Alexander Molodyk

Volatile Surfactant‐Assisted MOCVD: Application to LaAlO3 Thin‐Film Growth

A new approach to the CVD of oxides with kinetically hindered diffusion, called volatile surfactant-assisted (VSA) metal-organic chemical vapor deposition (MOCVD), consisting of film deposition in the presence of a volatile low melting point oxide (Bi 2 O 3 ) has been developed. The process was applied to the deposition of LaAlO 3 films, and a model of the process was proposed. Epitaxial and textured LaAlO 3 films on various substrates were obtained, both by thermal and VSA MOCVD. A marked improvement in crystalline quality and surface morphology was found for the films deposited by VSA MOCVD. LaAlO 3 films obtained in the presence of Bi 2 O 3 did not contain Bi. A significant increase (up to five times) of the deposition rate was observed for LaAlO 3 films deposited by VSA MOCVD compared with that for the films grown by thermal MOCVD.

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 perovskites with metallic conductivity

Abstract Single source MOCVD techniques were used to prepare perovskite films with metallic conductivity (CaRuO 3 , LaNiO 3 , La 0.5 Sr 0.5 CoO 3 and (La,Pr) 0.7 (Sr,Ca) 0.3 MnO 3 ). Structural and electric properties of the epitaxial layers on the coherent substrates are close to that of the films grown by PLD and magnetron sputtering. Peculiarities of the growth occur on the worse matched substrates, such as a mixture of two orientations, each aligned in the plane of the interface (LaNiO 3 /MgO) and variant structures in the films on YSZ. XRD of the films points to a pseudocubic lattice for all R 1 − x A x MO 3 films in spite of the distortions in the bulk material.

Pulsed-Field Magnetization of Superconducting Tape Stacks for Motor Applications

The potential of (RE)BCO superconducting bulks in rotating machine designs has been explored through numerous experimental prototypes, with the bulks being magnetized to act as held poles. However, stacks of superconducting tapes have emerged as a promising alternative for trapped held magnets partly because of their suitability for the pulsed-field method of magnetization, which is considered the most practical method of trapping flux. The benefits of using a stack of tapes as rotor held poles suitable for motors are reported. The ability to have a long rectangular stack allows for motor designs with more efficient held poles in terms of the flux produced per unit area of the pole and easy scalability. Such a rectangular stack was experimentally magnetized for the first time using a race-track-shaped pulsed-held coil giving a highly uniform and well-defined trapped held. The unique self-supporting 120 mm by 12 mm stack was produced by compressing a high-temperature-superconducting tape coated with a thin layer of solder. Shorter rectangular stacks were pulse magnetized over a temperature range of 10-77 K using a fully automated pulsed magnetization system.

The effect of stabilizer on the trapped field of stacks of superconducting tape magnetized by a pulsed field

Stacks of high temperature superconducting tape, magnetized using pulsed fields, provide a new type of permanent magnet using superconductors. To optimize the trapped field in such stacks, the role of stabilization layers was investigated by pulse magnetizing a 12 mm square stack of 15 tape layers over a temperature range of 15-77 K. The stacks consisted of commercial tape with a silver stabilizer of 1-3 mu m or tape with an additional 20 mu m layer of copper on top of 1 mu m of silver. It was found that the trapped field and flux are relatively insensitive to the stabilizer thickness, and 1 mu m of silver only, led to the highest trapped field. An FEM model was also developed for a stack that considered for the first time both the actual thickness of metallic and superconducting layers, to investigate the effect of heating and heat transfer when a stack of tapes is magnetized.

Magnetic levitation using high temperature superconducting pancake coils as composite bulk cylinders

Stacks of superconducting tape can be used as composite bulk superconductors for both trapped field magnets and for magnetic levitation. Little previous work has been done on quantifying the levitation force behavior between stacks of tape and permanent magnets. This paper reports the axial levitation force properties of superconducting tape wound into pancake coils to act as a composite bulk cylinder, showing that similar stable forces to those expected from a uniform bulk cylinder are possible. Force creep was also measured and simulated for the system. The geometry tested is a possible candidate for a rotary superconducting bearing. Detailed finite element modeling in COMSOL Multiphysics was also performed including a full critical state model for induced currents, with temperature and field dependent properties and 3D levitation force models. This work represents one of the most complete levitation force modeling frameworks yet reported using the H-formulation and helps explain why the coil-like stacks of tape are able to sustain levitation forces. The flexibility of geometry and consistency of superconducting properties offered by stacks of tapes, make them attractive for superconducting levitation applications.

Self-Supporting Stacks of Commercial Superconducting Tape Trapping Fields up to 1.6 T Using Pulsed Field Magnetization

(RE)Ba2Cu3O7-δ bulks are well known for their ability to trap high magnetic fields; however, it has been recently shown by the current authors that stacks of commercial YBCOcoated conductor tape can outperform YBCO bulks of similar size at temperatures below 60 K due to their superior thermal stability during multipulse magnetization. The latest progress in a comprehensive study being undertaken to optimize and tailor the stacks for applications will be discussed. In this paper, a method of binding layers of superconducting tape is reported, namely, soldering of Pb-Sn solder-coated high-temperature superconducting tape developed by SuperOx. The performance of tape before and after the soldering procedure is discussed, and a 100-layer stack, trapping a field of up to 1.6 T above the surface after pulse magnetization at 10 K, is reported.

All-MOCVD Technology for Coated Conductor Fabrication

The deposition of all buffer and YBCO layers for coated conductors via MOCVD represents one of the lowest possible capital and operational cost approaches to coated conductor manufacturing. Modular design of our prototype MOCVD system allows for either in-line or parallel fabrication of any number of buffer layers and YBCO layers. At 77 K in self-field Ic >; 200 A/cm has been reproducibly demonstrated on all-MOCVD architecture, the best up-to-date result being Ic = 236 A/cm and Jc = 2.13 MA/cm2. Measurements performed at 4.2 K in 12 T magnetic field have shown Je = 278 A/mm2. The results achieved, combined with the low cost, make the all-MOCVD coated conductors very promising materials for application both at liquid nitrogen and liquid helium temperatures.

Development of MOCVD Technology for Integrated YBCO Layer/Buffer Layer Fabrication for Coated Conductors

Chemical deposition of all buffer and YBCO layers is recognized as the most economical approach to coated conductor manufacturing. Metal Oxide Technologies Inc. (MetOx) has been developing a cost-effective technology to deposit all buffer and superconducting layers by MOCVD. High I_c = 201 A/cm and J_c = 1.53 MA/cm² values are obtained on ORNL RABiTS buffers. The best superconducting properties of MetOx YBCO films of J_c = 3.34 MA/cm² and I_c = 480 A/cm have been achieved on LANL IBAD buffers. MetOx MOCVD coated conductors demonstrate promising I_c = 137 A/cm and J_c = 1.10 MA/cm². Good superconducting performance has been demonstrated on several 1 m long YBCO tapes. Pinning enhancement via Y₂O₃ doping in YBCO has been successfully implemented. Very high MOCVD growth rates of 1.25 mum/min have been demonstrated producing well-textured superconducting YBCO films.