  Relaxor ferroelectrics are difficult to study and understand. The experiment
shows that at low energy scattering there is an acoustic mode, an optic mode,
dynamic quasi-elastic scattering and strictly elastic scattering as well as
Bragg peaks at the zone centre. We have studied the scattering using the TASP
spectrometer at PSI and have analysed the data using a model with interactions
between the different components particularly to determine the properties of
the elastic scattering. The quasi-elastic scattering begins to become
significant at the Burns temperature of 620 K. It steadily increases in
intensity on cooling reaching a maximum at ~400 K. Below this temperature the
strictly elastic scattering begins to increase and shows a broadened line shape
characteristic of crystals in a random applied field. We show that all the
results obtained from PMN for the elastic scattering are consistent with the
crystal having a random field transition at ~400 K. We have obtained similar
results for PMN-PT and PZN-PT suggesting that random fields of the nano-regions
also play an important role in these materials.
