Polar Properties and Hysteresis Loops in Multilayered Thin Films Ferroelectric/Virtual Ferroelectric

摘要

In the framework of Landau--Ginzburg--Devonshire (LGD) phenomenologicaltheory, the influence of misfit strains, surface energy, and finite-sizeeffects on phase diagrams, polar properties, and hysteresis loops has beencalculated for multilayered thin films of the type ferroelectric/virtualferroelectric. The influence of elastic deformations that arise at theinterface thin film--substrate owing to a mismatch between the latticeconstants in the film and the substrate on the phase diagrams of multilayeredthin films virtual ferroelectric SrTiO$_{3}$/ferroelectric BaTiO$_{3}$ has beenstudied for the first time. In contrast to bulk BaTiO$_{3}$, in which only fourphases (cubic, tetragonal, orthorhombic, and rhombohedral) can exist, it turnedout that six thermodynamically stable BaTiO$_{3}$ phases (paraelectric phaseand tetragonal (FEc), two monoclinic (FEaac and FEac), and two orthorhombic(FEa and FEaa) ferroelectric phases) can exist in multilayeredSrTiO$_{3}$/BaTiO$_{3}$ films. The main polar properties of hysteresis loops(shape, coercive field, and spontaneous polarization) in thin multilayeredSrTiO$_{3}$/BaTiO$_{3}$ films are calculated. It is shown that the systemdemonstrates a strong dependence of its polar properties on the thickness ofSrTiO$_{3}$ and BaTiO$_{3}$ layers, as well as on the elastic misfit strains,with SrTiO$_{3}$ playing the role of dielectric layer: the thicker the layer,the stronger is the depolarization field, which, in its turn, reduces thespontaneous polarization in the BaTiO$_{3}$ film.