Investigation of three-dimensional grain-boundary structures in oxides through multiple-scattering analysis of spatially resolved electron-energy-loss spectra

Abstract

Grain boundaries in oxide materials such as electroceramics, ferroelectrics, and high-T c superconductors are known to dominate their overall bulk properties. The critical first step in a fundamental understanding of how they control the properties of the material is a determination of the atomic structure of the boundary. While this determination has traditionally been performed by transmission-electron microscopy, the images that are generated are only a two-dimensional projection of the atomic columns in the grain-boundary core. In addition, as the images are least sensitive to light elements, such as oxygen, the complete three-dimensional boundary structure is particularly difficult to determine. Employing electron-energy-loss spectroscopy in a scanning transmission-electron microscope, it is possible to obtain an oxygen K-edge spectrum that contains information on the three-dimensional electronic structure of the boundary. Using the multiple-scattering methodology, originally developed for x-ray absorption near-edge structure, this can be directly related to the local threedimensional atomic structure. Contained in the spectrum is therefore all of the information needed to investigate the atomic scale structure-property relationships at grain boundaries. The application of the technique is demonstrated here for the 25°͓001͔ symmetric tilt boundary in SrTiO 3 .

Microwave loss mechanisms in Ba0.25Sr0.75TiO3 films

“…They are located within the non-stoichiometry grain boundaries [24]. It was shown, by using multiplescattering analysis of spatially resolved electron-energy-loss spectra, that the boundary between crystalline blocks in STO carries a certain amount of oxygen vacancies, which form a surface charge on the boundary [25]. This observation is in agreement with thermodynamic predictions [26].…”

Applications of STEM-EELS to complex oxides

“…While the mechanisms underlying CMR are not completely clear yet, it is widely accepted that minor nanoscale fluctuations of chemical composition can trigger not just CMR but also other manifestations of strong electronic correlations such as orbital ordering or charge ordering [24]. In this scenario, STEM-EELS techniques have been extensively used to simultaneously study the structure, chemistry and electronic properties of perovskite oxides both in bulk and also in low dimensionality environments such as thin films, nanowires, nanostructures, etc [5,9,11,14,23,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. In this section we will focus on two examples.…”

Studies of electronic structure of ZnO grain boundary and its proximity by using spatially resolved electron energy loss spectroscopy

“…4 -6 Although there have been a few studies concerning the use of electron probe to investigate the energy loss of the GBs, the majority is involved in the high-energy near-edge regime where only the unoccupied states in the conduction band are available. 5,6 The low loss region is, however, more or less disregarded. In general, the low loss study provides information of the interband transitions and may offer an alternative to examine the local electronic structure at high spatial extent.…”