Edge-Sharing Tetrahedra Realizing Superior Birefringence and High Deep-Ultraviolet Transmittance in α‑Be3(H2O)2(PO4)2 Crystal Synthesized by Mild Chemistry

A challenging topic for tetrahedra-based deep-ultraviolet (deep-UV, wavelength λ 3(H2O)2(PO4)2 crystal with edge-sharing BeO4 and its polymorph β-Be3(H2O)2(PO4)2 with common corner-sharing BeO4 were synthesized, both featuring a three-dimensional stable structure constructed by BeO4, BeO2(H2O)2, and PO4 tetrahedral units. Remarkably, α-Be3(H2O)2(PO4)2 manifests superior birefringence of 0.101 and high deep-UV transmittance of 167 nm, with the largest birefringent quality factor (BQF) of 0.75 among the known tetrahedra-based deep-UV materials. By contrast, β-Be3(H2O)2(PO4)2 manifests a small birefringence of 0.019 and 160 nm deep-UV transmittance, with only a mediocre BQF of 0.15. Further, computational investigations reveal that edge-sharing BeO4 makes a dominant contribution to the great birefringence. This study could push the synthesis of edge-sharing-tetrahedra materials and offers an alternative strategy toward designing high-performance tetrahedra-based deep-UV birefringence materials.针对基于四面体的深紫外（deep-UV）材料领域的一项挑战性课题，本研究成功合成了同时具有共边BeO4结构的α-Be3(H2O)2(PO4)2晶体，以及具有常见共顶点BeO4结构的多晶型β-Be3(H2O)2(PO4)2；二者均由BeO4、BeO2(H2O)2与PO4四面体单元构筑得到三维稳定结构。值得注意的是，α-Be3(H2O)2(PO4)2展现出优异的双折射率（0.101）与167 nm的高深紫外透过率，在已知的基于四面体的深紫外材料中拥有最高的双折射品质因数（BQF）0.75。相比之下，β-Be3(H2O)2(PO4)2的双折射率仅为0.019，深紫外透过率为160 nm，对应的双折射品质因数仅为0.15，性能平平。进一步的计算研究表明，共边BeO4结构对其优异的双折射率起到了主导性贡献。本研究可为共边四面体材料的合成提供助力，并为设计高性能基于四面体的深紫外双折射材料提供了新思路。