Ca3Be6B5O16F: the first alkaline-earth beryllium borate with fluorine anions

Abstract

The first all-alkaline-earth beryllium borate with fluorine anions, Ca₃Be₆B₅O₁₆F, was synthesized by a spontaneous crystallization flux method using LiF–B₂O₃ as the flux. The structural framework of Ca₃Be₆B₅O₁₆F is composed of the inter-connected [Be₆B₃O₁₆] and [BO₃] fundamental building blocks, with [CaO₇F] distorted polyhedra located in the interstitial sites. The [Be₆B₃O₁₆] group is discovered for the first time in beryllium borates. The UV-Vis-NIR diffuse-reflectance spectrum demonstrates that its UV cutoff edge is below 200 nm, and this is confirmed by first-principles studies. Thermal analysis reveals an incongruent feature at 1321 K. IR spectroscopy measurements are consistent with the crystallographic study. These data reveal that the crystal could have an application as a deep-ultraviolet optical material.