Regensburg 2002 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 6: Supraleitung: Elektronenstruktur, Phononen, Tunneln, Ordnungsparameter I
TT 6.2: Vortrag
Montag, 11. März 2002, 16:15–16:30, H19
c-axis deformations in the CuO2 planes of superconducting Pr0.5Ca0.5Ba2Cu3O7 and nonsuperconducting PrBa2Cu3O7 — •J. Röhler1, J. Puchalla1, M. Stranzenbach1, K.Q. Li2, and Z.X. Zhao2 — 1Universität zu Köln, D-50937 Köln, Germany — 2NLS, Academia Sinica, Beijing 10080, China
The absence of superconductivity in oxygen doped PrBa2Cu3O7 (Pr-123) is a longstanding experimental and theoretical issue of the cuprate superconductors. Cation doping of Pr-123 by partial substitution of Pr3+ with Ca2+ however was found to induce superconductivity, most recently in strongly doped bulk ceramics synthezised under high pressure. Pr0.5Ca0.5Ba2Cu3O7 exhibits Tc = 115 K, up to now the highest superconducting transition temperature in a lanthanide-123 material. We report the local atomic structure at the Pr site of Pr0.5Ca0.5Ba2Cu3O7 (Pr,Ca-123) as obtained from the extended absorption fine structure (EXAFS) at the Pr K-edge. A detailed comparison is made with the Pr K-EXAFS in nonsuperconducting Pr-123. While in orthorhombic and nonsuperconducting Pr-123 the bondlengths from Pr to the nn planar oxygen (O2,3) are degenerate at 2.45 Å, they split in tetragonal and superconducting (Pr,Ca)-123 by about 0.07 Å, similar as in Y-123 and the other superconducting lanthanide-123 materials. Even more dramatic is the variation of the bondlength from Pr to the nnn planar copper (Cu2): from 3.23 Å in superconducting Pr,Ca-123, also Y-123, to 3.27 Å in nonsuperconducting Pr-123, resulting in distinctly different deformation patterns of the quasi-2D CuO2 planes. We address possible relationships between these planar deformations and the relevant electronic structure.