β‐CsB₉O₁₄: A Triple‐Layered Borate with Edge‐Sharing BO₄ Tetrahedra Exhibiting a Short Cutoff Edge and a Large Birefringence

Abstract

The first triple-layered borate with edge-sharing BO₄ tetrahedra, β-CsB₉ O₁₄ was obtained under vacuum-sealed condition. It represents a new structure type and enriches the structural diversity of borates. Moreover, β-CsB₉ O₁₄ exhibits a short UV cutoff edge and a large birefringence, indicating that it could be regarded as a DUV birefringent crystal.