Layer and spontaneous polarizations in perovskite oxides and their interplay in multiferroic bismuth ferrite

TL;DR

This paper reviews the concepts of surface and layer polarization in perovskite oxides, focusing on their interplay in the multiferroic material bismuth ferrite, highlighting how its unique properties lead to self-compensating surface charge phenomena.

Contribution

It unifies the understanding of surface charge and layer polarization within the modern theory of polarization, illustrating their effects in BiFeO3 through computational and experimental analysis.

Findings

BiFeO3 exhibits self-compensating surface charge due to its polarization and layer charge magnitudes.

The study combines density functional theory, microscopy, and literature analysis to explore polarization effects.

Unique polarization and surface charge interplay in BiFeO3 influences its electrostatic stability.

Abstract

We review the concept of surface charge, first in the context of the polarization in ferroelectric materials, and second in the context of layers of charged ions in ionic insulators. While the former is traditionally discussed in the ferroelectrics community, and the latter in the surface science community, we remind the reader that the two descriptions are conveniently unified within the modern theory of polarization. In both cases, the surface charge leads to electrostatic instability - the so-called "polar catastrophe" - if it is not compensated, and we review the range of phenomena that arise as a result of different compensation mechanisms. We illustrate these concepts using the example of the prototypical multiferroic bismuth ferrite, BiFeO3, which is unusual in that its spontaneous ferroelectric polarization and its layer charges can be of the same magnitude. As a result, for certain combinations of polarization orientation and surface terminationits surface charge is self-compensating. We use density functional calculations of BiFeO3 slabs and superlattices, analysis of high-resolution transmission electron micrographs as well as examples from the literature to explore the consequences of this peculiarity.