Cationic Order-Disorder in Double Scheelite Type Oxides: the Case Study of Fergusonite LaSiMoO.

Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G. . , , 2091].

Local structure and oxide-ion conduction mechanism in apatite-type lanthanum silicates.

The local structure of apatite-type lanthanum silicates of general formula La(SiO)O has been investigated by combining the atomic pair distribution function (PDF) method, conventional X-ray and neutron powder diffraction (NPD) data and density functional theory (DFT) calculations. DFT was used to build structure models with stable positions of excess oxide ions within the conduction channel. Two stable interstitial positions were obtained in accordance with literature, the first one located at the very periphery of the conduction channel, neighbouring the SiO tetrahedral units, and the second one closer to the channel axis.