BaTi(BO3)2: an excellent birefringent material with highly coplanar isolated [BO3] groups

Abstract

A material with a large birefringence is needed for optical systems, and borate is a good choice as an excellent birefringent material. Herein, we report two borates BaM^IV(BO₃)₂ (M^IV = Ti, Sn), in which the [TiO₆] and [SnO₆] units have similar coordination environments. Moreover, the experimental birefringence of BaTi(BO₃)₂ is equal to or larger than 0.169 at 546 nm measured by using a polarizing microscope, which mainly originates from the high-density and parallel arrangement of the isolated [BO₃] groups. This discovery indicates that BaTi(BO₃)₂ can be a promising ultraviolet birefringent material.