Alpha-recoil damage in titanite (CaTiSiO₅): Direct observation and annealing study using high resolution transmission electron microscopy

“Tracks” of alpha-recoil nuclei have been observed directly in titanite (CaTiSiO₅). Recoil tracks in titanite are 4 to 6 nm in diameter and consist of a central aperiodic zone surrounded by a narrow (0–2 nm) outer zone that is essentially crystalline, but which exhibits modulated image contrast due to interstitial defects. Previous work has suggested that titanite is 2 to 3 times more sensitive to alpha-decay damage than other ceramic phases (e.g., zircon, ZrSiO₄). We find, however, that track diameters in titanite are essentially the same as reported for other phases, including zircon (ZrSiO₄), pyrochlore (NaCaTa₂O₆F), and zirconolite (CaZrTi₂O₇). An annealing study of titanite (300 to 700 °C, N₂) shows a two-stage recovery process. Track diameter decreases at 400 °C. An intermediate phase develops at 500 °C, and nearly all tracks are epitaxially recrystallized. At 700 °C, all tracks and the intermediate phase are gone.