9310222 Hochheimer This project employs unique high pressure and Brillouin light scattering techniques to investigate lattice dynamics, elastic behavior and phase transitions in materials exhibiting incommensurate phases. The materials being investigated include selenates and halides and have been chosen as model systems which should provide tests of recent theories of incommensurate phase transitions. The research will provide a better understanding of the coupling of acoustic phonons to excitations in the incommensurate phase, and will provide additional information about the role of anharmonic lattice potentials in the phase behavior. The research will provide fundamental information about solid state phase transitions which are important in many practical materials such as ferroelectric solids. %%% This is a fundamental study of the effect of pressure on the arrangement of atoms in solids that can show an unusual long range (larger that the crystal unit cell) modulation of the atomic positions in the solids. The reasons for phase transitions and changes in the atomic positions of the atoms in the materials under study are not well understood. They are important and underlie phase behavior in other solids, such as ferroelectric materials of technological importance. The changes in atomic positions will be investigated with both x-ray and optical spectroscopy techniques. ***
