Electrical conductivity studies were performed of solid acid phosphites MH(PO3H) with M = Li+, Na+, K+, Rb+, Cs+, NH4+. Superprotonic conductivity following a phase transition in the temperature range from 120 to 190C was observed for the monoclinic forms, including Na+, K+, Rb+, Cs+ and NH4+ derivatives. At temperatures beyond the superprotonic transition temperature, thermal decomposition occurred in the case of the Na+, Rb+ and NH4+ salts. No super-protonic phase transition was observed for orthorhombic LiH(PO3H). The magnitude of the superprotonic conductivity of KH(PO3H) and CsH(PO3H), which was known to be stable under H atmospheres from literature, amounts to 4.2 x 10−3/Ωcm at 140C and 3 x 10−3/Ωcm at 160C, respectively, which values were comparable to that of CsHSO4.

Superprotonic Conductivity in MH(PO3H) (M = Li+, Na+, K+, Rb+, Cs+, NH4+). W.Zhou, A.S.Bondarenko, B.A.Boukamp, H.J.M.Bouwmeester: Solid State Ionics, 2008, 179[11-12], 380-4