Interfacial nanolayers and permittivity of ferroelectric superlattices

In ferroelectric superlattices (SLs), the short-range interactions and intermixing between contacting dissimilar materials can lead to the formation of interfacial nanolayers with physical properties different from those of both constituents. We demonstrate theoretically that such nanolayers can give rise to a sizable dependence of the SL permittivity on the period even in the paraelectric regime. The results of dielectric measurements performed for coherent Ba0.8Sr0.2TiO3–Ba0.4Sr0.6TiO3 SLs are qualitatively consistent with the theoretical predictions. At the same time, the experimental data indicate that other factors also contribute to the variation of the permittivity with the period in ferroelectric superlattices and multilayers.