Dispersion of the acoustic phonon concerned with C66 of KD2PO4 observed by light scattering

Abstract we vector dependence of the light scattering spectra of DKDP is investigated for the scattering angles π/4, π/2 and 3π/4. Brillouin shift concerned with an elastic stiffness C 66 is obtained from the angular dependence of the quasi-longitudinal and quasi-transverse mode frequencies in the ab plane observed in the VV scattering. The results indicate that the phase velocity associated with C 66 decreases slightly near T tr in the case of π/4 scattering, but does not in π/2 and 3π/4 scatterings.