Single crystal X-ray and Mössbauer study of shocked ilmenite to 80 GPa

Abstract

Shock loading experiments on single crystal ilmenite (FeTiO₃) are carried out up to peak pressures of 80 GPa using a newly built two-stage light gas gun. Shock effects are investigated by means of X-ray precission technique and Mössbauer spectroscopy. Shock effects are largely controlled by the anisotropic nature of the ilmenite structure. Considerable deformations are observed even in a pressure level of 30 GPa in the shocked crystal when the shock propagation direction is parallel to the c axis, whereas little effects are seen up to 55 GPa when the crystal is shocked parallel to the c plane (cleavage plane). The greatest deformation is introduced in the planes containing the c axis, while less remarkable effects are seen in the plane perpendicular to the c axis. Residual effects are favorably compared with the compression anomalies found in the Hugoniot measurements by King and Ahrens (1976). Mössbauer measurements also reveal that a fraction of highly disturbed regions increases with increasing shock loading pressure. These observations are explained in terms of current heterogeneous yielding model of brittle substances under shock loading, where internal fragmentation is preferentially formed so as to give c-platelet domains that are mutually misoriented with each other.