Synthesis and characterization of a new mid-infrared transparent compound: acentric Ba5In4Te4S7

Abstract

A new noncentrosymmetric (NCS) sulfide, Ba₅In₄Te₄S₇, was synthesized by a conventional solid-state reaction in evacuated closed silica tubes. The compound crystallizes in the orthorhombic space group Imm2 (44), with unit cell parameters a = 39.110(3) Å, b = 4.3763(3) Å, c = 7.3452(6) Å, Z = 2, and V = 1257.18(17) ų. The 3D framework of Ba₅In₄Te₄S₇ is composed of infinite ^∞₁[InS₂Te₂]⁵⁻ and ^∞₁[In₂S₃Te₂]⁴⁻ anionic chains. The optical band gap of Ba₅In₄Te₄S₇ is 2.13 eV and it shows the UV-visible cutoff at 0.57 μm and the infrared transparency extends to 25 μm. The compound exhibits a powder second harmonic generation (SHG) signal at 2.05 μm with about half of the AgGaS₂ at a particle size of 74–106 μm. According to first-principles calculation, the calculated major SHG tensor element is d₃₂ = 18.8 pm V⁻¹. The SHG process of nonlinear optical response of Ba₅In₄Te₄S₇ originates from the electronic transitions from occupied S-3p and Te-5p states to unoccupied In-5s and In-5p states.