Structural studies on W6+ and Nd3+ substituted La2Mo2O9 materials

The structure of a series of new ionic conductors based in lanthanum molybdate (La2Mo2O9) has been investigated using transmission electron microscopy (TEM), high-resolution X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The superstructure 2ac×3ac×4ac of the low temperature α-polymorph relative to the β-polymorph was confirmed by HRTEM imaging and electron diffraction. Furthermore, the effects of partial cation substitution in the La2−xNdxMo2O9 and La2Mo2−yWyO9 series have been also evaluated in the search of new clues to understand the structure and stabilisation of the high temperature and better conductor β-polymorph. The thermal analysis studies show that Nd-substitution does not stabilise completely the β-polymorph at room temperature, although no superstructure ordering was observed by both XRD and HRTEM. On the other hand, W-substitution stabilises the cubic β-polymorph for image, although, electron diffraction indicates a slight distortion from the cubic symmetry for low W-content. This distortion disappears as the W content increases and the Rietveld refinements gradually render better results.