Solid State Syntheses of 12SrO·7Al2O3 and Formation of High Density Oxygen Radical Anions, O− and O2−

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• 作者：Katsuro Hayashi ; Naoto Ueda ; Satoru Matsuishi ; Masahiro Hirano ; Toshio Kamiya ; Hideo Hosono
• 刊名：Chemistry of Materials
• 出版年：2008
• 出版时间：October 14, 2008
• 年：2008
• 卷：20
• 期：19
• 页码：5987-5996
• 全文大小：366K
• 年卷期：v.20,no.19(October 14, 2008)
• ISSN：1520-5002

文摘

A new synthetic route via a solid-state reaction, the crystal structure of 12SrO·7Al₂O₃ (S₁₂A₇) incorporated with OH⁻ ions, and the formation of oxygen radical anions in S₁₂A₇ have been examined. Investigations using X-ray powder diffraction and thermogravimetric and evolved gas combined analyses demonstrate that homogenization promoted by molten Sr(OH)₂ hydrates and the presence of Sr-hydrogarnet precursors play crucial roles in the formation of S₁₂A₇. Rietveld analyses confirm the lattice framework of S₁₂A₇ has a structure identical to that of the nanoporous crystal 12CaO·7Al₂O₃ (C₁₂A₇, a mayenite structure) and demonstrate that two Sr²⁺ ions (pole Sr²⁺ ions) on the S₄ axis of a cage displace toward the cage center owing to the accommodation of an OH⁻ ion. An electron paramagnetic resonance study demonstrates that oxygen radical anions, O₂⁻ and O⁻, are generated in the cages with concentrations on the order of 10²⁰ cm⁻³ each by oxygen annealing. From the g-values observed at 77 K, the oxygen radical anions are interpreted as being sandwiched between the two pole Sr²⁺ ions rather than adsorbed on one side.