LIGHT-SCATTERING SPECTRA DEPENDING ON THE DIRECTION OF SCATTERING WAVE VECTOR IN KD2PO4 .1. BRILLOUIN SPECTRUM AND BROAD CENTRAL COMPONENT

The Brillouin and Rayleigh scattering spectra have been observed near the transition temperature Tc in the paraelectric phase of KD2PO4 as a function of the direction of the scattering vector q in several scattering geometries. The broad central component ascribed to dynamical spectrum of the Debye type relaxational mode by Reese et al. has been studied in both the ab- and the ac- scattering planes. Theoretical formulas are derived to explain q and temperature dependences of the intensity of the broad central spectrum. The frequency of the acoustic mode coupled with this mode is found not to decrease even near Tc in the wave-length region of the Brillouin scattering. The q dependence of the Brillouin scattering intensity has been measured and can be accounted for by the fundamental theory mentioned above. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.