LiCs3AlB7O14: achieving enhanced optical anisotropy via [AlO4] tetrahedron introduction to rearrange the anionic framework

Abstract

Borate has become a hot topic because of its rich structural chemistry and excellent properties for functional materials fields. The rearrangement of π-conjugated B–O units is key to enhancing the optical anisotropy, but it remains a challenge. Herein, by introducing [AlO₄] tetrahedra, a new congruent melting aluminoborate LiCs₃AlB₇O₁₄ with [B₇O₁₄] clusters was discovered. This work confirms that the introduction of [AlO₄] tetrahedra can lead to the rearrangement of anionic framework of the borate system and thereby enhance the birefringence of LiCs₃AlB₇O₁₄. The birefringence is about 4.1 times higher than that of its congener Li₄Cs₃B₇O₁₄ with the same [B₇O₁₄] clusters. Similarly, the effects of [AlO₄] tetrahedra on the rearrangement of the B–O anionic framework are also demonstrated in other known borates.