Neutron scattering studies of alkali metal--graphite intercalation compounds

Elastic and inelastic neutron scattering are reported for C/sub 8/Rb in the temperature range 4 to 800 K. Several phase transitions above room temperature are reported for the first time; these consist of changes in metal layer stacking and ultimately at 747 K the onset of 2D liquid behavior. Phonon dispersion of LA and LO modes propagating along c imply a 20% increase in the interlayer force constant relative to pure graphite. The zone boundary TA mode softens dramatically with increasing temperature, which may be related to the phase transitions

Neutron scattering study of the solid electrolyte: RbAg/sub 4/I/sub 5/

Neutron scattering experiments were performed on RbAg/sub 4/I/sub 5/ in order to probe: (1) The lattice dynamics above and below the phase transition at T/sub 2/ = 208.5 K; (2) The temperature dependence of the Ag/sup +/ occupancies below T/sub 2/; and (3) The diffusion of the Ag/sup +/ ions. No anomalous softening of the elastic constant C/sub 44/ was observed as had been reported by ultrasonic studies. Careful examination of the phonon intensities above and below T/sub 2/ suggest that the transition is discontinuous. The behavior of allowed reflections below T/sub 2/ mirror the temperature dependence of the Ag/sup +/ occupation factors. A broad overdamped excitation is observed throughout Q-space and becomes a propagating mode as the temperature is decreased. Nothing critical happens at T/sub 2/ or T/sub 1/