Crystal Chemistry of Ordered Rocksalt-Type SrCaNF

A new Group 2 bimetallic nitride fluoride phase of approximate composition SrCaNF has been prepared and characterized via high resolution single crystal X-ray diffraction. Single crystalline samples were prepared from reaction of SrF2 with Ca and Sr metal under nitrogen. Structural analysis indicates a cubic rocksalt-type phase with a unit-cell doubled along [100] relative to related M2NF rocksalt polymorphs due to ordering of N and F atoms. Sr and Ca atoms share a site. Excess F atoms present in the lattice are disordered over two crystallographically distinct interstitial sites, with charge compensation due to partial vacancies at normal F lattice positions as well as F substitution for some N atoms. There is also disorder at normal F lattice positions, which appears to correlate with the occupancy of nearby F interstitial sites. The refined composition is Sr1.01Ca0.99N0.94F1.18, and the cubic phase has space group Fd $$\overline{3}$$ m (No. 227) with a = 10.3404(10) A and Z = 16. High resolution single crystal X-ray diffraction was utilized to describe the crystal chemistry of the new ordered rocksalt-type compound, SrCaNF, which shows significant disorder, particularly with respect to positioning of F atoms.