Effect of alkali metal deintercalation on superconductivity in the K x Fe 2–y Se 2 system

In this work, the intercalation and subsequent deintercalation of alkali metal (K) were performed on new tetragonal β-FeSe compounds, and the effect on their superconductivity was studied. The FeSe precursor was intercalated with potassium by solid-state reaction, and then the potassium was selectively etched by topochemical reaction with polar chemical solvents. The K-intercalated FeSe showed phase separation, into a major insulating phase with Fe vacancy and a minor superconducting phase without vacancy. After the topotactic deintercalation reaction, the deintercalated FeSe exhibited increased lattice parameters compared to the pristine FeSe compound, and antiferromagnetic behavior instead of superconductivity. The magnetic property can be attributed to the phase separation of the K-intercalated phases. The deintercalated phase retained the β-FeSe structure with Fe vacancies, which changed the superconductor to an antiferromagnetic metal.