PREPARATION, CHARACTERIZATION, AND IONIC-CONDUCTIVITY OF NOVEL CRYSTALLINE, MICROPOROUS GERMANATES, M3HGE7O16.XH2O, M = NH4+, LI+, K+, RB+, CS+ X = 4-6 .2.

A series of crystalline, microporous germanates, M3HGe7O16.xH2O, M = NH4+, Li+, x = 6; M = K+, Rb+, Cs+, x = 4, were synthesized hydrothermally and characterized by powder X-ray diffraction, differential thermal analysis, and thermogravimetric analysis. Ionic conductivity in both hydrated and dehydrated samples was investigated by ac impedance in the temperature range 25-550-degrees-C. The protonic conductivity is highest in (NH4)3HGe7O16.6H2O, 3.1 x 10(-4) (OMEGA-cm)-1 at 144-degrees-C. The best ionic conductivity was found in Cs3HGe7O16, 2.0 x 10(-3) (OMEGA-cm)-1 at 400-degrees-C. The ionic conductivity of dehydrated M3HGe7O16 increases and the activation energy decreases with increasing cation radius from room temperature to 500-degrees-C. This behavior is consistent with a reduced Coulombic attraction between the mixed tetrahedral-octahedral (GeO4-GeO6) anion framework structure of the germanates and the cations located in their channels, compared with that in other zeolite-type compounds.