Phonons in PbMg 1/3 Nb 2/3 O 3 Measured by Inelastic Neutron Scattering

A detailed lattice-dynamic investigation on the relaxor ferroelectric PMN was started to search for "additional" modes (dispersion curves). But the results are complex with 4 branches observed below 6.5 THz, a broad unresolved continuum between 6.5 and 12 THz, a well defined excitation at 13.4 THz with longitudinal and transverse character and further weak signals above 16 THz. Possible effects caused by disorder are discussed.