Crystal structure of Mo substituted lanthanum tungstate La5.4W1 yMoyO12 delta 0 lt; y lt; 0.2 studied by X ray and neutron diffraction

A determination of the detailed crystal structure of an Mo substituted lanthanum tungstate series, La6 xW1 yMoyO12 0 y 0.2, is the oxygen deficiency , is presented. Material of composition La5.4W0.8Mo0.2O12 y 0.2 produced by the citrate complexation route based on the Pechini method was investigated by high resolution X ray diffraction and neutron diffraction in the temperature range 10 T 298 K. The results are compared with a nonsubstituted material La5.4WO12 . A structural model established earlier for lanthanum tungstates and Re substituted lanthanum tungstates is confirmed, according to which the Wyckoff site shared by La and W is split with half site occupancies Fm 33m space group, 48h site and also accommodates Mo atoms. Substitution of W by up to 20 mol Mo does not change the face centred cubic lattice Mo atoms substitute W statistically on both 4a and 48h Wyckoff sites of the crystal structure, which is described by the Fm 33m space group. These results were obtained from the combination of the average neutron scattering length and average X ray scattering power procedures with electron probe microanalysis. The temperature dependence of bond lengths in dry and wet D2O conditions shows that vacant oxygen sites are located on the 32f Wyckoff sites also in Mo substituted lanthanum tungstates, and that the bond lengths between La on 4b and O on 32f increase with increasing pO2 and pD2O, reflecting the filling of oxygen vacancies and the increase in coordination of La on 4