DIELECTRIC-PROPERTIES OF INCOMMENSURATE PHASES IN ORDER-DISORDER SYSTEMS

Dielectric response of incommensurate phases in order-disorder ferroel ectrics is studied by means of pseudospin formalism. The complex dynam ical susceptibility is calculated using the Bloch equations which are solved either by a perturbational approach or by a procedure introduce d recently by Lovesey et al. We derive formulae for susceptibility as a function of frequency which display multirelaxational behaviour due to the coupling of the homogeneous polar soft mode to higher-order (wi th respect to their wavevectors) modes.