Synergy between transmission electron microscopy and powder diffraction: application to modulated structures

Abstract

The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal X-ray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem. Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various TEM techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data. The following TEM methods are discussed: electron diffraction (selected area electron diffraction, precession electron diffraction), imaging (conventional high-resolution TEM imaging, high-angle annular dark-field and annular bright-field scanning transmission electron microscopy) and state-of-the-art spectroscopic techniques (atomic resolution mapping using energy-dispersive X-ray analysis and electron energy loss spectroscopy).

Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp

“…Some types of samples can be difficult to study with powder diffraction, but are excellent for study using TEM, for example multiphase samples, samples with local defects and modulated materials [4,5,6,7]. While often such materials can still be analysed with powder diffraction, the data might be difficult for interpretation due to a variety of factors such as the presence of a large number of reflections, reflection overlap and anisotropic reflection broadening.…”

“…Structure models for numerous modulated materials were solved using this combination of techniques, most frequently followed by subsequent refinement using powder diffraction data. Examples range from scheelites [37] to perovskite-based structures [38]; a description of the typical solution route has already been published in a previous review paper by Batuk et al [4]. …”

Transmission electron microscopy analysis of some transition metal compounds for energy storage and conversion

“…The properties of anode materials are largely related to their chemical composition, crystallographic structure, surface characteristics, structural defects, electronic structures as well as to a delicate interplay among these factors [12]. With respect to improving the electrochemical performance of TMC anodes, nanostructuring, surface engineering, introducing defects and constructing hybrid structures are the major effective strategies.…”

Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor‐Doped Pb‐Based Ferroelectrics

“…[13][14][15] These planar defects can be identified as CS planes (by comparing the images in Figure 1t ot hose of perovskite CS structures in Refs. [16,17,18]). An (h0l) p CS plane is formed by displacement of one part of the ABO 3 perovskite structure with respect to another over av ector 1 = 2 [110] p .T he displacement transforms corner-sharing BO 6 octahedra along the plane into edge-sharing BO 5 tetragonal pyramids (Figure 2a).…”

“…As aresult of the large relaxation at the CS planes,the structure is incommensurately modulated and we described it using a( 3 + +1)D structural model developed for (Pb,Bi) 1-x Fe 1+x O 3-y . [16,18] Them odel also allows interpretation of the XPD data of other Pb 1-x (Ti 1-z Fe z ) 1+x O 3-y members (see the crystallographic parameters in Table S3). The z = 0.95 compound is antiferromagnetically ordered at room temperature.T oavoid the magnetic contribution, the refinement was Ti ÀV CC O )C formed by an oxygen vacancy (square) and the Fe III ion in an incomplete FeO 5 polyhedron( red), in accordance with Refs.…”