Emergence of Superconductivity in '32522' Structure of (Ca_3Al_2O_(5-y))(Fe_2Pn_2) (Pn = As and P)

摘要

Using a high-pressure technique, we have successfully synthesized (Ca_3Al_2O_(5-y))(Fe_2Pn_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_c in iron-based superconductors, which offers a practical guideline for exploring new superconductors with higher T_c.