THE CRYSTAL-STRUCTURES OF NAMGPO4, NA2CAMG(PO4)(2) AND NA18CA13MG5(PO4)(18) - NEW EXAMPLES FOR GLASERITE RELATED STRUCTURES

Three phosphates with ((NaMPO4)-P-II)(x) composition have been synthes ized and characterized structurally. The low temperature modifications of NaMgPO4 and Na2CaMg(PO4)(2) crystallize in the orthorhombic space group P2(1)2(1)2(1), and the monoclinic space group P2(1)/c, respectiv ely. The phase transitions at high temperature were investigated by th ermal analysis and powder diffractometry. The high-temperature modific ation of Na2CaMg(PO4)(2) is isotypic with glaserite, K3Na(SO4)(2) as d etermined by Rietveld refinement. Na18Ca13Mg5(PO4)(18) crystallizes in the trigonal space group R (3) over bar m. The structures of all of t hese phosphates can be related to the arrangement of cations and phosp hate tetrahedra in the glaserite structure.