RIETVELD REFINEMENT OF THE ORTHORHOMBIC PBCA STRUCTURES OF RB2CDSI5BI12, CS2MNSI5O12 CS2COSI5O12 AND CS2NISI5O12 LEUCITES BY SYNCHROTRON X-RAY-POWDER DIFFRACTION

Analysis of high-resolution synchrotron X-ray powder diffraction patte rns for hydrothermally synthesized Rb2CdSi5O12 and Cs2MnSi5O12 leucite analogues, and dry-synthesized Cs2CoSi5O12 and Cs2NiSi5O12 leucite an alogues showed that they have an orthorhombic Pbca structure. The stru ctures have been refined by the Rietveld method, showing that the tetr ahedrally coordinated atoms (Si, Cd, Mn, Co and Ni) are ordered on sep arate sites. The Cs2MnSi5O12, Cs2CoSi5O12 and Cs2NiSi5O12 leucite samp les are unusual in containing SiO4, tetrahedra which are more distorte d, on average, than the larger MnO4, CoO4 and NiO4 tetrahedra. The JCP DS file numbers for Rb2CdSi5O12, Cs2MnSi5O12 and Cs2CoSi5O12 are 46-14 91, 46-1492 and 46-1493, respectively.