Prediction of Novel van der Waals Boron Oxides with Superior Deep‐Ultraviolet Nonlinear Optical Performance

Abstract Deep‐ultraviolet nonlinear optical (DUV NLO) materials are attracting increasing attention because of their structural diversity and complexity. Using the two‐dimensional (2D) crystal structure prediction method combined with the first‐principles calculations, here we propose layered 18‐membered‐ring (18MR) boron oxide B 2 O 3 polymorphs as high‐performance NLO materials. 18MR‐B 2 O 3 with the AA and AB stackings are potential DUV NLO materials. The superior performing 18MR‐B 2 O 3 AB has an unprecedentedly high second harmonic generation coefficient of 1.63 pm V −1 , the largest among the DUV NLO materials, three times larger than that of the advanced DUV NLO material KBe 2 BO 3 F 2 and comparable to that of β‐BaB 2 O 4 . Its unusually large birefringence of 0.196 at 400 nm guarantees the phase‐matching wavelength λ PM to reach this material's extreme absorption edge of ≈154 nm.