Phase characterization with selected area electron diffraction (SAED) represents a significant challenge when the pattern contains a substantial number of diffraction spots arranged in concentric but incomplete rings. This is a common situation when the crystallites are neither large enough to form a single crystal pattern nor sufficiently small and numerous to form continuous Debye-Scherrer rings. In such circumstances, it is often extremely difficult to distinguish between reflections belonging to a specific phase or to identify reflections that originate from secondary phases. To facilitate the process of phase identification for these kinds of multiphase samples, a macro script with the recursive acronym FINDS (FINDS Identifies Non-matrix Diffraction Spots) was developed on the ImageJ/FIJI platform. The program allows the user to mark diffraction spots of known phases by superimposed rings, making it easy to identify and address additional reflections between them. In addition to the full functionality of calculating and plotting the diffraction ring patterns of the known phases in different styles and colors, FINDS also provides tools for locating spot positions and determining the corresponding d-values of the reflections of interest. The effectiveness of this approach and of the developed program in assisting the process of phase identification with SAED patterns of multiphase samples is demonstrated by two representative examples. The macro code of FINDS is published under GNU General Public License v3.0 or later at https://doi.org/10.5281/zenodo.13748483.

The thermal transformation of a Brazilian antigorite heated dry from 600° to 1300°C, was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Below 600°C, the antigorite particles did not change morphologically or crystallographically, as evidence by the presence of the superlattice in the SAD patterns and lattice images. At 650°C, traces of antigorite remained, although the superlattice structure had disappeared and the first indications of forsterite formation were observed in the same SAD. Diffraction patterns of the transition phases showed various topotactical relationships between antigorite and forsterite. At 800°C, the crystallization to forsterite was much more pronounced. At 900°C, the individual particles retained their original shapes, but they were actually pseudomorphs, for their SAD patterns showed only forsterite. Between 1000° and 1300°C various topotactical relationships were observed. Although the overall transformation to forsterite appears to be similar for both chrysotile and antigorite, the transformation of antigorite took place at a slightly higher temperature (~50°C) with a larger number of topotactical relationships than for chrysotile. Enstatite was formed at 1300°C, but it was impossible to determine the topotactic relations between enstatite and forsterite, which was possible with chrysotile.

Electron diffraction is an essential characterization tool for materials scientists. When using the transmission electron microscope (TEM) to perform diffraction experiments, setting up the microscope for both calibration standards and unknown materials in a consistent method ensures that dependable results are obtained. Care must also be exercised to protect digital cameras from intense transmitted and diffracted beams to avoid damage. In Parts 1 and 2 of this series, procedures were presented for recording high-quality, well-calibrated, digital SAED patterns. In Part 3, aspects of diffraction analysis software packages and the reliability of data are discussed.

Electron diffraction is an essential tool for materials scientists to have in their characterization toolboxes. When using the transmission electron microscope (TEM) to perform diffraction experiments, setting up the microscope for both calibration standards and unknown materials in a consistent method will ensure that dependable results are obtained. Care must also be exercised to protect digital cameras from intense transmitted and diffracted beams to avoid damage. In Part 2 of this series a procedure is presented for the proper recording of SAED patterns.

Electron diffraction is an essential tool for materials scientists to have in their characterization toolboxes. When using the transmission electron microscope (TEM) to perform diffraction experiments, setting up the microscope for both calibration standards and unknown materials in a consistent method will ensure that dependable results are obtained. Care must also be exercised to protect digital cameras from intense transmitted and diffracted beams to avoid damage. A procedure is presented that will allow a microscopist to reproducibly configure the microscope and sample to acquire selected area electron diffraction patterns so that these issues are addressed.

The space symmetry of prehnite, a mineral which occurs in cavities and veins within skarn from the Tieshan iron mineral deposit, Daye, Hubei province, central China, has been determined using selected area electron diffraction (SAED) and convergent-beam electron diffraction (CBED) on the submicrometer scale. Our results confirm that natural prehnite may belong to space group Pncm. The unit-cell parameters of the prehnite investigated ( a = 0.458 nm, b = 0.555 nm and c = 1.853 nm) have been calculated using the multicrystal diffraction rings of gold, the internal standard.

A dual-beam focused ion beam microscope equipped with a nanomanipulator was used to fabricate slices from within individual hematite (α-Fe2O3) pseudocubes with selected orientations with respect to the original pseudocubes. Transmission electron microanalysis through selected area electron diffraction enabled assignment of each thin section to a particular zone of the hematite lattice. While the pseudocubes are composed of numerous crystallites, 25–50 nm in size, they are not simply polycrystalline particles. Electron diffraction of thin sections showed that while the pseudocubic hematite particles are composed of numerous coherent domains, the individual thin sections display a net crystallographic orientation to the underlying hematite lattice. Quantitative analysis of the lattice misorientation between coherent domains was calculated from the azimuthal spread of electron diffraction peaks and is consistent with a structure that contains small-angle grain boundaries. Based upon this analysis, we conclude that the pseudocubic hematite particles are mosaic crystals, composed of highly oriented coherent domains.

The distortions present in an electron diffraction pattern can be classified into two categories: one is radially invariant and the other is angularly invariant. We report a method to compensate these displacements undergone by diffraction features promoted by any kind of artifacts generated in parallel beam electron diffraction conditions. This approach is not aimed at quantifying these distortions but only intends to aid in the measurement of lattice parameters of crystals with a significant increase of accuracy and precision as compared to previous approaches. It is based on statistical estimations of the relative positions between diffraction rings and/or spots after performing a transformation of the digitalized patterns to polar coordinates. The analytical method is based on fitting a Gaussian type profile to intensity distributions. This makes it possible to determine the lattice parameters of a polycrystal or single crystal with relative errors smaller than 0.1% for diffractograms acquired in photographic films and below 0.01% for those collected in imaging plates.