Two perovskite-type fluorides K2NaVF6and(NH4)3VF6were synthesized under mild hydrothermal conditions.The structures of the compounds were determined by means of powder X-ray diffraction analysis.The Rietveld refinement indicates that K2NaVF6has a cubic elpasolite-type structure and crystallizes in space group Fm3m with lattice constant a=8.3180(2) nm.(NH4)3VF6has a cubic cryolite-type structure and crystallizes in space group Fm3m with lattice parameter a=9.090(1) nm.The compounds were further characterized by scanning electron microscopy(SEM),thermogravimetric(TG) and differential thermal analysis(DTA).The variable temperature magnetic susceptibility of these two compounds was characterized for the first time and the result shows that the magnetic ordering is related to the crystallographic features and isolated magnetic unit with the temperature decreasing.
