RADIATION-INDUCED CHANGES IN THE MECHANICAL PROPERTIES OF ZIRCON

We followed the radiation-damage process in zircon (ZrSiO₄) by analysis of changes in the mechanical properties using nanoindentation (Beirau et al. 2018). From this, evidence can be provided for percolation transitions occurring around 30 and 70 % amorphous fractions in the mineral. At the percolation points, the indentation hardness has found to deviate from its linear correlation with the elastic modulus, the shear modulus and the bulk modulus. Both percolation points generate anomalies in the hardness versus density evolution.

Further, recent results of nanoindentation high-resolution mapping that has been used to probe the mechanical properties of a natural, highly-zoned zircon will be presented. The zoning (~ 5 to 400 µm) is due to variations in the U and Th concentrations (dose ~ 3.7 x to 7.5 x 10¹⁸ α-decays/g). Our results show how multi-layered ceramic materials accommodate volume expansion and changes in mechanical properties due to radiation damage. The detailed investigation of fractures occurring only in the higher crystalline areas in the zircon, enlarge the understanding of crack propagation in initially crystalline material due to the strain induced by the heterogeneous distribution of U and Th. In addition, the variations in physical properties of zircon due to differences in radiation damage provide useful additional information for geo- and thermochronlogical data analysis.

Beirau, T., Nix, W.D., Ewing, R.C., Pöllmann, H., and Salje, E.K.H. (2018) Radiation-damage-induced transitions in zircon: Percolation theory applied to hardness and elastic moduli as a function of density. Appl. Phys. Lett. 112, 201901.