Effect of Isomorphic Atom Substitution on Lattice Parameters of TlBX_{2}-type Mixed Crystals

Authors: Hüsnü ÖZKAN, Nizami GASANLY, Ali ÇULFAZ

Abstract: The variation of the lattice parameters of TlBX_{2}-type mixed crystals with composition have been investigated by X-ray diffraction technique. The lattice anisotropy (c/a) of the mixed crystals changes linearly depending on substitution of the atoms located both at the centre and at the vertices of the BX_{4} tetrahedra. For some of the mixed crystals studied, structural phase transition (monoclinic \rightleftharpoons tetragonal) is observed due to atom substitution when the sum of tetrahedral covalent radii of the B and X atoms in BX_{4} tetrahedra reaches a critical value of about 0.255 nm.