Determination of the crystal structure of khanneshite by the Rietveld method

The crystal structure of khanneshite (Na2.75Ca0.23)2.98(Ba1.08Sr0.63Ca0.46Ce0.46La0.18Nd0.15Pr0.04)3.00 · (CO3)5 found in carbonatites from the Khibiny massif (the Kola Peninsula) was solved by the Rietveld method. The X-ray diffraction data were collected on a focusing STOE-STADIP diffractometer equipped with a bent Ge(111) primary-beam monochromator (λMoKα1 radiation, 2.00° < 2θ < 54.98°, 311 reflections). All the calculations were performed within the sp. gr. P63mc; a = 10.5790(1) Å, c = 6.5446(1) Å, V = 634.31(1) Å3, RP = 2.38, Rwp = 3.26, RB = 1.42, RF = 1.79. The atoms of the cations were refined with anisotropic thermal parameters.