Variation of the lattice parameters of TlTl1-xInxSe2 chain mixed crystals w
ith composition have been studied by X-ray diffraction technique. The latti
ce anisotropy (c/a) of the TlBX2-type mixed crystals changes linearly with
substitution of the atoms located bath at the center and at the vertices of
the BX4 tetrahedra. A brief survey of the important features of the effect
of isomorphic atom substitution on the lattice anisotropy of TlBX2-type mi
xed crystals with chain structure has been presented.