Hyper-expanded interlayer separations in superconducting barium intercalates of FeSe

Intercalation of Ba in β-FeSe by ammonothermal synthesis results in the formation of different superconducting phases with interlayer distance ranging between 8.4 and 13.1 Å. The values of Tc are primarily dependent on Ba content, and are further modulated by the interlayer spacing through facile intercalation and deintercalation of ammonia.