Neutron scattering study of the incommensurate phase transition in thiourea

This paper presents the neutron scattering results obtained in the high temperature and in the incommensurate phases of deuterated thiourea. In the high temperature phase we have evidence for a softening branch related to the phase instability. It is also shown that the ferroelectric transition (at Tc ≊ 188.6K) is not the lock-in one (with a lock-in wave vector = 0) but it is T1 (≊ 191.6K) which corresponds to lock-in phase transition. Between T1 and Tc the wave vector of the distortion is locked in b*/9. Finally a tentative to study the dynamics of the incommensurate phase is presented.