Synthesis and structure of β-Ca3Ga2N4, a ternary nitride with two interpenetrating three dimensional nets

We report the structure of a second polymorph of the ternary calcium gallium nitride Ca3Ga2N4, synthesized as crystals from the elements in sealed niobium tubes at 760°C using a Na/Ca melt as the growth medium. The material is an almost colorless transparent insulator. β-Ca3Ga2N4 crystallizes in I41/acd (No. 142) with a=b=11.210(1) Å, c=15.914(2) Å and Z=16. It contains a pair of identical, independent interpenetrating networks based on corner sharing GaN4 tetrahedra, which may be designated 3∞[[Ga4N6]N4/2] and are related to the 3∞[[Si]N4/2] framework in β-cristobalite.