Lonsdaleite’s modular structure
The aim of the research was constructing the lonsdaleite modular structure which is free from the structure model and which based on the representations of a hexagonal closest spherical packing. The object of research is the crystal structure of lonsdaleite. In the introduction, the problem of research is indicated - the differences in the structure of the lonsdaleite crystal from the requirements of the “standard” hexagonal closest packing (HCP) are found. In the main part of the article, the following tasks were solved: The symmetry of the electronic framework of lonsdaleite formed from valence electrons is analyzed. The smallest atomic volume, which makes it possible to construct a spherical structural module of lonsdaleite, is selected, the dimensions of this module are calculated. A spherical packing is constructed based on the proposed structural module. It is shown that the entire single crystal is a single macromolecule. The structure of lonsdaleite crystals is considered as a two-layer densest spherical packing, in which one densely packed layer contacts an identical layer located at a distance <i>h</i> = (√6/3)<i>a</i>, where <i>a</i> is the diameter of the sphere. Between these layers, there is a densely packed layer of spherеs of the same size, which is translationally symmetric to analogous layers with a period along the normal to the layer equal to <i>h</i>. Any of the carbon atoms (ions) that these spheres model, under these conditions will be in the center of a tetrahedron of four carbon atoms (ions). That is, in a tetrahedron of four closely packed atoms, there is a carbon atom of the same size. However, this condition is impracticable. The packing coefficient of such a structure is <i>k</i> ≈ 0,40, therefore, the principle of the closest packing is violated, which does not allow using the spherical model of the atom. The proposed modular structure of lonsdaleite helps to reduce these contradictions. It was concluded that lonsdaleite, as an HCP system, is not a lattice structure; in lonsdaleite, each interlayer plane is a twinning plane. It is not possible to construct a primitive cell on the three smallest edge vectors of the tetrahedron. Specialists in the field of crystal physics and structural crystallography can use the results obtained.