Syntheses, characterization, and optical properties of ternary Ba-Sn-S system compounds: Acentric Ba_7Sn_5S_(15), centric BaSn_2S_5, and centric Ba_6Sn_7S _(20)

摘要

Three new ternary Ba-Sn-S system compounds, acentric Ba_7Sn _5S_(15), centric BaSn_2S_5, and centric Ba_6Sn_7S_(20) have been designed and synthesized by a conventional high-temperature solid-state reaction method using the evacuated silica tubes. The crystal structure of Ba_7Sn_5S _(15) shows the coexistence of a SnS_4 tetrahedral and a Sn_2S_3 trigonal bipyramid. Importantly, the larger dipole moment of the [Sn_2S_3]~(2-) trigonal bipyramid group and the polarity enhancement of the bipyramidal arrangements result in a strong SHG effect at 2.05 μm, which is 10 times of the SHG intensity of the benchmark AgGaS_2 with the particle size of 30-46 μm and twice as much as that with the particle size of 150-212 μm. Evidently, the acentric Ba_7Sn_5S_(15) is a novel IR NLO crystal material with a wide mid-IR window and a strong SHG effect, which is the first reported among the Ba-Sn-S ternary system. Moreover, Ba_7Sn_5S _(15) can achieve type-I phase-matching that can be used for practical applications. In the centric BaSn_2S_5, all Sn atoms are coordinated by five S atoms to form novel SnS5 trigonal bipyramid polyhedrons. In the other centric Ba_6Sn_7S_(20), there is the coexistence of the two coordination patterns with a SnS5 trigonal bipyramid and SnS_4 tetrahedral polyhedrons, featuring a special crystal structure in the Ba-Sn-S system.