Cation distribution in cubic NaM(PO3)3 (M = Mg or Zn) using X-ray powder diffraction and solid state NMR †

Abstract

Solid state 23Na and 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy and X-ray powder diffraction have been used in combination to study the structure of the model phosphate phases NaMg(PO3)3 and NaZn(PO3)3. The similar X-ray scattering of Na and Mg make determination of the cation distribution in NaMg(PO3)3 difficult using X-ray data alone. However, the structure of NaZn(PO3)3 was successfully refined and an initial model for the cation distribution in the magnesium analogue proposed. The 23Na and 31P solid state NMR data confirm the similarities between the two structures, while the 23Na also suggested three sodium sites in a 2∶1∶1 ratio, consistent with the proposed crystallographic model. This allowed for a successful refinement of the structure of NaMg(PO3)3, confirming that the structures are indeed isostructural. Both structures contain chains of (PO3)nn− with Na+ and Mg2+/Zn2+ ions in distorted octahedral sites located between the polyphosphate chains.