Synthesis and Characterizations of Two Tellurides β-BaGaTe and BaGaGeTe with Flexible Chain Structure.

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides β-BaGaTe and BaGaGeTe have been discovered. β-BaGaTe crystallizes in the orthorhombic space group (no. 74) with unit cell constants of = 23.813(3) Å, = 11.9673(19) Å, and = 6.7215(9) Å, while BaGaGeTe crystallizes in the monoclinic space group 2/ (no. 14) with unit cell constants of = 13.6540(3) Å, = 9.6705(2) Å, and = 23.1134(7) Å. The structure of β-BaGaTe can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe] chains formed by edge-sharing GaTe tetrahedra, which are separated by Ba cations. In the crystal structure of BaGaGeTe, two kinds of 1D chains, namely chain 1 [(GaGe)Te] and chain 2 [(GaGe)Te], are stacked alternately and put together by the coulomb force with Ba cations. In addition, First-principles calculations indicate that β-BaGaTe has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.