Emergence of Superconductivity in 32522 Structure of (Ca3Al2O5-y)(Fe2Pn2) (Pn = As and P)

Using a high-pressure technique, we have successfully synthesized (Ca3Al2O5-y)(Fe(2)Pn(2)) (Pn = As and P), the first iron-based superconductors with the perovskite-based 32522 structure to be reported. The transition temperature (T-c) is 30.2 K for Pn = As and 16.6 K for Pn = P. The emergence of superconductivity is ascribed to the small tetragonal a-axis lattice constant of the materials. From these results, an empirical relationship is established between the a-axis lattice constant and T, in iron-based superconductors, which offers a practical guideline for exploring new superconductors with higher T-c.