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 high-performance 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 × 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·K) for Pna21-BaGeN2, 4.4 W/(m·K) for Pna21-SrSiN2, and 11.7 W/(m·K) for I42d-CaGeN2, which are larger than that of the infrared benchmark AgGaS2 (1.4 W/(m·K)). This study will provide an insight into explore new infrared NLO materials with high thermal conductivity in diamond-like nitrides.