Interlayer Water Molecules in the Vanadium Pentoxide Hydrate, V₂O₅·<i>n</i>H₂O. 6. Rigidity of Crystal Structure against Water Adsorption and Anisotropy of Electrical Conductivity

Abstract

The effect of H 2 O molecules on the electrical conductivity of vanadium pentoxide hydrate, V 2 O 5 · n H 2 O, was investigated in connection with their orientation through polarized FT-IR spectroscopy. It was confirmed that interlayer H 2 O molecules are isotropic in the ab plane of the layered structure, indicating that they are adsorbed randomly between the layered structures. This is in contrast to the anisotropy of electrical conductivity, which is related to the difference in the hopping distances between the a and b directions.The structure of V 2 O 5 · n H 2 O in a humid condition was also studied by means of FT-IR, ESR, and XRD measurements, which should strongly affect the electric conductivity. The infrared polychroic property of the skeletal vibrations of the sample remained unchanged with varying H 2 O content. However, the ESR spectra of V 4+, a trace amount of which is intrinsically present in the sample, indicated that a free rotational motion of V 4+ occurs when a double layer of H 2 O was formed. This substantiates the idea that some of the V 4+ ions, in additino to the V 5+ ions, are present in the interlayer spaces rather than entirely in the skeletons.