Double titanium and rare-earth phosphates

Abstract

Phosphates Ln_1/3Ti₂(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 Ln_1/3Ti₂(PO₄)₃ on the Ln³⁺ radius was observed to have a gadolinium kink.