LOW-FREQUENCY DISPERSION EXTENDED TO HIGHER FREQUENCIES - A NEW LOOK AT RELAXOR BEHAVIOR

A new theoretical framework and its experimental verification are pres ented in order to understand and generalize the dielectric response fo r relaxer ferroelectrics. By considering the fluctuating nanodomains o f relaxors as fluctuating 'giant dipoles' we argue that the relaxer ef fect is indeed a low-frequency dispersion (LFD) phenomenon extended to the r.f. range. Because of the presence of disorder in relaxer ferroe lectrics, configurational tunnelling plays an important role; we show that all the conditions necessary for LFD exist in the relaxers and at the same time we provide sufficient reasons to establish why LFD in r elaxers is extended as well as prominent in the r.f. range. Our model explains the importance of random electric fields for exhibiting relax er behaviour. Finally we substantiate our model by showing that dielec tric constant and dissipation values as well as dispersion in lead mag nesium niobate relaxer ferroelectrics are enhanced in a humid atmosphe re in agreement with many well known adsorbate systems showing LFD.