Hydrothermal synthesis of hydrous vanadium oxide bronzes MxV3Oδ(VO)y · nH2O (M = K, Rb, Ba)

Hydrous vanadium (IV, V) oxides containing K or Rb were synthesized by the hydrothermal method from VOSO4-M2SO4 (M = K, Rb) solutions. They were found to be isomorphous with previously reported Ba0.4V3O8(VO)0.4 · nH2O, whose structure consists of V3O8 layers which are bridged by V-O units (denoted by (VO)0.4 in the formula) forming a tunnellike opening to accommodate hydrous Ba ions. The isomorphous compounds can be formulated by MxV3O8(VO)y · nH2O (M = K, Rb, Ba; n = 0.6–0.7) where x and y show similar values of less than 0.5 as is accounted for by the crystal structure. The formation of this phase seems to be governed by the size of M cation whose ionic radius should lie in a limited range of 1.35 to 1.52 Å. The V3O8(VO)y framework structure of a bronze-like type is compared with the V2O5 framework of β-MxV2O5 (β bronze) and the V3O8 framework of H2V3O8.