Structure and morphology peculiarities of Bi₂₄(Si,M)₂O₄₀ (M = Mn, V) with sillenite structure

Chem. Met. Alloys 3 (2010) 96-100

https://doi.org/10.30970/cma3.0125

Tatyana I. MEL’NIKOVA, Galina M. KUZ’MICHEVA, Victor B. RYBAKOV, Nadezhda B. BOLOTINA, Alain COUSSON, Alexander B. DUBOVSKY

Single crystals in the form of cubes, tetrahedra or combinations of cubes and tetrahedra with sillenite structure in the Bi₂O₃–SiO₂–MnO₂ system, as well as bulk crystals (Bi₂₄Ge₂O₄₀ used as a seed crystal) in the Bi₂O₃–SiO₂–V₂O₅ system, have been grown by the hydrothermal method. The results of the crystal chemical analysis by X-ray diffraction, together with the formal charges of the cations calculated by the bond-valence method, allowed establishing the formation of phases of the general compositions Bi₂₄(Si,Mn)₂O₄₀ and Bi₂₄(Si,Bi,Mn)₂O₄₀ with Bi³⁺, Si⁴⁺, and Mn⁴⁺ ions, and Bi₂₄(Si,Bi,V)₂O₄₀ with Bi³⁺, Si⁴⁺, V⁴⁺, and V⁵⁺ ions. It was found that the phases of refined compositions Bi₂₄(Si⁴⁺_0.9(1)Mn⁴⁺_1.1)O₄₀, Bi₂₄(Si⁴⁺_0.04Bi³⁺_0.60Mn⁴⁺_1.36)(O_39.70□_0.30), Bi₂₄(Si⁴⁺_0.17(1)Bi³⁺_0.01Mn⁴⁺_1.82)(O_39.93(5)□_0.07), Bi₂₄(Si⁴⁺_1.160(6)Bi³⁺_0.430(V⁴⁺,V⁵⁺)_0.410)(O_39.970(20)□_0.030), and Bi₂₄(Si⁴⁺_1.150(6)Bi³⁺_0.452V⁵⁺_0.398)(O_39.930(20)□_0.070) crystallize in space group Р23, in contrast to Bi₂₄(Si⁴⁺_1.1Bi³⁺_0.1Mn⁴⁺_0.8)(O_39.95□_0.05) and Bi₂₄(Si⁴⁺_0.58Bi³⁺_0.02Mn⁴⁺_1.4)(O_39.99□_0.01), which adopt space group I23. The lower symmetry can be explained by a kinetic phase transition of order-disorder type associated with peculiarities of the structure (different atoms in the same crystallographic site) and growth conditions. The crystals with a combination of cubes and tetrahedra (initial charge Na₂SiO₃·9H₂О : Mn(NO₃)₂·6H₂O = 1:1) have space group I23, whereas the crystals with cube (Na₂SiO₃·9H₂О : Mn(NO₃)₂·6H₂O > 1) or tetrahedron (Na₂SiO₃·9H₂О : Mn(NO₃)₂·6H₂O < 1) habit crystallize in space groups I23 and P23.

Arrangement of polyhedra in sillenites: space group I23 (a), space group P23 (b).

Keywords

Sillenites / Composition / Crystal structure