Localization of Oxygen Interstitials in CeSrGa3O7+未 Melilite

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• 作者：Jungu Xu ; Xiaojun Kuang ; Emmanuel V茅ron ; Mathieu Allix ; Matthew R. Suchomel ; Florence Porcher ; Chaolun Liang ; Fengjuan Pan ; Mingmei Wu
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：November 3, 2014
• 年：2014
• 卷：53
• 期：21
• 页码：11589-11597
• 全文大小：574K
• ISSN：1520-510X

文摘

The solubility of Ce in the La_1鈥?i>xCe_xSrGa₃O_7+未 and La_1.54鈥?i>xCe_xSr_0.46Ga₃O_7.27+未 melilites was investigated, along with the thermal redox stability in air of these melilites and the conductivity variation associated with oxidization of Ce³⁺ into Ce⁴⁺. Under CO reducing atmosphere, the La in LaSrGa₃O₇ may be completely substituted by Ce to form the La_1鈥?i>xCe_xSrGa₃O_7+未 solid solution, which is stable in air to 鈭?00 掳C when x 鈮?0.6. On the other side, the La_1.54鈥?i>xCe_xSr_0.46Ga₃O_7.27+未 compositions displayed much lower Ce solubility (x 鈮?0.1), irrespective of the synthesis atmosphere. In the as-made La_1鈥?i>xCe_xSrGa₃O_7+未, the conductivity increased with the cerium content, due to the enhanced electronic conduction arising from the 4f electrons in Ce³⁺ cations. At 600 掳C, CeSrGa₃O_7+未 showed a conductivity of 鈭?0^鈥? S/cm in air, nearly 4 orders of magnitude higher than that of LaSrGa₃O₇. The oxidation of Ce³⁺ into Ce⁴⁺ in CeSrGa₃O_7+未 slightly reduced the conductivity, and the oxygen excess did not result in apparent increase of oxide ion conduction in CeSrGa₃O_7+未. The Ce doping in air also reduced the interstitial oxide ion conductivity of La_1.54Sr_0.46Ga₃O_7.27. Neutron powder diffraction study on CeSrGa₃O_7.39 composition revealed that the extra oxygen is incorporated in the four-linked GaO₄ polyhedral environment, leading to distorted GaO₅ trigonal bipyramid. The stabilization and low mobility of interstitial oxygen atoms in CeSrGa₃O_7+未, in contrast with those in La_1+xSr_1鈥?i>xGa₃O_7+0.5x, may be correlated with the cationic size contraction from the oxidation of Ce³⁺ to Ce⁴⁺. These results provide a new comprehensive understanding of the accommodation and conduction mechanism of the oxygen interstitials in the melilite structure.