Überstruktur des Strontiumvanadiumoxids, Sr0,5V2O5: ihre Zwillingsbildung, Gruppoid-Symmetrie und Interpretation als OD-Struktur

Abstract

Abstract The title compound has been considered to be isotypic with Ag0.68V2O5, a typical δ vanadium bronze crystallizing in space group C2/m. Through hydrothermal synthesis, however, crystals were obtained showing superlattice reflections. Triclinic, C[unk] (No. 2), a = 23.536(2) Å, b = 7.3985(3) Å, c = 8.801(1) Å, a = 90°, β = 88.28(1)°, γ = 90°, Z = 16. The structure was determined based on 2160 reflections of a specimen twinned about [010] | (010); R(F) = 0.032, Rw (F) = 0.024. Twinning about [100] or (001) was also observed. The structure includes V2O5 layers with Sr atoms sandwiched between them. The perfectly ordered arrangement of the Sr atoms leads to the superstructure. The V(V) and V(IV) positions can be distinguished. The structure has an idealized symmetry of a Brandt groupoid C2/m {t(1/4, 3/4, 0)}. An interpretation as OD structure is given to explain the mechanism of twinning.