Negatively Charged In-Plane and Out-Of-Plane Domain Walls with Oxygen-Vacancy Agglomerations in a Ca-Doped Bismuth-Ferrite Thin Film

Abstract

The interaction of oxygen vacancies and ferroelectric domain walls is of great scientific interest because it leads to different domain-structure behaviors. Here, we use high-resolution scanning transmission electron microscopy to study the ferroelectric domain structure and oxygen-vacancy ordering in a compressively strained Bi 0.9 Ca 0.1 FeO 3−δ thin film. It was found that atomic plates, in which agglomerated oxygen vacancies are ordered, appear without any periodicity between the plates in out-of-plane and in-plane orientation. The oxygen non-stoichiometry with δ ≈ 1 in FeO 2−δ planes is identical in both orientations and shows no preference. Within the plates, the oxygen vacancies form 1D channels in a pseudocubic [010] direction with a high number of vacancies that alternate with oxygen columns with few vacancies. These plates of oxygen vacancies always coincide with charged domain walls in a tail-to-tail configuration. Defects such as ordered oxygen vacancies are thereby known to lead to a pinning effect of the ferroelectric domain walls (causing application-critical aspects, such as fatigue mechanisms and countering of retention failure) and to have a critical influence on the domain-wall conductivity. Thus, intentional oxygen vacancy defect engineering could be useful for the design of multiferroic devices with advanced functionality.

Ca Solubility in a BiFeO3-Based System with a Secondary Bi2O3 Phase on a Nanoscale

“…A more detailed explanation of these mechanisms can be found elsewhere. 46 , 61 The relative enthalpy of solution for the Fe-oxidation mechanism was calculated as Here, E (BFO,Ca) and E (BO,Ca), are the total energies of the respective supercell containing Ca atoms, while E (BFO) and E (BO) are the energies for the supercells without Ca. The relative enthalpy of solution for the case of oxygen vacancy (V O ) compensation was defined similarly Here, E (BFO, 2Ca,V O ) and E (BO, 2Ca,V O ), are the total energies of the respective supercell containing two Ca atoms and one V O .…”

“…Cross-sectional TEM samples were fabricated by standard focused ion beam protocol with a Helios Nanolab FIB-SEM. − A probe-aberration-corrected FEI Titan 3 operated at 300 keV at a convergence angle of 19.7 mrad was used to gain all the STEM data. For HAADF imaging, a Fischione HAADF detector was used.…”

“…A more detailed explanation of these mechanisms can be found elsewhere. 46,61 The relative enthalpy of solution for the Fe-oxidation mechanism was calculated as…”

Modeling Chemical Exfoliation of Non-van der Waals Chromium Sulfides by Machine Learning Interatomic Potentials and Monte Carlo Simulations

“…To mitigate this challenge, researchers commonly employ special quasi-random structure (SQS) cells , as representative unit cells that effectively capture the statistical features of atomic disorder, enabling DFT predictions for compositions attainable within compact unit cells. To extrapolate to other compositions or facilitate large-scale simulations, the common practice is to employ a surrogate model like cluster expansion (CE). − While the on-lattice CE is well-suited for fixed-lattice alloy systems, nonstoichiometric systems frequently manifest significant deviations from the parent lattice and exhibit notable sensitivity of atomic arrangements to mechanical strains. − Therefore, a more dependable approach entails adopting an off-lattice model that incorporates both configurational and geometrical features of nonstoichiometric systems. Additionally, CE’s transferability to unobserved on-lattice configurations and compositions remains a subject warranting further investigation …”