Superconductivity at 40 K in Lithiation-Processed [(Fe,Al)(OH)][FeSe] with a Layered Structure.

Exploration of new superconductors has always been one of the research directions in condensed matter physics. We report here a new layered heterostructure of [(Fe,Al)(OH)][FeSe], which is synthesized by the hydrothermal ion-exchange technique. The structure is suggested by a combination of X-ray powder diffraction and the electron diffraction (ED). [(Fe,Al)(OH)][FeSe] is composed of the alternating stacking of a tetragonal FeSe layer and a hexagonal (Fe,Al)(OH) layer. In [(Fe,Al)(OH)][FeSe], there exists a mismatch between the FeSe sublayer and the (Fe,Al)(OH) sublayer, and the lattice of the layered heterostructure is quasi-commensurate. The as-synthesized [(Fe,Al)(OH)][FeSe] is nonsuperconducting due to the Fe vacancies in the FeSe layer. The superconductivity with a of 40 K can be achieved after a lithiation process, which is due to the elimination of the Fe vacancies in the FeSe layer. The is nearly the same as that of (Li,Fe)OHFeSe although the structure of [(Fe,Al)(OH)][FeSe] is quite different from that of (Li,Fe)OHFeSe. The new layered heterostructure of [(Fe,Al)(OH)][FeSe] contains an iron selenium tetragonal lattice interleaved with a hexagonal metal hydroxide lattice. These results indicate that the superconductivity is very robust for FeSe-based superconductors. It opens a path for exploring superconductivity in iron-base superconductors.