Structure of KCaPO4.H2O from X-ray powder diffraction data

The crystal structure of monoclinic KCaPO4.H2O has been solved from X-ray powder diffraction data. The cell dimensions, obtained by indexing methods, are a=7.5834 (9), b=8.1568 (11), c=7.6541 (8) A, β=102.975 (9)0. The space group is C2/m with Z=4. Initial positional parameters for the Ca, K and P atoms were obtained by solution of the Patterson map resulting from integrated intensities of 92 unambiguously indexed reflections. The remaining atoms were located by an interpretation of the Fourier difference map. The structure refinement was effected by the Rietveld method. The final indicators were RF=0.046, RB=0.054 and Rwp=0.137. The three-dimensional structure is built up from PO4 tetrahedra and CaO8 (two water molecules and six O atoms belonging to the phosphate groups) and KO8 (eight atoms belonging to the phosphate groups) polyhedra. (orig.)