MODULATED STRUCTURE ANALYSIS OF MUTUALLY INCOMMENSURATE COMPOSITE CRYSTAL (SnS)1.17NbS2
Y. Gotoh1, J. Akimoto1, Y. Oosawa1, M. Onoda2
1National Institute
of Materials and Chemical Research, Higashi 1-1, Tsukuba, Ibaraki
305-8565, Japan
2National Institute
for Research in Inorganic Materials, Namiki 1-1, Tsukuba, Ibaraki
305, Japan
The modulated structure of
incommensurate composite crystal, (SnS)1.17NbS2
with layered substructures, has been investigated on the basis of
(3+1)-dimensional superspace group approach using the X-ray
diffraction data collected by A. Meetsma, G. A. Wiegers, R. J.
Haange and J. L. de Boer [1]. From their average substructure
analysis, it has been found that the composite crystal is built
of three-atom-thick NbS2 sandwiches with Nb
trigonal-prismatically coordinated by S atoms and two-atom-thick
SnS double layers with NaCl-type arrangement and they are
alternately stacked. In the present work, structure model with
secondary harmonic modulation waves for all atomic position and
anisotropic thermal parameters of SnS part was adopted. The
superspace groups of subsystems employed were L C2mm
/ -1 -1 s for the NbS2 part and L C2mb /
-1 -1 1 for the SnS one [2]. The structure was refined by FMLSM
[3] using 732 reflections with 67 parameters. The final R and Rw
values have been smoothly converged to 0.044 and 0.048
respectively. The dimensionality of the structure and the lattice
stability of (SnS)1.17NbS2 were
investigated by the use of REMOS [4]. The intersubsystem
interaction will be also discussed.