Correlation of Tc with Crystal Chemical Parameters in High-Tc Cuprates, Diborides and Borocarbides: Concept of Arrangement and Function of Layered Superconductors
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.