Soft modes of collective domain-wall vibrations in epitaxial ferroelectric thin films

Abstract

Mechanical restoring forces acting on ferroelastic domain walls displaced from the equilibrium positions in epitaxial films are calculated for various modes of their cooperative translational oscillations. For vibrations of the domain-wall superlattice with the wave vectors corresponding to the center and boundaries of the first Brillouin zone, the soft modes are singled out that are distinguished by a minimum magnitude of the restoring force. It is shown that, in polydomain ferroelectric thin films, the soft modes of wall vibrations may create enormously large contribution to the film permittivity.

Nanoscale Origins of Nonlinear Behavior in Ferroic Thin Films

“…For example, scanning probe-based studies on ferroelectric thin fi lms by Shvartsman et al indicated that the piezoelectric coeffi cient may not be fi eld-dependent at the nanoscale. [ 12 ] From a theoretical perspective, efforts have ranged from the mechanisms mediated by dynamics of a single wall in the presence of static or moving pinning centers [13][14][15][16][17][18][19] to the nature of the order parameter that characterizes the domain wall. [20][21][22] Recent experimental studies have also highlighted the key role of collective domain wall interactions, [ 23 ] as well as the Rayleigh-like behavior of non-180 ° domain wall motion, [ 24 ] in contributing to nonlinear behavior.…”

Extrinsic contributions to the apparent thickness dependence of the dielectric constant in epitaxialPb(Zr,Ti)O3thin films

“…Other exceptions are related to the ferroelectric domain walls, which are structural defects that can bring significant extrinsic contributions to the dielectric constant derived from capacitance measurements performed at small electric fields. [16][17][18][19][20] However, most real samples are full of other defects, such as vacancies, impurities, dislocations, and grain boundaries, not to mention the electrode interfaces. All these can contribute in different ways to the dielectric response-i.e., to the dielectric constant.…”

Tackling Polar Response in Oxygen Deficient KTaO3Thin Films

“…The low values of ρ and λ corroborates the existence of oxygen vacancies in the as-processed films, as also revealed to above by the Poole-Frenkel formalism. Figure 5 shows the temperature dependence of ε and f rel = 1/τ obtained through the fitting procedure, where it is observed that ε(T ) reveals a defined maximum close to 367 • C. Contrarily, the relaxation frequency shows a broad maximum close to 250 • C. This behavior evidences the existence of a complex relaxation process occurring in the films [ [28][29][30]. The value of ε(∞) obtained is rather low (∼5), which is similar to the one for the optical dielectric constant, obtained from the Poole-Frenkel formalism.…”