Polymorphism, structures and phase transformation of K3[SO4]F

Abstract

The phase K3[SO4]F was found to be dimorphic, undergoing a reversible tetragonal (β) to cubic (α) phase transition at 585 °C. The room-temperature polymorph, β-K3[SO4]F, is isostructural with Ba3SiO5, as confirmed by Rietveld refinement of X-ray powder diffraction data: a= 7.2961(5), c= 10.854(1)Å, R= 0.0689 and Rwp= 0.0907. The α form is cubic, a≈5.43 Å, with probable space group Pmm. Partial Rietveld refinement suggested that it has an anti-perovskite structure. Lattice parameter measurements as a function of temperature showed no discontinuity at the α–β transition, which is therefore suggested to be a displacive second-order transition.