Mechanical properties of natural radiation damaged titanite and 3 temperature induced structural reorganization : A Nanoindentation and 4 Raman spectroscopic study

21 This study provides new insights into the relation between thermally-induced 22 structural reorganization and the macroscopic mechanical properties of radiation-damaged 23 titanite. The natural sample contains ca. 30% amorphous fraction. Low temperature annealing 24 affects only slightly the sample stiffness and leads to a softening resulting from the defect 25 2 annihilation in crystalline regions. In the high-temperature annealing regime, amorphous 26 domains recrystallize and this leads to further recovery of defects, reduction of interfaces, 27 grain growth, and, in general, an increase in the long-range order. The thermally-induced 28 recrystallization is accompanied by massive dehydration leading to considerable stiffening 29 and hardening. This interpretation of the recrystallization process in titanite based on the 30 correlation of new results from nanoindentation and Raman-spectroscopic measurements 31 complementing previous investigations using thermogravimetric and gas analyses by 32 Hawthorne et al. (1991) and infrared spectroscopy by Zhang et al. (2001). The new data 33 combined with previous work leads to a detailed description of the annealing behavior of a 34 radiation-damaged titanite, which is a complicated process that includes dehydration and 35 atomic-scale structural reorganization. In order to minimize the influence of surface 36 phenomena on the hardness measurements, the so-called “true” hardness was used instead of 37 the standard hardness calculation (Oliver and Pharr 1992). A comparison shows that the 38 Oliver & Pharr method clearly underestimates the hardness. 39 40