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

Abstract

Abstract Three phosphates with (NaMIIPO4) x composition have been synthesized and characterized structurally. The low temperature modifications of NaMgPO4 and Na2CaMg(PO4)2 crystallize in the orthorhombic space group P212121, and the monoclinic space group P21/c, respectively. The phase transitions at high temperature were investigated by thermal analysis and powder diffractometry. The high-temperature modification of Na2CaMg(PO4)2 is isotypic with glaserite, K3Na(SO4)2 as determined by Rietveld refinement. Na18Ca13Mg5(PO4)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.