An evaluation of phase separated, self-assembled LaMnO 3 -MgO nanocomposite films directly on IBAD-MgO as buffer layers
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Tolga Aytug,a) M. Parans Paranthaman, Keith J. Leonard, Andrew R. Lupini, Steve J. Pennycook, Harry M. Meyer, Kim Kim, Xiaofeng Qiu, and Sylvester Cook Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
James R. Thompson Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; and Department of Physics & Astronomy, The University of Tennessee, Knoxville, Tennessee 37996
David K. Christen and Amit Goyal Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Xumin Xiong and Venkat Selvamanickam SuperPower, Inc., Schenectady, New York 12304 (Received 14 October 2009; accepted 15 December 2009)
Technological applications of high temperature superconductors (HTS) require high critical current density, Jc, under operation at high magnetic field strengths. This requires effective flux pinning by introducing artificial defects through creative processing. In this work, we evaluated the feasibility of mixed-phase LaMnO3:MgO (LMO:MgO) films as a potential cap buffer layer for the epitaxial growth and enhanced performance of YBa2Cu3O7-d (YBCO) films. Such composite films were sputter deposited directly on IBAD-MgO templates (with no additional homo-epitaxial MgO layer) and revealed the formation of two phase-separated, but at the same time vertically aligned, self-assembled composite nanostructures that extend throughout the entire thickness of the film. The YBCO coatings deposited on these nanostructured cap layers showed correlated c-axis pinning and improved in-field Jc performance compared to those of YBCO films fabricated on standard LMO buffers. Microstructural characterization revealed additional extended disorder in the YBCO matrix. The present results demonstrate the feasibility of novel and potentially practical approaches in the pursuit of more efficient, economical, and high performance superconducting devices. I. INTRODUCTION
Since the discovery of high temperature superconductivity in copper oxide-based materials,1 in particular YBa2Cu3O7-d (YBCO), tremendous efforts have been focused on the use of these materials in practical applications such as motors, generators, and transmission lines. For operation in such power utility applications, one challenge is the requirement to maintain high critical current density, Jc, under high magnetic field strengths and field orientations. This requirement means that the quantized magnetic flux lines (vortices) in the high temperature superconducting (HTS) material must be immobilized through nanoscale materials defects. Even a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0073 J. Mater. Res., Vol. 25, No. 3, Mar 2010
though HTSs have many natural pinning defects, such as, oxygen/cation vacancies, grain boundaries, dislocations, and others, it has recently been shown that artificially introduced pinning centers are much more effective to enhance Jc in high magnetic fields and at high temperatures.2 Hence, over the past several years, extensive investigations have been conducted to incorporate a variety of artificia
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