Double titanium and rare-earth phosphates

Phosphates Ln1/3Ti2(PO4)3 (Ln = Y, La, Ce, Pr, Eu, Gd, Ho) were synthesized by the citrate solgel (Pechini) method. Solid-phase reactions were activated using dispersion, pressing, and sintering microadditives. Synthesized samples were characterized by X-ray diffraction (Rietveld method), IR spectroscopy, electron microscopy, and microprobe analysis. The specific features of their structure formation were studied. The studied phosphates were shown to crystallize in the NaZr2(PO4)3 (NZP/NASICON) structural type with space group R3. The framework of their structure is built of columns of TiO6 and РО4 polyhedra, and one of the two types of extraframework positions inside columns of polyhedra was occupied by Ln3+ cations at 2/3. The dependences of the unit cell parameters of Ln1/3Ti2(PO4)3 on the Ln3+ radius was observed to have a gadolinium kink.