Flexural rigidity of layers and its manifestation in the vibrational characteristics of strongly anisotropic layered crystals. Characteristic frequencies and stability conditions in quasi-two-dimensional systems

Abstract

The reasons for the appearance of flexural rigidity of layers in strongly anisotropic layered crystals are investigated. Structures consisting of loosely bound monatomic layers (specifically, graphite) as well as formed loosely bound structural elements each consisting of several monolayers which are coupled much more strongly with one another (for example, in dichalcogenide transition metals) are examined. The effect of the flexural rigidity on the phonon spectra of these compounds—quasi-flexural bending of the dispersion curves of phonon modes polarized in a direction normal to the layers—and the particularities appearing in the phonon densities of states as a result of quasi-flexural vibrational branches crossing low-frequency optical modes are analyzed.