Elastic properties of δ-AlOOH under pressure: First principles investigation

We have investigated the pressure dependence of elastic properties of a hydrous mineral, δ-AlOOH by first principles calculations in order to know the effects of hydrogen bond symmetrization which is predicted to occur in this phase at ∼30 GPa. Our calculations show that the elastic constants of δ-AlOOH with the asymmetric hydrogen bond ordering are significantly smaller than those with the symmetric one. Among them, diagonal C11 and C22 anomalously increase across the hydrogen bond symmetrization, while shear C44, C55 and C66 smoothly increase with pressure showing no anomalous behavior. Accordingly, the bulk modulus, VP and Vϕ show anomalous increase and the shear modulus and VS do not across the hydrogen bond symmetrization.