Ferroelectric Dead Layer Driven by a Polar Interface

TL;DR

This paper investigates how polar interfaces induce a non-switchable dead layer in thin-film ferroelectrics, affecting their stability and critical thickness, through first-principles and model calculations.

Contribution

It reveals the mechanism by which polar interfaces create a dead layer, highlighting the role of intrinsic electric fields and charge leakage in ferroelectric thin films.

Findings

Polar interfaces generate an intrinsic electric field that affects ferroelectric stability.

The dead layer's strength depends on ionic charge and screening length.

The mechanism influences the critical thickness for ferroelectricity.

Abstract

Based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As a representative model, we consider a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces that serve as doping layers. We find that the polar interfaces create an intrinsic electric field that is screened by the electron charge leaking into the BaTiO3 layer. The amount of the leaking charge is controlled by the boundary conditions which are different for three heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. Our first-principles and model calculations demonstrate that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces.