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Crystals of FeSe0.88 and FeSeMn0.1 have been grown from KCl solutions. Crystals measuring 2−3 mm across and 0.1−0.3 mm thick grow with a hexagonal plate like habit. Powder X-ray diffraction (XRD) measurements show strong peaks corresponding to the tetragonal α-FeSe phase and weak hexagonal β-FeSe peaks in both cases. The plate side of the crystal is identified to be the (101) face of the tetragonal α-FeSe. Energy dispersive X-ray spectroscopic (EDS) measurements show that Mn substitutes for Fe. Both types of crystals show a superconducting transition at 8 K in the DC magnetization measurements and a broad resistive transition with zero resistance at 7.5 K with an onset at 11 K. Specific heat measurements also confirm bulk superconductivity in the crystals. Crystals could also be grown using KBr as a solvent.

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X-ray absorption spectroscopy (XAS) Fe K-edge spectra of the FeSe x (x=1-0.8) single crystals cleaved in situ in vacuum reveal characteristic Fe 4sp states, a lattice distortion and the Se K-edge spectra point to a strong Fe 3d-Se 4p hybridization giving rise to itinerant charge carriers. A formal charge of ~1.8+ for Fe and ~2.2-for Se were evaluated from these spectra in the FeSe x (x=0.88). The charge balance between Fe and Se is assigned itinerant electrons located in the Fe-Se hybridization bond. As x decreases the 4p hole count increases and a crystal structure distortion is observed that in turn causes the Fe separation in the ab plane change from 4p orbital to varying (modulating) coordination. Powder x-ray diffraction (XRD) measurements also show a slight increase in lattice parameters as x decreases (increasing Se deficiency).