Low-frequency dispersion extended to higher frequencies: A new look at relaxor behaviour

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Abstract
A new theoretical framework and its experimental verification are presented in order to understand and generalize the dielectric response for relaxor ferroelectrics. By considering the fluctuating nanodomains of relaxors as fluctuating ‘giant dipoles’ we argue that the relaxor effect is indeed a low-frequency dispersion (LFD) phenomenon extended to the r.f. range. Because of the presence of disorder in relaxor ferroelectrics, configurational tunnelling plays an important role; we show that all the conditions necessary for LFD exist in the relaxors and at the same time we provide sufficient reasons to establish why LFD in relaxors is extended as well as prominent in the r.f. range. Our model explains the importance of random electric fields for exhibiting relaxor behaviour. Finally we substantiate our model by showing that dielectric constant and dissipation values as well as dispersion in lead magnesium niobate relaxor ferroelectrics are enhanced in a humid atmosphere in agreement with many well known adsorbate systems showing LFD.