For the composition–structure–property relationship, material properties can often be changed or even adjusted through some specific structural evolutions. Here, we report four antimony phosphates, K3SbP2O9, K2NaSbP2O8, α-NaSb3P2O10, and β-NaSb3P2O10, obtained by using the high-temperature solution method. The four compounds were in diverse space groups with isolated PO4 groups. The presence of Sb3+ cations with lone pairs not only induces the crystal structure symmetry transformation but also significantly enhances the birefringence. α-NaSb3P2O10 exhibits a significantly increased birefringence which is about 60 times that of K3SbP2O9 due to the introduction of lone pairs in metal cations. The useful strategies will have significant meaning for the discovery of new materials with large birefringence in the future.

The development of a data‐driven science paradigm is greatly revolutionizing the process of materials discovery. Particularly, exploring novel nonlinear optical (NLO) materials with the birefringent phase‐matching ability to deep‐ultraviolet (UV) region is of vital significance for the field of laser technologies. Herein, a target‐driven materials design framework combining high‐throughput calculations (HTC), crystal structure prediction, and interpretable machine learning (ML) is proposed to accelerate the discovery of deep‐UV NLO materials. Using a dataset generated from HTC, an ML regression model for predicting birefringence is developed for the first time, which exhibits a possibility of achieving fast and accurate prediction. Essentially, crystal structures are adopted as the only known input of this model to establish a close structure‐property relationship mapping birefringence. Utilizing the ML‐predicted birefringence which can affect the shortest phase‐matching wavelength, a full list of potential chemical compositions based on an efficient screening strategy is identified. Further, eight structures with good stability are discovered to show potential applications in the deep‐UV region, owing to their promising NLO‐related properties. This study provides a new insight into the discovery of NLO materials and this design framework can identify desired materials with high performances in the broad chemical space at a low computational cost.

Fluorine-containing compounds have stimulated the exploration of ultraviolet/deep-ultraviolet nonlinear optical (NLO) materials. Alkali/alkaline-earth metal phosphates are one of the important potential systems as NLO materials, while the common small birefringence limits the phase-matching (PM) ability in the ultraviolet/deep-ultraviolet region. Herein, by applying a “fluorination synergy-induced enhancement of optical property” strategy, novel structures of phosphate fluoride/fluorophosphate in BePO3F with good thermodynamic/dynamic stability and promising NLO-related properties are discovered via performing crystal structure prediction combined with first-principles calculations. BePO3F-I–VI exhibit relatively large birefringence of 0.025, 0.048, 0.049, 0.049, 0.059, and 0.063 at 1064 nm, respectively. Simultaneously, BePO3F-I (Pc) is a new thermodynamically stable phosphate fluoride which possesses a wide band gap (E g = 8.03 eV), large second-harmonic generation (SHG) coefficient (d 11 = 0.67 pm/V, 1.7 × KDP), and the shortest PM wavelength of 292 nm. Other five thermodynamically metastable noncentrosymmetric (NCS) BePO3F structures (II–VI) belong to fluorophosphates and exhibit deep-ultraviolet PM wavelengths of 187, 183, 186, 188, and 196 nm. It reveals that the aligned nonbonding O 2p orbitals of [BeO2F2] and [PO4] units lead to a large SHG coefficient in the phosphate fluoride BePO3F-I. For fluorophosphates (BePO3F-II–VI), the synergy of [BeO3] planar units and [PO3F] units induces relatively large birefringence. Our research results provide an idea for exploring novel high-performance NLO materials.