DYNAMICS OF THE COMMENSURATE-INCOMMENSURATE PHASE-TRANSITION IN C2O4DND4, 1 2D2O - A POLARIZED RAMAN-STUDY UNDER PRESSURE/

Polarized low frequency Raman spectra of AHOD have been measured at 6. 4 kbar both in the normal and in the incommensurate phases. The evolut ions of two central peaks, visible in the two phases, and of the three acoustic modes made active by the incommensurate distortion have been analyzed. The results are in good agreement with the values deduced f rom a recent neutron experiment in the normal phase [10], and extend t hem to the incommensurate one. In particular, the ND4+ residence time is determined through various methods in the latter phase, and provide s evidence for an increase of the barrier height with respect to the d isordered phase.