RIETVELD ANALYSIS OF INCOMMENSURATE COMPOSITE CRYSTALS Sr_xTiS₃ (x=1.1-1.2). M. Onoda, M. Saeki, A. Yamamoto and K. Kato National Institute for Research in Inorganic Materials,1-1 Namiki, Tsukuba, Ibaraki 305, Japan

The structures of incommensurate composite crystals Sr_xTiS₃ (x= 1.1-1.2) have been analyzed on the basis of a four-dimensional superspace group pR3₁m_s using the powder X-ray diffraction data and the Rietveld analysis process.

The trigonal composite crystal Sr_xTiS₃ has the existence range of x=1.1-1.2 according to the starting ratio of Sr/Ti in the synthesis process. All reflections including weak satellites could be indexed by four integers h, k, l and m with the reflection conditions -h+k+l=3n for hklm and m=2n for 0klm. Cell constants are approximately a_l=a₂= 11.5, a₃ = c_TiS3=3.0Å and [[sigma]]=( 0 0 c_TiS3/c_Sr )=(0 0 0.57), and Z=3. The agreement of each Rietveld analysis was fairly good.

Fig. 1. Projections of the modulated structure.