Structural studies on W and Nd substituted La2Mo2O9 materials |
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Authors: | David Marrero-Ló pez,Wuzong Zhou,Pedro Nú ñ ez |
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Affiliation: | a Departamento de Química Inorgánica, Universidad de La Laguna, E38200 La Laguna, Tenerife, Canary Islands, Spain b Instituto de Ciencia de Materiales de Barcelona, ICMAB-CSIC, Campus UAB, 08193 Bellaterra, Spain c School of Chemistry, Purdie Building, University of St Andrews, St Andrews, Fife KY16 9ST, UK |
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Abstract: | 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 y>0.25, 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. |
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Keywords: | La2Mo2O9 Ionic conductor HRTEM Superstructure Phase transition |
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