Rietveld refinement of the langbeinite-type mixed-metal phosphate K2Ni0.5Zr1.5(PO4)3

Dipotassium [nickel(II) zirconium(IV)] tris-(orthophosphate) was prepared from a self-flux in the system K2O-P2O5-NiO-K2ZrF6. The title compound belongs to the langbeinite family and is built up from two [MO6] octa-hedra [M = Ni:Zr with mixed occupancy in ratios of 0.21 (4):0.79 (4) and 0.29 (4):0.71 (4), respectively] and [PO4] tetra-hedra inter-linked via vertices into a (3) ∞[M 2(PO4)3] framework. Two independent K(+) cations are located in large cavities of the framework, with coordination numbers to O(2-) anions of nine and twelve. The K, Ni, and Zr sites are located on threefold rotation axes.