Impedance spectroscopy was used to investigate the long-range ionic conductivity of the microporous, zincosilicate VPI-9 (Si/Zn = 4.0) (framework type VNI) containing the alkali cations Li+, Na+, K+, Rb+, and Cs+, and the alkaline earth cations Mg2+, Ca2+, and Sr2+. Monovalent cation-exchanged samples Li- and Na-VPI-9 lost X-ray crystallinity upon vacuum dehydration at 450C, whereas K-, Rb-, and Cs-VPI-9 remained crystalline and exhibited conductivities of 1.7 x 10−4, 3.5 x 10−4 and 4.9 x 10−4S/cm, respectively, at 450C and activation energies of 0.72, 0.64 and 0.69eV, respectively, in the range of 150 to 450C. Divalent cation-exchanged sample Mg-VPI-9 also lost X-ray crystallinity, but Ca- and Sr-VPI-9 remained crystalline and exhibited conductivities of 2.3 x 10−6 and 7.7 x 10−7S/cm, respectively, at 450C, and activation energies of 0.88 and 0.91eV, respectively, at 150 to 450C. When compared to aluminosilicate zeolite X (Si/Al = 1.25) exchanged with the same cations, all crystalline M-VPI-9 materials had greater conductivities than did M-X, with the exception of K-X (1.6 x 10−3S/cm at 450C), with the greatest differences arising between the divalent exchanged materials. Dense, crystalline zincosilicate samples with the compositions K2ZnSixO2(x+1) (x = 2−5), Rb2ZnSi5O12, and Cs2ZnSi5O12 were also prepared and characterized for

comparison with the microporous materials and exhibiting much lower conductivities than their microporous counterparts at the same composition.

Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9. J.C.McKeen, M.E.Davis: Journal of Physical Chemistry C, 2009, 113[22], 9870–7

Table 48

Diffusion Parameters for Various Zeolites