  The problems of participation of crystal chemical factors in creating of
conditions to occurrence of a superconducting state in layered superconductors
are considered. On the basis of the experimental data, given in the literature,
new correlations of Tc with relation of crystal chemical parameters in high-Tc
cuprates, diborides and borocarbides are established, the critical crystal
chemical parameters controlling Tc are selected, and their functions increating
of prerequisites to the occurrence of superconductivity are determined. The
similar character of the correlations allows to make conclusion about the
common arrangement and function of layered superconductors irrespective of a
nature of their superconductivity. The distinctions of crystal chemical
characteristic of low-temperature superconductors from high-temperature ones
are considered as the factors, which suppress superconductivity. It was shown,
that the superconducting process is concentrated in an anisotropic
three-dimensional fragment - sandwich, which arrangement and function allows to
have stream of charge carriers and besides the space for its carry and resource
of effect on this stream. If in a superconductor there are several such
fragments, the Tc value of compound is defined by intrinsic Tc of that
fragment, whose parameters are closer to optimal. The crystal chemical concept
of arrangement and function of layered superconducting materials is advanced.
It shows what conditions are necessary in addition to ones defining
metal-insulator transition for appearance of superconductivity.
