Baric exothermic fragmentation of crystals

Abstract

Currently, an extensive study of the properties of matter at high pressures is underway. However, little attention is paid to the baric fragmentation of the crystal. Our work is devoted to the study of the nature of this effect. Based on the analytical method (i.e. without computer simulation), the change in the specific (per unit area) surface energy (σ) of the crystal from the normalized volume (v/v_o) along various isotherms was studied. It is shown that there is a maximum on the isotherm σ(v/v_o), with (v/v_o)_max < 1. With an isothermal deviation (at decreasing or increasing) of the v/v_o value from the (v/v_o)_max, the σ(v/v_o) function decreases, passing at certain values, (v/v_o)_frS < (v/v_o)_max < 1 or (v/v_o)_frL > 1, to the negative values. This behavior of the σ(v/v_o) function at v/v_o < (v/v_o)_frS or v/v_o > (v/v_o)_frL should cause spontaneous fragmentation of the crystal, in which the crystal will strive in any way to increase its specific (per atom) surface: either free (when stretched), or intercrystalline (when compressed). It is indicated that the crystal under all-round stretching passes into the liquid or gas phase without reaching the (v/v_o)_frL value. However, a negative value of the surface energy can be achieved with all-round compression of the crystal. It is shown that the negative value of the σ(v/v_o) function should stimulate both fragmentation of the crystal structure and heating of the fragmenting medium (exothermic effect) and the appearance of additional pressure in this medium due to the appearance of the inner surface. Calculations of (v/v_o)_max and (v/v_o)_frS values for Ne, Li and Au crystals at different temperatures have been performed. Based on the experimental data, the pressures are indicated, which correspond to the calculated (v/v_o)_frS values. It was shown that these static pressures are quite achievable in modern experiments.