Fabrication of Y y -Pr 1-y -Ba-Cu-O Thin Films and Superlattices of -Ba-Cu-O/Y y -Pr 1-y -Ba-Cu-O
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FABRICATION OF Y -Pri -Ba-Cu-O THIN FILMS AND SUPERLAITICES 6 F V-Ba-Cu-O/Y-Pr 1-y-Ba-Cu-O X. D. Wu1 ), M. S. Hegde2 ), X. X. Xi3), Q. Li3), A. Inam 3), S. A. Schwarz 4), J. A. Martinez5 ), B. J. Wilkens4 ), J. B. Barner4 ), C. C. Chang4 ), L. Nazar4 ), C. T. Rogers4) and T. Venkatesan 4) ')Exploratory Research and Development Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 2 )Indian Institute of Science, Bangalore, India 56102 3)Physics Department, Rutgers University, Piscataway, NJ 08854 4)Bellcore, Red Bank, NJ 07701 5 IDepartamento de Fisica, Universidad Nacional de La Plata (UNLP), Argentina ABSTRACT We have prepared epitaxial thin films of Y -Pr -Ba-Cu-O (y= 1 to 0) and superlattices of Y-Ba-Cu-O/Y -Pr1 -Ba-Cu-O using pulsed laser deposition technique. The zero resistance transition tempyeratures of Yv-Prl -Ba-Cu-O bulk samples are reproduced in the films. The composition oscillations idi the 7uperlattices are observed by SIMS. The films and superlattices are found to have c-axis orientations and good crystallinity. INTRODUCTION Superconducting thin films of YBa^Cu 30 7-x (Y-Ba-Cu-O) with T of 90 K and JC of 5x106 A/cm2 at 77 K have been prepared in-situ successfully by a numiber of groups [1], while good in-situ processes are yet to be developed for the Bi and TI based superconducting systems. Utilizing high quality Y-Ba-Cu-O thin films the intrinsic properties of the superconductors could be studied. On the other hand, alloying the superconductors in the cation sites may also give information on the mechanism of superconductivity in these systems. This is the main reason for the fabrication Yy-Pr -y-BaCu-O thin films and Y-Ba-Cu-O/Yy-Pr 1 -y-Ba-Cu-O superlattices. The lattice constants of the Y -Pr1 -Ba-Cu-O decrease almost linearly with y, from a=0.392 nm, b=0.388 nm and c-=-l.17 lrn for y= o to a-= 0.388 nm, b=0.382 nm and c = 1.168 nm for y= 1 with an orthorhombic structure throughout the entire alloying region [2]. Therefore, the lattice mismatch between Y-Ba-Cu-O and Pr-Ba-Cu-O is less than 1.5% for all three axes, providing a condition for epitaxial growth of Y-Ba-Cu-O on Pr-Ba-Cu-O. Furthermore, Y -Pr, -Ba-Cu-O can be prepared at the same growth conditions for YBaCuO. EpitaxialYgrowth of YBaCuO/PrBaCuO/YBaCuO trilayers has been shown [3,4] with the demonstration of ac and dc Jesophson effects in the SNS junction device fabricated from such trilayer structures [5]. He ion backscattering minimum yield of 6% on the YBaCuO top layer was observed [3], indicating high crystalline nature of the trilayers. Layer-by-layer growth of the superconductors would allow the synthesis of novel structures and possibly new metastable phases. Initial attempts to grow the new superconductors layer-by-layer have not been so successful [6]. Recently, excellent Y-BaCu-O/Dy-Ba-Cu-O superlattices with the shortest periodicity of 2.4 nm have been made by dc magnetron sputtering [7]. We have demonstrated that epitaxial Y-Ba-Cu-O/Pr-Ba-CuO superlattices with a similar periodicity can be prepared by a pulsed
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