Electronic structure of solids and their plastic properties

This article examines the relationship between the electronic structure and the mechanical properties of solids. It is shown that these properties depend on the spatial distribution of valence electron density—whether it is isotropic or anisotropic. This distribution determines the geometry of the interatomic interaction potential. In the case of an anisotropic distribution, an asymmetric potential with directional bonding is formed. Solids with such an interatomic interaction potential possess a stable crystal lattice. Conversely, when the valence electron distribution is isotropic, a spherically symmetric interatomic interaction potential is formed. In this case, the crystal lattice of solids becomes unstable under shear deformations. The cause of this instability is self-compression, which arises due to the spherically symmetric nature of the interatomic interaction potential. The plasticity and strength of solids depend on the state of the crystal lattice. Solids with a stable crystal lattice are strong and non-plastic, whereas those with an unstable lattice are plastic and lack strength. A plasticity model of the crystal is proposed, in which the unstable crystal lattice is stabilized by a surface layer whose properties and structure differ from those of the inner layers. The resistance to shear of atomic planes in such a crystal is primarily determined by the surface layer. The magnitude of this resistance depends on the crystal size: in small crystals, the resistance to atomic plane displacement is high, approaching the theoretical limit. In large crystals, this resistance is comparable to the shear resistance in a crystal model with an edge dislocation. The presence of internal defects further increases crystal strength.