Properties of Epitaxial Films Made of Relaxor Ferroelectrics

Finite-temperature properties of epitaxial films made of Ba(Zr; Ti)O-3 relaxor ferroelectrics are determined as a function of misfit strain, via the use of a first-principles-based effective Hamiltonian. These films are macroscopically paraelectric at any temperature, for any strain ranging between similar or equal to - 3% and similar or equal to +3%. However, original temperature-versus-misfit strain phase diagrams are obtained for the Burns temperature (T-b) and for the critical temperatures (T-m,T-z and T-m,T-IP) at which the out-of-plane and in-plane dielectric response peak, respectively, which allow the identification of three different regions. These latter differ from their evolution of T-b, T-m,T-z, and/or T-m,T-IP with strain, which are the fingerprints of a remarkable strain-induced microscopic change: each of these regions is associated with its own characteristic behavior of polar nanoregions at low temperature, such as strain-induced rotation or strain-driven elongation of their dipoles or even increase in the average size of the polar nanoregions when the strength of the strain grows.