Electrochemical method has been used to insert K/Na into FeSe lattice to prepare alkali-intercalated iron selenides at room temperature. Magnetization measurement reveals that KxFe2Se2 and NaxFe2Se2 are superconductive at 31 K and 46 K, respectively. This is the first successful report of obtaining metal-intercalated FeSe-based high-temperature superconductors using electrochemical method. It provides an effective route to synthesize metal-intercalated layered compounds for new superconductor exploration.

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs 3 structural units in SnAs-based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li 0.6 Sn 2 As 2 and NaSnAs through a topotactic structural transformation of trigonal SnAs 3 to square SnAs 4 under pressure, resulting in a record-high T c among all synthesized SnAs-based compounds. Meanwhile, the conductive channel transfers from the out-of-plane p z orbital to the in-plane p x + p y orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p-orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.