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Title:	Understanding the origin of the recovery of superconductivity in halogenated YBCO single crystal : atomic structure study
Author:	Dieng, Lamine Mohamed Kollakoye
View Online:	njit-etd2004-081 (xviii, 138 pages ~ 6.5 MB pdf)
Department:	Federated Physics Department of NJIT and Rutgers-Newark
Degree:	Doctor of Philosophy
Program:	Applied Physics
Document Type:	Dissertation
Advisory Committee:	Tyson, Trevor (Committee chair) Croft, Mark C. (Committee member) Murnick, Daniel Ely (Committee member) Federici, John Francis (Committee member) Fiory, Anthony (Committee member)
Date:	2004-05
Keywords:	Superconductivity YBCO Bromination Halogenation
Availability:	Unrestricted
Abstract:	The recovery of superconductivity in underdoped YBa2Cu3O6+y (YBCO) by exposure to bromine, iodine, chlorine and fluorine is a long-standing problem which has not been clearly resolved. The key question concerns the role of these halogens in the lattice. In order to shed light to this problem, we have performed multiple-edge x-ray absorption fine structure (XAFS) measurements about the Y K, Ba L3, I L3, Cu K and Br K-edges at room temperature on brominated (non-brominated) and iodinated (non-iodinated) YBCO single crystals. Our XAFS results at the Br K (brominated) and I L3 -edges (iodinated) reveal that bromine and iodine do not enter the perfect YBCO lattice. However, the XAFS fitting results at the Br K and I L3-edges reveal that Br and I do occupy the Cu(l) sites of the oxygen deficient YBCO in nanoclusters. From the polarized x-ray absorption near edge measurements (XANES) at the Cu K-edge, the nanoclusters were found to be randomly oriented with respect to the "host" crystal and with respect to the polarization vector.