Large Birefringent Materials, Na₆Te₄W₆O₂₉ and Na₂TeW₂O₉: Synthesis, Structure, Crystal Growth, and Characterization

Abstract

A new d⁰ transition metal tellurite, Na₆Te₄W₆O₂₉, was synthesized by solid-state methods. The material crystallizes in monoclinic space group <i>P</i>2₁/<i>c</i> (No. 14) with the following values: <i>a</i> = 7.3297(3) Å, <i>b</i> = 21.9057(9) Å, <i>c</i> = 10.2871(3) Å, β = 133.490(2)°, and <i>Z</i> = 2. Additionally, large crystals of Na₆Te₄W₆O₂₉ (13 mm × 11 mm × 10 mm) and Na₂TeW₂O₉ (23 mm × 5 mm × 3 mm) were grown by the top seeded solution growth method. In addition to the crystal growth, refractive indices were measured, and the Sellmeier equations were fitted by using the minimum deviation technique. Interestingly, the two reported compounds exhibit relatively large birefringences: Δ<i>n</i>₃ = <i>n</i>_<i>z</i> – <i>n</i>_<i>x</i> = 0.0828–0.1248 from 1062.6 to 450.2 nm for Na₆Te₄W₆O₂₉, and Δ<i>n</i>₃ = <i>n</i>_<i>z</i> <i>– n</i>_<i>x</i> = 0.1471–0.2069 from 1062.6 to 450.2 nm for Na₂TeW₂O₉. The results indicate that Na₆Te₄W₆O₂₉ and Na₂TeW₂O₉ may have uses in applications involving birefrigent materials