The structure and superconducting properties of FeSe depend on stoichiometric precision in a narrow phase field with formation temperatures above 300° C. A complete understanding of crystalline growth and phase transformations of iron chalcogenides is important for control of structure, composition and superconducting properties of these materials.

We report a synchrotron X-ray diffraction study on in situ crystal growth and phase transformation of FeSe compounds for notional starting composition Fe:Se ~ 1.03. Reaction between iron and selenium during this investigation hints at a direct crystallographic relationship of specific planes within the hexagonal and tetragonal forms of FeSe as well as the suggestion that FeSe2 is a precursor for formation of Fe3Se4, hexagonal Fe0.88Se and ultimately β-FeSe.

This dataset contains structural data on FeSe compounds during these phase transformations induced by in situ heating of elemental Fe and Se in an oxygen-free environment.  Raw data from synchrotron and also TOPAS refinements of these raw data in .xye file format.