Synthesis and characterization of phosphates in molten systems Cs2O–P2O5–CaO–MIII2O3 (MIII—Al, Fe, Cr)

The crystallization of complex phosphates from the melts of Cs2O–P2O5–CaO–MIII2O3 (MIII—Al, Fe, Cr) systems have been investigated at fixed value Cs/P molar ratios equal to 0.7, 1.0 and 1.3 and Са/Р=0.2 and Ca/МIII=1. The fields of crystallization of CsCaP3O9, β-Ca2P2O7, Cs2CaP2O7, Cs3CaFe(P2O7)2, Ca9MIII(PO4)7 (MIII—Fe, Cr), Cs0.63Ca9.63Fe0.37(PO4)7 and CsCa10(PO4)7 were determined. Obtained phosphates were investigated using powder X-ray diffraction and FTIR spectroscopy. Novel whitlockite-related phases CsCa10(PO4)7 and Cs0.63Ca9.63Fe0.37(PO4)7 have been characterized by single crystal X-ray diffraction: space group R3c, a=10.5536(5) and 10.5221(4) Å, с=37.2283(19) and 37.2405(17) Å, respectively.

Graphical AbstractStructural relationships between β-Ca3(PO4)2 and synthesized compounds is shown in terms aliovalent substitution of calcium atoms, which residue on three-fold axis, by other metals in β-Ca3(PO4)2 framework.Figure optionsDownload as PowerPoint slideResearch highlights
► Phase formation in the melts of Cs2O–P2O5–CaO–MIII2O3 (MIII—Al, Fe, Cr) systems were determined.
► The composition and structure of the compounds depend on the nature of MIII and initial ratio of Cs/P.
► Obtained compounds have been characterized by powder X-ray diffraction and FTIR spectroscopy.
► Crystal structures of CsCa10(PO4)7 and Cs0.63Ca9.63Fe0.37(PO4)7 were determined by single crystal XRD.