Comparison of yttrium polyphosphate Y(PO₃)₃ prepared by sol–gel process and solid state synthesis

Preparation of Y(PO₃)₃ polyphosphate was investigated by sol–gel process and solid state synthesis. Crystallization temperature range and purity of samples arising from both synthesis methods were compared. XRD patterns recorded from powders annealed at different temperature evidenced that the stability domain of Y(PO₃)₃ is much wider for sol–gel derived samples. Furthermore ³¹P NMR analysis demonstrated the presence of YPO₄ impurity along with Y(PO₃)₃ resulting from solid state route for any sintering temperature. Regarding the sol–gel procedure, effects of the elimination of KCl by-product on the presence of carbon residues in the final materials was studied by IR and Raman spectroscopies as well as EPR measurements. It was shown that when KCl is removed at the end of the synthesis, the crystallization of Y(PO₃)₃ phase takes place over a very short domain and leads to grey black powder unsuitable for further optical investigations.