Synthesis, crystal structure, and chemical stability of the superconductor FeSe1−x

Abstract

We report on a comparative study of the crystal structure and the magnetic properties of FeSe1−x (x=0.0–0.15) superconducting samples by neutron powder-diffraction and magnetization measurements. The samples were synthesized by two different methods: a “low-temperature” one using powders as a starting material at T≃700 °C and a “high-temperature” method using solid pieces of Fe and Se at T≃1075 °C. The effect of a starting (nominal) stoichiometry on the phase purity of the obtained samples, the superconducting transition temperature Tc, as well as the chemical stability of FeSe1−x at ambient conditions were investigated. It was found that in the Fe-Se system, a stable phase exhibiting superconductivity at Tc≃8 K exists in a narrow range of selenium concentration (FeSe0.974±0.005).