  We report a detailed spectroscopic study of the pressure induced
neutral-ionic phase transition (NIT) of the mixed-stack charge-transfer (CT)
crystal tetrathiafulvalene-chloranil (TTF-CA). We show that the pressure
induced phase transition is still first-order and involves the presence of an
intermediate disordered phase, defined by the coexistence of two species of
different ionicity. Further application of pressure gradually converts this
phase into an homogeneous ferroelectric phase with a single ionicity. In
addition, we detect strong pretransitional phenomena which anticipate the
intermediate phase and are indicative of a precursor dynamic regime dominated
by fluctuations.
