Abstract
The grain boundary (GB) plays a critical role in a material’s properties and device performance. Therefore, the characterization of a GB’s atomic structure and electrostatic characteristics is a matter of great importance for materials science. Here, we report on the atomic structure and electrostatic analysis of a GB in a SrTiO3 bicrystal by four-dimensional scanning transmission electron microscopy (4D-STEM). We demonstrate that the Σ5 GB is Ti-rich and poor in Sr. We investigate possible effects on the variation in the atomic electrostatic field, including oxygen vacancies, Ti-valence change, and accumulation of cations. A negative charge resulting from a space-charge zone in SrTiO3 compensates a positive charge accumulated at the GB, which is in agreement with the double-Schottky-barrier model. It demonstrates the feasibility of characterizing the electrostatic properties at the nanometer scale by 4D-STEM, which provides comprehensive insights to understanding the GB structure and its concomitant effects on the electrostatic properties.
Highlights
The grain boundary (GB) plays a critical role in a material’s properties and device performance
This difference signal is proportional to the beam deflection along the direction connecting the two segments.[6−9] Shibata et al described how the application of a segmented detector in differential phase-contrast imaging (DPC)-STEM imaging enables a real-time reconstruction of the HAADF image, the electric-field-vector map, and the chargedensity map and allows the simultaneous acquisition of the local atomic structure and electrostatic information from the same area.[7]
Blocking grain boundaries in ionic solids, which explains the electrical behavior of GBs by the presence of a GB-core charge, whose electric field is compensated by a space charge on both sides of the GB.[1,13−17] For example, positively charged defects, e.g., oxygen vacancies or excess cations at an acceptor-doped SrTiO3 GB, form a potential barrier
Summary
The grain boundary (GB) plays a critical role in a material’s properties and device performance. The phase is reconstructed from the scattered exit electron wave through the object, which enables imaging of the electrostatic potential with nanometer spatial resolution.[1−5] More recently, differential phase-contrast imaging (DPC) has been used to reconstruct the electrostatic potential at atomic resolution through the difference signal of opposed detector segments This difference signal is proportional to the beam deflection along the direction connecting the two segments.[6−9] Shibata et al described how the application of a segmented detector in DPC-STEM imaging enables a real-time reconstruction of the HAADF image, the electric-field-vector map, and the chargedensity map and allows the simultaneous acquisition of the local atomic structure and electrostatic information from the same area.[7] Further progress was achieved by the use of pixelated detectors instead of segmented detectors. These descriptions via charged defects and space-charge layers are indirectly deduced from experimental data of bulk properties, e.g., from impedance spectroscopy or I−V properties.[13,19−22]
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