LiV₃Se₂O₁₂: A Promising Giant-Birefringent Crystal Enabled by Significant Structural Distortion

Layered or pseudo-layered crystalline structures are particularly prone to exhibiting pronounced birefringence effects due to their anisotropic nature. In this investigation, we developed a novel strategy for designing birefringent materials with 2D architectures by synergistically combining the structural diversity of V─O coordination groups with lone pair electron functional groups. Guided by this strategy, we successfully synthesized two compounds, LiV₃Se₂O₁₂ and RbVSeO₅. Remarkably, LiV₃Se₂O₁₂ is grown into a centimeter-sized single crystal using a high-temperature solution method, which is analogous to the "one-pot" approach. This "one-pot" approach not only minimizes chemical waste but also simplifies the growth process, which offers a time-efficient and practical route for obtaining large-sized single crystals. Structurally, LiV₃Se₂O₁₂ features 2D [V₃Se₂O₁₂]_∞ layers, which are constructed from triangular pyramidal [SeO₃] groups and 1D [V₃O₁₃]_∞ chains. To the best of our knowledge, LiV₃Se₂O₁₂ exhibits the largest birefringence (experimental Δn = 0.45 at 546 nm) among vanadate and selenate systems, which also surpasses the commercial YVO₄ crystal. This exceptional birefringence highlights the potential of LiV₃Se₂O₁₂ as a promising candidate for future applications in birefringent materials.