Characterization and thermal behavior of amorphous rare earth phosphates

Abstract

Amorphous cerium and terbium pyrophosphates were synthesized by precipitation method at 353 K. The characterization of these amorphous phosphates was carried out by using X-ray powder diffraction (XRD), thermal gravimetric and differential thermal analysis (TG–DTA), Fourier-transformed infrared spectroscopy (FT-IR), and Raman spectroscopy, especially focusing on the thermal behavior dependence on the calcination temperatures. The amorphous state of the as-prepared cerium phosphate was stable up to 723 K, and it crystallized at 773 K to form a mixture of cerium pyrophosphate (CeP 2O 7) and cerium orthophosphate (CePO 4). Heating at higher temperatures accelerates the phase change from pyrophosphate to orthophosphate accompanying the formation of metaphosphate (CeP 3O 9), and above 1173 K, only a single phase of CePO 4 was obtained. In the case of terbium phosphate, crystallization of amorphous phase occurred at 973 K to produce a mixture of TbPO 4 and Tb 2P 4O 13. The Tb 2P 4O 13 phase decomposed into TbP 3O 9 and TbPO 4 at 1673 K, and these compounds remained even after the calcination at 1873 K.