Theoretical investigations on ternary defective diamond-like infrared nonlinear optical materials in Be-Ga-Se system
Linan Wang, Dongdong Chu, Deqiang Yin, Congwei Xie, Zhihua Yang, Junjie Li, Shilie Pan
Abstract
Beryllium (Be) has made great success in developing Be-based oxide deep-ultraviolet (DUV) nonlinear optical (NLO) materials, but the development of Be-based chalcogenide infrared (IR) NLO materials is still tardy because of the lack of rational material design strategy and in-depth understanding on the composition-structure-propertiy relationships in the compounds. In this work, by coupling [BeSe 4 ] with NLO-active [GaSe 4 ] tetrahedral groups, one thermodynamically stable and three metastable defective diamond-like (DL) BeGa 2 Se 4 (BeGSe) compounds, BeGSe-I ( I 4 ¯ 2 m ), BeGSe-II ( I 4 ¯ ), BeGSe-III ( Pc ) and BeGSe-IV ( P 4 ¯ 2 m ), have been predicted by Universal Structure Predictor: Evolutionary Xtallography (USPEX) code and phonon dispersion spectra. Notably, BeGSe-II and BeGSe-III show high thermal conductivities (6.520 W/m/K for BeGSe-II, 3.835 W/m/K for BeGSe-III), and achieve a good balance between wide band gap ( E g ≥ 3.0 eV) and large NLO effect (≥ 1.0 × AGS) for an excellent IR NLO material. Meanwhile, the charge transfer enhanced band gap mechanism, and covalent radius, bulk modulus effected lattice thermal conductivity in the defective DL-AGa 2 Se 4 (A = Be, Mg, Zn, Cd, Hg) were also uncovered. The results give insights into the design of new defective DL compounds with wide band gap and high thermal conductivity based on [BeSe 4 ] tetrahedron.