The protonic conductivity of these materials was measured by means of  in situ  isotopic exchange, using Van der Pauw and 2-electrode geometries for the high-temperature and low-temperature phases, respectively. A proton/deuteron conductivity ratio of about 2.3, in the high-temperature phase, was suggested to be mainly the result of an 0.02eV higher activation energy for deuteron conductivity. This was attributed to a difference in zero-point energy. The low-temperature phases exhibited no large isotope effects, and therefore no sign of proton tunnelling.

T.Norby, M.Friesel, B.E.Mellander: Solid State Ionics, 1995, 77, 105-10