Structure of redox intercalated (NH₄)_0.5V ₂o₅·mH₂O xerogel using the pair distribution function technique

The structure of (NH₄)_0.5V₂O ₅·mH₂O (m ≈ 0.9), a representative member of the family of intercalated solids with reduced V₂O₅ xerogel framework, has been successfully determined using the atomic pair distribution function (PDF) technique. We show that at the atomic scale (NH ₄)_0.5V₂O₅·mH₂O is isostructural with pristine V₂O₅·nH₂O that features a double layer of V₂O₅ separated by water molecules and ammonium ions in a monoclinic unit cell (space group C2/m) with parameters a = 11.845(1) Å, b = 3.677(1) Å, c = 9.058(1) Å, and β = 88.635°. Vanadium oxide network in (NH₄) _0.5V₂O₅·mH₂O is slightly expanded when compared to that in pristine V₂O ₅·nH₂O, reflecting the elongation of V-O bonds in the former material. The results presented here prove that the redox intercalation of V₂O₅·nH₂O xerogel is indeed a topotactic reaction.