Structure-Forming Role of Heavy Cations in Sr3B2SiO8 (Sr(B,Si)O2.67) and Ba3B6Si2O16 Borosilicates

Resumo

The crystallographic analysis of the orthorhombic (Pnma) structure of Sr₃B₂SiO₈ ≈ (Sr(B,Si)O_2.67) shows that its experimentally found symmetry is determined by the geometry of the Sr sublattice where the anion radical without this symmetry simulates it by the statistical averaging of four variants of real configurations. With a reduced fraction of heavy atoms in the triclinic (Р1) structure of Ba₃B₆Si₂O₁₆, the Ba and Si cations whose sublattice determines the presence of additional pseudosymmetry form the skeleton of the structure.