Composition variations of lattice parameters of TlIn(Se1 – x)2, TlIn(Se1 – xSx)2, and TlIn1 – xGaxSe2 mixed crystals

Abstract

AbstractTlInSe2 and TlInTe2 crystallize in a tetragonal cell (space group 14/mcm) (MÜLLER et al.). A primitive cell of these ternary crystals contains two formula units. All the Tl atoms in these compounds are univalent. The In atoms are trivalent being in a tetrahedral environment consisting of Se or Te atoms. InSe4 or InTe4 fragments of a unit cell form the chains extended along c‐axis coinciding with [001] directions. Such chains are bonded to each other by Tl atoms.TlGaSe2 and TlInS2 crystals belong to the monoclinic system (space group C2/c) (MÜLLER, HAHN; WONG‐NG et al.). The primitive cell of these crystals contains eight formula units. The lattice of TlGaSe2 crystals consists of strictly periodic two‐dimensional layers arranged parallel to the (001) plane. Each successive layer is turned through a right angle with respect to the previous one. The fundamental structural unit of a layer is the Ga4Se10 polyhedron representing a combination of four elementary GaSe4 tetrahedra linked together by bridging Se atoms. The Tl atoms are in trigonal prismatic voids resulting from the combination of the Ga4Se10 polyhedra into a layer. The Tl atoms form nearly planar chains along the [110] and [110] directions.