Discovery of the Ca4Al2O6Fe2Pn2 "Al-42622(Pn)" and Ca3Al2O5Fe2Pn2 "Al-32522(Pn)" (Pn = As, P) superconductors

Highlights: ► Perovskite type blocking layered high-Tc superconductors discovery. ► High pressure synthesis technique. ► Ca3Al2O5Fe2Pn2 (Pn = As, P) is first superconductor with "32522" structure. ► "Al-42622" has smallest a-axis lattice constant and As–Fe–As bond angle. ► Important materials for future developments. -- Abstract: Here we report on the discovery of the perovskite type blocking layered, Ca4Al2O6−yFe2As2 (Al-42622(Pn)) and Ca3Al2O5−yFe2As2 (Al-32522(Pn)) (where Pn = As, P), iron based superconductors. These new materials are synthesized by using high-pressure synthesis method. Al-42622 shows a superconducting critical temperatures Tc at 28.3 K for Pn = As and 17.1 K for Pn = P. Al-32522(Pn) shows a Tc at 30.2 K for Pn = As and 16.6 K for Pn = P. Al-42622(Pn) contains smallest a-axis lattice parameters among the iron-pnictide superconductors while Al-32522(Pn) is the first superconductor in the "32522" type crystal structure. More details on synthesis and characterization of these materials will be given in this paper