Synthesis and structural characterization of the hexagonal anti-perovskite Na2CaVO4F.

The structural details of the ordered hexagonal oxyfluoride Na 2 CaVO 4 F prepared by solid-state synthesis using stoichiometric amounts of V 2 O 5 , CaCO 3 , Na 2 CO 3 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 FNa 4 Ca 2 octahedra while the VO 4 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. [ABSTRACT FROM AUTHOR]