Predicting Diamond-like Nitrides as Infrared Nonlinear Optical Materials with High Thermal Conductivity

Exploration of new infrared nonlinear optical (NLO) materials is urgently needed owing to the lack of highperformance crystals to break through strict conditions of wide band gaps, large NLO coefficients, and a high laser-induced damage threshold. Herein, the high-throughput prediction strategy has been implemented, and a series of predicted nitrides in the AII-M-N systems (AII = Mg, Ca, Sr, Ba, Zn; M = Si, Ge) with the stoichiometric ratios 1:6:8, 1:7:10, 2:5:8, 5:2:6, and 1:1:2 are discovered. Among them, six diamond-like nitrides with the stoichiometric ratio of 1:1:2 are highlighted, namely, Pna21-AIISiN2 (AII = Ca, Sr) (Z = 4), Pna21-AIIGeN2 (AII = Sr, Ba) (Z = 4), and I42d-AIIGeN2 (AII = Mg, Ca) (Z = 4). The six diamond-like nitrides realize a balance between large NLO coefficients 0.5-2.0 x AgGaS2 (d36 = 13.4 pm/V) and wide band gaps of 3.30-4.72 eV due to the strong covalent interaction in M-N (M = Si, Ge) bonds. Simultaneously, the six diamond-like nitrides exhibit high Debye temperatures (634.4-913.1 K), which are beneficial to improving their thermal conductivities. Typically, the thermal conductivities at 300 K are 2.9 W/(m center dot K) for Pna21-BaGeN2, 4.4 W/(m center dot K) for Pna21-SrSiN2, and 11.7 W/(m center dot K) for I42d-CaGeN2, which are larger than that of the infrared benchmark AgGaS2 (1.4 W/(m center dot K)). This study will provide an insight into explore new infrared NLO materials with high thermal conductivity in diamond-like nitrides.