Analysis of environment of alkali atoms in oxygen-containing compounds with Voronoi-Dirichlet polyhedra

It is shown that coordination numbers ( CN ) of alkali atoms can be determined in crystal structures by means of Voronoi-Dirichlet polyhedra without using crystal-chemical radii. It is found that a domain with constant volume corresponds to an alkali atom at CN ≥ 6. The conclusion about correctness of application of the model of deformable spheres for the description of alkali atoms in a crystal field is drawn.