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Observation of Changes in the Atomic and Electronic Structure of Single-Crystal Yba2Cu3O6.6 Accompanying Bromination



L M. Dieng, A Y. Ignalov, T A. Tyson, Mark Croft, A Dogan, C Y. Kim, Joseph Woicik, J Grow


To ascertain the role of bromination in the recovery of superconductivity in underdoped YBa2Cu3O6+y (YBCO) we have performed polarized multiple-edge x-ray absorption fine structure (XAFS) measurements on normal (y nearly equal to} 0.6) and brominated (Br/Cu nearly equal to} 1/30, y nearly equal to}0.6) single crystals with superconducting transitions at 63K and 89 K, respectively. The brominated sample becomes strongly heterogeneous on an atomic length scale. Approximately one-third of YBCO is locally decomposed yet incorporated as a well-ordered host lattice as nanoscale regions. The decomposed phase consists of heavily distorted domains with an order not following that of the host lattice. Structurally, these domains are fragments of the YBCO lattice that are discontinued along the Cu (1)-O (1) containing planes. The local structure is consistent with the cluster expansions: Y-O (2,3)8-Cu (2)8- , Ba-O8-Cu (2)4Cu(1)2-...and Cu-O4-...about the Y, Ba and Cu sites. Interatomic distances and Debye-Waller factors for the expansions were determined from fits to Y K-, Ba L3- and Cu K-edge XAFS data at room temperature. Br K-edge data reveal that Br does not enter substitutionally or interstitally into the perfect YBCO lattice. However, Br does occupy the Cu (1) sites in a nanofragment of the YBCO lattice, forming Br-O(4)-Ba-Cu2(1)Cu(2)-...nanoclusters. From polarized measurements, these nano-clusters were found to be almost randomly oriented with respect to the host crystal and probably are the nucleus of the decomposed phase. This heterogeneity brings about the unusual structural and electronic properties of the normal state previously reported in the literature. Implications on diffraction, transport, and magnetization measurements are discussed.
Physical Review B (Condensed Matter and Materials Physics)
No. 1


br, bromination, host, k-edge, underdoped, YBCO


Dieng, L. , Ignalov, A. , Tyson, T. , Croft, M. , Dogan, A. , Kim, C. , Woicik, J. and Grow, J. (2002), Observation of Changes in the Atomic and Electronic Structure of Single-Crystal Yba<sub>2</sub>Cu<sub>3</sub>O<sub>6.6</sub> Accompanying Bromination, Physical Review B (Condensed Matter and Materials Physics) (Accessed December 8, 2023)
Created June 30, 2002, Updated October 12, 2021