Tin mordenite containing phosphotungstic acid was prepared by the wet
impregnation method. Upon exposure of the samples at 100% RH, the wate
r uptake was found to determine changes in the crystallographic struct
ure. A corresponding increase in proton conductivity was revealed by a
c-impedance measurements, up to a value of 7.7 x 10(-2) Ohm(-1) cm(-1)
for fully hydrated samples.