Relative humidity influence on the water content and on the protonic conductivity of the phosphatoantimonic acids HnSbnP2O3n+5, xH2O (n = 1, 3, 5)

The phosphatoantimonic acids HnSbnP2O3n+5, xH2O (n = 1, 3, 5) have been prepared from the corresponding potassium compounds by ion-exchange in acidic medium. For n = 1 and 3 they are layered materials. When n = 5 the covalent framework is three dimensional with large interconnected channels. The title acids are all hydrated and their water content, lattice parameters and protonic conductivity have been studied at 20°C as a function of the relative humidity. When n = 1 a great part of the water content is physisorbed and the electrical behavior is that of a particle hydrate. For n = 3, the compound is a true lattice hydrate and the protonic conductivity is closely related to the water content. This is also the case when n = 5; however the contribution of surface water to the proton diffusion is clearly evidenced.