Synthesis and structural characterization of the hexagonal anti-perovskite Na₂CaVO₄F

The structural details of the ordered hexagonal oxyfluoride Na₂CaVO₄F prepared by solid-state synthesis using stoichiometric amounts of V₂O₅, CaCO₃, Na₂CO₃ and NaF were characterized using high-resolution neutron powder diffraction. The structural changes between 25 °C and 750 °C revealed that the two structural subunits in this material behave different when heated: there is an expansion of the face-shared FNa₄Ca₂ octahedra while the VO₄ tetrahedra due to increased thermal disorder reveal marginal bond contractions. Bond valences and the global instability index point to significant structural disorder at 750 °C. - Graphical abstract: The structure of the novel oxyfluoride Na₂CaVO₄F is studied at room temperature and high-temperatures. The structure can be viewed as layers of compression and elongation of polyhedral subunits, which change as a function of temperature. - Highlights: • The novel oxyfluoride, Na₂CaVO₄F, is synthesized via solid-state method. • High-resolution neutron diffraction data is used to analyze the structure of Na₂CaVO₄F. • Structural subunits exhibit expansion and contraction with increasing temperature. • Higher temperatures increase instability within the structure of Na₂CaVO₄F.