BaAlPO4F2: structure and properties of the first barium fluoroaluminophosphate with the mixed anion group [Al2PO8F5]

Abstract

Mixed-anionic compounds are attractive candidates for probing optical crystals due to their interesting physicochemical properties. Herein, the first barium fluoroaluminophosphate, BaAlPO₄F₂, was synthesized for the first time by high temperature reactions in a closed system. In its structure, the [PO₄] group bonds with [Al₂O₆F₅] dimers to form the unusual [Al₂PO₅F₄]_∞ 2D layers and the Ba²⁺ cations reside in the interlayer space. This paper discusses the flexibility and diversity of the P–O and Al–O/F assembly structures, which provides a research direction for exploring new structural materials. In addition, first-principles calculations on BaAlPO₄F₂ were also performed to investigate the relationship between its crystal structure and optical properties.