Annealing of metamict gadolinite-(Y): X-ray diffraction, Raman, IR, and Mössbauer spectroscopy

Radiation induced disorder in gadolinite that led to metamictization with an upper degree of amorphization of 18% was thermally annealed between room temperature and 1273 K. The degree of annealing was calibrated using the anti-symmetric Si–O–Si Raman-active stretching mode near 902 cm−1. Annealing increased with increasing temperature with a rapid critical recrystallization at ca. 943 K. This annealing on a short length scale was then complemented by investigations of long-range ordering seen by X-ray diffraction. The same critical temperature was found, and in addition further increase of long-range order extended to 1073 K. Metamict gadolinite contains only Fe2+ within experimental uncertainty.