Pb₂TeV₂O₁₀: A Lead Vanadate Tellurate with Wide Mid-IR Transparency and Large Birefringence Induced by Multiple Birefringence-Active Groups

Birefringent materials as the key materials in laser science and technology have attracted continuous attention due to their ability to modulate polarized light. Herein, a new lead vanadate tellurate, Pb₂TeV₂O₁₀, has been synthesized through the rational integration of different kinds of birefringence-active functional units. Pb₂TeV₂O₁₀ features a unique two-dimensional (2D) [TeV₂O₁₀]_∞ layered structure consisting of [VO₆]^7- and [TeO₆]^6- octahedra, and Pb²⁺ cations reside between the [TeV₂O₁₀]_∞ layers. In addition, the rare edge-sharing mode of [VO₆]^7- and [TeO₆]^6- octahedra was found in this structure. Attributed to the high polarizability and appropriate arrangement of PbO₈, VO₆, and TeO₆ units, Pb₂TeV₂O₁₀ possesses a great theoretical birefringence of 0.275 at 532 nm, which is the largest among the vanadate tellurate family. The spectral tests also prove that Pb₂TeV₂O₁₀ showcases a broad transparency window (439 nm-10 μm), covering an important mid-infrared (IR) atmospheric window (3-5 μm). In addition, in order to improve the transparency, alkali and alkaline earth metal cations were introduced by the substitution strategy, and then the compound K₂Sr₂Te₂O₉ was synthesized. It owns a shorter ultraviolet (UV) cutoff edge of 234 nm and a wider transparency window (234 nm-13.8 μm). The findings of Pb₂TeV₂O₁₀ and K₂Sr₂Te₂O₉ enrich the structure chemistry of the tellurate family and provide new insights for designing new compounds with large optical anisotropy and wide spectral transparency.