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Some Advances in High-Temperature Superconductor Coatings

Advances were made in characterization and deposition of high-Tc films.

Several advances were made in a program focused on the science and technology of high-temperature superconductors [especially yttrium barium copper oxide ("YBCO")] deposited on normal electrical conductors. This program was part of a continuing effort to develop superconductor-coated normal conductors for use in electric-power systems of interest to the Air Force.

The advances are summarized as follows:

•Characterization of high-temperature superconductors in general and YBCO in particular.

A method, based on in situ Fouriertransform infrared (FTIR) reflectivity measurements, of monitoring the temperature and optical properties of high-critical- temperature (high-Tc) superconducting films in real time during the deposition and post-deposition processing of those films was developed. The method was then used to track the evolution of material phases during a high-rate deposition process in which YBCO was formed by electron-beam co-evaporation from Y, Ba, and Cu targets in the presence of oxygen. In somewhat simplified terms, it was found that the deposit starts as a glassy precursor of partially oxidized Y, Ba, and Cu ions and, as the oxygen pressure is increased, evolves to the desired superconducting YBa2Cu3O7 phase (sometimes called "123 YBCO"). The method is expected to be utilized in future efforts to optimize processing to obtain 123 YBCO.

A profiling technique was developed as a means of studying selected transport properties (specifically, the normal-state resistivity and the superconducting critical current density) as functions of position through the depth of a high-Tc film. The basic idea of the technique is to measure the transport properties as successive layers are etched away and to obtain the desired values through calculation of differences between successive measurements after each etching step. By use of this technique, it was determined that each of several YBCO films formed as described above was not homogeneous and, instead, consisted of a top layer having excellent high-Tc superconducting properties and a lower layer that was nearly electrically insulating. The origin of the layered nature of the films later came to be understood in the light of the knowledge gained through the FTIR study described above plus supplementary knowledge gained by use of x-ray diffraction.

•248 YBCO as a superconductive coating material.

Another superconducting phase of YBCO, known in the art as "248 YBCO," was investigated as an alternative to 123 YBCO. Prior to this research, it was considered to be difficult to synthesize 248 YBCO in film form because of high oxygen pressure needed for equilibrium growth. This research led to a nonequilibrium process for growing a 248 YBCO film. In this process, a film consisting of a glassy precursor of the 248 phase is formed by pulsed laser deposition at a high temperature. The precursor film is then subjected to a heat treatment in which it is exposed to oxygen at temperature greater than the deposition temperature.

•Other activities.

This research program also included other activities not directly connected with the advances described above. One such activity involved characterization of thin films of MgB2. Another such activity was collaboration in invention of a new memory cell based on switching of a magnetic dot with a single Josephsonjunction readout. The advantage of such a memory cell is that it holds promise to be scalable to sizes much smaller than those of traditional memory cells.

This work was done by M. R. Beasley of Stanford University for the Air Force Research Laboratory

Topics:
Coatings, colorants and finishes Coatings, colorants, and finishes Collaboration and partnering Education and training Heat treatment Insulation Magnetic materials Materials Metallurgy Oxygen People and personalities Research and development Superconductors
This Brief includes a Technical Support Package (TSP).
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Some Advances in High-Temperature Superconductor Coatings

(reference AFRL-0065) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the February, 2008 issue of Defense Tech Briefs Magazine (Vol. 2 No. 1).

    Read more articles from the archives here.

    Overview

    The document is a final report on a research program focused on the materials science of high-temperature superconducting coated conductors, particularly Yttrium Barium Copper Oxide (YBCO), which are of significant interest for electric power systems, especially for the Air Force. The research was conducted by Stanford University under the sponsorship of the Air Force Office of Scientific Research from February 15, 2004, to July 14, 2007.

    The program aimed to address three main elements:

    1. Understanding Materials Science: The first objective was to comprehend the fundamental materials science involved in the deposition of YBCO at high rates necessary for the economic manufacture of coated conductors. This involves exploring the physical and chemical processes that govern the deposition techniques, which are crucial for producing high-quality superconducting films.

    2. Exploration of Alternatives: The second focus was on investigating variants and alternatives to YBCO that could also serve as coated conductors. This exploration is vital for identifying materials that may offer improved performance or lower production costs, thereby expanding the potential applications of superconducting materials in various technologies.

    3. In Situ Process Monitoring: The third element involved the development and application of in situ deposition process monitoring tools. These tools are designed to provide real-time feedback during the deposition process, allowing for adjustments that can enhance the quality and consistency of the coated conductors.

    In addition to these primary objectives, the report mentions that other topics were addressed as special opportunities arose during the program's evolution. These additional topics are briefly discussed at the end of the report.

    The document also includes administrative details such as distribution statements, security classifications, and contact information for responsible personnel. It emphasizes the importance of the research in advancing the understanding and application of superconducting materials, which have the potential to revolutionize electric power systems by enabling more efficient energy transmission and storage.

    Overall, the report highlights the significance of high-temperature superconducting coated conductors in modern technology and the ongoing efforts to improve their manufacturing processes and material properties.

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