LINEAR AND NONLINEAR LIGHT-SCATTERING NEAR THE PHASE-TRANSITION IN KH(2)PO(4)

The angular and temperature dependence of the linear light scattering and the temperature dependence of the second-harmonic nonlinear light scattering were studied ill two different samples of KH2PO4 (KDP) crys tal: one from a zone close to the seed and another from a zone far fro m the seed. The angular dependence of the intensity of the linearly sc attered light front the sample from the zone close to the seed shows a strong peak for the near Z(YX)Y scattering. This scattering originate s from growth bands parallel to the (0 (1) over bar 1) lattice planes in the pyramidal growth sector. The temperature dependence of the magn itude of this peak shows a considerable increase in the vicinity of th e phase transition from the paraelectric to ferroelectric phase. Such an increase in the linear light scattering was not observed in the sam ple from the zone far from the seed. The anomalies related to the grow th bands parallel to the (010) lattice planes in the prismatic growth sector were investigated also by second-harmonic light scattering. Her e again a considerable increase in the intensity of the frequency-doub led scattered light was observed in the vicinity of the phase-transiti on temperature. The results of the light-scattering experiments are co mpared with an x-ray topographic study of the lattice defects.