Sound velocity measurements of ε–FeOOH up to 24 GPa

Abstract

The sound velocity and density of ε–FeOOH have been simultaneously measured up to 24 GPa at room temperature using an ultrasonic pulse–echo–overlap method and a Kawai–type multi–anvil apparatus at BL04B1 in SPring–8. In the experimental pressure range, the velocity of both the P– and S–waves of ε–FeOOH was ~ 15% lower than that of an isostructural phase δ–AlOOH. The pressure dependence of the determined adiabatic bulk modulus (K_S) increased in the higher pressure range beyond 17 GPa, whereas that of the axial ratios a/c and b/c did not transition from negative to positive. A similar change of pressure dependence of K_S was observed in δ–AlOOH, which is followed by a transition of proton distribution state to disordered, but the axial ratios of ε–FeOOH indicate that the transition would not occur up to 24 GPa.