Sr2GaScO5, Sr10Ga6Sc4O25, and SrGa0.75Sc0.25O2.5: a Play in the Octahedra to Tetrahedra Ratio in Oxyg

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• 作者：Sergey V. Chernov ; Yuri A. Dobrovolsky ; Sergey Ya. Istomin ; Evgeny V. Antipov ; Jekabs Grins ; Gunnar Svensson ; Nadezhda V. Tarakina ; Artem M. Abakumov ; Gustaaf Van Tendeloo ; Sten G. Eriksson ; Seikh M. H. Rahman
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：January 16, 2012
• 年：2012
• 卷：51
• 期：2
• 页码：1094-1103
• 全文大小：538K
• 年卷期：v.51,no.2(January 16, 2012)
• ISSN：1520-510X

文摘

Three different perovskite-related phases were isolated in the SrGa_1鈥?i>xSc_xO_2.5 system: Sr₂GaScO₅, Sr₁₀Ga₆Sc₄O₂₅, and SrGa_0.75Sc_0.25O_2.5. Sr₂GaScO₅ (x = 0.5) crystallizes in a brownmillerite-type structure [space group (S.G.) Icmm, a = 5.91048(5) 脜, b = 15.1594(1) 脜, and c = 5.70926(4) 脜] with complete ordering of Sc³⁺ and Ga³⁺ over octahedral and tetrahedral positions, respectively. The crystal structure of Sr₁₀Ga₆Sc₄O₂₅ (x = 0.4) was determined by the Monte Carlo method and refined using a combination of X-ray, neutron, and electron diffraction data [S.G. I4₁/a, a = 17.517(1) 脜, c = 32.830(3) 脜]. It represents a novel type of ordering of the B cations and oxygen vacancies in perovskites. The crystal structure of Sr₁₀Ga₆Sc₄O₂₅ can be described as a stacking of eight perovskite layers along the c axis ...[鈭?Sc/Ga)O_1.6鈥揝rO_0.8鈥?Sc/Ga)O_1.8鈥揝rO_0.8鈭抅₂.... Similar to Sr₂GaScO₅, this structure features a complete ordering of the Sc³⁺ and Ga³⁺ cations over octahedral and tetrahedral positions, respectively, within each layer. A specific feature of the crystal structure of Sr₁₀Ga₆Sc₄O₂₅ is that one-third of the tetrahedra have one vertex not connected with other Sc/Ga cations. Further partial replacement of Sc³⁺ by Ga³⁺ leads to the formation of the cubic perovskite phase SrGa_0.75Sc_0.25O_2.5 (x = 0.25) with a = 3.9817(4) 脜. This compound incorporates water molecules in the structure forming SrGa_0.75Sc_0.25O_2.5路xH₂O hydrate, which exhibits a proton conductivity of 2.0 脳 10^鈥? S/cm at 673 K.