A one-step synthesis of rare-earth phosphate-borosilicate glass composites

A new 1-step method for synthesizing glass-ceramic composites consisting of rare earth phosphates (REPO₄) dispersed in borosilicate glass (BG) is reported herein as an alternative to the 2-step approach that is traditionally used. The effect of annealing time and annealing temperature on the formation of the 1-step glass-ceramic composites was investigated. Backscattered electron images and energy dispersive X-ray maps were collected to observe the morphology and chemical distribution in the glass-ceramic composites. X-ray diffraction was used to study the long-range order and X-ray absorption near edge spectroscopy was used to study the local environment of La, Y, P and Si. All analyses showed glass-ceramic composites made by the 1 and 2-step methods were similar to each other except for the Si L_2,3-edge XANES spectra, which showed a slight change between the glass-ceramic composite materials made by the different synthesis methods. Xenotime-type phosphates (YPO₄) were observed to be more soluble in the borosilicate glass than the monazite-type phosphates (LaPO₄). This was attributed to the difference in the field strength of the rare-earth ions as a result of the difference in the ionic radii. Glass-ceramic composites made by the 1-step method were shown to form in 1 day at 1100 °C and in 3 days at 1000 °C without a significant change in glass or ceramic composition compared to the 1-step composite synthesized at 1100 °C for 3 days.