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

 

Chem. Met. Alloys 3 (2010) 96-100

 

Tatyana I. MELNIKOVA, Galina M. KUZMICHEVA, 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 Bi2O3SiO2MnO2 system, as well as bulk crystals (Bi24Ge2O40 used as a seed crystal) in the Bi2O3SiO2V2O5 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)(O39.700.30), Bi24(Si4+0.17(1)Bi3+0.01Mn4+1.82)(O39.93(5)0.07), Bi24(Si4+1.160(6)Bi3+0.430(V4+,V5+)0.410)(O39.970(20)0.030), and Bi24(Si4+1.150(6)Bi3+0.452V5+0.398)(O39.930(20)0.070) crystallize in space group 23, in contrast to Bi24(Si4+1.1Bi3+0.1Mn4+0.8)(O39.950.05) and Bi24(Si4+0.58Bi3+0.02Mn4+1.4)(O39.990.01), 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 Na2SiO39H2 : Mn(NO3)26H2O = 1:1) have space group I23, whereas the crystals with cube (Na2SiO39H2 : Mn(NO3)26H2O > 1) or tetrahedron (Na2SiO39H2 : Mn(NO3)26H2O < 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