Characterization of FeSe single crystals

✍ Scribed by Hiroyuki Takeya; Shigeru Kasahara; Kazuto Hirata; Takashi Mochiku; Akira Sato; Yoshihiko Takano

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 482 KB
• Volume: 470
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2009.10.041

✦ Synopsis

Superconductivity at 8 K was reported in b-FeSe with a tetragonal PbO structure but not in d-FeSe with a hexagonal NiAs structure. The superconducting transition temperature was then increased up to 37 K (on-set) by high pressure on polycrystalline samples. We report a study of the characterization on single crystals of FeSe superconductors. FeSe single crystals were grown using two methods, simple cooling from stoichiometric melt and flux using NaCl/KCl. While a ball-shaped aggregation composed of thick FeSe crystals was grown from the stoichiometric melt, thin hexagonal-shaped crystals with a size up to 1 mm were grown using the NaCl/KCl flux. The two different crystals indicated superconductivity around at 8 K in spite of their hexagonal shape, suggesting a non-superconducting compound with the NiAs-type hexagonal structure. According to the analyses using an X-ray diffractometer and a scanning electron microscope, the crystals contain microcracks that could be caused by stress. We assume that the hexagonal-shaped crystals grown at high temperature may turn partly to tetragonal b-FeSe at the b-d structure transition temperature.