Lithium dynamics in the zeolite-like lithosilicate RUB-29 and its high-temperature structure after dehydration (Cs14Li42Si72O172)
Microporous and Mesoporous Materials 108(1-3): 1-12
The thermally induced modifications of the zeolite-like lithosilicate RUB-29 (Cs14Li24[Li18Si72O172]center dot 14H(2)O, space group I222, a= 11.208(1), b = 17.286(1), c = 23.536(1) angstrom, and V = 4660(1) angstrom(3) [S.-H. Park, J.B. Parise, H. Gies, H. Liu, C.P. Grey, B.H. Toby, J. Am. Chem. Soc. 122 (44) (2000) 11023-11024]) have been studied focusing on static and dynamical disorder of Li. After the water loss, dehydrated RUB-29 (HT-d-RUB-29) maintains the basic space group 1222 at high temperatures from 473 up to 1073 K. However, the distribution of extra-framework Li and Cs cations in HT-d-RUB-29 became distinctly different from those in the original structure. In particular, extra-framework Li cations located within porous 8- and 10-membered ring-channels, where these Li cations were partially coordinated with zeolitic water in the original structure, migrate into densely packed Li2O-layers after dehydration. As a result of the migration, the number of empty sites relevant for Li hopping in Li2O-layers decreases, which give a negative effect on the long-range charge transfer in dehydrated RUB-29. Its DC conductivity values estimated from AC impedance spectra lie between 2 x 10(-5) and 6 x 10-5 S cm(-1) at 873 K, and a low activation energy of 51 kJ/mol (congruent to 0.53 eV) could be determined for the bulk charge transfer process in dehydrated RUB-29. (c) 2007 Elsevier Inc. All rights reserved.