Superconductivity of FeSe0.89 crystal with hexagonal and tetragonal structures

In this paper, the FeSe0.89 crystal is grown by the flux method. Structural measurements imply that hexagonal and tetragonal crystal phases coexist in our sample, which are confirmed by x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). According to the electrical properties, the FeSe0.89 crystal undergoes a superconducting transition at TC = 9.91 K. The experimental results demonstrate that the FeSe0.89 crystal is a type-II superconductor with Hc1(0) of 9.5 Oe and Hc2(0) of 33.4 T. The coherent length ξ(0), Ginzberg-Landau parameter κ(0) and penetration length λ(0) are calculated to be approximately 3.14, 321 and 1007.9 nm, respectively.