Acta Crystallographica Section B

Structural Science

Volume 54, Part 4 (August 1998)

research papers

Acta Cryst. (1998). B54, 358-364 [ doi:10.1107/S0108768197017886 ]

X-ray Diffraction Study of the Crystal Structure of the Tl Ternary Chalcogenides Tl_2xIn_2(1-x)Se₂, x = 0.2, 0.3,0.9

K. G. Hatzisymeon, S. C. Kokkou, A. N. Anagnostopoulos and P. I. Rentzeperis

Abstract: A series of thallium ternary chalcogenides with the composition Tl_2xIn_2(1-x)Se₂, x = 0.2, 0.3,...0.9, have been studied by X-ray powder and, for some of them, single-crystal diffraction. They are tetragonal, space group I4/mcm, Z = 4, and isostructural with the binary semiconductor TlSe. Their crystal structures have been solved by direct methods and refined by the Rietveld method to a precision which is satisfactorily comparable to single-crystal results. As x is changed from x = 0.2 to x = 0.9 the unit-cell parameters and volume decrease or increase following Kurnakov's law, which is valid for solid solutions. Refined positional parameters of Se, In-Se and Tl-Se bond lengths vary with x also according to the same law. The distribution of In and Tl cations in 4(a) and 4(b) sites depends on the stoichiometry x and the crystals are composed of [In³⁺Se₂] $_{\infty}^-$ chains along the c axis in which InSe₄ tetrahedra share edges; the chains are interconnected with Tl⁺(In⁺) ions.