Abstract
This contribution begins with a discussion of the homogeneous Landau theory for
bulk ferroelectrics with spatially uniform polarizations, reviewing first- and
second-order transitions and the dielectric response. Next, we allow the polarization
to vary with position within a bulk sample, and discuss Landau–Ginzburg theory and
correlation functions. Surface boundary conditions, corresponding to the situation for
thin films, are then added and the resulting polarization profile is discussed. Here,
screening effects, depolarization fields and strain will be important. The enigmatic
extrapolation length is described with remarks about its underlying physical
meaning. Then we switch to a treatment of inhomogeneous systems in the
bulk, where strain effects and domain formation become very important. We
end with a number of open questions for further exploration. Generally, we
emphasize the underlying philosophy and methodology of this phenomenology.