Probing the effect of radiation damage on the structure of rare-earth phosphates

Synthetic analogues of naturally occurring monazite (REPO₄; RE = La to Gd) and xenotime (RE′PO₄; RE′ = Tb to Lu and Y) minerals have been identified as potential wasteforms for nuclear waste. High energy ion-implantation of crystalline materials simulates radiation-induced structural damage and allows for the radiation resistance of a crystal structure to be probed. The structural stability of Au⁻ ion-implanted La_1-xYb_xPO₄ materials was investigated using micro-X-ray diffraction (μ-XRD) and glancing angle X-ray absorption near-edge spectroscopy (GA-XANES) in this study. The long- and short-range order of La_1-xYb_xPO₄ (x = 0, 0.3, 0.7, 1.0) is affected by ion-implantation and, thus, the materials are prone to structural damage. The structures of some members of the La_1-xYb_xPO₄ series (x = 0.7 and 1.0) were observed to partially recover after being implanted with Au⁻ ions to a high dose. The structures of all members of the La_1-xYb_xPO₄ series were observed to recover from damage resulting from ion-implantation after annealing the materials at temperatures ≥300 °C. - Highlights: • Structural stability of La_1-xYb_xPO₄ was studied using glancing angle XANES. • Loss of short- and long-range order in La_1-xYb_xPO₄ due to ion-implantation observed. • High dose of Au⁻ ions induced partial recrystallization of YbPO₄ and La_0.3Yb_0.7PO₄. • Glancing angle XANES spectra were sensitive to changes in the structure. • Annealing was found to result in the recrystallization of the damaged structure.