The annealing behaviour of metamict titanite, which exhibited moderate structural damage arising from the α-decay of U and Th, was studied by using single-crystal synchrotron radiation and optical birefringence techniques. Progressive and isothermal annealing experiments yielded a temperature-dependent response in the diffraction and optical signals. The low-temperature regime (around 673K) was characterized by the preferred annealing of Frenkel defects. This resulted in small changes in the unit-cell volume, and the Bragg intensities, on a timescale of several hours. After constant heating at higher temperatures, the metamict titanite exhibited 2-stage kinetics; with the most rapid effects appearing during the first 2 hours of annealing, and less significant changes appearing after the initial annealing period. The rapid annealing of Frenkel defects occurred first, followed by the recrystallization of more highly damaged regions. The single-crystal studies revealed lower temperatures for pronounced annealing effects than those previously reported in powder-diffraction studies (at about 100K).

Thermal Annealing of Metamict Titanite - a Synchrotron Radiation and Optical Birefringence Study. C.Paulmann, U.Bismayer, L.A.Groat: Zeitschrift für Kristallographie, 2000, 215[11], 678-82