Growth and superconductivity of FeSe$_{x}$ crystals*

Stimulated by the recent discovery of high temperature superconductivity in ferrous pnictides, other iron-based planar compounds have been revisited to search for superconductivity. The most promising outcome of this effort is the discovery of superconductivity in \textit{ alpha}\textbf{ - }FeSe$_{x}$ which is less toxic but has a FeSe$_{4}$ tetrahedra planar crystal sublattice similar to that consisting FeAs$_{4}$ in the oxypnictides. Investigations on the superconductivity in FeSe$_{x}$ can shed light on the superconducting mechanism in oxypnictides. We report the growth of FeSe$_{x}$ crystals through a vapor self-transport approach. Both tetragonal and hexagon shaped FeSe$_{x}$ crystals with a lateral dimension of up to a few millimeters were obtained and their superconductivity was investigated with both magnetization and resistive measurements. We systematically explored the effect of synthesis parameters such as Fe/Se ratio, sintering temperature and cooling rate on the quality of the crystals.