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)(O39.70□0.30), 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 Ð23, in contrast to Bi24(Si4+1.1Bi3+0.1Mn4+0.8)(O39.95□0.05) and Bi24(Si4+0.58Bi3+0.02Mn4+1.4)(O39.99□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 Na2SiO3·9H2Î : Mn(NO3)2·6H2O = 1:1) have space
group I23, whereas the crystals with cube (Na2SiO3·9H2Î : Mn(NO3)2·6H2O > 1) or
tetrahedron (Na2SiO3·9H2Î : 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