Synthesis and Modulated Crystal Structure of KBaNbS4

Abstract

AbstractSingle crystals of KBaNbS4 have been prepared by the reaction of Nb with an in situ formed melt of K2S3, BaS, and S at 500 °C. Satellite reflections observed in X‐ray diffraction experiments of these crystals indicate the presence of a one‐dimensional lattice distortion. The modulated structure has been solved and refined from X‐ray data using the superspace group approach. KBaNbS4 can be described in the (3 + 1)‐dimensional superspace group Pnma(α00)0s0 with lattice parameters a = 9.187(1), b = 7.001(1), and c = 12.494(1) Å and a modulation vector q = (0, 0.629(1), 0). In the structure the NbS4 tetrahedra are stacked along the a axis and show a slight tilting against each other. The K+ and Ba2+ ions follow this tilting, both are slightly shifted from their positions in the average structure. The modulation does not lead to a significant change in the coordination spheres of the metal atoms. The small effects of the modulation correspond to the relatively weak intensities of the satellite reflections. Results of temperature dependent X‐ray investigations indicate that K+ librates at higher temperatures and the surrounding S2− anions follow this motion. With decreasing temperature the libration of K+ is reduced and the coordination geometry freezes under formation of an incommensurate modulation. The heavier Ba and Nb atoms are also affected by positional modulation of the substructure and accommodate to their environment.