Olga Reutova#, Wenqi Jin#, Congwei Xie, Junjie Li, Zhihua Yang*, Xueling Hou*, Shilie Pan

Cite this article: https://doi.org/10.1016/j.cjsc.2026.100924

Publication date:

Keywords: Fluorooxoborates; Second harmonic generation; Structure prediction; polytypism; Theory of symmetry; OD-theory; Density functional theory

ABSTRACT

Topology-symmetry analysis based on order-disorder theory for polytypic structures is a useful tool for understanding structure-property relationships, and it could serve as a basis for structure predictions and materials design. This approach systematically characterizes structural fragments and their stacking sequences through partial symmetry operations. Here, the nonlinear optical (NLO) fluorooxoborate family AB4O6F (A = Na, K, Rb, Cs, NH4) and the alkali-aluminum borate fluorides AAlB3O6F (A = K, Rb, Cs) are investigated within order-disorder (OD) theory framework and described via symmetry groupoids. By enumerating admissible stacking operations, we derived several hypothetical Maximum Degree of Order (MDO) polytypes for NaB4O6F, CsB4O6F, CsKB8O12F2, CsAlB3O6F, RbB4O6F and RbAlB3O6F. New noncentrosymmetric polytype of RbB4O6F (sp.gr. Pnn2) and centrosymmetric polytype of RbAlB3O6F (sp.gr. P21/с) are predicted. Furthermore, we discuss the influence of layer symmetry and stacking topology on optical properties. The results demonstrate that the competition between different stacking manifolds provides a plausible explanation for the occurrence of stacking faults in this family of materials.