New Series of Nickel-Based Pnictide Oxide Superconductors (Ni2Pn2)(Sr4Sc2O6) (Pn= P, As)

We have discovered new nickel-based pnictide oxide superconductors, (Ni 2 Pn 2 )(Sr 4 Sc 2 O 6 ) ( Pn = P, As). These compounds have a tetragonal unit cell with a space group of P 4/ n m m and they consist of alternate stacking of anti-fluorite Ni 2 Pn 2 layers and K 2 NiF 4 -type Sr 4 Sc 2 O 6 blocking layers. Lattice parameters were a = 4.044 Å and c = 15.23 Å for (Ni 2 P 2 )(Sr 4 Sc 2 O 6 ) and a = 4.078 Å and c = 15.41 Å for (Ni 2 As 2 )(Sr 4 Sc 2 O 6 ), indicating their thicker blocking layers than that of LaNiPO ( c ∼8.1 Å). Both (Ni 2 P 2 )(Sr 4 Sc 2 O 6 ) and (Ni 2 As 2 )(Sr 4 Sc 2 O 6 ) exhibited superconductivity with zero resistivity at 3.3 and 2.7 K, respectively. The perfect diamagnetism observed in both compounds guaranteed their bulk superconductivity.