Disorder and dynamics in pollucite from 133Cs and 27Al NMR

Pollucite, CsAlSi2O6, a Cs polymorph of leucite (KAISi(2)O(6)), has been proposed for ceramic immobilization of Cs-135 and Cs-137 fission products. Cs NMR of both low- (tetragonal) and high-temperature (cubic) forms of pollucite exhibit a considerable distribution of local Cs environments. Si-29 and Al-27 NMR data from directly prepared pollucite show greater Al/Si disorder than either leucite, or pollucite produced by ion exchange. Little evidence for Cs motion is observed in tetragonal or cubic pollucite, and only at high temperatures (similar to 850 degrees C) is any substantial dynamic behavior detected. Dynamic NMR lineshape calculations allow a determination of the frequency of Cs motion and diffushity.