  High resolution data on low energy phonon branches (acoustic and soft optic)
along the three principal symmetry axes in pure KTaO3 were obtained by cold
neutron inelastic scattering between 10 and 80 K. Additional off-principal axis
measurements were performed to characterize the dispersion anisotropy (away
from the <100> and <110> axes). The parameters of the phenomenological model
proposed by Vaks are refined in order to successfully describe the experimental
low temperature (10 < T < 100 K) dispersion curves, over an appreciable
reciprocal space volume around the zone center (|q| < 0.25 rlu). The refined
model, which involves only 4 temperature-independent adjustable parameters, is
intended to serve as a basis for quantitative computations of multiphonon
processes.
