Sol-gel prepared glasses were studied, and a striking improvement in the protonic conductivity was observed upon increasing the P2O5 content. This was attributed to changes in the glass structure (including a reduction in the degree of cross-linking) and to an increase in the specific surface area of the glass; due to non-bridging O (P=O) in the P-O tetrahedron. Other factors were suggested to include the formation of a stronger H bond between the hydroxyl and P=O groups, and a resonance effect in the O3-xPO(OH)x unit.

Role of P2O5 in Protonic Conduction in Sol-Gel Derived Binary Phosphosilicate Glasses. C.Wang, Y.Abe, T.Kasuga, M.Nogami: Journal of the Ceramic Society of Japan, 1999, 107[11], 1037-40