Crystal structure of the new FeSe1−x superconductor

The newly discovered superconductor FeSe1−x (x≈ 0.08, Tconset≈ 13.5 K at ambient pressure rising to 27 K at 1.48 GPa) exhibits a structural phase transition from tetragonal to orthorhombic below 70 K at ambient pressure—the crystal structure in the superconducting state shows remarkable similarities to that of the REFeAsO1−xFx (RE = rare earth) superconductors.