Low energy phonon spectrum and its parameterization in pure KTaO_3 below 80 K

摘要

High resolution data on low energy phonon branches (acoustic and soft optic) along the three principal symmetry axes in pure KTaO_3 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 [28] are refined in order to successfully describe the experimental low temperature (10 < Τ < 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 or quantitative computations of multiphonon processes.