Static elasticity of cordierite I: Effect of heavy ion irradiation on the compressibility of hydrous cordierite

Abstract

The effect of ion beam irradiations on the elastic properties of hydrous cordierite was investigated by means of Raman and X-ray diffraction experiments. Oriented single crystals were exposed to swift heavy ions (Au, Bi) of various specific energies (10.0–11.1 MeV/u and 80 MeV/u), applying fluences up to 5 × 1013 ions/cm2. The determination of unit-cell constants yields a volume strain of 3.4 × 10−3 up to the maximum fluence, which corresponds to a compression of non-irradiated cordierite at ~480 ± 10 MPa. The unit-cell contraction is anisotropic (e 1 = 1.4 ± 0.1 × 10−3, e 2 = 1.5 ± 0.1 × 10−3, and e 3 = 7 ± 1 × 10−4) with the c-axis to shrink only half as much as the axes within the ab-plane. The lattice elasticity for irradiated cordierite (ϕ = 1 × 1012 ions/cm2) was determined from single-crystal XRD measurements in the diamond anvil cell. The fitted third-order Birch–Murnaghan equation-of-state parameters of irradiated cordierite (V 0 = 1548.41 ± 0.16 A3, K 0 = 117.1 ± 1.1 GPa, ∂K/∂P = −0.6 ± 0.3) reveal a 10–11 % higher compressibility compared to non-irradiated cordierite. While the higher compressibility is attributed to the previously reported irradiation-induced loss of extra-framework H2O, the anomalous elasticity as expressed by elastic softening (β a −1 , β b −1 , β c −1 = 397 ± 9, 395 ± 28, 308 ± 11 GPa, ∂(β −1)/∂P = −4.5 ± 2.7, −6.6 ± 8.4, −5.4 ± 3.0) appears to be related to the framework stability and to be independent of the water content in the channels and thus of the ion beam exposure.