Role of the third-order elasticity modulus in stabilizing Na crystals at high pressures

Abstract

Born’s criterion of crystal stability with respect to small variations of homogeneous deformations is formulated in a quasi-harmonic approximation. It is shown that the third-order Landau potential with respect to a tensor’s components of Lagrangian deformation is sufficient for predicting the critical pressure at which the cubic structure becomes unstable. The accuracy of prediction is no worse than that of the available experimental data.