Original scientific paper
(Ba/Sr)O-BI-layer ordering in the RE2(Ba/Sr)2GaCu2O9 superconducting cuprate
Ognjen Milat
; Institute of Physics of the University, Bijenička 46, HR-10001, Zagreb, Croatia
Ivica Aviani
; Institute of Physics of the University, Bijenička 46, HR-10001, Zagreb, Croatia
Abstract
Ordering in the (Ba/Sr/Nd)O bi-layers (of "Rock-Salt" type structure) of the RE2(Ba0.65Sr0.20Nd0.15)2GaCu2O9 high-Tc superconducting cuprate was investigated by electron microscopy and diffraction. Besides the average layered structure based on the tetragonal perovskite cell ap×ap×cp and the meandering chain superstructure based on the orthorhombic 4ap×2ap×cp cell in the GaO-layers, an additional ordering was found in the pairs of (Ba/Sr/Nd)O-...-(Ba/Sr/Nd)O layers. We propose a model for ordering of 3Ba and 1Sr cations on a two-dimensional 2ap×2ap lattice cell in each (Ba/Sr/Nd)O layer. This compositional intra-layer ordering is accompanied by the inter-layer plane stacking disorder. The 4-fold symmetry of the average tetragonal structure is preserved, while the translation parameters in the (a,b) plane are doubled. This local ordering in the RS-type bi-layers hardly affects the symmetry of the basic structure; however, it may act as a source of weak anisotropy in the CuO2-layers.
Keywords
Hrčak ID:
299841
URI
Publication date:
1.3.1997.
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