Mullite-type dibismuth-nonaoxometallates-(III): The effects of strontium doping

GESING TH.; SCHOWALTER M.; WEIDENTHALER C.; MURSHED M.M.; NÉNERT G.; MENDIVE C.; CURTI M.; ROSENAUER A.; SCHNEIDER H.; FISCHER R.X.

Bergen

Congreso; The 27th European Crystallographic Meeting; 2012

European Crystallographic Association

Strontium doped dibismuth-nonaoxometallate-(III) phases were produced at 1023 K. Partial substitution of bismuth by strontium in the (Bi1-xSrx)2M4O9-x structure (M = Al, Ga) yields oxygen vacancies for charge balance. Introducing oxygen vacancies into the structure causes the rearrangement of associated M2O7 double-tetrahedra forming “M3O10” tri-clusters which were identified by multi-quantum MAS NMR. Both STEM-EDX and XPS showed a homogeneous distribution of strontium in the bulk and on the surface, respectively. Moreover, XPS confirms the trivalent state of bismuth after doping. The orientations of bismuth 6s2 lone electron pairs were calculated using DFT methods. Additionally, while replacing half of the bismuth atoms by strontium (Fig. 1the resulting structural distortions were calculated taking different possibilities into account. The amount of strontium in the crystal structure of the aluminum containing phase was further confirmed from the decomposition product SrAl12O19 formed during the temperature-dependent X-ray powder diffraction. Thermal expansion coefficients were calculated out of these evaluated data. The crystal structural proof was carried out refining (Bi0.94Sr0.06)2Al4O8.94 combined from powder neutron and X-ray diffraction data. Rietveld refinements clearly showed that partial occupation of one oxygen site and the simultaneous shift of two aluminum atoms from the double-tetrahedra to two tri-cluster sites occurred. Thermal expansion and high-temperature neutron diffraction powder data analysis confirms the thermal stability of the Sr-doped phases up to 1250 K.