采用高温熔融-自发结晶法成功获得一种新型混合金属硫化物Ba7AgGa5S15。该化合物结晶于非中心对称的P31c空间群(No.159), 晶胞参数为a=0.964 53(10) nm, c=1.805 9(4) nm, Z=2。其结构是由［Ga4S10］T2超四面体与［AgS4］四面体共顶点连结形成的含有18元环孔道的三维网状框架, 孤立的［Ga(2)S4］四面体填充在孔道中, Ba2+填充在该三维框架结构的空隙当中。第一性原理计算研究了该化合物的电子结构、态密度、双折射率、二阶非线性光学系数, 以及倍频密度。结果表明, 该化合物具有大的光学带隙(3.76 eV), 其带隙主要由S 3p, Ba 5d和Ga 4s轨道决定; 其d33方向上的倍频系数约为AgGaS2的0.4倍, 主要倍频贡献来源于［AgS4］和［GaS4］四面体。该研究表明在Ag-Ga-S体系中引入Ba2+, 形成的Ba7AgGa5S15表现出比AgGaS2更宽的带隙, 有利于产生高的激光损伤阈值(LDT)。

A new metal-mixed chalcogenide Ba7AgGa5S15 was successfully synthesized by high temperature flux spontaneously crystallization method. The compound crystallizes in the asymmetric space group P31c(No.159) with the cell parameters of a=0.964 53 (10) nm, c=1.805 9 (4) nm and Z=2. The structure of Ba7AgGa5S15 is regarded as an 18-member tunnel-contained three-dimensional (3D) framework formed by the［Ga4S10］ T2 supertetrahedra and the［AgS4］ tetrahedra by sharing vertexes. Isolated［Ga(2)S4］ tetrahedra locate inside the tunnels and the Ba2+ cations insert in the space of the framework. The optical properties of the title compound were systematically studied based on first-principles calculations, which includes the electronic structure, density of states, birefringence, the second order nonlinear optical (NLO) coefficients and the second-harmonic generation (SHG) density. The results show that Ba7AgGa5S15 has a direct band gap of 3.76 eV, which is mainly determined by the S 3p, Ba 5d and Ga 4s orbitals. The NLO coefficient in the d33 direction is ~0.4 times that of AgGaS2(AGS), and the main contribution of SHG is from [AgS4] and [GaS4] tetrahedrons. This work indicates that introducing alkali earth metal Ba2+ into the Ag-Ga-S system could effectively enlarge the band gap of the formed Ba7AgGa5S15 compared with classical AGS compound, which is helpful in producing higher laser damage threshold (LDT).