Structure and proton conduction in pyrochlore-type antimonic acid: a neutron diffraction study

Abstract The structure of pyrochlore-type antimonic acid, HSbO 3 · 0.5H 2 O, has been investigated using powder diffraction of neutrons. The structure (space group Fd3m ) contains an [Sb 2 O 6 2− ] framework, with interstitial oxygens present as a mixture of H 2 O and H 3 O + . Three H-atom sites have been identified, (1) close to the [Sb 2 O 6 2− ] framework in hydroxyl groups (SbOH), (2) H in water molecules H-bonded to framework hydroxyls, and (3) H in H 3 O + ions H-bonded to O-atoms of the intercavity windows. An intraframework equilibrium of the type Sb  OH + H 2 O ⇋ Sb  O − + H 3 O + provides the mechanism for intracavity chemical exchange and proton conduction.