Theoretical investigations on ternary defective diamond-like infrared nonlinear optical materials in Be-Ga-Se system

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 [BeSe4] with NLO-active [GaSe4] tetrahedral groups, one thermodynamically stable and three metastable defective diamond-like (DL) BeGa2Se4 (BeGSe) compounds, BeGSe-I (I4¯ 2 m), BeGSe-II (I4¯), BeGSe-III (Pc) and BeGSe-IV (P4¯ 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 (Eg ≥ 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-AGa2Se4 (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 [BeSe4] tetrahedron.