Surface-screening mechanisms in ferroelectric thin films and their effect on polarization dynamics and domain structures

Abstract

For over 70 years, ferroelectric materials have been one of the central research topics for condensed matter physics and material science, an interest driven both by fundamental science and applications. However, ferroelectric surfaces, the key component of ferroelectric films and nanostructures, still present a significant theoretical and even conceptual challenge. Indeed, stability of ferroelectric phase per se necessitates screening of polarization charge. At surfaces, this can lead to coupling between ferroelectric and semiconducting properties of material, or with surface (electro) chemistry, going well beyond classical models applicable for ferroelectric interfaces. In this review, we summarize recent studies of surface-screening phenomena in ferroelectrics. We provide a brief overview of the historical understanding of the physics of ferroelectric surfaces, and existing theoretical models that both introduce screening mechanisms and explore the relationship between screening and relevant aspects of ferroelectric functionalities starting from phase stability itself. Given that the majority of ferroelectrics exist in multiple-domain states, we focus on local studies of screening phenomena using scanning probe microscopy techniques. We discuss recent studies of static and dynamic phenomena on ferroelectric surfaces, as well as phenomena observed under lateral transport, light, chemical, and pressure stimuli. We also note that the need for ionic screening renders polarization switching a coupled physical-electrochemical process and discuss the non-trivial phenomena such as chaotic behavior during domain switching that stem from this.

Thermooptical evidence of carrier-stabilized ferroelectricity in ultrathin electrodeless films

“…A model considered a single-domain ferroelectric film, which possesses out-of-plane (normal to substrate surface) polarization and contains free charge carriers 8,9,42,43 . The polarization P ( z ) was calculated using the Landau-Ginzburg-Devonshire theory with the Euler-Lagrange equation and three types of electrostatic boundary conditions: the film is short-circuited between perfect conducting electrodes (Fig.…”

“…As known, species adsorbed on the film surfaces can ensure surface screening, thus acting as an electrode 11,12,43,46 . A combined effect of the internal screening by charge carriers and surface screening by adsorbed species can stabilize ferroelectricity in our films on LSAT and STO.…”

Ferromagnetic-like behavior of Bi0.9La0.1FeO3–KBr nanocomposites

“…Below we will try to prove that the appropriate mechanism turned out to be ferro-magnetoionic coupling, that is a natural extension of ferro-ionic and anti-ferroionic couplings [47,48,49,50] revealed earlier in ultra-thin ferroelectric films exposed to ionic exchange with ambient media (see original papers [51,52], review [53] and Refs therein). Following Stephenson and Highland (SH) model [51,52] the screening by ions is electrically coupled to the electrochemical processes at the ferroelectric surface, and thus, the stabilization of ferroelectric state in ultrathin PbTiO 3 films occurs due to the chemical switching [54,55,56].…”

Size effect of soft phonon dispersion in nanosized ferroics

“…Anna N. Morozovska 1,2* and Eugene A. Eliseev , (A.1) The boundary conditions for , derived from the variation of the free energy Eqs.…”