  In the work the analysis of crystal chemical researches of nickel
borocarbides RNi2B2C (R = rare earth) is given. The reasons of representation
of dependence of Tc from crystal chemical parameters by two separate curves for
magnetic and nonmagnetic R are considered. Common for all R dependences of Tc
from crystal chemical parameters similar existing in layered
quasi-two-dimensional systems (HTSC cuprates and diborides) are established.
The absence of influence on borocarbides Tc of magnetic properties R is
determined. On the basis of the found correlations the radii of a number of
rare earths are precised and Tc of compounds at various substitutions R are
calculated.

Superconductivity;Materials Science