Symmetry control of cation substitution in ‘antizeolite’ borates

Abstract

‘Antizeolite’ borates are a family of inorganic compounds with structure based on fixed (pseudo)tetragonal [Ba12(BO3)6]6+ sublattice, and various anionic clusters occupying ‘channels’ in the sublattice. An ability to host different anionic clusters provides a convenient way to tune such functional properties of materials based of ‘antizeolite’ borates as dichroism, luminescence etc. We demonstrated the dependence of extent of Sr2+→Ba2+ substitution in the cationic sublattice of antizeolite barium borates on the symmetry of initial compound. The latter is controlled by ‘guest’ anionic clusters in the channels of sublattice. In the case of initially orthorhombic [Ba12-xSrx(BO3)6](BO3)2 solid solution, the structure adapts to the increase in Sr2+ content (up to Sr/(Ba+Sr) ratio of at least 39 wt. %) by tetragonalization of the sublattice. In contrast, in tetragonal [(Ba1-xSrx)12(BO3)6](BO3)[LiF4] solid solution another structural mechanism of Sr2+ accommodation takes place, which results in the (2a,2c) modulation and is limited by maximum Sr/(Ba+Sr) ratio of 10-20 wt. %.