ATOMIC-SCALE TRANSMISSION ELECTRON MICROSCOPY OF SUPERSTRUCTURES IN NATURAL COMMENSURATE AND INCOMMENSURATE PYRRHOTITES

Pyrrhotite represents an extended class of minerals that show metal-ion deficiency and associated ordering of vacancies. Depending on their superstructures, pyrrhotite varieties exhibit different magnetic states. Although extensive studies have been conducted on these materials over the past century, the details of their superstructures remain unclear, in particular at the atomic scale. Here, atomic-resolution Z-contrast imaging is utilized to investigate the structural details of a natural pyrrhotite that contains commensurate and incommensurate polymorphs. By using Z-contrast image intensities of Fe columns and quantitative measurements of their positions, we determine the superstructures of both varieties to the atomic scale. Based on these results, perspectives for quantitative counting of Fe vacancies are discussed.