NaPb2(CO3)2Fx(OH)1-x(0 < x ≤ 1): A new member of alkali-lead carbonate fluoride system with large birefringence.

A new member of alkali-lead carbonate fluoride system, NaPb 2 (CO 3) 2 F x (OH) 1-x (0 < x ≤ 1), has been found. The NaPb 2 (CO 3) 2 F 0.9 (OH) 0.1 as one of representatives, its crystal structure has been identified by single crystal X-ray diffraction analysis, which crystallized in the hexagonal system with a centrosymmetric P6 3 /mmc (No. 194) space group. The structure exhibited a two-dimensional crystal structure consisting of double-layered [Pb 2 (CO 3) 2 (F/O)] ∞ with (F/O) acted as bridge. The crystal exhibited high transparency in a wide spectral region ranging from UV to near-IR and a wide band gap of 4.28 ​eV. To compare with isomorphic KPb 2 (CO 3) 2 F, the first-principles calculations for NaPb 2 (CO 3) 2 F were preformed, showing a large birefringence (Δn ​= ​0.269, λ ​= ​1064 ​nm), and indicating its potential applications as UV birefringence crystal. NaPb 2 (CO 3) 2 F x (OH) 1-x with two-dimensional crystal structure exhibits large birefringence. Image 1 [ABSTRACT FROM AUTHOR]