Microstructure and formation mechanism of cylindrical and conical scrolls of the misfit layer compounds PbNbnS2n+1

Under adequate growth conditions the mixed layer compounds (PbS)(1+x)(NbS2)(n) and (BiS)(1+x)(NbS2)(n) are shown to crystallize from the vapour phase partly as hollow cylindrical scrolls, which can be either chiral or achiral. Also conically wound scrolls are formed. The observations of the growth nuclei suggests a formation and growth mechanism based on the spontaneous curling up of thin triangular flakes as a consequence of the lattice parameter difference between the constituent lamellae of the mixed layer compounds. Morphological observations are supported by electron diffraction patterns, which are interpreted in terms of the reciprocal space of conically wound fibres, first presented here and developed in detail in Ref. [20] [S. Amelinckx et al., Acta Cryst., submitted]. The scroll nature of rolled microstructures allows for the formation of long and complicated periodic sequences of orientation variants.