The crystal structures of NaMgPO4, Na2CaMg(PO4)2 and Na18Ca13Mg5(PO4)18: new examples for glaserite related structures

Abstract Three phosphates with (NaM II PO 4 ) x composition have been synthesized and characterized structurally. The low temperature modifications of NaMgPO 4 and Na 2 CaMg(PO 4 ) 2 crystallize in the orthorhombic space group P 2 1 2 1 2 1 , and the monoclinic space group P 2 1 / c , respectively. The phase transitions at high temperature were investigated by thermal analysis and powder diffractometry. The high-temperature modification of Na 2 CaMg(PO 4 ) 2 is isotypic with glaserite, K 3 Na(SO 4 ) 2 as determined by Rietveld refinement. Na 18 Ca 13 Mg 5 (PO 4 ) 18 crystallizes in the trigonal space group R [unk] m . The structures of all of these phosphates can be related to the arrangement of cations and phosphate tetrahedra in the glaserite structure.