BaLiTe2O5X (X = Cl, Br): mixed alkali/alkaline-earth metal tellurite halides with [Te2O5]∞ chains

Abstract

Isostructural mixed alkali/alkaline-earth metal tellurite halides BaLiTe₂O₅X (X = Cl, Br) have been successfully synthesized by a mild hydrothermal method, which possess the [Te₂O₅]_∞ chains formed by the corner-sharing connections of the TeO₃ and TeO₄ polyhedra. The [Te₂O₅]_∞ chains are bridged via the LiO₃ polyhedra to form the [LiTe₂O₅]_∞ layers with 4- and 6-membered rings. The adjacent [LiTe₂O₅]_∞ layers are linked via the BaO₉ polyhedra to form the [BaLiTe₂O₅]_∞ double layers, which are further connected via weak Ba–X–Li interactions to generate a 3D framework. Analysis of different lithium tellurites shows that the different arrangements of the Te–O and Li–O units in the lithium tellurites can be attributed to the cation–cation repulsion and lone-pair effect. Both compounds display good thermal stability, wide optical bandgaps (4.25 and 4.13 eV), and large birefringence. First-principles calculations indicate that the TeO_n groups and X⁻ determine the optical properties of BaLiTe₂O₅X (X = Cl, Br).