Microstructure of radiation-damaged zircon under pressure

Radiation-damaged zircons have been studied at high pressures, up to 7 GPa, by means of single-crystal X-ray diffraction at room temperature. The zircons studied contained high fractions of amorphous material (65 and 85%, respectively). Peak profiles of selected Bragg reflections at room pressure give evidence of the complex microstructure of defective crystalline regions. A differential stress of ∼20 GPa is found between expanded and compressed regions. Two clear stages are observed as a function of pressure: (i) below 3 GPa, diffraction maxima do not show significant changes; (ii) above 3 GPa, a simultaneous increase in peak intensity and decrease in mosaic spread is observed. The effects are attributed to reorientation of crystalline domains within the amorphous matrix. The starting peak profile is recovered after releasing pressure, implying that no significant defect healing is induced in this pressure range, and that all observed effects are reversible. Results are interpreted in terms of the non-uniform structure of amorphous cascades.