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

Abstract

“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.