IMPORTANCE OF TRUE SATELLITE REFLECTIONS IN THE ANALYSIS OF MODULATED, COMPOSITE CRYSTAL-STRUCTURES .1. A NEW REFINEMENT OF [M(2)CU(2)O(3)](7+DELTA)[CUO2](10), M=BI0.06SR0.46CA0.48

A new structural model for the composite crystal bismuth strontium cal cium cuprate [M(2)Cu(2)O(3)](7+delta)[CuO2](10) With M=Bi0.06Sr0.46Ca0 .48 and delta=0.03 has been determined, The structure is orthorhombic with a=11.380 (2), b=12.960 (4) Angstrom and incommensurate along c. S ublattice 1 of composition (CuO2)(4) has c(1)=2.7522 (4) Angstrom and sublattice 2 of composition (M(2)Cu(2)O(3))(4) has c(2)=3.9155 (5) Ang strom; superspace group F222(001 + gamma)001; modulation vector q(1)=g amma c(2) With gamma=0.7029 (2). The structural analysis has been bas ed on 603 main reflections, 428 first-order and 64 second-order satell ite reflections. The final residual is R=0.0632 for all reflections, R =0.0614 for main reflections, R=0.0735 for first-order and R=0.1084 fo r second-order satellite reflections; lambda=0.6565 Angstrom, mu=19.4 mm(-1). The satellite reflections have been collected with X-ray synch rotron radiation. In this context, special experimental problems are d iscussed, It is shown that the true satellite reflections, which are t he satellite reflections that are not also main reflections for one of the sublattices, are necessary in the least-squares refinement in ord er to avoid large correlations between displacive modulation amplitude s and thermal vibration amplitudes and thus to obtain a reasonable coo rdination chemistry.