Stacking design of inverse Perovskites: The systems (Sr _3-xBa_xN)E, E = Bi, Sb

The first representatives of 4H (BaMnO₃-type structure, P6 ₃/mmc, Z = 4) and 9R (BaMnO₃-type structure, R3m, Z = 9) inverse Perovskite phases are presented. The phases are obtained within the solid solutions (Sr_3-xBa_xN)E with E = Bi, Sb. The crystal structures and homogeneity ranges were studied by combined X-ray and neutron diffraction as well as chemical analyses. The cubic Perovskite phase with Bi (Sb) is stable in the range of 0.00 ≤ x ≤ 0.90(5) (0.00 ≤ x ≤ 1.30(5)), the 4H variant is stable for 1.55(5) ≤ x ≤ 2.10(5) (1.85(5) ≤ x ≤ 2.45(5)), the 9R structure is stable for 2.50(2) ≤ x ≤ 2.55(2) (2.56(2) ≤ x ≤ 2.60(2)), and the 2H phase is stable for 2.75(5) ≤ x ≤ 3.00 (2.80(5) ≤ x ≤ 3.00). Ba occupies preferable sites in the hexagonal stacking of close packed layers of alkaline earth metal ions and E^3-; Sr is mainly located in cubic stacked layers. The phase order upon going from cubic (Sr₃N)E to 2H-type (Ba₃N)E concomitant to the pronounced Sr/Ba partial order can, in general, be rationalized considering the Coulomb repulsion of nitride ions, as well as the size and charge density of the alkaline earth metal ions.