Solving δ-Bi2O3-related superstructures by combining neutron powder diffraction and ab initio calculations

Ab initio calculations have used to perturb the oxygen lattice surrounding dopant transition metal cations in fluorite-type δ-Bi2O3-related superstructure phases. The geometry-optimised structures were used as starting models for Rietveld-refinement of high-resolution neutron powder diffraction data, leading to more stable and reliable results than could be otherwise obtained. The advantage of the calculations is that they choose the initial displacements of atoms away from the undistorted sublattice using energy minimisation, in cases where pure Rietveld-refinement has no basis on which to make the correct choice. This approach is extended from the recent successful case of Bi94Nb32O221 to the disordered phases Bi14WO24 and Bi14MoO24