The Misfit Dislocation Core Phase in Complex Oxide Heteroepitaxy

Abstract

Misfit dislocations form self-organized nanoscale linear defects exhibiting their own distinct structural, chemical, and physical properties which, particularly in complex oxides, hold a strong potential for the development of nanodevices. However, the transformation of such defects from passive into potentially active functional elements necessitates a deep understanding of the particular mechanisms governing their formation. Here we combine different atomic resolution imaging and spectroscopic techniques to determine the complex structure of misfit dislocations in the perovskite type La 0.67 Sr 0.33 MnO 3 /LaAlO 3 heteroepitaxial system. It is found that while the position of the film-substrate interface is blurred by cation intermixing, oxygen vacancies selectively accumulate at the tensile region of the dislocation strain field. Such accumulation of vacancies is accompanied by the reduction of manganese 2 cations in the same area, inducing chemical expansion effects which partly accommodate the dislocation strain. The formation of oxygen vacancies is only partially electrically compensated and results in a positive net charge q ~ +0.3±0.1 localized in the tensile region of the dislocation, while the compressive region remains neutral. Our results highlight a prototypical core model for perovskite based heteroepitaxial systems and offer insights for predictive manipulation of misfit dislocation properties.

Dislocations Accelerate Oxygen Ion Diffusion in La0.8Sr0.2MnO3 Epitaxial Thin Films

“…It was found that Mn at the dislocation core occupies the La site and thus forms antisite defects . Also, a higher oxygen vacancy concentration in the dislocation core region was observed, , which is in a good agreement with our study.…”

Epitaxial LaMnO 3 films with remarkably fast oxygen transport properties at low temperature

“…3). This can be justied considering the model reported by Bagués et al 42 for LSM/LAO lms, where the formation and accumulation of oxygen vacancies is promoted around the dislocation core area. In their study, by a combination of transmission electron microscopy imaging and spectroscopic techniques, the authors provided experimental evidence of the presence of oxygen vacancies in the tensile region of the dislocation, the reduction of neighboring Mn cations generating electrostatic interactions and leading to the formation of La 0 Mn antisite defects.…”

Observation of unexpected uniaxial magnetic anisotropy in La 2/3 Sr 1/3 MnO 3 films by a BaTiO 3 overlayer in an artificial multiferroic bilayer

“…The local color variations observed in the strain maps reflect homogeneous and dislocation-free STO and LSMO layers, and a BTO layer with several linear defects, most of which are concentrated close to the BTO/LSMO interfaces. Misfit dislocation-free epitaxial growth of LSMO films under (001)-oriented STO substrates is expected and widely reported [2,[47][48][49][50] due to their small mismatch (≈0.7%); dislocations appear in LSMO under compressive strain [51][52][53], while twin walls are expected under tensile strain [54][55][56] with the thickness-dependent elastic deformations already in LSMO/STO systems [54]. Linear defects in the BTO layer are promoted by the large mismatch between the lattice parameters of the BTO and the strained LSMO film (≈2.4%).…”