in external magnetic field, the Lorentz force direction is affecting the critical currents of 2G HTS tapes. Two hypotheses were suggested as a reason for this phenomenon. This is the result of the properties of crystal lattice in a 2G HTS tape or of spatial inhomogeneity of critical currents across the width of HTS tapes. In this paper, the verification of hypotheses was done by the cutting of wide 2G HTS tapes into narrow tapes and measuring of critical-current anisotropy in narrowed tapes. We present the experimental results and their discussion. We concluded that the spatial inhomogeneity of critical-current density in the cross section of a tape is the reason for the Lorentz force direction influence on the anisotropy of 2G HTS tape critical currents.

Thin film nanocomposites based on YBCO with defects comprised of self-assembled inclusions

The critical current of YBCO superconducting coatings in external magnetic field can be enhanced by incorporating high density of extended nanometer-sized defects to act as pinning centers for magnetic vortexes. One particular variant involves the deposition superconducting film with columnar defects comprised of self-assembled BaZrO3, BaSnO3 or BaHfO3 nanoinclusions. Here we report the results of our study of YBCO films with different inclusions prepared by MOCVD. For the first time, we succeeded in growth of YBCO films with oriented nanoinclusions of BaCeO3 phase and demonstrate that it does not reduce Tc of YBCO, in contrast to BaZrO3 or BaSnO3. The best composite thin films revealed the Tc value of about 88K and critical current density at 77K above 1MA/cm2 in self-field and around 0.3 MA/cm2 in 1 T (B//c).

Insulation effect on thermal stability of Coated Conductors wires in liquid nitrogen

Superconducting wires are not perfectly homogeneous in term of critical current as well as stabilization. In resistive fault current limiter applications this could lead to hot spots if the fault current is only slightly above the nominal current of the device. Increasing stabilization by using thicker silver coating for example may prevent this problem but this method implies longer wire length to maintain the same impedance during a fault. Very efficient cooling in another way to prevent hot spots, this can be achieved in nucleate boiling regime. Optimal insulation can be used to prevent film boiling regime, staying in nucleate boiling regime in a much broader temperature range. In this work a novel technique is used to monitor in real time the temperature of the wire during the quench. Using this method several increasing insulation thicknesses are tested, measuring for each the heat exchange rate to the nitrogen bath. Exchange rate measurements are made in quasistatic regime and during the re-cooling of the wire. SuperOx wires provided with different insulation thicknesses exhibit an excellent stability, far above a bare wire. On the other side, for very thick insulations the stability gain is lost. Re-cooling speeds dependency on insulation thicknesses is measured too.