Electron crystallography as a complement to X-ray powder diffraction techniques

Abstract

Abstract. Electron microscopy techniques yield information for crystal structure analysis that is remarkably complementary to that obtained from X-ray powder diffraction data. Structures of polycrystalline materials that resist solution by either method alone can sometimes be solved by combining the two. For example, the intensities extracted from an X-ray powder diffraction pattern are kinematical and can be interpreted easily, while those obtained from a typical selected area electron diffraction (SAED) or precession electron diffraction (PED) pattern are at least partially dynamical and therefore more difficult to use directly. On the other hand, many reflections in a powder diffraction pattern overlap and only the sum of their intensities can be measured, while those in an electron diffraction pattern are from a single crystal and therefore well separated in space. Although the intensities obtained from either SAED or PED data are less reliable than those obtained with Xrays, they can be used to advantage to improve the initial partitioning of the intensities of overlapping reflections. However, it is the partial crystallographic phase information that can be extracted either from high-resolution transmission electron microscopy (HRTEM) images or from PED data that has proven to be particularly useful in combination with high-resolution X-ray powder diffraction data. The dual-space (reciprocal and real space) structure determination programs Focus and Superflip have been shown to be especially useful for combining the two different types of data.

Comparative Study of Selenides and Tellurides of Transition Metals (Nb and Ta) with Respect to its Catalytic, Antimicrobial, and Molecular Docking Performance

“…XRD is the primary technique used for the identification of crystal structure but can barely be used for heterogeneous nanocrystalline samples. It is capable of detecting electron density distribution only due to relatively weak interaction of X-rays with electrons alone while in high-resolution TEM, electron beam strongly interacts both with electric as well as nuclear field, thus giving highly magnified crystal structure as compared to that of X-ray diffraction [ 59 , 60 ]. Figure 3 b-e demonstrates the (SAED) patterns of corresponding samples with concentric rings indexed to hkl reflection planes which are consistent with XRD results [ 61 , 62 ].…”

Crystal Structures from Powder Diffraction: Principles, Difficulties and Progress

“…Electron diffraction has developed rapidly in recent times as a complementary technique with powder diffraction: first, in collaboration with X-ray powder diffraction providing additional information in the phasing process [36] and, nowadays, as a stand-alone technique for ab initio crystal structure solution [37]. The interaction of electrons with the electron density of the crystal being much stronger than that of X-rays means that a single grain (very small single crystal) is enough to produce an exploitable diffraction signal.…”

Exploring Polycrystalline Materials: High-throughput Phase Elucidation Using Serial Rotation Electron Diffraction

“…Re ections with equal or similar d-spacings overlap in the one-dimensional pattern, making the phase and structure identi cation of polycrystalline materials by PXRD di cult and time-consuming, and sometimes impossible [17][18][19] . Challenges arise when a polycrystalline product contains 1) multiple phases, 2) phases with ultra-low contents (<1%), 3) phases with similar unit cells, and/or 4) structures with large unit cells or low symmetries 20 . Some of the more interesting crystalline materials may therefore easily be ignored or overlooked.…”