Dynamics of intercalated molecules: Pt. 3

The neutron diffraction pattern of 'C24Cs'(CD4)sub(x) has been studied as a function of filling, x, and temperature from 4 K up to the gas desorption point at 170 K. At low temperatures, peaks due to coexisting (√ 7 x √ 7) commensurate and a 3.2% expanded incommensurate phase have been detected in the ratio of ca. 3:1, respectively. At higher temperatures, as methane is desorbed, the lattice-vector changes are small but the expanded lattice peak loses intensity first, between 130 and 154 K. Above 154 K a single broad peak at the commensurate lattice position gradually weakens as gas is lost, indicating the persistence of this more stable phase. These data are compared with the results of sorption potential and molecular dynamics simulations. Evidence for two different c-axis stacking sequences in our C28Cs sample before and after sorption is presented. (author)