title: Ferroelectric phase transitions in small particles and local regions.
abstract: Phase transitions in spherical particles of a cubic ferroelectric are considered within Landau-Ginzburg-Devonshire theory. Concentrating on effects of the depolarizing field, we study competition between states with homogeneous polarization and vortex structures. For large radii of the sphere (R>Rc), the phase transition is into a vortex state while for R<Rc it might be into an homogeneous state. Rc is proportional to the square root of the dielectric constant of the environment. If this constant is of the order of unity, a transition into homogeneous state is practically impossible. The obtained results are applied to a discussion of the formation of "polar nanoclusters" in relaxors.
authors.affiliation: Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, Madrid 28049, Spain and Jozef Stefan Institute, P.O. Box 3000, 1001 Ljubljana, Slovenia.
authors.forename: A P
authors.initials: AP
authors.lastname: Levanyuk
authors.forename: R
authors.initials: R
authors.lastname: Blinc