Unravelling Crystal Superstructures and Transformations in the La6–xMoO12−δ (0.6 ≤ x ≤ 3.0) Series: A System with Tailored Ionic/Electronic Conductivity
| Autor: | Jesús Canales-Vázquez, J.M. Porras-Vázquez, Lucía Vizcaíno-Anaya, Adrián López-Vergara, Lucía dos Santos-Gómez, David Marrero-López, Enrique R. Losilla, Gianguido Baldinozzi |
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| Přispěvatelé: | Universidad de Málaga [Málaga] = University of Málaga [Málaga], Laboratoire Structures, Propriétés et Modélisation des solides (SPMS), Institut de Chimie du CNRS (INC)-CentraleSupélec-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Universidad de Castilla-La Mancha (UCLM) |
| Rok vydání: | 2020 |
| Předmět: |
Materials science
General Chemical Engineering Analytical chemistry Ionic bonding Sintering chemistry.chemical_element [CHIM.MATE]Chemical Sciences/Material chemistry 02 engineering and technology General Chemistry Conductivity 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Fluorite 0104 chemical sciences Dielectric spectroscopy Crystal chemistry [CHIM.CRIS]Chemical Sciences/Cristallography Materials Chemistry Lanthanum 0210 nano-technology Monoclinic crystal system |
| Zdroj: | Chemistry of Materials Chemistry of Materials, American Chemical Society, In press, ⟨10.1021/acs.chemmater.0c02673⟩ |
| ISSN: | 1520-5002 0897-4756 |
| Popis: | International audience; Crystalline La6-xMoO12-δ materials with different lanthanum/molybdenum ratios (0.6 ≤ x ≤ 3.0) have been prepared via a freeze-drying precursor route. The influence of the lanthanum content, sintering temperature and cooling rate on the phase existence range and polymorphism was evaluated. Lanthanum rich compounds present three different polymorphs: a cubic (disordered) fluorite and two complex rhombohedral superstructures related to the fluorite. For the first time, the structural resolution of these rhombohedral superstructures, 7×7×1 and 5×5×1, has been successfully accomplished by neutron pow-der diffraction and transmission electron microscopy studies. As the La/Mo ratio decreases, the cubic symmetry is stabilized, although a phase transformation from cubic to monoclinic occurs at a low cooling rate. Impedance spectroscopy measure-ments under different atmospheres (dry and wet N2 and 5% H2-Ar) show that all materials exhibit mixed proton-electronic conductivity. The n-type electronic conductivity is attributed to Mo6+ reduction and increases for those phases with lower lanthanum content, i.e. for quenched samples, from 5 mS cm-1 for La5.4MoO11.1 to 9.5 mS cm-1 for La4MoO9 at 700 ºC in very reducing and wet conditions, which are significantly better than the values published to date for mixed lanthanum tungstates/molybdates. This make these materials potential candidates for hydrogen separation membranes. |
| Databáze: | OpenAIRE |
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