Perovskite Distortion Inverted: Crystal Structures of (A3N)As (A = Mg, Ca, Sr, Ba).

Powder samples of the compounds (A3N)As (A = Mg, Ca, Sr, Ba) were prepared by reacting the respective alkaline earth metal nitrides and arsenic in nickel ampoules. (Mg3N)As crystallizes in a cubic unit cell (space group Pm3m, no. 221) with inverse perovskite structure. The analogous compounds of calcium, strontium, and barium crystallize in an orthorhombic unit cell (space group Pnma, no. 62) as distorted inverse perovskites in the GdFeO3 structure type. The degree of distortion was quantified based on a newly developed vectorial comparison of the atomic sites of coordination polyhedra with the ideal positions (PolyDis). Based on this analysis, the distortion increases with the size of the alkaline earth metal cation. [ABSTRACT FROM AUTHOR]