D. Grebille et al., STATIC DISORDER IN THE INCOMMENSURATE STRUCTURE OF THE HIGH T-C SUPERCONDUCTOR BI(2)SR(2)CACU(2)O8+DELTA, Acta crystallographica. Section B, Structural science, 52, 1996, pp. 628-642
The incommensurate modulated structure of the high T-c superconductor
of nominal composition Bi2Sr2CaCu2O8 has been refined using an optimiz
ed data set of 1530 reflections (496 main reflections, 753 first-order
and 281 second-order satellites) in superspace group Bbmb(0 beta 1) u
sing a Fourier expansion of the modulation functions up to second orde
r. A large improvement of the R (wR) factor [global: 0.056 (0.051); ma
in reflections: 0.049 (0.043); first-order satellites: 0.056 (0.058);
second-order satellites: 0.078 (0.079)] is obtained by the introductio
n of a static modulated disorder on the Bi site without any thermal fa
ctor modulation and by considering occupational modulation functions.
A detailed comparison with previous studies in modulated structure mod
els or in supercell models is given, in particular for the description
of the BiO layers.