In Situ Tem Observation of Radiation Induced Amorphizatton of Crystals with Apatite Structure

Temperature dependence of amorphization doses for 1.5 MeV Kr ion irradiated Ca₁₀(PO₄)₆F₂ and Ca₂La₈(SiO₄)₆O₂ were studied with in situ transmission electron microscopy. At low temperatures, Ca₁₀(PO₄)₆F₂ became amorphized at lower doses than Ca₂La₈(SiO₄)₆O₂. However, the critical amorphization dose increased much more rapidly for the former above 350 K than the latter. Compared to Ca₂La₈(SiO₄)₆O₂ at 475 K, Ca₁₀(PO₄)₆F₂ required a dose nearly five times higher to become amorphous. Based on the dose-temperature curves, activation energies for the crystal structure recovery process were determined to be 0.07 eV for Ca₁₀(PO₄)₆F₂ and 0.13 eV for Ca₂La₈(SiO₄)₆O₂respectively. The lower critical amorphization dose and lower activation energy for recovery of Ca₁₀(PO₄)₆F₂ are attributed to the weaker P-O bond and the higher fluorine mobility in the structure.