On the negative values of surface energy under compression or tension of crystal

Abstract

The dependences of the specific surface energy σ and its isochoric derivative with respect to temperature on the relative volume V/V 0 and temperature of the crystal of a simple substance are studied. The conditions which should be satisfied by the function σ(V/V 0) under crystal tension or compression are determined. It was shown that the isothermal dependence σ(V/V 0) has a maximum at (V/V 0)max < 1, decreases under compression or tension with respect to (V/V 0)max, passing at certain values, (V/V 0) frS < (V/V 0)max < 1 and (V/V 0) frL < (V/V 0)max, to the negative region, σ(V/V 0) fr = 0. It was found that this causes crystal fragmentation during uniform compression in the region V/V 0 < (V/V 0) frS or uniform tension in the region V/V 0 < (V/V 0) frL . Therefore, at V/V 0 < (V/V 0) frS , the intercrystallite surface should increase; at V/V 0 < (V/V 0) frL , the free surface should increase. It was shown that there is a characteristic temperature Tσ above which the crystal surface energy is negative at any pressure, σ(T≥T σ)≤0. The calculations showed that the values of (V/V 0) frL are in the liquid-phase region. Therefore, the fragmentation condition is not reached during uniform tension of the crystal. The evolution of the dependence σ(V/V 0) is studied during an isomorphic decrease in the nanocrystal size or during isomeric deformation of its shape.