The synthesis and structural characterization of Na[sub 3]WO[sub 3]N

The authors report the discovery of a new ternary oxynitride, Na[sub 3]WO[sub 3]N. Na[sub 3]WO[sub 3]N is synthesized by exposing a eutectic melt consisting of 1/2Na[sub 2]O:1Na[sub 2]WO[sub 4] to a flow of ammonia gas at 695[degrees]C. The compound crystallizes in the acentric space group Pmn2[sub 1] with a = 7.2481(3) [angstrom], b = 6.2728(3) [angstrom], and c = 56493(2) [angstrom]. The structure was determined from synchrotron X-ray powder diffraction data and refined using the Rietveld analysis on neutron powder diffraction data. It is isostructural to the low temperature form of Li[sub 3]PO[sub 4] which can be derived from an ordered wurtzite structure-type with all the atoms having tetrahedral coordination. Alternatively, the structure can be described as being [open quotes]salt-like[close quotes] consisting of isolated (WO[sub 3]N)[sup [minus]3] tetrahedral polyanions separated by Na[sup +].