  Motivated by the unusual soft mode anomalies in the relaxor ferroelectrics,
we present a numerical study of vibrational excitations of a disordered lattice
model with chemical order on the nano-scale. We find an Ioffe-Regel crossover
in acoustic modes separating propagating low-frequency modes from the
intermediate frequency diffusons, and localized modes at the high-frequency end
of the spectrum. At a fixed degree of disorder, we find increasing uncertainty
in the momentum of long wave-length optical modes with decrease in the size of
nano-ordered regions. We determine the cause for this to be a strong mixing
between acoustic and optical modes, believed to be central to the model of
waterfall phonon anomalies.
