Localized defects in radiation-damaged zircon

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Abstract
The crystal structure of a radiation-damaged natural zircon, ZrSiO_{4} (\alpha-decay radiation dose is ca 1.8 × 10^{18} α-decay events g−1), has been determined. The anisotropic unit-cell swelling observed in the early stages of the amorphization process (0.17% along the a axis and 0.62% along the c axis compared with the undamaged material) is a consequence of the anisotropy of the expansion of ZrO_{8} polyhedra. Larger anisotropic displacement parameters were found for Zr and O atoms, indicating that the distortion produced by \alpha particle-induced localized defects mainly affects the ZrO_{8} unit. The overall shape of SiO_{4} tetrahedra remains essentially undistorted, while Si—O bonds are found to lengthen by 0.43%.