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Title: Phase Relations in the Ba-Y-Cu-O Films on SrTiO 3 for the Ex Situ BaF 2 Process

Abstract

In situ x-ray diffraction was used to establish the phase relations in high-{Tc} superconductor Ba-Y-Cu-O films grown on SrTiO{sub 3} through the ex situ BaF{sub 2} process. These relations differ from bulk equilibrium phase assemblages in the BaO-Y{sub 2}O{sub 3}-CuO{sub x} system. In particular, BaY2CuO5 (the 'green phase'), a common impurity phase in bulk processing, is absent in the films. Because of the absence of this green phase, the compositional stability field of Ba{sub 2}YCu{sub 3}O{sub 6+x} expands considerably as compared to that of the bulk system, resulting in the tie lines Ba{sub 2}YCu{sub 3}O{sub 6+x}-Y{sub 2}O{sub 3} and Ba{sub 2}YCu{sub 3}O{sub 6+x}-Y{sub 2}Cu{sub 2}O{sub 5}.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2];  [3]
  1. National Institute of Standards and Technology (NIST)
  2. ORNL
  3. Los Alamos National Laboratory (LANL)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
OE USDOE - Office of Electric Transmission and Distribution
OSTI Identifier:
931502
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; YTTRIUM OXIDES; BARIUM OXIDES; COPPER OXIDES; PHASE STUDIES; SUBSTRATES; STRONTIUM OXIDES; TITANIUM OXIDES; HIGH-TC SUPERCONDUCTORS

Citation Formats

Wong-Ng, W., Levin, I., Otani, M., Vaudin, M., Cook, L. P., Cline, J., Feenstra, Roeland, and Holesinger, T. G.. Phase Relations in the Ba-Y-Cu-O Films on SrTiO3 for the Ex Situ BaF2 Process. United States: N. p., 2007. Web. doi:10.1063/1.2713124.
Wong-Ng, W., Levin, I., Otani, M., Vaudin, M., Cook, L. P., Cline, J., Feenstra, Roeland, & Holesinger, T. G.. Phase Relations in the Ba-Y-Cu-O Films on SrTiO3 for the Ex Situ BaF2 Process. United States. doi:10.1063/1.2713124.
Wong-Ng, W., Levin, I., Otani, M., Vaudin, M., Cook, L. P., Cline, J., Feenstra, Roeland, and Holesinger, T. G.. Mon . "Phase Relations in the Ba-Y-Cu-O Films on SrTiO3 for the Ex Situ BaF2 Process". United States. doi:10.1063/1.2713124.
@article{osti_931502,
title = {Phase Relations in the Ba-Y-Cu-O Films on SrTiO3 for the Ex Situ BaF2 Process},
author = {Wong-Ng, W. and Levin, I. and Otani, M. and Vaudin, M. and Cook, L. P. and Cline, J. and Feenstra, Roeland and Holesinger, T. G.},
abstractNote = {In situ x-ray diffraction was used to establish the phase relations in high-{Tc} superconductor Ba-Y-Cu-O films grown on SrTiO{sub 3} through the ex situ BaF{sub 2} process. These relations differ from bulk equilibrium phase assemblages in the BaO-Y{sub 2}O{sub 3}-CuO{sub x} system. In particular, BaY2CuO5 (the 'green phase'), a common impurity phase in bulk processing, is absent in the films. Because of the absence of this green phase, the compositional stability field of Ba{sub 2}YCu{sub 3}O{sub 6+x} expands considerably as compared to that of the bulk system, resulting in the tie lines Ba{sub 2}YCu{sub 3}O{sub 6+x}-Y{sub 2}O{sub 3} and Ba{sub 2}YCu{sub 3}O{sub 6+x}-Y{sub 2}Cu{sub 2}O{sub 5}.},
doi = {10.1063/1.2713124},
journal = {Applied Physics Letters},
number = ,
volume = 90,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Thin Y-Ba-CU-O films were prepared {ital in}-{ital situ} by low-temperature codeposition on Al{sub 2}O{sub 3} substrates. The temperatures during preparation did not exceed 600 {degree}C. As a source of Ba the BaF{sub 2} was used. The zero resistance {ital T}{sub {ital c}} values were higher than 84 K, {ital J}{sub {ital c}} =4{times}10{sup 4} A/cm{sup 2} at 4.2 K/OT. The Auger electron spectroscopy analysis has shown almost a homogeneous distribution of the film components throughout the film thickness. X-ray diffraction revealed the presence of unoriented 1-2-3 phase besides BaF{sub 2} and CuO and, one undefined phase, which might be oxyfluoridemore » compound.« less
  • Thin films of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}}{sub {ital x}} (YBCO) with and without underlayers of SrTiO{sub 3} (STO) were deposited via pulsed laser deposition onto substrates of sapphire and silicon-on-sapphire (SOS) in a single vacuum step. The YBCO films with STO underlayers displayed better superconducting transitions than the YBCO films without underlayers, with zero-resistance temperatures of 86.5 and 75 K for films with underlayers on sapphire and SOS substrates, respectively. X-ray diffraction and secondary-ion mass spectroscopy have been used to explore the role played by the STO underlayer in improving film quality.
  • Superconducting Y-Ba-Cu-O (YBCO) films have been prepared by {ital ex situ} O{sub 2} annealing of multilayer films deposited on yttria-stabilized zirconia substrates by sequential rf diode sputtering of Y{sub 2}O{sub 3}, BaF{sub 2}, and CuO targets, all of which are chemically stable. If sputtering is performed in an Ar ambient, the as-deposited films contain sufficient F to require its removal by annealing in wet O{sub 2} at about 800 {degree}C or above before the superconducting YBCO phase can be formed by annealing in dry O{sub 2}. However, sputtering in an Ar-O{sub 2} ambient greatly reduces the F content, making itmore » possible to obtain the superconducting phase by annealing in dry O{sub 2} only. If the ambient contains about 20% O{sub 2}, films with {ital T}{sub {ital c}} ({ital R}=0){gt}85 K can be prepared without wet-O{sub 2} annealing. The Ar-O{sub 2} process therefore has the potential for {ital in} {ital situ} preparation of superconducting YBCO films.« less
  • We report the formation of excellent quality epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ films on (100) SrTiO/sub 3/ and (100) ZrO/sub 2/ (yttria stabilized) substrates in the temperature range of 500--650 /sup 0/C by XECl excimer laser ablation in a 0.2 Torr oxygen ambient. By applying a dc bias voltage of +300 V to an interposing ring, we were able to reduce the substrate temperatures from 650 to 500 /sup 0/C for obtaining epitaxial films. The quality of the epitaxial films was found to decrease with temperature, particularly below 550 /sup 0/C. The thickness of the superconducting films was varied frommore » 500 to 5000 A with superconducting transition temperatures T/sub c/ (zero resistance) varying from 87 to 90 K for 650 /sup 0/C deposits. The critical current density J/sub c/ of films was found to vary linearly with temperature with values of (zero magnetic field at 77 K) 5.0 x 10/sup 6/ and 1.0 x 10/sup 6/ for films deposited at 650 /sup 0/C on (100) SrTiO/sub 3/ and (100) yttria-stabilized zirconia substrates, respectively. X-ray diffraction, transmission electron microscopy, electron channeling patterns, and Rutherford backscattering (RBS)/channeling showed excellent epitaxial quality of films on both substrates with best values of minimum ion channeling yield of 3.5% on (100) SrTiO/sub 3/ substrates.« less
  • High throughput, sharp interfaces, and selective deposition with direct ion-, electron-, and photon-beam-controlled techniques are some of the key driving forces for the development of superconducting thin films by the metalorganic chemical vapor deposition technique. In this paper, we report on the {ital in} {ital situ} deposition of a buffer layer of BaF{sub 2} and high-temperature superconducting thin films of Y-Ba-Cu-O by metalorganic chemical vapor deposition (MOCVD) on silicon substrates. These films have an on-set temperature of 90 K and zero resistance at 73 K. The use of BaF{sub 2} as a buffer layer on Si substrates suggests the possibilitymore » of three-dimensional integration with high-temperature superconducting thin films, for hybrid superconductor/semiconductor devices as well as superconducting switches and other related devices. To the best of our knowledge, this is the first report of the deposition of high-temperature superconducting thin films on Si by MOCVD.« less