Cascos V, Martínez-Coronado R, Fernández-Díaz M T, Alonso J A
Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Cantoblanco, E-28049 Madrid, Spain.
Departamento de Química Inorgánica, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
Materials (Basel). 2020 Oct 6;13(19):4441. doi: 10.3390/ma13194441.
New polycrystalline SrMoMO (M = Fe and Cr) scheelite oxides have been prepared by topotactical oxidation, by annealing in air at 500 °C, from precursor perovskites with the stoichiometry SrMoMO (M = Fe and Cr). An excellent reversibility between the oxidized Sr(Mo,M)O scheelite and the reduced Sr(Mo,M)O perovskite phase accounts for the excellent behavior of the latter as anode material in solid-oxide fuel cells. A characterization by X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) has been carried out to determine the crystal structure features. The scheelite oxides are tetragonal, space group (No. 88). The Rietveld-refinement from NPD data at room temperature shows evidence of oxygen vacancies in the structure, due to the introduction of Fe/Cr cations in the tetrahedrally-coordinated B sublattice, where Mo is hexavalent. A thermal analysis of the reduced perovskite (SrMoMO) in oxidizing conditions confirms the oxygen stoichiometry obtained by NPD data; the stability range of the doped oxides, below 400-450 °C, is lower than that for the parent SrMoO oxide. The presence of a Mo/Mo mixed valence in the reduced SrMoMO perovskite oxides confers greater instability against oxidation compared with the parent oxide. Finally, an XPS study confirms the surface oxidation states of Mo, Fe, and Cr in the oxidized samples SrMoFeO and SrMoCrO.
通过在500℃空气中退火，由化学计量比为SrMoMO（M = Fe和Cr）的前驱体钙钛矿进行拓扑氧化制备了新型多晶SrMoMO（M = Fe和Cr）白钨矿氧化物。氧化态的Sr(Mo,M)O白钨矿与还原态的Sr(Mo,M)O钙钛矿相之间具有出色的可逆性，这使得后者作为固体氧化物燃料电池的阳极材料表现优异。已通过X射线粉末衍射（XRD）和中子粉末衍射（NPD）进行表征以确定晶体结构特征。白钨矿氧化物为四方晶系，空间群 （编号88）。室温下NPD数据的Rietveld精修表明，由于在四面体配位的B亚晶格中引入了Fe/Cr阳离子（其中Mo为六价），结构中存在氧空位。在氧化条件下对还原态钙钛矿（SrMoMO）进行的热分析证实了NPD数据所得到的氧化学计量；掺杂氧化物的稳定范围低于400 - 450℃，低于母体SrMoO氧化物。与母体氧化物相比，还原态SrMoMO钙钛矿氧化物中Mo/Mo的混合价态使其在氧化时更不稳定。最后，XPS研究证实了氧化样品SrMoFeO和SrMoCrO中Mo、Fe和Cr的表面氧化态。
