DYNAMICS OF THE COMMENSURATE-INCOMMENSURATE PHASE-TRANSITION IN C2O4D ND4, 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 evolutions 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 from a recent neutron experiment in the normal phase [10], and extend them to the incommensurate one. In particular, the ND4+ residence time is determined through various methods in the latter phase, and provides evidence for an increase of the barrier height with respect to the disordered phase.