Huang Chunmei,Mutailipu Miriding,Zhang Fangfang,Griffith Kent J.,Hu Cong,Yang Zhihua,Griffin John M.,Poeppelmeier Kenneth R.,Pan Shilie
More than 3900 crystalline borates, including borate minerals and synthetic inorganic borates, in addition to a wealth of industrially-important boron-containing glasses, have been discovered and characterized. Of these compounds, 99.9 % contain only the traditional triangular BO 3 and tetrahedral BO 4 units, which polymerize into superstructural motifs. Herein, a mixed metal K 5 Ba 2 (B 10 O 17 ) 2 (BO 2 ) with linear BO 2 structural units was obtained, pushing the boundaries of structural diversity and providing a direct strategy toward the maximum thresholds of birefringence for optical materials design. 11 B solid-state nuclear magnetic resonance (NMR) is a ubiquitous tool in the study of glasses and optical materials; here, density functional theory-based NMR crystallography guided the direct characterization of BO 2 structural units. The full anisotropic shift and quadrupolar tensors of linear BO 2 were extracted from K 5 Ba 2 (B 10 O 17 ) 2 (BO 2 ) containing BO 2 , BO 3 , and BO 4 and serve as guides to the identification of this powerful moiety in future and, potentially, previously-characterized borate minerals, ceramics, and glasses.
The design and synthesis of new deep-ultraviolet (DUV) optical materials are important but challenging. It is well known that the polarizability anisotropy of linear [BO 2 ] − is larger than those of [BO 3 ] 3− and [BO 4 ] 5− , which is the better choice for exploring excellent optical materials. Here, we search for such crystals in borate systems based on the unusual fundamental structural unit [BO 2 ] − . By combining the linear [BO 2 ] − with the traditional triangular [BO 3 ] 3− and tetrahedral [BO 4 ] 5− units, a new mixed metal borate, Rb 5 Ba 2 (B 10 O 17 ) 2 (BO 2 ) was obtained via high-temperature solution method. It exhibits excellent optical properties including a DUV transmission window (188 nm) and suitable birefringence (0.06). It also has good thermal stability and its crystal plates can be prepared easily. Furthermore, the strategies of designing borates with [BO 2 ] − units have been proposed from the transformation of crystal framework and the preparation method.
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