α-Bi2Sn2O7 -: a 176 atom crystal structure from powder diffraction data

Pyrochlore-type bismuth tin oxide, Bi2Sn2O7, is a technologically important material used in applications such as catalysis and gas sensing. Its room temperature structure has been solved by a method of simulated annealing of combined X-ray and neutron diffraction data, followed by Rietveld refinement. With 176 crystallographically independent atoms in the asymmetric unit, it is one of the largest structures solved to-date from powder diffraction data. In addition to the number of unique atoms, additional crystallographic difficulty stems from the fact that the true symmetry of this structure is lower than the apparent metric symmetry of the unit cell.