New phases in the Na3PO4-Mg-3(PO4)(2) binary quenched from 1000 degrees C

A reinvestigation of the Na3PO4-Mg-3(PO4)(2) binary at 1000 degreesC has id entified two new ternary oxide phases and confirmed the existence of an ort horhombic solid solution phase in the vicinity of NaMg4(PO4)(3). Cubic gamm a -Na3PO4 shows a solid solution up to similar to 20 mol.% Mg-3(PO4)(2). Be tween similar to 24 and similar to 29 mol.% a new gamma -Na3PO4- related rh ombohedral superstructure phase is observed. At similar to 44 mol.% Mg-3(PO 4)(2) a new phase with a cristobalite-related structure is observed, which on cooling rapidly to room-temperature transforms to KGaO2-type (Pbca: a=10 .409(2)Angstrom, b=14.492(2)Angstrom, c=5.211(1)Angstrom). The NaMg4(PO4)(3 ) solid-solution phase extends between similar to 72 and 80 mol.% Mg-3(PO4) (2). Surprisingly, and contrary to previous investigations, there is no pha se at 50 mol.%, i.e. with stoichiometry NaMgPO4. All high-temperature annea ling was performed in sealed Pt tubes to prevent loss of components to the atmosphere, which is suspected as the reason for the quite different result s reported by some previous workers.