Ba6Sn6Se13: a new mixed valence selenostannate with NLO property

Abstract

A new ternary selenostannate Ba₆Sn₆Se₁₃ has been synthesized by a high temperature solid-state method. The compound crystallizes in the non-centrosymmetric orthorhombic space group P2₁2₁2₁ and may be represented as Ba₆Sn₅²⁺Sn⁴⁺Se₁₃ with mixed valence Sn atoms. Sn⁴⁺ cations lie in a tetrahedral environment, while Sn²⁺ cations are found in two kinds of coordination environments: the trigonal pyramid and quadrangular pyramid. SnSe_n (n = 3, 4, 5) polyhedra are further connected to generate a three-dimensional framework with Ba²⁺ residing in cavities. Ba₆Sn₆Se₁₃ shows moderate nonlinear optical response and is the first reported NLO compound in the Ba–Sn–Se system. In addition, diffuse reflectance spectroscopy measurement indicates that the band gap of Ba₆Sn₆Se₁₃ is 1.52(2) eV and thermal analysis suggests that the compound melts incongruently. The theoretically calculated SHG response and band gap are in good agreement with experimental results.