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Phase Transformations in the High-Tc Superconducting Compounds, Ba_2RCu_3O_(7–δ) (R = Nd, Sm, Gd, Y, Ho, and Er)

Wong-Ng, W. and Cook, L. P. and Su, H. B. and Vaudin, M. D. and Chiang, C. K. and Welch, D. R. and Fuller, E. R., Jr. and Yang, Z. and Bennett, L. H. (2006) Phase Transformations in the High-Tc Superconducting Compounds, Ba_2RCu_3O_(7–δ) (R = Nd, Sm, Gd, Y, Ho, and Er). Journal of Research of the National Institute of Standards and Technology, 111 (1). pp. 41-55. ISSN 1044-677X. PMCID PMC4654609.

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The phase transformation between the orthorhombic and tetragonal structures of six high-Tc superconductors, Ba2RCu3O7−δ, where R = Nd, Sm, Gd, Y, Ho, and Er, and δ = 0 to 1, has been investigated using techniques of x-ray diffraction, differential thermal analysis/thermogravimetric analysis (DTA/TGA) and electron diffraction. The transformation from the oxygen-rich orthorhombic phase to the oxygen-deficient tetragonal phase involves two orthorhombic phases. A superlattice cell caused by oxygen ordering, with a′ = 2a, was observed for materials with smaller ionic radius (Y, Ho, and Er). For the larger lanthanide samples (Nd, Sm, and Gd), the a′ = 2a type superlattice cell was not observed. The structural phase transition temperatures, oxygen stoichiometry and characteristics of the Tc plateaus appear to correlate with the ionic radius, which varies based on the number of f electrons. Lanthanide elements with a smaller ionic radius stabilize the orthorhombic phase to higher temperatures and lower oxygen content. Also, the superconducting temperature is less sensitive to the oxygen content for materials with smaller ionic radius. The trend of dependence of the phase transformation temperature on ionic radius across the lanthanide series can be explained using a quasi-chemical approximation (QCA) whereby the strain effect plays an important role on the order-disorder transition due to the effect of oxygen content on the CuO chain sites.

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Additional Information:© 2006 National Institute of Standards and Technology. Accepted: January 3, 2006. Thanks to Ms. R. Drew for performing the ac magnetic susceptibility measurements. We also gratefully acknowledge the financial support of the Department of Energy (DOE) for Wire/Tapes Development, and also for the portion of the research carried out at Brookhaven National Laboratory, operated by Brookhaven Science Associates, LLC under Contract No.DE-AC02-98CHI-886 with the U.S. Department of Energy. The United States Government retains, and the publisher, by accepting the article for publication, acknowledges, a world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
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Department of Energy (DOE)DE-AC02-98CHI-886
Issue or Number:1
PubMed Central ID:PMC4654609
Record Number:CaltechAUTHORS:20110623-113606109
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24184
Deposited By: Ruth Sustaita
Deposited On:23 Jun 2011 21:26
Last Modified:03 Oct 2019 02:54

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