Rietveld refinement of the langbeinite-type mixed-metal phosphate K₂Ni_0.5Zr_1.5(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] octa­hedra [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] tetra­hedra inter­linked via vertices into a ³_∞[M₂(PO₄)₃] framework. Two independent K⁺ cations are located in large cavities of the framework, with coordination numbers to O²⁻ anions of nine and twelve. The K, Ni, and Zr sites are located on threefold rotation axes.