Abstract
Partial study of the Na2O-CaO-P2O5-SiO2 system evidenced two compounds corresponding to Na2Ca5(PO4)4 and NaCa6(PO4)3SiO4, instead of Na3Ca6(PO4)5 and Na2Ca4(PO4)2SiO4 previously reported in the literature. Na2Ca5(PO4)4 and NaCa6(PO4)3SiO4 are ordered phases both belonging to a large solid solution domain with general formula Na2-xCa5+x(PO4)4-x(SiO4)x. The Na2-xCa5+x(PO4)4-x(SiO4)x solid solution structure was shown to be a superstructure of the glaserite-type structure.
