NEUTRON SCATTERING STUDY OF K2ZNBR4

An inelastic neutron scattering study has been performed on the single crystal of monoclinic K2ZnBr4. Dispersion relations for transverse ac oustic (TA) phonons were determined in the a, a*-c*, c*, 2a*-c* and b directions at room temperature. In addition to the TA mode, low-ener gy modes were observed in the scan along the 2a-c* direction. The tem perature dependence of the low-energy mode suggests that an optical mo de softens at the paraelectric-ferroelectric transition of 155 K.